Van's Air Force
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0-320 vs 0-360 fuel consumption
- Thread starter nturner
- Start date
gmcjetpilot
Well Known Member
Apples and Apples
The down side is the engine will cost more and weigh about 25 -30 lbs more. 160HP in any 2 seat RV will rock your world. However chances are after a year or so you will want more HP. Resale will be better with 180HP, but that is not a factor since you should build it for you ro fly, not sell. You will get your money back from a 180HP engine if you did sell your RV.
The fuel issue: Well you can throttle a 180HP back and get like 160HP burns, or you can fly higher and get better equivalent miles per gallons. Also remember the faster you climb and cruise the quicker you get there, thus reducing fuel. So apples and apples , the two engines have similar efficency. The way you fly will determine economy. On the other end, fly wide open at sea level (100%) power, the 180HP has potential to burn a lot more fuel. So if you can?t control your self you might want a 150HP.
The book absolute 180HP fuel burns: 55%=7.8gal/hr, 65%=9gal/hr, 75%=10.6gal/hr. 100% is around 14.5 gal/hr. You can get these down 2%-6% with mods like electronic ignition. I also like to fly at 65% or less. At 12,000 feet, WOT & 2450 RPM (constant speed prop) you would be at 65% power (117HP) and 9 gal/hr. If you had 160HP you would need to fly at about 73% power WOT to keep up, and the max altitude you could fly to make 73% is about 8,000'. The fuel burn of a O-320 might be a little higher and at a higher RPM (more noise). So with a 180HP you can fly higher, go a little faster (less drag at 12 vs. 8) with the same fuel burn. However most just push the throttle forward and go faster and burn the extra fuel. Depending on the flight profile and how you fly (x-c or local) you can burn equivelant gallons. It depends on your throttle hand and how high you are willing or able to fly(O2).
Bottom line, you never can have enough power, and I have 180HP in my RV-7 (my RV-4 was 150HP and went very fast). You still can't lose with 160HP. The key to performance and overall joy is only part HP. The rest is keeping it light ( and advantage of the O-320), simple and not going too far from the plans. Don't let fuel burn keep you away from the bigger engine, because if you are careful you can minimize the burn by flying at 65% or less. Even at 55% power flying around the airport in your RV, you will still be backing thru town at 160MPH. Cessna or Piper guys are Lucky to go 110 MPH with high power RV's are very efficient and can get in 24-26 MPG range, easy regardless of HP. 180HP is 20 more HP and 20 more HP worth of fuel burn, but it's adjustable with that black and red and blue knobs.
Take Care George
Well it is a bigger picture than just fuel. With a 180HP will burn about .6-.8 gal/hour more. You will use a little less runway (25-75ft), climb faster (250-300fpm) and cruise 8 MPH faster. However you can burn less gas with the 180HP.nturner said:
The down side is the engine will cost more and weigh about 25 -30 lbs more. 160HP in any 2 seat RV will rock your world. However chances are after a year or so you will want more HP. Resale will be better with 180HP, but that is not a factor since you should build it for you ro fly, not sell. You will get your money back from a 180HP engine if you did sell your RV.
The fuel issue: Well you can throttle a 180HP back and get like 160HP burns, or you can fly higher and get better equivalent miles per gallons. Also remember the faster you climb and cruise the quicker you get there, thus reducing fuel. So apples and apples , the two engines have similar efficency. The way you fly will determine economy. On the other end, fly wide open at sea level (100%) power, the 180HP has potential to burn a lot more fuel. So if you can?t control your self you might want a 150HP.
The book absolute 180HP fuel burns: 55%=7.8gal/hr, 65%=9gal/hr, 75%=10.6gal/hr. 100% is around 14.5 gal/hr. You can get these down 2%-6% with mods like electronic ignition. I also like to fly at 65% or less. At 12,000 feet, WOT & 2450 RPM (constant speed prop) you would be at 65% power (117HP) and 9 gal/hr. If you had 160HP you would need to fly at about 73% power WOT to keep up, and the max altitude you could fly to make 73% is about 8,000'. The fuel burn of a O-320 might be a little higher and at a higher RPM (more noise). So with a 180HP you can fly higher, go a little faster (less drag at 12 vs. 8) with the same fuel burn. However most just push the throttle forward and go faster and burn the extra fuel. Depending on the flight profile and how you fly (x-c or local) you can burn equivelant gallons. It depends on your throttle hand and how high you are willing or able to fly(O2).
Bottom line, you never can have enough power, and I have 180HP in my RV-7 (my RV-4 was 150HP and went very fast). You still can't lose with 160HP. The key to performance and overall joy is only part HP. The rest is keeping it light ( and advantage of the O-320), simple and not going too far from the plans. Don't let fuel burn keep you away from the bigger engine, because if you are careful you can minimize the burn by flying at 65% or less. Even at 55% power flying around the airport in your RV, you will still be backing thru town at 160MPH. Cessna or Piper guys are Lucky to go 110 MPH with high power RV's are very efficient and can get in 24-26 MPG range, easy regardless of HP. 180HP is 20 more HP and 20 more HP worth of fuel burn, but it's adjustable with that black and red and blue knobs.
Take Care George
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dan
Well Known Member
It's not cut and dried.
You can't just say a 360 burns more fuel than a 320. It's not that cut and dried.
My IO-360-A1B6 burns measurably less fuel (1+gph) than every 320 and 360 equipped RV I've flown with. Electronic ignition and balanced fuel injection (LOP) go a long way to boosting economy. I also believe the Vetterman exhaust for the horizontal induction IO-360 happens to be extremely efficient...much more so than even Vetterman exhaust for vertical induction engines. I have no idea why...but anyway...
Literally this past Saturday, I was cruising alongside an RV-6 that has a stock O-320 and Hartzell 2-blade (albeit a slightly smaller prop chord-wise than mine, as per engine model limitations).
At 8500', he was running full throttle at 2600 RPM, burning 7.5gph. I was running 18.9" at 2370 RPM burning 5.9gph.
Granted, he had a passenger with him while I didn't (although my plane is heavier to begin with), so this is an apples to oranges comparison. But I burn the same or less fuel than this particular O-320 equipped RV-6 when we fly together. And when flying with O-360 equipped RVs, I consistently burn 1+ gph less across the board. 7.5 when they're burning 8.5.
How much fuel you burn has more to do with more factors than just cubic inches. To say a 360 burns more fuel than a 320 is a generalization.
Your mileage may vary!
)_( Dan
RV-7 N714D
http://www.rvproject.com
You can't just say a 360 burns more fuel than a 320. It's not that cut and dried.
My IO-360-A1B6 burns measurably less fuel (1+gph) than every 320 and 360 equipped RV I've flown with. Electronic ignition and balanced fuel injection (LOP) go a long way to boosting economy. I also believe the Vetterman exhaust for the horizontal induction IO-360 happens to be extremely efficient...much more so than even Vetterman exhaust for vertical induction engines. I have no idea why...but anyway...
Literally this past Saturday, I was cruising alongside an RV-6 that has a stock O-320 and Hartzell 2-blade (albeit a slightly smaller prop chord-wise than mine, as per engine model limitations).
At 8500', he was running full throttle at 2600 RPM, burning 7.5gph. I was running 18.9" at 2370 RPM burning 5.9gph.
Granted, he had a passenger with him while I didn't (although my plane is heavier to begin with), so this is an apples to oranges comparison. But I burn the same or less fuel than this particular O-320 equipped RV-6 when we fly together. And when flying with O-360 equipped RVs, I consistently burn 1+ gph less across the board. 7.5 when they're burning 8.5.
How much fuel you burn has more to do with more factors than just cubic inches. To say a 360 burns more fuel than a 320 is a generalization.
Your mileage may vary!
)_( Dan
RV-7 N714D
http://www.rvproject.com
gmcjetpilot
Well Known Member
Dan are you bragging?
I know you have a very efficient RV-7 with a 200HP engine Dan, but to quote you, it is not that cut and dried. Drag of the airframe is an issue. Granted you mentioned weight difference, but that does not account for the large 1.6 gal/hr difference; With like airframes it does not compute. I believe you, but to go approx the same airspeed with similar airframes you need about the same HP (ignore prop efficency?). One way to improve specific fuel efficency is higher compression. Electronic ignition is as you said is a plus, but no more than 6% (may be 0.50 gal/hr). If the O-320 was a 150HP that might account for some difference (low compression). Any way I understand your point but the numbers you have are amazing. You are picking up an extra .5 to 1 gal/hr over what I can account for with just the ignition. I know you are FI and understand you have mastered the lean of peek method. May be that makes up for the gal/hr? (What are you doing Dan)
Anyway, good on ya, it must be the excellent workmanship and that IO360
Cheers George
Not sure that is at me Dan, but that is not what I said. I give an example of a high flying 180HP RV (65%) Vs. a Lower flying 160HP RV at about 75%. The 180HP will be flying faster and burning equivalent fuel or even less by 0.5gal/hr.dan said:
I know you have a very efficient RV-7 with a 200HP engine Dan, but to quote you, it is not that cut and dried. Drag of the airframe is an issue. Granted you mentioned weight difference, but that does not account for the large 1.6 gal/hr difference; With like airframes it does not compute. I believe you, but to go approx the same airspeed with similar airframes you need about the same HP (ignore prop efficency?). One way to improve specific fuel efficency is higher compression. Electronic ignition is as you said is a plus, but no more than 6% (may be 0.50 gal/hr). If the O-320 was a 150HP that might account for some difference (low compression). Any way I understand your point but the numbers you have are amazing. You are picking up an extra .5 to 1 gal/hr over what I can account for with just the ignition. I know you are FI and understand you have mastered the lean of peek method. May be that makes up for the gal/hr? (What are you doing Dan)
Anyway, good on ya, it must be the excellent workmanship and that IO360
Cheers George
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Bryan Wood
Well Known Member
My 0-320
Here's the numbers on my 0-320, at least as best as I can tell. Mine lives in a RV-9A and has one lightspeed electronic ignition and one mag. I have 9:1 H pistons, with everything else stock swinging a Hartzell C/S. The fuel injection is missing on my engine probably because of the amount of money that I sent to the engine builder.
My longest trip was from CA to Fort Worth and my fuel burns were pretty consistant at 7.8gph running 50 rop at full throttle and 2600 rpm. I made the trip east at 9,500 or 11,500' and west at 12,500. Really, I didn't see a real change in fuel burns and now use 8gph for flight planning with confidence.
Lately I've been running oversquare at lower altitudes up to approx. 6500' with settings of 25"/2300rpm and the speeds seem better, the chts are cooler and the fuel burns seem less by about 1/2 gph. I'm really liking this oversquare thing with the noise levels being much lower and speeds noticably higher (3-5 knots) than running at 24sq. There does seem to be some oil usage when running oversquare, I'm not sure if it is from higher pressures in the cylinders or what. I know the oversquare technique is contraversial and will probably start a new debate which I welcome. I'm still trying to learn what works.
As for flying beside a plane with an injected 200hp as Dan shared, well I did exactly that a few months ago along the Monterey Coast. The airplane was an RV-6 with a hartzell C/S. The owner had to power back dramatically for me to fly along side of him. I don't know the exact numbers anymore but I remember them making me feel pretty bad. I know that I was at 24"/2500rpm to stay with him and he was around 20"/2200rpm or so. I remember doing the math in my head at the time and wishing that I had gone with an 0-360 even though Van was against it in the RV-9's.
Anyway, I was literally parked next to Dan on Saturday and it was great meeting you.
Regards,
Bryan
Here's the numbers on my 0-320, at least as best as I can tell. Mine lives in a RV-9A and has one lightspeed electronic ignition and one mag. I have 9:1 H pistons, with everything else stock swinging a Hartzell C/S. The fuel injection is missing on my engine probably because of the amount of money that I sent to the engine builder.
My longest trip was from CA to Fort Worth and my fuel burns were pretty consistant at 7.8gph running 50 rop at full throttle and 2600 rpm. I made the trip east at 9,500 or 11,500' and west at 12,500. Really, I didn't see a real change in fuel burns and now use 8gph for flight planning with confidence.
Lately I've been running oversquare at lower altitudes up to approx. 6500' with settings of 25"/2300rpm and the speeds seem better, the chts are cooler and the fuel burns seem less by about 1/2 gph. I'm really liking this oversquare thing with the noise levels being much lower and speeds noticably higher (3-5 knots) than running at 24sq. There does seem to be some oil usage when running oversquare, I'm not sure if it is from higher pressures in the cylinders or what. I know the oversquare technique is contraversial and will probably start a new debate which I welcome. I'm still trying to learn what works.
As for flying beside a plane with an injected 200hp as Dan shared, well I did exactly that a few months ago along the Monterey Coast. The airplane was an RV-6 with a hartzell C/S. The owner had to power back dramatically for me to fly along side of him. I don't know the exact numbers anymore but I remember them making me feel pretty bad. I know that I was at 24"/2500rpm to stay with him and he was around 20"/2200rpm or so. I remember doing the math in my head at the time and wishing that I had gone with an 0-360 even though Van was against it in the RV-9's.
Anyway, I was literally parked next to Dan on Saturday and it was great meeting you.
Regards,
Bryan
Running LOP reduces fuel flow considerably. One client runs an O-320 with EFI and EI and reports fuel flows now of 6.5GPH at 75% compared to 7.8 before with the carb and mags. Airspeed is within 2 knots as close as he can tell. It serves to reason that if the average AFR on with a carb is 14 to 1 before roughness is encountered and say 16 to 1 with EFI running 50F LOP, fuel savings of over 10% are possible and clearly demonstrated here. This fellow reports EGT spread from coldest to hottest cylinders was 175F with the carb and 30F with the EFI without touching the probes. This large spread is common on carbed O-320 and O-360s from owners I have polled with updraft induction which points to relatively poor mixture distribution.
Several factors at play
This is not a straight forward question. A parallel valve O-360 (180hp) will weigh only 5lb or so more than a similat O-320. An angle valve IO-360 (200hp) can weigh over 30lb more than an O-320.
Fuel consumption at a give speed is lower with a larger engine, particularly if it has a constant speed propeller. The only data I have is a fixed pitch O-320 (150 & 160) running with a c/s O-360. With the 150hp O-320 running full throttle at 8000' (ish), the O-360s burn a gallon to a 1 1/2 gph less when flying together. In this case the O-320 would be burning around 9 gph. I understand that 200hp IO-360s burn less than 180s when flying together, at the same speed. The 160 conversion keeps the fuel flow (roughly) the same, but makes you go slightly quicker. Again, I would expect the c/s O-360s to burn less fuel for the same speed.
Of course, at full throttle an O-360 equipped aircraft will go faster, and burn more fuel, than one with an O-320. It will also climb more quickly and put an even wider grin on your face.
I think the c/s prop makes a difference, I have no data for an O-320 with c/s, or for an O-360 with fp.
A 180hp O-360 costs very little more than an O-320, unless you get a really good deal on an O-320 the O-360 would be the engine of choice for me. I also think a c/s prop is very worthwhile (grin factor increases again!).
Pete
PS My EGT spread is as indicated above with a carb. If I was starting from scratch I would go with fuel injection any day.
This is not a straight forward question. A parallel valve O-360 (180hp) will weigh only 5lb or so more than a similat O-320. An angle valve IO-360 (200hp) can weigh over 30lb more than an O-320.
Fuel consumption at a give speed is lower with a larger engine, particularly if it has a constant speed propeller. The only data I have is a fixed pitch O-320 (150 & 160) running with a c/s O-360. With the 150hp O-320 running full throttle at 8000' (ish), the O-360s burn a gallon to a 1 1/2 gph less when flying together. In this case the O-320 would be burning around 9 gph. I understand that 200hp IO-360s burn less than 180s when flying together, at the same speed. The 160 conversion keeps the fuel flow (roughly) the same, but makes you go slightly quicker. Again, I would expect the c/s O-360s to burn less fuel for the same speed.
Of course, at full throttle an O-360 equipped aircraft will go faster, and burn more fuel, than one with an O-320. It will also climb more quickly and put an even wider grin on your face.
I think the c/s prop makes a difference, I have no data for an O-320 with c/s, or for an O-360 with fp.
A 180hp O-360 costs very little more than an O-320, unless you get a really good deal on an O-320 the O-360 would be the engine of choice for me. I also think a c/s prop is very worthwhile (grin factor increases again!).
Pete
PS My EGT spread is as indicated above with a carb. If I was starting from scratch I would go with fuel injection any day.
jonbakerok
Well Known Member
Goal to save gas? Buy an O-320.
Nothing wrong with that, but when you started this thread, you seemed to be concerned about saving gas. If that's still a concern, I suggest you re-read the second post.
GMCJETPILOT says he gets 7.8 GPH at 55%. My 160hp O-320 gets 6.4 GPH at that setting. At current Houston fuel prices ($3.20), that means a two hour weekend burger run costs me $40.96. An O-360 would cost $49.92 to get to the same burger. The difference pays for the burger. Or to look at in another way, a 38 gallon fillup buys me 5.9 hours in the air vs. 4.8. That's over an hour of free flying on every tankful (and an extra hundred miles of range when I'm cross-country).
I'm happy with my O-320. I still blast off at over 2000 fpm and I still have to be careful not to run over the spam cans. But if I were a jet pilot or if did a lot of formation flying with other RV's, I might not like it as well. It's all about the mission.
nturner said:
Nothing wrong with that, but when you started this thread, you seemed to be concerned about saving gas. If that's still a concern, I suggest you re-read the second post.
GMCJETPILOT says he gets 7.8 GPH at 55%. My 160hp O-320 gets 6.4 GPH at that setting. At current Houston fuel prices ($3.20), that means a two hour weekend burger run costs me $40.96. An O-360 would cost $49.92 to get to the same burger. The difference pays for the burger. Or to look at in another way, a 38 gallon fillup buys me 5.9 hours in the air vs. 4.8. That's over an hour of free flying on every tankful (and an extra hundred miles of range when I'm cross-country).
I'm happy with my O-320. I still blast off at over 2000 fpm and I still have to be careful not to run over the spam cans. But if I were a jet pilot or if did a lot of formation flying with other RV's, I might not like it as well. It's all about the mission.
RVbySDI
Well Known Member
I have a question for Johnbakerok on your post. You wrote:
What I am reading here is that you are comparing fuel burn and RPM % between the 160hp O-320 and the 180hp (I)O-360. But the other factor that you are leaving out is the MPH of the two airplanes and engines while flying at that 55%.
You mention the price of that $100 hamburger flight:
The question is the difference in how fast you are able to fly to point B from point A for the extra $8.96 in fuel cost. I may be missing something here, Someone please correct me if I am totally off base with this thought, but running an O-320 at 55% means that the airplane will not be flying as fast through the air as the (I)O-360 running at 55%. That extra $8.96 is buying you more speed equating to less time in the air.
My thoughts are that if you wanted to use the 360 engine to get to your favorite hamburger place at the same cost and speed that you use with your 320 engine you would slow that 360 down to whatever the RPM % would be for that engine that equates to a 320's 55%. At that setting you would essentially burn the same amount of fuel and be flying at the same airspeed.
Steve
RVBYSDI
What I am reading here is that you are comparing fuel burn and RPM % between the 160hp O-320 and the 180hp (I)O-360. But the other factor that you are leaving out is the MPH of the two airplanes and engines while flying at that 55%.
You mention the price of that $100 hamburger flight:
The question is the difference in how fast you are able to fly to point B from point A for the extra $8.96 in fuel cost. I may be missing something here, Someone please correct me if I am totally off base with this thought, but running an O-320 at 55% means that the airplane will not be flying as fast through the air as the (I)O-360 running at 55%. That extra $8.96 is buying you more speed equating to less time in the air.
My thoughts are that if you wanted to use the 360 engine to get to your favorite hamburger place at the same cost and speed that you use with your 320 engine you would slow that 360 down to whatever the RPM % would be for that engine that equates to a 320's 55%. At that setting you would essentially burn the same amount of fuel and be flying at the same airspeed.
Steve
RVBYSDI
kentb
Well Known Member
Fuel is converted to work
There is a standard formula that I have been told: 1 gallon of fuel will convert to 10 hp per hour. If you have a 180hp engine and ask it to produce 180hp then it will cost you 18 gal/hr. If you ask the engine to produce 160hp the cost goes down to 16 gal/hr.
So the engine choice for conversion of fuel to power doesn't matter. The use of the power being converted into speed (distance) is where the choice becomes interesting. Each pound that your carry will need power to move it through the air. Any disturbance in the air flow over your plane will need more power (that a drag).
You can make a better preforming plane by keeping the weight down and keeping the drag down.
The 360 will weigh a little more then the 320.
I am building a 9A and will be putting a IO320 in it. This is the biggest that Vans says to fly with. If I were building a -7 I would put a 360 in it. This will cost a little more to operate, in that your are packing a couple more pounds, but gives you the chance to climb and fly faster, if you want to pay for the extra fuel.
Kent
There is a standard formula that I have been told: 1 gallon of fuel will convert to 10 hp per hour. If you have a 180hp engine and ask it to produce 180hp then it will cost you 18 gal/hr. If you ask the engine to produce 160hp the cost goes down to 16 gal/hr.
So the engine choice for conversion of fuel to power doesn't matter. The use of the power being converted into speed (distance) is where the choice becomes interesting. Each pound that your carry will need power to move it through the air. Any disturbance in the air flow over your plane will need more power (that a drag).
You can make a better preforming plane by keeping the weight down and keeping the drag down.
The 360 will weigh a little more then the 320.
I am building a 9A and will be putting a IO320 in it. This is the biggest that Vans says to fly with. If I were building a -7 I would put a 360 in it. This will cost a little more to operate, in that your are packing a couple more pounds, but gives you the chance to climb and fly faster, if you want to pay for the extra fuel.
Kent
mlw450802
Well Known Member
Kent,kentb said:
I think the most commonly held conversion for the average Otto cycle engine is 0.5lb fuel per horsepower per hour.
180 hp would burn 90lb per hour or ~15 gph.
This of course assumes reasonable fuel/air ratios, compression ratios yadda yadda yadda.
Running rich would likely produce results closer to the ones you stated.
-mike
RVbySDI
Well Known Member
Kentb,
If I do some math here:
55% of 180HP
.55 * 180 = 99HP
55% of 160HP
.55 * 160 = 88HP
1 gal equates to 10 hp per hour at these figures comes out to:
9.9 gph for the 180 hp engine at 55%
8.8 gph for the 160 hp engine at 55%
so if I want the 180 hp engine to run at the same fuel burn as the 160 hp engine I have to run it at 49% of max RPM.
88 / 180 = .48888889
Given that everything else would be equal on the 360 powered airplane vs. the 320 powered airplane (i.e. drag aerodynamics, prop efficiencies, etc.) the two airplanes should burn the same amount of fuel if the 360 flies at 49% of the max RPM while the 320 flies at 55% of the max RPM. Except for the added weight penalty that would exist if the 360 powered airplane weight is more than the 320, the two airplanes should be very close to flying at the same speed if the 360 was running at 49% and the 320 were flying at 55%.
To me it comes down to the other factors that may exist. According to conversations I have had with various engine manufacturers (Mattatuck, Penn Yenn Aero, ECI) the weight difference between the two engines is somewhere between 12 to 25 lbs. Give or take a lb or so. When it comes to the cost of these two engines if I place an IO-360 in my plane the price is going to be relatively a wash between it and the IO-320. Give or take a hundred dollars or so. Again, this is according to my conversations with the aforementioned engine manufacturers.
I am gaining 20 more hp with the 180 version for that 12 to 25 lb penalty. I don't see that weight affecting me near as much as the extra 20 HP will when I am on a 3000' grass strip in Colorado, Wyoming, Idaho, Montana (read "high in the mountains" here) in the summer with a temperature of 90 degrees. In this scenario I would be very glad to have another 20 HP at full rev in my airplane. If 12 to 25 lbs is a critical amount of weight I would be more interested in trading out that weight in fancy IFR equipment, fancy interiors or other areas than to shave it off of the engine.
Another issue is the engine noise and wear and tear. An engine running at 49% has got to be quieter than one running at 55%. There also has got to be less wear and tear on the internal components of that engine running at a slower rate. Granted it may not be of a significant difference but the difference must exist however small it may be.
Ultimately it is of value to me to have another 20hp when you need it most (at climb out on a hot summer day and a short field). The fuel management and speed of the airplane comes down to my piloting skills in managing the engine while at cruise. If I can have that extra power for minimal cost at critical times I would prefer it than not. To me it is somewhat like the issue of leaving runway behind you on take off rollout or while running out of runway when landing because you landed halfway down the strip. If you can gain the extra HP at a minimal cost in price, weight, etc. why wouldn't you put it in your airplane?
Just my humble opinion,
Steve
RVBYSDI
If I do some math here:
55% of 180HP
.55 * 180 = 99HP
55% of 160HP
.55 * 160 = 88HP
1 gal equates to 10 hp per hour at these figures comes out to:
9.9 gph for the 180 hp engine at 55%
8.8 gph for the 160 hp engine at 55%
so if I want the 180 hp engine to run at the same fuel burn as the 160 hp engine I have to run it at 49% of max RPM.
88 / 180 = .48888889
Given that everything else would be equal on the 360 powered airplane vs. the 320 powered airplane (i.e. drag aerodynamics, prop efficiencies, etc.) the two airplanes should burn the same amount of fuel if the 360 flies at 49% of the max RPM while the 320 flies at 55% of the max RPM. Except for the added weight penalty that would exist if the 360 powered airplane weight is more than the 320, the two airplanes should be very close to flying at the same speed if the 360 was running at 49% and the 320 were flying at 55%.
To me it comes down to the other factors that may exist. According to conversations I have had with various engine manufacturers (Mattatuck, Penn Yenn Aero, ECI) the weight difference between the two engines is somewhere between 12 to 25 lbs. Give or take a lb or so. When it comes to the cost of these two engines if I place an IO-360 in my plane the price is going to be relatively a wash between it and the IO-320. Give or take a hundred dollars or so. Again, this is according to my conversations with the aforementioned engine manufacturers.
I am gaining 20 more hp with the 180 version for that 12 to 25 lb penalty. I don't see that weight affecting me near as much as the extra 20 HP will when I am on a 3000' grass strip in Colorado, Wyoming, Idaho, Montana (read "high in the mountains" here) in the summer with a temperature of 90 degrees. In this scenario I would be very glad to have another 20 HP at full rev in my airplane. If 12 to 25 lbs is a critical amount of weight I would be more interested in trading out that weight in fancy IFR equipment, fancy interiors or other areas than to shave it off of the engine.
Another issue is the engine noise and wear and tear. An engine running at 49% has got to be quieter than one running at 55%. There also has got to be less wear and tear on the internal components of that engine running at a slower rate. Granted it may not be of a significant difference but the difference must exist however small it may be.
Ultimately it is of value to me to have another 20hp when you need it most (at climb out on a hot summer day and a short field). The fuel management and speed of the airplane comes down to my piloting skills in managing the engine while at cruise. If I can have that extra power for minimal cost at critical times I would prefer it than not. To me it is somewhat like the issue of leaving runway behind you on take off rollout or while running out of runway when landing because you landed halfway down the strip. If you can gain the extra HP at a minimal cost in price, weight, etc. why wouldn't you put it in your airplane?
Just my humble opinion,
Steve
RVBYSDI
There are many other factors involved in SFC. Some engine are significantly more efficient than others in converting a pound of fuel to hp. Compression ratio, ignition advance and air/fuel (AFR) and exhaust scavenging can have a profound affect. In most cases, operating a smaller engine at closer to WOT is more efficient than a larger engine at partially closed throttle due to lower pumping losses. All things being equal, an O-320 is likely to get better fuel economy than an O-360 at 75% cruise power and below. You may be going slightly slower under certain conditions however.
An average small Lycoming with a carb and mags operates at a SFC of around .46lbs./hp/hr. when leaned to just lean of the onset roughness. With EFI and EI along with higher CR pistons and efficient exhaust, some are well below .40 because they can operate LOP (lean of peak) with better mixture distributiion. While power does drop off slightly LOP, tis is more than offset by lower fuel flows.
An average small Lycoming with a carb and mags operates at a SFC of around .46lbs./hp/hr. when leaned to just lean of the onset roughness. With EFI and EI along with higher CR pistons and efficient exhaust, some are well below .40 because they can operate LOP (lean of peak) with better mixture distributiion. While power does drop off slightly LOP, tis is more than offset by lower fuel flows.
jonbakerok
Well Known Member
Want cheap? O-320.
First, I just want to re-iterate that my only point is that you should choose the engine that meets your goal. I don't have a favorite engine -- I'd just rather fly cheap than go fast(er).
Also, I'm no aeronautical engineer -- just a guy capable of basic arithmetic. I think that's all we need to settle this, but if someone else has more powerful math to prove that bigger is cheaper, show me and I'll try to follow it. By the way, I'm going to use Van's numbers for the RV6A for comparison, since I've verified them myself:
180hp at 55% at 8000 ft, using 99hp = 176 MPH
160hp at 55% at 8000 ft, using 88hp = 169 MPH
Here goes:
Is 180 HP cheaper at the same power setting (55%) because it flies faster?
Scenario: two-hour burger run
In two hours, at 55%, my 160hp RV6 flies 338 miles round trip (great diner at Fredericksburg, by the way!).
2 hours X 6.4 GPH = 12.8 gallons
The same plane, but with 180hp, flies 338 miles at 176mph. Total air time: 1.92 hours (beating me to the burger by about 5 minutes).
1.92 hours X 7.8 GPH = 14.98 gallons.
But I saved 2.18 gallons, or $6.98. That's a burger.
Why does it work that way? Because the airframe needs about 20% more power to get 10% more speed. The curve's going the wrong way to make up in speed what you lack in efficiency.
Ahh, but can't you just set your throttle to produce the same horsepower from your O-360 as I do from my O-320? Nope, because the O-360 weighs about 30 pounds more than an O-320. The energy to carry that extra metal has to come from somewhere. So, if you use the same horsepower in a heavier plane, the angle of attack increases slightly to maintain lift, which means you're slower, which means you're in the air longer, which means you burn more gas.
So the moral is: There ain't no free lunch (just free burger <grin>).
RVbySDI said:
First, I just want to re-iterate that my only point is that you should choose the engine that meets your goal. I don't have a favorite engine -- I'd just rather fly cheap than go fast(er).
Also, I'm no aeronautical engineer -- just a guy capable of basic arithmetic. I think that's all we need to settle this, but if someone else has more powerful math to prove that bigger is cheaper, show me and I'll try to follow it. By the way, I'm going to use Van's numbers for the RV6A for comparison, since I've verified them myself:
180hp at 55% at 8000 ft, using 99hp = 176 MPH
160hp at 55% at 8000 ft, using 88hp = 169 MPH
Here goes:
Is 180 HP cheaper at the same power setting (55%) because it flies faster?
Scenario: two-hour burger run
In two hours, at 55%, my 160hp RV6 flies 338 miles round trip (great diner at Fredericksburg, by the way!).
2 hours X 6.4 GPH = 12.8 gallons
The same plane, but with 180hp, flies 338 miles at 176mph. Total air time: 1.92 hours (beating me to the burger by about 5 minutes).
1.92 hours X 7.8 GPH = 14.98 gallons.
But I saved 2.18 gallons, or $6.98. That's a burger.
Why does it work that way? Because the airframe needs about 20% more power to get 10% more speed. The curve's going the wrong way to make up in speed what you lack in efficiency.
Ahh, but can't you just set your throttle to produce the same horsepower from your O-360 as I do from my O-320? Nope, because the O-360 weighs about 30 pounds more than an O-320. The energy to carry that extra metal has to come from somewhere. So, if you use the same horsepower in a heavier plane, the angle of attack increases slightly to maintain lift, which means you're slower, which means you're in the air longer, which means you burn more gas.
So the moral is: There ain't no free lunch (just free burger <grin>).
gmcjetpilot
Well Known Member
Oh my gosh....
Again a great time for a cafe foundation test, what is cheaper to operate?
You can crunch numbers all day (some of which are incorrect, but you know who you are), however proof is in the flight test numbers. Dan started this. He has a 200HP engine, heavy, bigger pulse and all that stuff, but burned less gas than a 320 and 360 (180HP) engine, so that blows all your theories away.
Enough talk. How about you all do some side-by-side fly offs with O-320/O-360 and IO-320/IO-360 (180HP). Also we would need to have matched props and airframes (fixed vs. fixed. C/S Vs. C/S, and RV-X vs. RV-X). Dan's story is not the first time I have heard of this, where the bigger engine burns less fuel.
By the way O-320 is lighter by 10 lbs than the O-360. The IO-360 (200hp) is heaver than an IO-360 (180hp) by 23lbs. If you look at the finished weights of RV's O-320's are always the lightest (by a good margin) and IO-360 (200hp) powered RV's are always the heavier finished RV's (by a good amount), 180hp RV's falling in the middle. The weight of O-320 Rv's tend to be even lighter because they use fixed props more. The weight of the 200hp RV's tend to be even higher weight because they tend to always make use of C/S props. Remember Dan claims his IO-360-200HP burns less than RV's with both O-320 and O-360 flying side-by-side at the same speed. You can't argue with side-by-side fly offs. His 200HP burns less than all the planes he flys with? ( I gave the reasons, electonic ignition, Lean of peak operations in my previous post?)
Yes, as for the weight vs. performance, it does make difference, but very little, especially in cruise. Climb perf. Vs. weight does matter more, but 20-40lbs is not a big deal. Look at Van's numbers for solo wt vs. gross weight performance. If you are only talking about the weight of engine 10-20lbs, I doubt this alone would make much diff. HP (excess available HP above what is required for level flight at that speed) does affect climb rate the most. More HP=More climb
(Right from Lycoming web site, Clones weigh a little more)
O-320 (150hp) 244 lb
O-320 (160hp) 255 lb
IO-320 (160hp) 259 lb
O-360 (180hp) 265 lb
IO-360 (180hp) 270 lb
IO-360 (200hp) 293 lb
FUEL BURN: The bigger the engine the more fuel you will burn if you fly by % power alone. If you fly by comparing airspeed and you had extras like fuel injection adn electronic ignition you may see a difference on a long flight. You can only run lean of peek with fuel injection. However if you have the power you are going to use it on take off and initial climb and will tend to burn more fuel overall, but you get the benefit of shorter take off, better obstacle clearance and faster climb. You can take off at partial power, but who does that?
If you always fly long X-C, high altitude (mountain strips) or with two people, the superior power to get off the ground and fly higher, taking advantage of possible tail-winds can give you a real Econ. advantage. The greater the HP the higher you can fly. My previous example clearly shows a 180hp at 65% (12,500 feet) is making as much as an O-320 at almost 75% power. Since the O-320 must stay at 7,000 feet to make 75% the 180HP can fly higher at the same effective HP but lower % power. Higher altitude = less drag. Again it is the way you fly. I fly local way more than long X-C, so this advantage is much less for local flights. Bottom line you can always throttle back and lean out with any engine, but if you have a (I)O-360 you have the extra HP if you need it.
Price: O-320 is not a lot cheaper if buying new. As I said most want an 180HP engine and the O-360 (180HP) has a great reputation, so RV?s with more HP sell for more. Also if you fly formation with other RV's using 180hp, you will have a little harder time keeping up. The O-320 is similar to the O-360 in design, but it does not have the same bullet proof reputation of the O-360. No doubt it is as good, but may be it gets mixed up in some unrelated H2AD history or abused more in trainers. There are crank and cylinder differences. I can?t say the O-360 is better, but it has a mythical reputation for being very reliable. May be something to it.
Fuel injection may be worth the expense and weight. From Lycoming's publications the Lean of Peak does not work as well on smaller engines at larger engines. The reason is they claim the smaller engine will get rougher sooner. So LOP ops with the IO-320 might will not give as much fuel savings as a IO-360 can. This is Lycoming's own tech pub on the topic. Carbs are cheaper to buy. If you buy a fuel injected engine you have to be dedicated to getting matched injectors, learning to run lean of peak and make the effort to do it as much as possible (by flying under 75% power).
G
Again a great time for a cafe foundation test, what is cheaper to operate?
You can crunch numbers all day (some of which are incorrect, but you know who you are), however proof is in the flight test numbers. Dan started this. He has a 200HP engine, heavy, bigger pulse and all that stuff, but burned less gas than a 320 and 360 (180HP) engine, so that blows all your theories away.
Enough talk. How about you all do some side-by-side fly offs with O-320/O-360 and IO-320/IO-360 (180HP). Also we would need to have matched props and airframes (fixed vs. fixed. C/S Vs. C/S, and RV-X vs. RV-X). Dan's story is not the first time I have heard of this, where the bigger engine burns less fuel.
By the way O-320 is lighter by 10 lbs than the O-360. The IO-360 (200hp) is heaver than an IO-360 (180hp) by 23lbs. If you look at the finished weights of RV's O-320's are always the lightest (by a good margin) and IO-360 (200hp) powered RV's are always the heavier finished RV's (by a good amount), 180hp RV's falling in the middle. The weight of O-320 Rv's tend to be even lighter because they use fixed props more. The weight of the 200hp RV's tend to be even higher weight because they tend to always make use of C/S props. Remember Dan claims his IO-360-200HP burns less than RV's with both O-320 and O-360 flying side-by-side at the same speed. You can't argue with side-by-side fly offs. His 200HP burns less than all the planes he flys with? ( I gave the reasons, electonic ignition, Lean of peak operations in my previous post?)
Yes, as for the weight vs. performance, it does make difference, but very little, especially in cruise. Climb perf. Vs. weight does matter more, but 20-40lbs is not a big deal. Look at Van's numbers for solo wt vs. gross weight performance. If you are only talking about the weight of engine 10-20lbs, I doubt this alone would make much diff. HP (excess available HP above what is required for level flight at that speed) does affect climb rate the most. More HP=More climb
(Right from Lycoming web site, Clones weigh a little more)
O-320 (150hp) 244 lb
O-320 (160hp) 255 lb
IO-320 (160hp) 259 lb
O-360 (180hp) 265 lb
IO-360 (180hp) 270 lb
IO-360 (200hp) 293 lb
FUEL BURN: The bigger the engine the more fuel you will burn if you fly by % power alone. If you fly by comparing airspeed and you had extras like fuel injection adn electronic ignition you may see a difference on a long flight. You can only run lean of peek with fuel injection. However if you have the power you are going to use it on take off and initial climb and will tend to burn more fuel overall, but you get the benefit of shorter take off, better obstacle clearance and faster climb. You can take off at partial power, but who does that?
If you always fly long X-C, high altitude (mountain strips) or with two people, the superior power to get off the ground and fly higher, taking advantage of possible tail-winds can give you a real Econ. advantage. The greater the HP the higher you can fly. My previous example clearly shows a 180hp at 65% (12,500 feet) is making as much as an O-320 at almost 75% power. Since the O-320 must stay at 7,000 feet to make 75% the 180HP can fly higher at the same effective HP but lower % power. Higher altitude = less drag. Again it is the way you fly. I fly local way more than long X-C, so this advantage is much less for local flights. Bottom line you can always throttle back and lean out with any engine, but if you have a (I)O-360 you have the extra HP if you need it.
Price: O-320 is not a lot cheaper if buying new. As I said most want an 180HP engine and the O-360 (180HP) has a great reputation, so RV?s with more HP sell for more. Also if you fly formation with other RV's using 180hp, you will have a little harder time keeping up. The O-320 is similar to the O-360 in design, but it does not have the same bullet proof reputation of the O-360. No doubt it is as good, but may be it gets mixed up in some unrelated H2AD history or abused more in trainers. There are crank and cylinder differences. I can?t say the O-360 is better, but it has a mythical reputation for being very reliable. May be something to it.
Fuel injection may be worth the expense and weight. From Lycoming's publications the Lean of Peak does not work as well on smaller engines at larger engines. The reason is they claim the smaller engine will get rougher sooner. So LOP ops with the IO-320 might will not give as much fuel savings as a IO-360 can. This is Lycoming's own tech pub on the topic. Carbs are cheaper to buy. If you buy a fuel injected engine you have to be dedicated to getting matched injectors, learning to run lean of peak and make the effort to do it as much as possible (by flying under 75% power).
G
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RVbySDI
Well Known Member
Thanks for all the great info guys!
Kentb, gmcjetpilot, johnbakerok,
I greatly appreciate your incites into this subject as engine decisions for my RV are one of the issues I am really deliberating hard over.
johnbakerok, I am also very interested in flying as cheaply as possible. So the IO-320 is an engine that I have not ruled out. However, one of the factors that is pulling me toward the IO-360 in my RV9A (even though Van's does not recommend anything over the 160 hp Lycoming for this airplane) is the fact that I am as much interested in using some of the "newer" (really not new at all) technologies that are being utilized in some of the new lycoming clones. I definetly am not at all interested in a carbeurated engine! If I am forced to accept old school manufacturing of engines, I sure hope I can at least replace 70 year old technology when it comes to fuel systems and ignition systems.
Gmcjetpilot's weight measurements are showing that an IO-320 weighs 259 lb while the IO-360 weighs 270 lbs. Since the price difference of these two engines is relatively non-existant, I am inclined to go ahead and buy the IO-360 when I can have a 20 hp gain for the difference in weight. I intend to use my airplane for XC flying. Being able to cruise higher while throttling back to conserve fuel is important to me. So is my ability to climb out of short fields on high density hot summer days with a fully loaded airplane.
I agree with all of you concerning the need to match the engine of the aircraft with the mission of the flying intended for the airplane. So far in my research, balancing price, performance, efficiencies, weight, durability and resale value I am seeing that for what I hope to do with my plane the best choice is going to be the IO-360 when it comes to existing available "aircraft" engines. Of course, since I am a far cry away from installing said engine I could have my mind changed if someone out there presents new information on some new engine design that meets these needs. Dan's comments that his 200 hp IO-360 is burning less fuel while having the added hp greatly intrigues me. Enough that I felt compelled to respond to this thread rather than simply sit back and read others post to it.
Again, thanks for all the very interesting input on these engine choices. I look forward to being able to continue to read further posts on the subject.
Steve
RVBYSDI
Kentb, gmcjetpilot, johnbakerok,
I greatly appreciate your incites into this subject as engine decisions for my RV are one of the issues I am really deliberating hard over.
johnbakerok, I am also very interested in flying as cheaply as possible. So the IO-320 is an engine that I have not ruled out. However, one of the factors that is pulling me toward the IO-360 in my RV9A (even though Van's does not recommend anything over the 160 hp Lycoming for this airplane) is the fact that I am as much interested in using some of the "newer" (really not new at all) technologies that are being utilized in some of the new lycoming clones. I definetly am not at all interested in a carbeurated engine! If I am forced to accept old school manufacturing of engines, I sure hope I can at least replace 70 year old technology when it comes to fuel systems and ignition systems.
Gmcjetpilot's weight measurements are showing that an IO-320 weighs 259 lb while the IO-360 weighs 270 lbs. Since the price difference of these two engines is relatively non-existant, I am inclined to go ahead and buy the IO-360 when I can have a 20 hp gain for the difference in weight. I intend to use my airplane for XC flying. Being able to cruise higher while throttling back to conserve fuel is important to me. So is my ability to climb out of short fields on high density hot summer days with a fully loaded airplane.
I agree with all of you concerning the need to match the engine of the aircraft with the mission of the flying intended for the airplane. So far in my research, balancing price, performance, efficiencies, weight, durability and resale value I am seeing that for what I hope to do with my plane the best choice is going to be the IO-360 when it comes to existing available "aircraft" engines. Of course, since I am a far cry away from installing said engine I could have my mind changed if someone out there presents new information on some new engine design that meets these needs. Dan's comments that his 200 hp IO-360 is burning less fuel while having the added hp greatly intrigues me. Enough that I felt compelled to respond to this thread rather than simply sit back and read others post to it.
Again, thanks for all the very interesting input on these engine choices. I look forward to being able to continue to read further posts on the subject.
Steve
RVBYSDI
Apples to apples comparisons are difficult
Steve,
Don't be surprised if you don't exactly meet your weight predictions (although it sounds like that does not matter to you too much). I think George's numbers require much more detail concerning accessories before being taken as gospel. I find it hard to believe that a 160hp engine is 10lb heavier than a 150? Also a Superior O-360 will not weigh the same as a similar Lycoming in the same state (for example, I believe a set of Superior cylinders are 3-4lb heavier than a set of Lycomings) - but this is probably spiltting hairs.
As for fuel consumption, all I can say is that it's not just Dan's experience that the bigger the engine the lower the consumption for any given speed. When I have flown my 150hp fp 6A with 180hp cs 6s side by side on long trips the 180hp aircraft always burn less - usually by over a gallon an hour. I am usually running WOT (so around 65% at 7500/8500/9500'). If we flew at 120 kt then the story might be different - but not many RV pilots cruise at 120 kt! I am told that when 180hp aircraft fly with 200hp aircraft the story is the same again.
The issue with 200hp engines is that they are much more expensive (can be $8K more expensive).
All in all an interesting thread. Pete.
Steve,
Don't be surprised if you don't exactly meet your weight predictions (although it sounds like that does not matter to you too much). I think George's numbers require much more detail concerning accessories before being taken as gospel. I find it hard to believe that a 160hp engine is 10lb heavier than a 150? Also a Superior O-360 will not weigh the same as a similar Lycoming in the same state (for example, I believe a set of Superior cylinders are 3-4lb heavier than a set of Lycomings) - but this is probably spiltting hairs.
As for fuel consumption, all I can say is that it's not just Dan's experience that the bigger the engine the lower the consumption for any given speed. When I have flown my 150hp fp 6A with 180hp cs 6s side by side on long trips the 180hp aircraft always burn less - usually by over a gallon an hour. I am usually running WOT (so around 65% at 7500/8500/9500'). If we flew at 120 kt then the story might be different - but not many RV pilots cruise at 120 kt! I am told that when 180hp aircraft fly with 200hp aircraft the story is the same again.
The issue with 200hp engines is that they are much more expensive (can be $8K more expensive).
All in all an interesting thread. Pete.
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osxuser
Well Known Member
The statement about the bigger power pulse isn't true. The O-360 and O-320 bore is exactly the same. The difference is the length of the stroke. The power pulse on a lycoming derived engine will always be to rough to be pleasent, unfortunely, Continental doesn't have a equvialent design over 125 HP.
Here is Apple/Oranges for you. I currently fly a Cessna 177 Cardinal (O-360 A1A, Harzell CS). The is a Carb and mags, certified Lycoming, in a certfied airframe. No variables such as EI or EFI. I flight plan for 7.5GPH on a long trip, WOT/2350rpm at 10,000' running as lean as the engine will run. Once your below 65% power, your not going to damage the engine by running LOP or at peak, so thats not an issue up high. I went from Brackett Field, CA (KPOC) to Klamath Falls Oregon on 37 Gallons. Now with an O-320 F/P that came with the C-177, that would have been quite impossible, only because it doesn't have enough power to get up to 10,500' where I was cruising. Because of that, I would have had to be lower, and run a higher power setting to get the some ground speed. With the higher power setting I wouldn't have been able to run the mixture LOP, and would have been burning quite a bit more gas.
The above is nothing that hasn't already been said on this thread, and the apples/oranges part comes in here. The C-177 is under powered with the stock O-320, and the STCed O-360/CS setup remedies the problem. The RV on the other had is already overpowered with the O-320, so the curve (As was mentioned before) is on the downhill side.
I must also point out however, the 30LB difference you speak of is between a O-320 and a ANGLE VALVE IO-360 which is a difference of at least 40HP. The difference in weight between an O-320 and PARRALLEL VALVE O-360 (In the conversion of the C-177 at least) was 8LB. Which can be made up for either by tuneing the durn thing, or by putting on skytec starter. The constent speed prop is a must on any installation that your planning to go anywhere in. The FP will be outperformed on one side (climb) or the other (cruise) so it's pointless to try to compare the weight savings there unless your planning on <100NM trips down low.
My current problem is deciding between a TNIO-320 or TNIO-360 for my yet-to-be-aquired RV-7. I think I'm gonna go with the 360 because of the better climb performance. Also because the guys I'll be flying with all have Lancairs or Glasairs, and I need the little bit of edge that 180HP will provide. My main reason for deciding on Turbo Normalized power is my constant desire to go HIGH. I plan on a balence FI so I can run LOP at 75% power, and that should get me where I need to go on decent amounts of fuel really high (Average cruise altitude is 10K with a C-177, can you imagine with an RV where I'll be?)
Here is Apple/Oranges for you. I currently fly a Cessna 177 Cardinal (O-360 A1A, Harzell CS). The is a Carb and mags, certified Lycoming, in a certfied airframe. No variables such as EI or EFI. I flight plan for 7.5GPH on a long trip, WOT/2350rpm at 10,000' running as lean as the engine will run. Once your below 65% power, your not going to damage the engine by running LOP or at peak, so thats not an issue up high. I went from Brackett Field, CA (KPOC) to Klamath Falls Oregon on 37 Gallons. Now with an O-320 F/P that came with the C-177, that would have been quite impossible, only because it doesn't have enough power to get up to 10,500' where I was cruising. Because of that, I would have had to be lower, and run a higher power setting to get the some ground speed. With the higher power setting I wouldn't have been able to run the mixture LOP, and would have been burning quite a bit more gas.
The above is nothing that hasn't already been said on this thread, and the apples/oranges part comes in here. The C-177 is under powered with the stock O-320, and the STCed O-360/CS setup remedies the problem. The RV on the other had is already overpowered with the O-320, so the curve (As was mentioned before) is on the downhill side.
I must also point out however, the 30LB difference you speak of is between a O-320 and a ANGLE VALVE IO-360 which is a difference of at least 40HP. The difference in weight between an O-320 and PARRALLEL VALVE O-360 (In the conversion of the C-177 at least) was 8LB. Which can be made up for either by tuneing the durn thing, or by putting on skytec starter. The constent speed prop is a must on any installation that your planning to go anywhere in. The FP will be outperformed on one side (climb) or the other (cruise) so it's pointless to try to compare the weight savings there unless your planning on <100NM trips down low.
My current problem is deciding between a TNIO-320 or TNIO-360 for my yet-to-be-aquired RV-7. I think I'm gonna go with the 360 because of the better climb performance. Also because the guys I'll be flying with all have Lancairs or Glasairs, and I need the little bit of edge that 180HP will provide. My main reason for deciding on Turbo Normalized power is my constant desire to go HIGH. I plan on a balence FI so I can run LOP at 75% power, and that should get me where I need to go on decent amounts of fuel really high (Average cruise altitude is 10K with a C-177, can you imagine with an RV where I'll be?)
kentb
Well Known Member
Imho
osxuer,
I think that the bigger pulses are there. If not why would there be rpm restriction with 360 engine and certian props? Also when you add electronic ignition there are more restrictions on rpm with the 360, but not with the 320.
You have the same number of power pulses per minute and are getting more power. You will have bigger pulses of power with each ignition of fuel.
steve,
I know of someone at Indepence, Or. that put a 360 in an RV9A. He justified it, because he would give up the CS prop and the weight would be the same.
He has sense stated that he wished he had stuck with Vans recomindation.
I want to be able to go as fast as I can, use the least amount of fuel and do it with the lease money spent. You don't always get to do what you want, but I think that going with the largest engine (wieght/hp) that is recomended for the airframe is as close as is reasonable to do.
I am putting an IO320 with Hartzel CS prop and an electronic ignition in place of one mag. This will be a little on the heavy side for RV9A's, but the combination will get me off the ground quick (even at high airports out west), let me set economic cruse (fuel useage) and will have no prop rpm rescrictions.
This setup is traditional enough that I will only have 25 hour fly off, and resale value will be highest. I think that if you have that does not fall with in the recommendation of the designer you will decrease your resale value.
Happy building,
Kent
osxuer,
I think that the bigger pulses are there. If not why would there be rpm restriction with 360 engine and certian props? Also when you add electronic ignition there are more restrictions on rpm with the 360, but not with the 320.
You have the same number of power pulses per minute and are getting more power. You will have bigger pulses of power with each ignition of fuel.
steve,
I know of someone at Indepence, Or. that put a 360 in an RV9A. He justified it, because he would give up the CS prop and the weight would be the same.
He has sense stated that he wished he had stuck with Vans recomindation.
I want to be able to go as fast as I can, use the least amount of fuel and do it with the lease money spent.
You don't always get to do what you want, but I think that going with the largest engine (wieght/hp) that is recomended for the airframe is as close as is reasonable to do.I am putting an IO320 with Hartzel CS prop and an electronic ignition in place of one mag. This will be a little on the heavy side for RV9A's, but the combination will get me off the ground quick (even at high airports out west), let me set economic cruse (fuel useage) and will have no prop rpm rescrictions.
This setup is traditional enough that I will only have 25 hour fly off, and resale value will be highest. I think that if you have that does not fall with in the recommendation of the designer you will decrease your resale value.
Happy building,
Kent
osxuser
Well Known Member
It really depends on the (I)O-360 used. I believe the -A1B6 has no restrictions because of the harmonic balence on the crank. I obviously have no proof of my observations, just what would appear to be logical to me. I've also never noticed a difference in the smoothness of the O-360A1A I fly on the Cardinal and the O-320H2AD or E2D's that I've flown on 172's.kentb said:
Marginally at worst
steve,
I know of someone at Indepence, Or. that put a 360 in an RV9A. He justified it, because he would give up the CS prop and the weight would be the same.
He has sense stated that he wished he had stuck with Vans recomindation.
I want to be able to go as fast as I can, use the least amount of fuel and do it with the lease money spent.
I am putting an IO320 with Hartzel CS prop and an electronic ignition in place of one mag. This will be a little on the heavy side for RV9A's, but the combination will get me off the ground quick (even at high airports out west), let me set economic cruse (fuel useage) and will have no prop rpm rescrictions.
This setup is traditional enough that I will only have 25 hour fly off, and resale value will be highest. I think that if you have that does not fall with in the recommendation of the designer you will decrease your resale value.
Happy building,
Kent
I don't think that putting an (I)O-360 in a RV9 would hurt the value at all. I think a high percentage of them are built that way. That said the 320 is a great engine as well, and I think that the CS prop is a must either way. So if I had to choose between a 360 FP or a 320 CS I'd have to go with the 320 too. But this is coming from a guy who wanted to built his own crossflow Lyc IO-360 out of TIO540 Cylinders and high comp pistons, I just like power I guess. Now I'm going for IO-360 turbo normalized.
gmcjetpilot
Well Known Member
The golden rule and a Turbo RV to fly with Lancairs?
Coming from a Cessna I guess you are just thinking of building your first kit plane at this point. A suggestion is to keep it simple, light and build it per plans. Forget power pulses, keep it simple and start building.
Cheers George RV-4, RV-7
I am not sure how you can make the comment, "A high percentage (RV-9's) are built that way ((I)O-360). I suggest the golden rule: Build it per plans. Van's aircraft has designed the RV-9(A) airframe around the (I)O-320 engine and a max 160HP. I would not exceed Van's recommended, weight, HP. If you want an (I)O-360 build a RV-7. As the builder you can modify your kit as you like, but unless you have experience as an aircraft designer you can get your self into trouble, exceeding airframe load factor or speed limitations.osxuser said:I don't think that putting an (I)O-360 in a RV9 would hurt the value at all. I think a high percentage of them are built that way. That said the 320 is a great engine as well, and I think that the CS prop is a must either way. So if I had to choose between a 360 FP or a 320 CS I'd have to go with the 320 too. But this is coming from a guy who wanted to built his own crossflow Lyc IO-360 out of TIO540 Cylinders and high comp pistons, I just like power I guess. Now I'm going for IO-360 turbo normalized.
I must point out the delta weight between an O-320 to IO-360 (200hp) is more like +40lbs, and finished RV's using these two engines have delta empty weights in the order of 70-118 lbs. The engine and installation of an IO-360 (200HP) is heavy. Weight is an issue, and if you have not flown a RV before or have much experience with them, you can tell the difference between a light one and a heavy one.osxuser said:
You may want to build a Lancair or Glasair. RV's are well suited for lower altitudes and for local flying in and out of short strips, fun aerobatics as well as occasional cross-country flights (where you can still see the ground). If you want to climb to altitude and suck O2 for fun, than by all means get a turbo charger. However the RV is designed for a "Total Performance" mission, as Van would say; A normal aspirated engine is well suited for the RV mission, fun. Sucking O2 at altitude is not fun for me. I fly enough at flight levels at work; down low is where the fun is. Even with normal aspirated engine you can fly well in the O2 altitudes with a RV. (I have been to 17,500 in my RV-4, but it is most happy in the lower teens solo and 8,500-12,500 at gross.) Have you ever owned a turbo charged engine? There are a few turbo RV's. It has been done, but it is crowded under the cowl. Also flying freight and charters years ago in turbo twins, I can tell you turbo chargers are a big maintenance issue. I always heard the mechanics talk about it. However if that is going to float your boat go for it, but I think a turbo charger is a better match in a Lancair if you are going to fly high long distance from one super slab runway to another, most of the time. The RV is for fun, flying just for the sake of flying, so it lends itself for formation flying, aerobatics, local dog fights and short X-C fly outs, as well as the occasional long X-C flights. A turbo is a waste of money, but if you just want to motor along straight and level at altitude with O2 than a RV will do that, but there are better airframes for this kind of flying. If you want to just fly along with Lancairs, get a Lancair. With a turbo the RV will do a OK job keeping up with a turbo Glasair or Lancair at altitude, but you will have a hard time. That is not what the RV is about.osxuser said:
Coming from a Cessna I guess you are just thinking of building your first kit plane at this point. A suggestion is to keep it simple, light and build it per plans. Forget power pulses, keep it simple and start building.
Cheers George RV-4, RV-7
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RVbySDI
Well Known Member
Hmmm!
If you know any more specifics on your acqaintence's complaint about the 360 I would like to hear more.
My thoughts on putting an IO-360 in my RV9A has been driven by the cost and the weight of the engine. From my initial research the difference in price for an IO-360 and an IO-320 is negligable if not non-existant all together. In fact, some manufacturers are quoting a cheaper price for the IO-360 over the IO-320. With price not an issue then weight becomes the other deciding factor. So far I have not seen any numbers that show me that a 180 HP IO-360 weight is going to be more to the point that the added weight would offset the additional 20 HP. In addition, after talking with ECI at Oshkosh I am very interested in their new induction system, fuel injection system and cylinders. They were claiming that these changes will shave a considerable amount of weight off of their engines (somewhere around 10-14 lbs). If so, then given the weight numbers everyone is talking about concerning the 360 and 320 engines, going with a fixed pitched cruise prop with the newer ECI engine and its component systems could offset whatever that weight difference may be between the 180 HP IO-360 and the 160 HP IO-320. If this proves to be true, then, along with the price between the two engines, the weight difference becomes a non-factor also.
I would welcome comments from anyone who would have any first hand knowledge about the motivation for Van's limitations on engine sizes. With my limited experience with RV construction, and more importantly with RV design, my thoughts are that weight is a primary reason why Vans has chosen to limit the engine choice for the RV9 to the 160 HP engines. Yes, I do acknowledge that the airframe does not require and therefore may not benefit from a higher HP engine, especially at cruise. But I do not see why it could not benefit from the added HP during take-off.
The factors that tend to direct me toward thinking about the IO-360 are based on price and weight of the engine. So given that these two variables could very well turn out to be non-issues I find myself leaning toward supplying the airframe with the extra 20 HP that the IO-360 can provide. I definetly welcome any and all comments on these engines but so far there has not been anyone that has given me a definitive, indisputable reason why the limitation is set at 160 HP on the engine choices for the RV9 and consequently why a 180 HP IO-360 wouldn't work as well or maybe better. I am definetly not interested in the 200 HP version and have no problems recognizing that that higher HP engine is major overkill with this plane. But I do not see that the issue is as "cut and dried" with the 180 HP engine.
If any of my thoughts are in error I welcome reading any and all posts that shoot down my "theories". I just request that they be mercy shootings rather than cold blooded pot shots as I am just your average guy with no great amounts of knowledge or experience that, perhaps for reasons of insanity, has decided that being able to build an airplane is a real possibility. Therefore, I am ill equiped to be able to avoid or repel such said pot shots.
Steve
RVBYSDI
If you know any more specifics on your acqaintence's complaint about the 360 I would like to hear more.
My thoughts on putting an IO-360 in my RV9A has been driven by the cost and the weight of the engine. From my initial research the difference in price for an IO-360 and an IO-320 is negligable if not non-existant all together. In fact, some manufacturers are quoting a cheaper price for the IO-360 over the IO-320. With price not an issue then weight becomes the other deciding factor. So far I have not seen any numbers that show me that a 180 HP IO-360 weight is going to be more to the point that the added weight would offset the additional 20 HP. In addition, after talking with ECI at Oshkosh I am very interested in their new induction system, fuel injection system and cylinders. They were claiming that these changes will shave a considerable amount of weight off of their engines (somewhere around 10-14 lbs). If so, then given the weight numbers everyone is talking about concerning the 360 and 320 engines, going with a fixed pitched cruise prop with the newer ECI engine and its component systems could offset whatever that weight difference may be between the 180 HP IO-360 and the 160 HP IO-320. If this proves to be true, then, along with the price between the two engines, the weight difference becomes a non-factor also.
I would welcome comments from anyone who would have any first hand knowledge about the motivation for Van's limitations on engine sizes. With my limited experience with RV construction, and more importantly with RV design, my thoughts are that weight is a primary reason why Vans has chosen to limit the engine choice for the RV9 to the 160 HP engines. Yes, I do acknowledge that the airframe does not require and therefore may not benefit from a higher HP engine, especially at cruise. But I do not see why it could not benefit from the added HP during take-off.
The factors that tend to direct me toward thinking about the IO-360 are based on price and weight of the engine. So given that these two variables could very well turn out to be non-issues I find myself leaning toward supplying the airframe with the extra 20 HP that the IO-360 can provide. I definetly welcome any and all comments on these engines but so far there has not been anyone that has given me a definitive, indisputable reason why the limitation is set at 160 HP on the engine choices for the RV9 and consequently why a 180 HP IO-360 wouldn't work as well or maybe better. I am definetly not interested in the 200 HP version and have no problems recognizing that that higher HP engine is major overkill with this plane. But I do not see that the issue is as "cut and dried" with the 180 HP engine.
If any of my thoughts are in error I welcome reading any and all posts that shoot down my "theories". I just request that they be mercy shootings rather than cold blooded pot shots as I am just your average guy with no great amounts of knowledge or experience that, perhaps for reasons of insanity, has decided that being able to build an airplane is a real possibility. Therefore, I am ill equiped to be able to avoid or repel such said pot shots.
Steve
RVBYSDI
Steve,
I can tell you this, a TMXIO-360 vertical sump engine weighs in at 7 lbs more then a TMXIO-320 vertical sump engine configured with the same accessories. These are not book weights but actual weight differences, of complete engines, on the same scale. Same approximate 7lb difference when both are configured with a carburetor. I would assume that those weight differences would hold true for two engines from Lycoming. However, if you were to compare a Superior IO/O-360 to the Lycoming 320 or our TMX320 the weight difference would jump up a bit as the XP360 is heavier then the engine from Lycoming or us.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts
are hopefully helpful to you. Please use the information provided responsibly and at you own risk."
I can tell you this, a TMXIO-360 vertical sump engine weighs in at 7 lbs more then a TMXIO-320 vertical sump engine configured with the same accessories. These are not book weights but actual weight differences, of complete engines, on the same scale. Same approximate 7lb difference when both are configured with a carburetor. I would assume that those weight differences would hold true for two engines from Lycoming. However, if you were to compare a Superior IO/O-360 to the Lycoming 320 or our TMX320 the weight difference would jump up a bit as the XP360 is heavier then the engine from Lycoming or us.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts
are hopefully helpful to you. Please use the information provided responsibly and at you own risk."
gmcjetpilot
Well Known Member
I think Van could answer the question best since they designed the kit and have been doing it for 30 years or so. My guess is with more than 160 hp you can exceed placard airspeed limitations. There are many planes out there (including the jet I fly) that can easily exceed Vne/Vmo in level flight.RVbySDI said:
As far as engine weight I did a survey of over 115 completed RV's with all kinds of engines and props. Empty weights are always less with (I)O-320's than (I)O-360's (comparing like props). Obviously you can save weight and make up difference in engine weight in other areas (prop, avionics, paint, interior, lights), so weight of the engine may not be a big factor if you don't go crazy with other items.
From my data: The differnce in empty weight is about 47LBs between 320's and 360's with fixed pitch props. Not real scientific there are is a real differences in actual finished RV's. The avg weight of RV-7A's are 52LB's heaver than RV-9A's.
Total...Prop..........MIN......MAX......AVG
60.......FIX...........874......1170......1041
55.......CS...........1010......1244......1111
41.......320...........874......1168......1034 \
60.......360...........986......1189......1084 /..50lb delta
14.......IO360.......1103.....1244......1151
32.......320Fix........874......1106......1019 \
28.......360Fix........986......1170......1066 /..47lb delta
9.........320CS......1010......1168......1084 \
32.......360CS......1026......1189......1101 /..17lb delta
14.......IO360CS...1103......1244......1151
(320 & 360 is both carb and FI, IO360 = 200HP only)
From Lycomings web site the delta weight is 11LBs between a IO-320 and IO-360 (18HP) engines.
Cheers George
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ddurakovich
Well Known Member
Is it possible that there is a mentality out there that believes that "Since I have a bigger engine I can therefore haul a bigger load, so I don't need to worry about total weight?" As such, there is less attention paid to keeping overall weight down.gmcjetpilot said:
The obvious fallacy of that is airframe stress loading, but I wonder.....
Dave
osxuser
Well Known Member
gmcjetpilot said:
First of all, I'm building a 7, not 9. So this whole conversation is scholastic in nature for me. As mentioned above, the weight delta for a parallel O-360 and
O-320 is not much. The specific fuel consumption of the O-360 is better anyway, so you could alway derate the IO-360 to 160HP (Ala C172R) and restrict the RPM to 2400rpm to save on noise.
I'm an professional A&P mechanic, so I know aircraft systems very well. I've seen the way the RV is built, and thats why I choose to build it over the plastic airplanes. Turbo normalizing is a very smart way to go because it keeps the engine within it's operating pressures, as well as keeping the specific fuel consumption high. It also maximizes the airframes cruise efficiency. I use airplanes to go places, if I was doing afternoon flying, i'd buy a pitts. Plastic airplanes don't appeal to me, I've thought about a RV 9 or 10, but the 7 is faster than the 9, and the 10 just costs too much. I have considered what I want for quite a while, and know the 7 is for me.
gmcjetpilot
Well Known Member
To turbo or not?
"Turbo normalizing is a very smart way to go because it keeps the engine within it's operating pressures, as well as keeping the specific fuel consumption high." Yes it will keep the fuel consumption high, that is not all goodness. Really you will not improve fuel consumption; I fact it will increase it. You will however (may be?) improve fuel burn per miles, miles per gallon (if your high flying does not put you into headwinds). The ability to keep high % HP at high altitudes is the key to "normalizing" turbo charging. Turbo benefit is only going to start kicking in above 8,000 feet. To really get the benefit you need to be sniffing O2 and fly above 12,500. May be go the FL180 and get an IFR clearance (required). This may be the way you fly so great. The best way to improve fuel efficency is with higher compression, whether thru HC pistons, turbo (boost) or supercharger. Boost is good but has very critical pilot operational requirements. As far as "keeping within it's operating pressures", even a normalizing turbo will actually make temps: Oil, CHTs and Turbine Inlet more critical with increasing altitude. Less air density less cooling available.
Let's not make "Turbo" more complicated than it is; it just compresses intake air going into the engine for greater density, using a turbine powered by exhaust gases. That is IT. Compressing air makes it hot. Hot air going into the engine can cause detonation and robs the engine of power, so it needs to be cooled with an intercooler. An intercooler is simply an air-to-air heat exchanger. This allows you to maintain more power to a higher altitude, thus allowing you to take advantage of less airframe drag by flying higher (due to less air density at altitude). You can still fly high with out a turbo, but you will be going slower than the same engine turbo charged. This is good because the higher you go the less power you make, the less gas you burn. The turbo at higher power will go faster but it will burn more fuel than if you did not have a turbo. Flying slower (with out a turbo) puts you closer to the best L/D (L over D or Lift over Drag). So you may arrive a little later with out the turbo but you will burn less gas. The myth of Turbo dispelled, faster yes (may be depending on winds aloft) but less gas? NO not really.Also if you want best miles per gallons by flying high and you have nice tail winds, flying slower is better, taking advantage of the winds. Remember the Turbo just lets you burn more fuel higher up. Since we are not pressurized (cabin) a turbo is not needed for that purpose.
As far as It also maximizes the airframes cruise efficiency." Due to Vne, you will run in to flutter limits of the airframe very very fast, thus limiting the speed you can fly at altitude due to airframe limits. If you don't believe me call Van's aircraft and ask them what the draw back is of a turbo on a RV. You can't exceed Vne with out risk of flutter. Remember Vne is based on TAS not IAS or CAS.
Most GA pilots do not understanding high altitude flight or do they need to. You know what the coffin corner is? As you know the higher you fly the higher your stall true airspeed will be. Also the higher you fly the lower your indicated flutter speed (Vne) will be. At some altitude the two will run together. Going faster will cause flutter and going slower will cause a stall. This is called the coffin corner and happens to commercial jets, depending on weight and thrust available in the high 30 to 40 thousand feet. So if you want to fly above say 18,000 Feet (FL180 or Flight-level-one-eight-oh) you need an IFR flight plan. Oh Joy. Lets assume your turbo gets you to FL250, which it should since a non-turbo will crawl to FL230 to FL250, you start running into very cold temps and a frosted windscreen. An O2 mask will now be needed, Oxygen cannulas are no good. Lets say you fly higher? You need DME. Well lets just stop here. What are you doing at FL250 in a single engine airplane for a routine flight? The time to climb to that altitude and fuel on board is just not an efficient flight profile. This is all assuming you can maintain engine temps and airframe hi-lo limits. So you say you added more fuel capacity. Great Turbo, fuel and no payload due to gross weight limits. Also flying in the flight levels in a single engine non-pressurized aircraft is sporty. You will be on airways, not flying direct and likely getting vectored OFF the airway and back to make room for faster traffic. Basically you will be in the way. Trust me I once flew a Cessna Citation II (Slow-tation, bird strike from the rear and all that); I was is the way at Mach .65 in the low 30's. I just don't see the RV being a good airframe for a Turbo. A Lancair, with more fuel, pressurization, higher aspect ratio wing and higher flutter speed...Yea, but than Lancairs are not flying out of 1000 foot grass strips. Of course you can buy 2 or 3 RVs for the price of a Lancair.
As a Pro Mechanic you understand limitations. So throwing on a turbo will actually make more issues regarding airframe and engine temp / detonation limits. If you just throw a turbo on an existing engine you may want to read the key reprints from Lycoming regarding this mod, or call Lycoming and ask about field turbo mods and burned pistons. I think you said you where going to buy an engine Lycoming designed for a turbo? $$$$$$$$$ What is that going to cost with an intercooler? I just can't see this is a must have.
My point is the RV is not that kind of plane, and RV's don't need turbo chargers to perform well at altitude. If you are going on your Cessna's performance with an 180HP and C/S prop, you need to fly a RV, if you have not already. I don't know if you have flown a RV or not, so sorry. With the engine you have in your Cessna, in a RV-7, I guarantee it will roll your socks down. You will be quite happy with the performance with out a Turbo. It will rock your world. If you are trying to keep cost down and make it simple, light and per plans, trust me, you don't NEED a turbo charger, but your the man.
I look forward to seeing you project turbo or not. One last note, have you flown with O2 for extended periods? I have, in a Ted Smith Aerostar TS61, for hours and hours, and O2 is miserable and dries you out. Filling bottles is a pain, but you know that already. Also despite the claim a RV-7 NEEDS weight on the nose, it does not. The lighter the better. What will a turbo cost in dollars, weight & build time?
If that is what you want, than that is that. I am a professional pilot and a former aerospace engineer/consultant, in my opinion the turbo is not a good match for the RV for they way most fly, except in the most special cases, such as you say. Pitts special or not, when you get your RV flying I guarantee you will be doing a lot more local flying and loops-N-rolls with out your Lancair buddy. RV's are just too much fun to bore holes in the sky, straight and level, sucking O2 with dry nasal passages, but each to his own.
It is common to think the turbo is magic. Well it is, it lets you go faster higher up, while burning more gas. There is no free lunch. You will pay dearly for a turbo. The RV is about Fun and low maintenance and flys like hell on wings with out a turbo. Not trying to talk you out of it, but you make it sound like a no brainer. Many have thought about turbos on RV's for a long time. There are reasons why there are so few.
Cheers George
If you still want a turbo? Look at this mess of an installation:
http://www.vansairforce.com/community/showthread.php?t=2649
I love to look at a complex installation, I hate to maintain one.
(click to enlarge, view of oil cooler and big tube goes from NACA scoop to intercooler. Notice the size of the oil cooler!)
Kent, no offense, good choice, I am building my second RV and it is a RV-7.osxuser said:
"Turbo normalizing is a very smart way to go because it keeps the engine within it's operating pressures, as well as keeping the specific fuel consumption high." Yes it will keep the fuel consumption high, that is not all goodness. Really you will not improve fuel consumption; I fact it will increase it. You will however (may be?) improve fuel burn per miles, miles per gallon (if your high flying does not put you into headwinds). The ability to keep high % HP at high altitudes is the key to "normalizing" turbo charging. Turbo benefit is only going to start kicking in above 8,000 feet. To really get the benefit you need to be sniffing O2 and fly above 12,500. May be go the FL180 and get an IFR clearance (required). This may be the way you fly so great. The best way to improve fuel efficency is with higher compression, whether thru HC pistons, turbo (boost) or supercharger. Boost is good but has very critical pilot operational requirements. As far as "keeping within it's operating pressures", even a normalizing turbo will actually make temps: Oil, CHTs and Turbine Inlet more critical with increasing altitude. Less air density less cooling available.
Let's not make "Turbo" more complicated than it is; it just compresses intake air going into the engine for greater density, using a turbine powered by exhaust gases. That is IT. Compressing air makes it hot. Hot air going into the engine can cause detonation and robs the engine of power, so it needs to be cooled with an intercooler. An intercooler is simply an air-to-air heat exchanger. This allows you to maintain more power to a higher altitude, thus allowing you to take advantage of less airframe drag by flying higher (due to less air density at altitude). You can still fly high with out a turbo, but you will be going slower than the same engine turbo charged. This is good because the higher you go the less power you make, the less gas you burn. The turbo at higher power will go faster but it will burn more fuel than if you did not have a turbo. Flying slower (with out a turbo) puts you closer to the best L/D (L over D or Lift over Drag). So you may arrive a little later with out the turbo but you will burn less gas. The myth of Turbo dispelled, faster yes (may be depending on winds aloft) but less gas? NO not really.Also if you want best miles per gallons by flying high and you have nice tail winds, flying slower is better, taking advantage of the winds. Remember the Turbo just lets you burn more fuel higher up. Since we are not pressurized (cabin) a turbo is not needed for that purpose.
As far as It also maximizes the airframes cruise efficiency." Due to Vne, you will run in to flutter limits of the airframe very very fast, thus limiting the speed you can fly at altitude due to airframe limits. If you don't believe me call Van's aircraft and ask them what the draw back is of a turbo on a RV. You can't exceed Vne with out risk of flutter. Remember Vne is based on TAS not IAS or CAS.
Most GA pilots do not understanding high altitude flight or do they need to. You know what the coffin corner is? As you know the higher you fly the higher your stall true airspeed will be. Also the higher you fly the lower your indicated flutter speed (Vne) will be. At some altitude the two will run together. Going faster will cause flutter and going slower will cause a stall. This is called the coffin corner and happens to commercial jets, depending on weight and thrust available in the high 30 to 40 thousand feet. So if you want to fly above say 18,000 Feet (FL180 or Flight-level-one-eight-oh) you need an IFR flight plan. Oh Joy. Lets assume your turbo gets you to FL250, which it should since a non-turbo will crawl to FL230 to FL250, you start running into very cold temps and a frosted windscreen. An O2 mask will now be needed, Oxygen cannulas are no good. Lets say you fly higher? You need DME. Well lets just stop here. What are you doing at FL250 in a single engine airplane for a routine flight? The time to climb to that altitude and fuel on board is just not an efficient flight profile. This is all assuming you can maintain engine temps and airframe hi-lo limits. So you say you added more fuel capacity. Great Turbo, fuel and no payload due to gross weight limits. Also flying in the flight levels in a single engine non-pressurized aircraft is sporty. You will be on airways, not flying direct and likely getting vectored OFF the airway and back to make room for faster traffic. Basically you will be in the way. Trust me I once flew a Cessna Citation II (Slow-tation, bird strike from the rear and all that); I was is the way at Mach .65 in the low 30's. I just don't see the RV being a good airframe for a Turbo. A Lancair, with more fuel, pressurization, higher aspect ratio wing and higher flutter speed...Yea, but than Lancairs are not flying out of 1000 foot grass strips. Of course you can buy 2 or 3 RVs for the price of a Lancair.
As a Pro Mechanic you understand limitations. So throwing on a turbo will actually make more issues regarding airframe and engine temp / detonation limits. If you just throw a turbo on an existing engine you may want to read the key reprints from Lycoming regarding this mod, or call Lycoming and ask about field turbo mods and burned pistons. I think you said you where going to buy an engine Lycoming designed for a turbo? $$$$$$$$$ What is that going to cost with an intercooler? I just can't see this is a must have.
My point is the RV is not that kind of plane, and RV's don't need turbo chargers to perform well at altitude. If you are going on your Cessna's performance with an 180HP and C/S prop, you need to fly a RV, if you have not already. I don't know if you have flown a RV or not, so sorry. With the engine you have in your Cessna, in a RV-7, I guarantee it will roll your socks down. You will be quite happy with the performance with out a Turbo. It will rock your world. If you are trying to keep cost down and make it simple, light and per plans, trust me, you don't NEED a turbo charger, but your the man.
I look forward to seeing you project turbo or not. One last note, have you flown with O2 for extended periods? I have, in a Ted Smith Aerostar TS61, for hours and hours, and O2 is miserable and dries you out. Filling bottles is a pain, but you know that already. Also despite the claim a RV-7 NEEDS weight on the nose, it does not. The lighter the better. What will a turbo cost in dollars, weight & build time?
If that is what you want, than that is that. I am a professional pilot and a former aerospace engineer/consultant, in my opinion the turbo is not a good match for the RV for they way most fly, except in the most special cases, such as you say. Pitts special or not, when you get your RV flying I guarantee you will be doing a lot more local flying and loops-N-rolls with out your Lancair buddy. RV's are just too much fun to bore holes in the sky, straight and level, sucking O2 with dry nasal passages, but each to his own.
It is common to think the turbo is magic. Well it is, it lets you go faster higher up, while burning more gas. There is no free lunch. You will pay dearly for a turbo. The RV is about Fun and low maintenance and flys like hell on wings with out a turbo. Not trying to talk you out of it, but you make it sound like a no brainer. Many have thought about turbos on RV's for a long time. There are reasons why there are so few.
Cheers George
If you still want a turbo? Look at this mess of an installation:
http://www.vansairforce.com/community/showthread.php?t=2649
I love to look at a complex installation, I hate to maintain one.
(click to enlarge, view of oil cooler and big tube goes from NACA scoop to intercooler. Notice the size of the oil cooler!)
Last edited:
RVbySDI
Well Known Member
Weight is important!
Thanks Mahlon, GMCJetPilot, Osxuser, Kentb.
Mahlon I looked for you at Oshkosh but never was able to find you there. Were you at Oshkosh? I was hoping to be able to talk to you in some detail about engines. I went to the Teledyne Continental tent that had the Mattituck sign on it but no one that I asked could direct me to you. Anyway, about the engine choices, weight of the firewall forward components is very important to me, not just the engine weight by itself. I intend to fly with a fixed pitch cruise prop on my RV9. I feel that going with a constant speed only increases the weight and complexity of the firewall forward. Even though many feel that flying with a constant speed increases your management of speed I don't feel the need for it with the RV.
I do intend to build light. I hope it turns out to be a reality as I am aware of the dreaded weight creep that occurs in the build process. I have built one plane already (not an RV) and that is exactly what happened with it. I intended to keep it as light as possible but the total weight ended up exceeding my target by 25 lbs. In fact I have just added an ELT to that plane so now I am creeping up even more. Everytime I add functionality to the plane I increase weight a pound at a time.
All of this is to say that at present I have not made my mind up about the IO-360 vs. IO-320. As I have been saying, it boils down to price and weight. The reality is that if those two variables could be met with other engine designs I wouldn't be looking at Lycoming clones in the first place and perhaps would be installing a Subaru or Rotary engine. I think they have more current up to date systems that function much better than the "airplane" engines. I know, I know, they are not time tested like the Lycomings/Continentals. However, since those engines do not seem to be falling under my budget for either price or weight I am looking at the old technology instead of the new.
Hey Eggenfelner, and others in your position, read this to say that I believe you would outsell Lycoming in a heart beat if you wouldn't charge premium prices for new technology!!! People do not want to pay premium prices for unproven design! If you want a business model down this line, lets see. . . I don't know. . . Oh, I know, what about say MICROSOFT! Now there is a business model that sure seems to be working. Look back to their start when they were pricing their systems against big ol' giants like Lycoming. I think that giant was called IBM. They definetly did not charge premium prices for their new software programs to try to outperform IBM but look where they are now!
Wow, sorry guys. Got way off topic on that thought. My appologies to all.
GMCJetpilot even though I am not interested in Turbos I found your post on that issue extremely interesting and informative. As far as your posts on the weights, that information is extremely helpful also. It all gives me food for thought. As far as the flutter speeds for the RV (Vne) and higher HP engines pushing the airframe to that level or beyond, I am aware that is an issue with the 180 HP engine. However, I would hope that I can become as good a pilot handling my "overpowered" RV in the same responsible manner as you do while piloting your "overpowered" jet aircraft. If I am able to instill in my flying habits the same amount of knowledge about the engine/airframe construction as the builder had when he built it I think I should be able to fly it responsibly.
Lastly, Kentb and Osxuser I appologize for interjecting my conversation about RV9's in this RV7 thread. I had initially looked at this thread as a discussion of engine differences regardless of the type of aircraft it was going into. I was not aware until later on that it was in the RV7 thread of postings. I think that whichever airframe we all are choosing the discussion of which engine to use is always going to be a valid discussion. I will continue to read with enthusiasm further postings on the subject.
Steve
RVBYSDI
Thanks Mahlon, GMCJetPilot, Osxuser, Kentb.
Mahlon I looked for you at Oshkosh but never was able to find you there. Were you at Oshkosh? I was hoping to be able to talk to you in some detail about engines. I went to the Teledyne Continental tent that had the Mattituck sign on it but no one that I asked could direct me to you. Anyway, about the engine choices, weight of the firewall forward components is very important to me, not just the engine weight by itself. I intend to fly with a fixed pitch cruise prop on my RV9. I feel that going with a constant speed only increases the weight and complexity of the firewall forward. Even though many feel that flying with a constant speed increases your management of speed I don't feel the need for it with the RV.
I do intend to build light. I hope it turns out to be a reality as I am aware of the dreaded weight creep that occurs in the build process. I have built one plane already (not an RV) and that is exactly what happened with it. I intended to keep it as light as possible but the total weight ended up exceeding my target by 25 lbs. In fact I have just added an ELT to that plane so now I am creeping up even more. Everytime I add functionality to the plane I increase weight a pound at a time.
All of this is to say that at present I have not made my mind up about the IO-360 vs. IO-320. As I have been saying, it boils down to price and weight. The reality is that if those two variables could be met with other engine designs I wouldn't be looking at Lycoming clones in the first place and perhaps would be installing a Subaru or Rotary engine. I think they have more current up to date systems that function much better than the "airplane" engines. I know, I know, they are not time tested like the Lycomings/Continentals. However, since those engines do not seem to be falling under my budget for either price or weight I am looking at the old technology instead of the new.
Hey Eggenfelner, and others in your position, read this to say that I believe you would outsell Lycoming in a heart beat if you wouldn't charge premium prices for new technology!!! People do not want to pay premium prices for unproven design! If you want a business model down this line, lets see. . . I don't know. . . Oh, I know, what about say MICROSOFT! Now there is a business model that sure seems to be working. Look back to their start when they were pricing their systems against big ol' giants like Lycoming. I think that giant was called IBM. They definetly did not charge premium prices for their new software programs to try to outperform IBM but look where they are now!
Wow, sorry guys. Got way off topic on that thought. My appologies to all.
GMCJetpilot even though I am not interested in Turbos I found your post on that issue extremely interesting and informative. As far as your posts on the weights, that information is extremely helpful also. It all gives me food for thought. As far as the flutter speeds for the RV (Vne) and higher HP engines pushing the airframe to that level or beyond, I am aware that is an issue with the 180 HP engine. However, I would hope that I can become as good a pilot handling my "overpowered" RV in the same responsible manner as you do while piloting your "overpowered" jet aircraft. If I am able to instill in my flying habits the same amount of knowledge about the engine/airframe construction as the builder had when he built it I think I should be able to fly it responsibly.
Lastly, Kentb and Osxuser I appologize for interjecting my conversation about RV9's in this RV7 thread. I had initially looked at this thread as a discussion of engine differences regardless of the type of aircraft it was going into. I was not aware until later on that it was in the RV7 thread of postings. I think that whichever airframe we all are choosing the discussion of which engine to use is always going to be a valid discussion. I will continue to read with enthusiasm further postings on the subject.
Steve
RVBYSDI
GEORGE,
I liked your comments on the coffin corner- important stuff to consider. My experience with turbocharging however differs from some of your statements:
"The ability to keep high % HP at high altitudes is the key to "normalizing" turbo charging. Turbo benefit is only going to start kicking in above 8,000 feet. To really get the benefit you need to be sniffing O2 and fly above 12,500."
You get a big advantage with turbocharging at any altitude above sea level. Racers see approx 20% loss of power at 5000 ft without forced induction. High altitude performance is a plus.
You can still fly high with out a turbo, but you will be going slower than the same engine turbo charged. This is good because the higher you go the less power you make, the less gas you burn. The turbo at higher power will go faster but it will burn more fuel than if you did not have a turbo.
Forced induction is a cheap and relatively lightweight way to significantly increase the (effective) displacement of an engine; a way to force in more fuel and air that provides more HP. When we use a larger bore or longer stroke to increase displacement, we add weight, internal stress, and increased fuel consumption over the entire engine speed spectrum.
With turbocharging, your contention (go slower at same power output) is only true because of potential weight increases, not for anything inherent to turbochargin. The advantage of turbocharging (over supercharging and natural induction) is that you can cruise without paying an efficiency penalty WITH the benefit of having significant up per end HP on tap when you want it.
IMHO, automotive conversions are better suited to turbocharging than air-cooled engines because of overheating/cooling issues, big differences in fuel injection tuning capability, and the higher rpm envelope used.
I liked your comments on the coffin corner- important stuff to consider. My experience with turbocharging however differs from some of your statements:
"The ability to keep high % HP at high altitudes is the key to "normalizing" turbo charging. Turbo benefit is only going to start kicking in above 8,000 feet. To really get the benefit you need to be sniffing O2 and fly above 12,500."
You get a big advantage with turbocharging at any altitude above sea level. Racers see approx 20% loss of power at 5000 ft without forced induction. High altitude performance is a plus.
You can still fly high with out a turbo, but you will be going slower than the same engine turbo charged. This is good because the higher you go the less power you make, the less gas you burn. The turbo at higher power will go faster but it will burn more fuel than if you did not have a turbo.
Forced induction is a cheap and relatively lightweight way to significantly increase the (effective) displacement of an engine; a way to force in more fuel and air that provides more HP. When we use a larger bore or longer stroke to increase displacement, we add weight, internal stress, and increased fuel consumption over the entire engine speed spectrum.
With turbocharging, your contention (go slower at same power output) is only true because of potential weight increases, not for anything inherent to turbochargin. The advantage of turbocharging (over supercharging and natural induction) is that you can cruise without paying an efficiency penalty WITH the benefit of having significant up per end HP on tap when you want it.
IMHO, automotive conversions are better suited to turbocharging than air-cooled engines because of overheating/cooling issues, big differences in fuel injection tuning capability, and the higher rpm envelope used.
kentb
Well Known Member
My closing thoughts. (not likely)
George,
kentb is kent and osxuser is osxuser. Great post though and I agree completely.
Steve,
You posted "However, I would hope that I can become as good a pilot handling my "overpowered" RV in the same responsible manner as you do while piloting your "overpowered" jet aircraft. If I am able to instill in my flying habits the same amount of knowledge about the engine/airframe construction as the builder had when he built it I think I should be able to fly it responsibly.".
I am sure that George has had an extensive amount of training to be able to correctly manage his overpowered jet. Far beyond what most of us spam can/RV drivers have had. I am sure that with enough experience and training we could all learn to handle most any plane, but what about the next guy that gets in the plane you build?
By the way I am also working on an RV9A and think that this group is just fine for sharing our ideas. The RV7 builders might not be struggling over the 320/360 issues, but could be thinking about 360/470, and most of this information we are discussing will apply for them also.
Kent
George,
kentb is kent and osxuser is osxuser. Great post though and I agree completely.
Steve,
You posted "However, I would hope that I can become as good a pilot handling my "overpowered" RV in the same responsible manner as you do while piloting your "overpowered" jet aircraft. If I am able to instill in my flying habits the same amount of knowledge about the engine/airframe construction as the builder had when he built it I think I should be able to fly it responsibly.".
I am sure that George has had an extensive amount of training to be able to correctly manage his overpowered jet. Far beyond what most of us spam can/RV drivers have had. I am sure that with enough experience and training we could all learn to handle most any plane, but what about the next guy that gets in the plane you build?
By the way I am also working on an RV9A and think that this group is just fine for sharing our ideas. The RV7 builders might not be struggling over the 320/360 issues, but could be thinking about 360/470, and most of this information we are discussing will apply for them also.
Kent
RVbySDI
Well Known Member
No disrespect intended
I most certainly did not mean my statement as any disrespect toward George. George, my appologies if it sounded that way. I was simply saying that I hope I can be able to manage the speed on the upper end of the spectrum if I decide to build in that direction similar to other pilots who have done so.
It is hard to think about my finished airplane being flown by someone else if I were to sell it. I guess we all think we will be the owner for life of our projects. I am reminded of an article I read some years past in which the NTSB investigated a fatal accident when a foolish (read this as "foolish" behavior rather than a "fool") pilot had bought an experimental aerobatic biplane from an individual and immediately proceeded to do multiple high G maneuvers in it calling out "Hey guys watch this. . ." to his onlookers (I assume over the radio). Needless to say some part failed on the aircraft, it folded up, and this pilot was never able to act foolish again. The moral of the story that the writer was trying to convey was, even if the aircraft you buy was built for certain performance characteristics that does not mean that a person can buy that type of aircraft and push it to its limits without some serious soul searching and thorough examination of the aircraft. Of course, building an airplane that can exceed the structural limits of the design is an important issue to consider. Which is why I am discussing all of these issues with all of you here before I go do something "foolish" myself.
Steve
RVBYSDI
I most certainly did not mean my statement as any disrespect toward George. George, my appologies if it sounded that way. I was simply saying that I hope I can be able to manage the speed on the upper end of the spectrum if I decide to build in that direction similar to other pilots who have done so.
It is hard to think about my finished airplane being flown by someone else if I were to sell it. I guess we all think we will be the owner for life of our projects. I am reminded of an article I read some years past in which the NTSB investigated a fatal accident when a foolish (read this as "foolish" behavior rather than a "fool") pilot had bought an experimental aerobatic biplane from an individual and immediately proceeded to do multiple high G maneuvers in it calling out "Hey guys watch this. . ." to his onlookers (I assume over the radio). Needless to say some part failed on the aircraft, it folded up, and this pilot was never able to act foolish again. The moral of the story that the writer was trying to convey was, even if the aircraft you buy was built for certain performance characteristics that does not mean that a person can buy that type of aircraft and push it to its limits without some serious soul searching and thorough examination of the aircraft. Of course, building an airplane that can exceed the structural limits of the design is an important issue to consider. Which is why I am discussing all of these issues with all of you here before I go do something "foolish" myself.
Steve
RVBYSDI
But wait a minute...........
Okay guys, I waded through almost all of the discussion so far and I have not seen one word mentioned about thermodynamic efficiency.
I have seen two same airframes, one with an O-320 150HP and the other with an O-320 160 HP, and the 160 HP consistently burned less fuel when flying at the same speed as the 150HP. The only explanation I could come up with was the 160 had better thermodynamic efficiency. With all being the same the only difference is the 160 had a higher compression ratio which made better use of the fuel consumed. So, any time you can increase the compression ration for a give amount of cubes you will burn less fuel to obtain a given power output.
Throw that information into your burger runs and see where it takes you.
Roger Ping
RV-9 160 HP C/S Going to the airport this weekend!
Okay guys, I waded through almost all of the discussion so far and I have not seen one word mentioned about thermodynamic efficiency.
I have seen two same airframes, one with an O-320 150HP and the other with an O-320 160 HP, and the 160 HP consistently burned less fuel when flying at the same speed as the 150HP. The only explanation I could come up with was the 160 had better thermodynamic efficiency. With all being the same the only difference is the 160 had a higher compression ratio which made better use of the fuel consumed. So, any time you can increase the compression ration for a give amount of cubes you will burn less fuel to obtain a given power output.
Throw that information into your burger runs and see where it takes you.
Roger Ping
RV-9 160 HP C/S Going to the airport this weekend!
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Steve, Yes I was at Oshkosh all day, every day, from Sunday to Saturday and went home on Sunday the last day of the show. Sorry I missed you. Feel free to call...1-8020-624-6680.
Our sales booth was in Building C and I was working at the engine workshop we hold daily in the Exxon tent, which was located near the FAA building and next to Klein Tools and Harley Davidson displays.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts
are hopefully helpful to you. Please use the information provided
responsibly and at you own risk."
Our sales booth was in Building C and I was working at the engine workshop we hold daily in the Exxon tent, which was located near the FAA building and next to Klein Tools and Harley Davidson displays.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts
are hopefully helpful to you. Please use the information provided
responsibly and at you own risk."
gmcjetpilot
Well Known Member
Thank you
Steve:
No offense taken and very well said. Pulling the go-fast-lever back is not rocket science; If I can figure it out, any one can. Really most RV's are not in danger of exceeding Vne in level flight. The RV-7 Vne is 230 MPH. Not many RV-7's do 230mph straight and level at sea level or any altitude. In a dive yes, you can very easily go too fast. Vne (the red line on the airspeed) is for sea level only, it goes down with altitude. As you go up with a normal engine, the diminishing power keeps you from exceeding Vne, in level flight. Vne is virtually impossible to exceed in level flight as you climb. With a turbo that is another issue. Turbo charged engines could be a different story (above 20,000'). Even high performance gliders have Vne placards vs. altitude. May be not a bad idea for any highflying RV turbo or not, especially with a turbo. On jets the Vmo bug or marker moves on the airspeed indicator automatically.
Roger Ping:
You are right compression is more efficency. An aircraft engine compresses at a ratio of 6.75:1 to 9.7:1, while a diesel engine compresses at a ratio as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency. In airplanes with very large piston bores (piston faces) and air-cooling we face detonation, but not it the conservative ranges of a stock Lycoming. A 160HP has a compression of 9.0:1 is starting to get high, compared to the 8.5:1 of the 180hp or 7.0:1 for the 150hp. Keep in mind Lycoming tried 9.7:1 in a certified 125hp version of the O-235 and took it off the market. It worked on the dyno but in the field it was a bust, with many burned pistons. 9:0:1 is a good compression limit for the Lycoming. 9.5:1 is on the edge in my opinion for normal flying. However the higher compression does improve efficency. Also remember going from 150hp to 160hp may mean only a 4 mph increase in top speed, so a 150 hp is still a good amount of power in a light RV.
I think given the choice of the 150hp vs. 160hp I would go 160hp. However some would say you can't run 80 octane or auto gas with a 160hp. True, but I would not use auto gas in an airplane myself, even with a lower compression engine. 80 octane is pretty rare and getting more rare every day.
Back to turbo's for a second, which keeps the MAP close to sea level as long as possible, usually around 20,000' (Turbo critical altitude) and than drops off about 1" per thousand feet. In any case the turbo is not a boost, it just maintains (normalizes). Not that a turbo can't provide boost pressures above normal, some do, but you can run into detonation. Lycomings dedicated turbo engines have oil squirters directed on the back of the pistons to cool them. Also remember the supercharged military engines ran on 130 octane (purple) stuff (now long gone). All we have is 100LL @ $3.25 a gallon. Turbos are wonderful: higher altitude capability, faster climb rates and faster cruise at altitude. At first glance this seem perfect, but there are a lot of factors. Just like high compression pistons, we need and want reliability and a margin of safety from causing engine damage (unless you are into racing and willing to sacrifice reliability). There is no such thing as free lunch.
To get to your point, if the choice is for a (I)O-320 150/160hp I would go (160hp) using Av gas. However I am building a RV-7 and I have a O-360A1A with a Hartzell HC-C2YK.
Note: not all O-320's can be converted from 150hp to 160hp (easily). The narrow deck 150HP O-320?s may need cylinder change and jug hold down stud changes. The wide decks need only new pistons.
Cheers George
Steve:
No offense taken and very well said. Pulling the go-fast-lever back is not rocket science; If I can figure it out, any one can. Really most RV's are not in danger of exceeding Vne in level flight. The RV-7 Vne is 230 MPH. Not many RV-7's do 230mph straight and level at sea level or any altitude. In a dive yes, you can very easily go too fast. Vne (the red line on the airspeed) is for sea level only, it goes down with altitude. As you go up with a normal engine, the diminishing power keeps you from exceeding Vne, in level flight. Vne is virtually impossible to exceed in level flight as you climb. With a turbo that is another issue. Turbo charged engines could be a different story (above 20,000'). Even high performance gliders have Vne placards vs. altitude. May be not a bad idea for any highflying RV turbo or not, especially with a turbo. On jets the Vmo bug or marker moves on the airspeed indicator automatically.
Roger Ping:
You are right compression is more efficency. An aircraft engine compresses at a ratio of 6.75:1 to 9.7:1, while a diesel engine compresses at a ratio as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency. In airplanes with very large piston bores (piston faces) and air-cooling we face detonation, but not it the conservative ranges of a stock Lycoming. A 160HP has a compression of 9.0:1 is starting to get high, compared to the 8.5:1 of the 180hp or 7.0:1 for the 150hp. Keep in mind Lycoming tried 9.7:1 in a certified 125hp version of the O-235 and took it off the market. It worked on the dyno but in the field it was a bust, with many burned pistons. 9:0:1 is a good compression limit for the Lycoming. 9.5:1 is on the edge in my opinion for normal flying. However the higher compression does improve efficency. Also remember going from 150hp to 160hp may mean only a 4 mph increase in top speed, so a 150 hp is still a good amount of power in a light RV.
I think given the choice of the 150hp vs. 160hp I would go 160hp. However some would say you can't run 80 octane or auto gas with a 160hp. True, but I would not use auto gas in an airplane myself, even with a lower compression engine. 80 octane is pretty rare and getting more rare every day.
Back to turbo's for a second, which keeps the MAP close to sea level as long as possible, usually around 20,000' (Turbo critical altitude) and than drops off about 1" per thousand feet. In any case the turbo is not a boost, it just maintains (normalizes). Not that a turbo can't provide boost pressures above normal, some do, but you can run into detonation. Lycomings dedicated turbo engines have oil squirters directed on the back of the pistons to cool them. Also remember the supercharged military engines ran on 130 octane (purple) stuff (now long gone). All we have is 100LL @ $3.25 a gallon. Turbos are wonderful: higher altitude capability, faster climb rates and faster cruise at altitude. At first glance this seem perfect, but there are a lot of factors. Just like high compression pistons, we need and want reliability and a margin of safety from causing engine damage (unless you are into racing and willing to sacrifice reliability). There is no such thing as free lunch.
To get to your point, if the choice is for a (I)O-320 150/160hp I would go (160hp) using Av gas. However I am building a RV-7 and I have a O-360A1A with a Hartzell HC-C2YK.
Note: not all O-320's can be converted from 150hp to 160hp (easily). The narrow deck 150HP O-320?s may need cylinder change and jug hold down stud changes. The wide decks need only new pistons.
Cheers George
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Increasing the CR on a given engine design will generally increase its thermal efficiency until you get to about 15 to 1. However this is limited in the real world to HUCRs of around 9.5 like George says here when running 100LL in air cooled engines. With FADECs or programmable EI, CRs may be able to be somewhat higher as total timing can be retarded at high manifold pressures to prevent detonation while advancing timing at lower MAPs in cruise to take full advantage of the higher thermal efficiency offered by higher CRs.
There has been some discussion before elsewhere about Vne speeds. These are IAS on most aircraft I am aware of, not TAS. In an atmo piston engine aircraft, if you cannot exceed Vne at SL, you sure can't do it at higher altitudes. Even in turbocharged aircraft, you are unlikely to ever exceed Vne in level flight at any altitude unless you are pulling at lot more than 200hp. IAS drops off with altitude so there are no worries here.
George is pretty much correct in saying that a turboed RV would not be worth the trouble for most owners. Oxygen is a big pain and there is little to be gained in speed below 10,000 with a turbo. Only if your mission profiles are frequently above 12,000 feet might you consider this or more importantly for some, if you are flying in and out of high elevation airports with heavy loads, a turbo can be a huge advantage, especially with trees and mountains about.
Fuel flows are not always higher with turbo engines, there are many factors involved like turbo matching, intercooler effectiveness, compression ratio etc. We have found in over 25 years of building and testing turbo engines that the work recovered during the intake stroke from the compressor outweighs the losses caused by backpressure increases from the turbine on a well designed system. Our turbo Subaru RV6A has some of the lowest fuel flows of any Sube RV at speeds in the 160 knot range for instance.
With modern turbos and wastegate systems applied to both air and liquid cooled aircraft engines, combined with proper engineering, design and materials applied to the exhaust and intercooler system, we don't see any significant increase in maintenance worries. A poorly matched turbo, improperly mounted with inferior tubing and design, WILL certainly increase reliability concerns and maintenance.
I would stress that applying a turbo to your RV is an engineering excercise. You better have a good grasp of engines, materials, turbocharging, intercooling, fabrication and airflow if you want it to be successful and reliable. There is a lot more to this than bolting on a normalized Lyc and flying off into the blue.
There has been some discussion before elsewhere about Vne speeds. These are IAS on most aircraft I am aware of, not TAS. In an atmo piston engine aircraft, if you cannot exceed Vne at SL, you sure can't do it at higher altitudes. Even in turbocharged aircraft, you are unlikely to ever exceed Vne in level flight at any altitude unless you are pulling at lot more than 200hp. IAS drops off with altitude so there are no worries here.
George is pretty much correct in saying that a turboed RV would not be worth the trouble for most owners. Oxygen is a big pain and there is little to be gained in speed below 10,000 with a turbo. Only if your mission profiles are frequently above 12,000 feet might you consider this or more importantly for some, if you are flying in and out of high elevation airports with heavy loads, a turbo can be a huge advantage, especially with trees and mountains about.
Fuel flows are not always higher with turbo engines, there are many factors involved like turbo matching, intercooler effectiveness, compression ratio etc. We have found in over 25 years of building and testing turbo engines that the work recovered during the intake stroke from the compressor outweighs the losses caused by backpressure increases from the turbine on a well designed system. Our turbo Subaru RV6A has some of the lowest fuel flows of any Sube RV at speeds in the 160 knot range for instance.
With modern turbos and wastegate systems applied to both air and liquid cooled aircraft engines, combined with proper engineering, design and materials applied to the exhaust and intercooler system, we don't see any significant increase in maintenance worries. A poorly matched turbo, improperly mounted with inferior tubing and design, WILL certainly increase reliability concerns and maintenance.
I would stress that applying a turbo to your RV is an engineering excercise. You better have a good grasp of engines, materials, turbocharging, intercooling, fabrication and airflow if you want it to be successful and reliable. There is a lot more to this than bolting on a normalized Lyc and flying off into the blue.
Jconard
Well Known Member
QUOTE: There has been some discussion before elsewhere about Vne speeds. These are IAS on most aircraft I am aware of, not TAS.
WRONG, WRONG, WRONG, WRONG, WRONG!
VNE is true airspeed, and as altitude goes up, VNE goes down and the aircraft approaches flutter.
QUOTE: Fuel flows are not always higher with turbo engines
misleading....fuel flow will be the same at the same power, but if the turbo is in fact helping to produce more power, it will be burning more fuel.
QUOTE: With modern turbos and wastegate systems applied to both air and liquid cooled aircraft engines, combined with proper engineering, design and materials applied to the exhaust and intercooler system, we don't see any significant increase in maintenance worries.
Who is "WE"? Virtualy every owner and mechanic of factory turbo aircraft report increase maintenance cost, and accelerated wear as a result of the turbo installation. Unless you think you can better engineer the system than could rajay, or Lycoming, or Continental..etc... this is simply a ridiculous statement. If on the other hand by "WE" you mean people who have turbo charged cars, and believe without support that their experience with those applications will be relevant to aircraft use, you may have an audience.
WRONG, WRONG, WRONG, WRONG, WRONG!
VNE is true airspeed, and as altitude goes up, VNE goes down and the aircraft approaches flutter.
QUOTE: Fuel flows are not always higher with turbo engines
misleading....fuel flow will be the same at the same power, but if the turbo is in fact helping to produce more power, it will be burning more fuel.
QUOTE: With modern turbos and wastegate systems applied to both air and liquid cooled aircraft engines, combined with proper engineering, design and materials applied to the exhaust and intercooler system, we don't see any significant increase in maintenance worries.
Who is "WE"? Virtualy every owner and mechanic of factory turbo aircraft report increase maintenance cost, and accelerated wear as a result of the turbo installation. Unless you think you can better engineer the system than could rajay, or Lycoming, or Continental..etc... this is simply a ridiculous statement. If on the other hand by "WE" you mean people who have turbo charged cars, and believe without support that their experience with those applications will be relevant to aircraft use, you may have an audience.
keen9a
Well Known Member
Vne
Vne can be given in either IAS or TAS depending on the limiting factor at a given altitude (it can vary with other factors too). However, Van's sets Vne based on flutter testing which is a function of TAS, probably because even at sea level, flutter occurs before any structual issues.
Flutter = TAS
Loads = IAS
A few issues back, there was a discussion of turbo's and Vne in the RVator. I'm not at home right now, so I can't tell you the exact issue.
Vne can be given in either IAS or TAS depending on the limiting factor at a given altitude (it can vary with other factors too). However, Van's sets Vne based on flutter testing which is a function of TAS, probably because even at sea level, flutter occurs before any structual issues.
Flutter = TAS
Loads = IAS
A few issues back, there was a discussion of turbo's and Vne in the RVator. I'm not at home right now, so I can't tell you the exact issue.
gmcjetpilot
Well Known Member
Vne
The reason Vne is set as the max INDICATED speed for general aviation aircraft is because that is all that is required. Also most GA aircraft speeds are well below Vne even at sea level, and that margin goes up with altitude. However with our fast airplanes we have less margin. With a turbo, if you maintained 100% power to approx 12,000 feet you would exceed the Vne in a RV. If you maintained 75% power, you would exceed Vne around 20,000. With a normal aspirated engine we can only maintain 75% power to approx 8,000 and typical TAS below 200MPH , well below the Vne of 230mph. If you don't have a turbo you can really only get into trouble quickly by descending too fast at higher altitudes. (Then article in the RVator ref'ed and in the following months follow up article gives an example of a RV-4 guy flying at 12,500, who dove down to get below a cloud layer while maneuvering , felt flutter. When he did the math on the ground later, he realized even though he was below red line (indicated), he was well above it in TAS.)
IAS is basically dynamic pressure or "q" (que). Yes structural loads are pressure, loads.
Flutter is a dynamic phenomenon and is a function of the speed of the molecules flowing (true airspeed) past a control surface. If there is an upset or small impulse in the control surface it can start to oscillate or flutter (if the speed is of the air flow is fast enough). It is like a vibration response at the natural frequency of that "system" , which can increase in magnitude very fast, destroying the structure. (For flight test pilots they over shoot the target speed and put the plane in a slight climb before they "slap" the control, so the aircraft is already slowing down incase it gets out of hand.) One test pilot I met flying a modified light twin, doing flutter test for certification, did this and BROKE THE AIRPLANE IN HALF! He just un-buckled and bailed out over the back of the pilot seat and out a large hole where the plane use to be.
Large jets can have flutter of the entire wing. These large wings are very "elastic" and have large deflections and masses like engines hanging off them. In fact weight is put into the wing structure, not to make it stronger but increase its stiffness and change its response frequencies, just to avoid flutter. This is a complex area of engineering structures called aero elasticity, part aerodynamics and part structural. Our short little stubby wings are not flutter critical, we are more likely to pull them off due to high load factors, which is a function of speed, (Q) dynamic pressure.
The Lockheed Electra had whirl flutter where the engine actually excited the engine support and wing structure to flutter. The Tacoma Narrows Bridge South Of Seattle failed because the wind was gusting just at the right frequency. It is well understood now, so no worries, build it per plans and fly with the limitations, you will be OK. However for those brave souls who think they can fly IFR in icing conditions, ice can cause a change in control surface mass and may cause flutter. More likely it will just kill lift, thrust, block control surface effectiveness and increase aircraft weight. However there are many documented cases where ice caused loss of the aircraft. The very first Lear Jets to name one. They keep crashing and no one knew why. Water was freezing in the surface and changing the mass balance. A drain hole was the fix, but several planes where lost before this was found. Moral of the story when you start to screw with the airframe or power plant specified by Van's you are a test pilot.
In the ref article above, by Van, the last sentence says something about: "If you must hurl your self thru the sky with a turbo charger he recommends you don't do it with a RV and use an airframe better suited for that purpose." This was my original suggestion the Kent who seemed like all he wanted to do was fly in the flight levels as fast as he could with a turbo RV to fly with Lancairs.
Cheers George
6th issue 2004.keen9a said:
The reason Vne is set as the max INDICATED speed for general aviation aircraft is because that is all that is required. Also most GA aircraft speeds are well below Vne even at sea level, and that margin goes up with altitude. However with our fast airplanes we have less margin. With a turbo, if you maintained 100% power to approx 12,000 feet you would exceed the Vne in a RV. If you maintained 75% power, you would exceed Vne around 20,000. With a normal aspirated engine we can only maintain 75% power to approx 8,000 and typical TAS below 200MPH , well below the Vne of 230mph. If you don't have a turbo you can really only get into trouble quickly by descending too fast at higher altitudes. (Then article in the RVator ref'ed and in the following months follow up article gives an example of a RV-4 guy flying at 12,500, who dove down to get below a cloud layer while maneuvering , felt flutter. When he did the math on the ground later, he realized even though he was below red line (indicated), he was well above it in TAS.)
IAS is basically dynamic pressure or "q" (que). Yes structural loads are pressure, loads.
Flutter is a dynamic phenomenon and is a function of the speed of the molecules flowing (true airspeed) past a control surface. If there is an upset or small impulse in the control surface it can start to oscillate or flutter (if the speed is of the air flow is fast enough). It is like a vibration response at the natural frequency of that "system" , which can increase in magnitude very fast, destroying the structure. (For flight test pilots they over shoot the target speed and put the plane in a slight climb before they "slap" the control, so the aircraft is already slowing down incase it gets out of hand.) One test pilot I met flying a modified light twin, doing flutter test for certification, did this and BROKE THE AIRPLANE IN HALF!
He just un-buckled and bailed out over the back of the pilot seat and out a large hole where the plane use to be. Large jets can have flutter of the entire wing. These large wings are very "elastic" and have large deflections and masses like engines hanging off them. In fact weight is put into the wing structure, not to make it stronger but increase its stiffness and change its response frequencies, just to avoid flutter. This is a complex area of engineering structures called aero elasticity, part aerodynamics and part structural. Our short little stubby wings are not flutter critical, we are more likely to pull them off due to high load factors, which is a function of speed, (Q) dynamic pressure.
The Lockheed Electra had whirl flutter where the engine actually excited the engine support and wing structure to flutter. The Tacoma Narrows Bridge South Of Seattle failed because the wind was gusting just at the right frequency. It is well understood now, so no worries, build it per plans and fly with the limitations, you will be OK. However for those brave souls who think they can fly IFR in icing conditions, ice can cause a change in control surface mass and may cause flutter. More likely it will just kill lift, thrust, block control surface effectiveness and increase aircraft weight. However there are many documented cases where ice caused loss of the aircraft. The very first Lear Jets to name one. They keep crashing and no one knew why. Water was freezing in the surface and changing the mass balance. A drain hole was the fix, but several planes where lost before this was found. Moral of the story when you start to screw with the airframe or power plant specified by Van's you are a test pilot.
In the ref article above, by Van, the last sentence says something about: "If you must hurl your self thru the sky with a turbo charger he recommends you don't do it with a RV and use an airframe better suited for that purpose." This was my original suggestion the Kent who seemed like all he wanted to do was fly in the flight levels as fast as he could with a turbo RV to fly with Lancairs.
Cheers George
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gmcjetpilot
Well Known Member
Turbos are cool
It is pure freaking magic the power small turbo car engines make with boost. However I pointed out an air-cooled aircraft engine with big piston areas has detonation limitations a car engine does not have. Cars have knock sensors, torque info from transmission, electronic ignition turned to control detonation, water cooling and tiny-teeny-piston areas. Basically detonation is not as critical in a small water cooled car engine and you can hear it. Water cooling is a whole other issue. However there are water cooled Lycomings (but what to do with radiators?). I know the P-51 was water cooled, but a +2000 hp supercharged Rolls Royce V12 can stand a little radiator drag. Cool jugs is here and the video of the engine running sounds like a car engine: http://www.liquidcooledairpower.com/cj-overview.shtml
(under MULTIMEDIA on the left side, mid way down for video)
Turbo chargers heat the engine up, due to the process of compressing air and making more power. The fact the air is getting thinner (as you climb), cooling is being reduced, while power (heat) remains stays high. However, there are technologies like intercoolers and large oil coolers to mitigate this. This is where the No Free Lunch thing comes in. More expensive equipment, weight and complexity. That does not take anything away from how cool and efficient the turbo is. Using WASTE exhaust gas that you where throwing away anyway, to do work is just plain elegant, not with standing the drawbacks. As I said the right engine for the right mission and airframe. A turbo pressurized Lancair is obvious turbo choice. Clearly flying high (above FL180) begs for a turbo charger.
I just simply have no desire to fly high in an un-pressurized single engine plane. Just a personal opinion, preference, of what I think sport flying is about, but understand and respect the aspects of turbo charging and the desire of those who want it. One way to go higher with out a turbo is just get more HP, like an IO-360(200HP) pumped up to 9.2 to 1 compression, electronic ignition, etc.... Van lists the service ceiling at 25,500' (22,500' gross wt.), which by definition is 100fpm climb, for a stock 200hp. Obviously hanging on the prop at FL250 is not practical, but clearly altitudes up towards 18,000 are practical. Again not going as fast TAS wise but than you will be at about 53% power (over 100hp), which is enough to fly on. If you are fuel injected and can use Lean of peak technique you could have some very low fuel flow. However all the monkey motions of O2 and not being able to see the scenery does not excite me. I used +200hp as an example of minimizing loss of hp with altitude, but any engine in a RV will get you well above 12,500' and still scoot fast.
Cheers George
Turbo charging is great, but you have to pay for it. If you are making more power, regardless of how you make it , you are paying for it. There is something nice about flying at 55% power, if that is all you need. RV 's go very fast on little power, turbo or not. Clearly a turbo makes you go faster, but you have to pay for it in more ways then one.cobra said:
It is pure freaking magic the power small turbo car engines make with boost. However I pointed out an air-cooled aircraft engine with big piston areas has detonation limitations a car engine does not have. Cars have knock sensors, torque info from transmission, electronic ignition turned to control detonation, water cooling and tiny-teeny-piston areas. Basically detonation is not as critical in a small water cooled car engine and you can hear it. Water cooling is a whole other issue. However there are water cooled Lycomings (but what to do with radiators?). I know the P-51 was water cooled, but a +2000 hp supercharged Rolls Royce V12 can stand a little radiator drag. Cool jugs is here and the video of the engine running sounds like a car engine: http://www.liquidcooledairpower.com/cj-overview.shtml
(under MULTIMEDIA on the left side, mid way down for video)
Turbo chargers heat the engine up, due to the process of compressing air and making more power. The fact the air is getting thinner (as you climb), cooling is being reduced, while power (heat) remains stays high. However, there are technologies like intercoolers and large oil coolers to mitigate this. This is where the No Free Lunch thing comes in. More expensive equipment, weight and complexity. That does not take anything away from how cool and efficient the turbo is. Using WASTE exhaust gas that you where throwing away anyway, to do work is just plain elegant, not with standing the drawbacks. As I said the right engine for the right mission and airframe. A turbo pressurized Lancair is obvious turbo choice. Clearly flying high (above FL180) begs for a turbo charger.
I just simply have no desire to fly high in an un-pressurized single engine plane. Just a personal opinion, preference, of what I think sport flying is about, but understand and respect the aspects of turbo charging and the desire of those who want it. One way to go higher with out a turbo is just get more HP, like an IO-360(200HP) pumped up to 9.2 to 1 compression, electronic ignition, etc.... Van lists the service ceiling at 25,500' (22,500' gross wt.), which by definition is 100fpm climb, for a stock 200hp. Obviously hanging on the prop at FL250 is not practical, but clearly altitudes up towards 18,000 are practical. Again not going as fast TAS wise but than you will be at about 53% power (over 100hp), which is enough to fly on. If you are fuel injected and can use Lean of peak technique you could have some very low fuel flow. However all the monkey motions of O2 and not being able to see the scenery does not excite me. I used +200hp as an example of minimizing loss of hp with altitude, but any engine in a RV will get you well above 12,500' and still scoot fast.
Cheers George
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Jconard said:
Here is one definition that quotes IAS: An aircraft's Vne is the velocity that should never be exceeded. Generally, Vne is specified as an indicated airspeed in either knots or miles per hour. Most airspeed indicators have a red line indicating Vne for that particular aircraft.
I found several other references on various FAA website pages stating Vne was related to CAS. Nothing I found mentioned Vne and TAS in the same sentence.
Most of the military aircraft my father flew- P51, F86 had limiting Vnes always stated in IAS. These designs were not flutter limited I would guess but possibly air load limited. The F86 had no mach limit however.
It would appear that RVs are flutter limited. This difference is what sparked the discussion in the RVator a while back. Thanks George for your thorough discussion of this topic. I'm chicken up in the yellow arc zone at altitude which would be prudent in my turbo.
It is a documented fact that the compressor contributes substantial work to reduce pumping losses during the intake stroke on 4 cycle engines. Hence why blown radials were cruised at high MAP, low rpm for best SFCs. We see the same thing in extensive dyno testing.
WE are flying a turbocharged RV so I'm putting my money where my mouth is.
My point was here that less complicated and more reliable pnuematic wastegate controllers are available for use on experimental aircraft. We don't need to use complicated hydraulic controllers with their associated problems.
The accelerated wear is often the result of the pilot handling the engines. I know of pilots who have broken a Lyc 541 in 10 minutes and another fellow who owns 3 P Navajos who gets 1800 hours on condition without touching his.
While some cert turbo installations are quite good, others make me wonder what these people were thinking. Hanging 25-30 lb. Garretts off 1600F .035 wall tubing with a little stay maybe is BAD engineering and leads to all the cracked primaries seen on many turbo aircraft. I know, my friend welds this crap up every week. Many could use proper mounts, more slip joints and bellows to cover thermal expansion in all planes and proper .058-.065 wall tubing. Yes, I can do a better job than some of these guys did.
gmcjetpilot
Well Known Member
Turbos and alternate engines
Cheers George
The water cooled alternate engine guys have an advantage with water cooling. Turbo technology in the auto industry is very advanced. If you are going with a Rotary or Subaru I think not using a turbo or supercharging is a waste, for these engines, because they are made for boost and in a way they need the boost. The size of these engines from a displacement stand-point is small. A Lycoming 360 is about 5.9 liters. A Mazda effective displacement is about 1.3 liters and the Subaru is about 2.5 liters. In other words these engines are 1/2 to 1/4 the Lycoming's displacement. This is not a put down, it is amazing they put the power out the HP they do, however they do it with high RPM's and turbo or supercharger's. This is fine, but the high RPM makes a reduction drive to get prop RPM down a requirement. The Lycomings direct drive has its advantages, as does it's simple air cooled design. The auto engines are well suited for turbo charging. It can be done on a Lycoming, but the small displacement and water cooled heads are more tolerant of higher compression.rv6ejguy said:
Cheers George
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osxuser
Well Known Member
Wow, this thread got some replys fast. Some very good points brought up, and I'm glad it has remain cordual throughout. I'll tell you a bit more about how my plan developed since people seem skeptical that i've put any thought into this.
Ultimate nicety would be a IO-390 with no turbo, even a angle valve 360 might do (With the 10-1 pistons, EI, and balence FI). On the other hand, alot of my background comes from the Cardinal Flyers Online and the Tornado Alley Turbo normalizing kit for the C177 RG (IO-360 A1B6, 200HP). Many owners cruise these in the mid-teens gaining about 35KT's over stock, running 65% Power LOP burning 9-11GPHish.
Now what I plan to do with the RV is take a Parallel valve IO360 (180HP), drop a automatic wastegate turbo normalizer system on it, and fly it the same way. I'm not looking for all out speed, or to go about 20,000 feet. I'm not trying to compete with Lancair IV-p's. Most of the guys I know fly 320's or 360's. One has a Glasair I RG. I also don't plan on keeping up with them on long cross countries, just when they play around in formation locally.
I know of all the maintainence issues and firewall forward design issues involved. The particular RV-8 that was in Sport Aviation awhile ago had a 200HP 360 turboed, and they reported 231mph in the mid teens. Thats about where I want to be. And I will always have the option to pull the power back as needed. I think my general mission profile was a bit exaggerated in the minds of those who think I need to spend more on plastic planes
Orginally I had an even more ambitious plan. Take a standard IO-360, and fit it with 10:1 pistons with TIO 540 crossflow cylinders. The main problem is A would it work? B: what to do with the exhaust coming out of the top of the engine. After a bit of converse with my local homebuilt gurus, that plan got axed.
Ultimate nicety would be a IO-390 with no turbo, even a angle valve 360 might do (With the 10-1 pistons, EI, and balence FI). On the other hand, alot of my background comes from the Cardinal Flyers Online and the Tornado Alley Turbo normalizing kit for the C177 RG (IO-360 A1B6, 200HP). Many owners cruise these in the mid-teens gaining about 35KT's over stock, running 65% Power LOP burning 9-11GPHish.
Now what I plan to do with the RV is take a Parallel valve IO360 (180HP), drop a automatic wastegate turbo normalizer system on it, and fly it the same way. I'm not looking for all out speed, or to go about 20,000 feet. I'm not trying to compete with Lancair IV-p's. Most of the guys I know fly 320's or 360's. One has a Glasair I RG. I also don't plan on keeping up with them on long cross countries, just when they play around in formation locally.
I know of all the maintainence issues and firewall forward design issues involved. The particular RV-8 that was in Sport Aviation awhile ago had a 200HP 360 turboed, and they reported 231mph in the mid teens. Thats about where I want to be. And I will always have the option to pull the power back as needed. I think my general mission profile was a bit exaggerated in the minds of those who think I need to spend more on plastic planes
Orginally I had an even more ambitious plan. Take a standard IO-360, and fit it with 10:1 pistons with TIO 540 crossflow cylinders. The main problem is A would it work? B: what to do with the exhaust coming out of the top of the engine
. After a bit of converse with my local homebuilt gurus, that plan got axed.
gmcjetpilot
Well Known Member
Vne RED line
On fast high flying turbo props and jets the Red line MOVES on the airspeed indicator as you climb. With a steam gage ASI it is an electric powered pointer that moves down to a lower indicate speed as you climb. On EFIS with speed tape it shows the same red line and yellow line we see on our airspeed indicators. The pointer or EFIS red line is corrected by a ADC (airdata computer), adjusting the displayed speed limit, based on altitude and airspeed. In fact above FL250 you stop using Kts and go to Mach number, which is a constant limit since it is a ratio of the sound of speed, which goes down with altitude, and aircraft TAS. That is why jets have Mach meters as well as airspeed indicators. (766mph@SL and 660mph@FL370, where it remains constant.) Since jets like to cruise at .78-.82 mach the typical true airspeed of a jet is around 530 mph.
Since most GA planes don't fly high enough or fast enough, flutter in level flight is not an issue. However glider pilots in high perf ships can go well above FL200 or even FL250, they do worry about Vne and have a correction table next to their airspeed indicator. With the gliders low drag airframe and high altitude it is easy to exceed Vne at those extreme altitudes. Indicated or true is not important, we only have indicated airspeed (pitot static) and all the other info is derived from that and other factors (alt, temp, etc), but the fact is the airspeed indicator is lying to us when we fly at altitude, so just an awarness is all we need. George
On fast high flying turbo props and jets the Red line MOVES on the airspeed indicator as you climb. With a steam gage ASI it is an electric powered pointer that moves down to a lower indicate speed as you climb. On EFIS with speed tape it shows the same red line and yellow line we see on our airspeed indicators. The pointer or EFIS red line is corrected by a ADC (airdata computer), adjusting the displayed speed limit, based on altitude and airspeed. In fact above FL250 you stop using Kts and go to Mach number, which is a constant limit since it is a ratio of the sound of speed, which goes down with altitude, and aircraft TAS. That is why jets have Mach meters as well as airspeed indicators. (766mph@SL and 660mph@FL370, where it remains constant.) Since jets like to cruise at .78-.82 mach the typical true airspeed of a jet is around 530 mph.
Since most GA planes don't fly high enough or fast enough, flutter in level flight is not an issue. However glider pilots in high perf ships can go well above FL200 or even FL250, they do worry about Vne and have a correction table next to their airspeed indicator. With the gliders low drag airframe and high altitude it is easy to exceed Vne at those extreme altitudes. Indicated or true is not important, we only have indicated airspeed (pitot static) and all the other info is derived from that and other factors (alt, temp, etc), but the fact is the airspeed indicator is lying to us when we fly at altitude, so just an awarness is all we need. George
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kentb
Well Known Member
Hello George
You seam to have me confused with another poster. I think that it is OSXUSER that has the turbo and Lancair buddys.
My almost completed RV9A will have an IO320, CS, one mag and one EI. I may carry a portable O2 so that I can fly in the mid teens while crossing the Rockies, but other wise will stay down lower.
Kent
gmcjetpilot said:
You seam to have me confused with another poster. I think that it is OSXUSER that has the turbo and Lancair buddys.
My almost completed RV9A will have an IO320, CS, one mag and one EI. I may carry a portable O2 so that I can fly in the mid teens while crossing the Rockies, but other wise will stay down lower.
Kent
gmcjetpilot
Well Known Member
I am dizzy
It is a lot more fun, anyone can fly over the top sucking gas. Do you live in Denver? I get dizzy thinking of flying that high.
I don't have much experience in the Rockies except at work and being at FL350 westbound and getting mountain wave, speed gain of 30-40kts and updrafts the autopilot had a hard time keeping up with. I wounder what the ride would be like in the RV a thousand feet or so above the peeks with the wind blowing? YeeHaww!
I flew out of Seattle for years and flew over the cascades a lot, both low and over the top. Over the top is the way to go, but seriously it is fun flying low in the passes.
I really had fun flying in the saw tooth moutains and landing and RON'ing at Johnson Creek Airport, Yellow Pine, ID.
Cheers George
Sorry Kent, MID TEENS? Fly down low on the deck thru those mountain passes.kentb said:You seam to have me confused with another poster. I think that it is OSXUSER that has the turbo and Lancair buddys.
My almost completed RV9A will have an IO320, CS, one mag and one EI. I may carry a portable O2 so that I can fly in the mid teens while crossing the Rockies, but other wise will stay down lower.
Kent
It is a lot more fun, anyone can fly over the top sucking gas. Do you live in Denver? I get dizzy thinking of flying that high. I don't have much experience in the Rockies except at work and being at FL350 westbound and getting mountain wave, speed gain of 30-40kts and updrafts the autopilot had a hard time keeping up with. I wounder what the ride would be like in the RV a thousand feet or so above the peeks with the wind blowing? YeeHaww!
I flew out of Seattle for years and flew over the cascades a lot, both low and over the top. Over the top is the way to go, but seriously it is fun flying low in the passes.
I really had fun flying in the saw tooth moutains and landing and RON'ing at Johnson Creek Airport, Yellow Pine, ID.
Cheers George
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kentb
Well Known Member
I live in Oregon
Hello George,
My hanger is at the Aurora airport. It's handy have Van's at my beck-n-call.
I have only flown over (through) the Rockies so far, in my C172 no less. I want the option to go over if needed and a chance to get over some mild weather too.
Kent
Hello George,
My hanger is at the Aurora airport. It's handy have Van's at my beck-n-call.
I have only flown over (through) the Rockies so far, in my C172 no less. I want the option to go over if needed and a chance to get over some mild weather too.
Kent
mgomez
Well Known Member
Weight has a small effect on top speed
I have read this thread with interest. I just wanted to add this little tidbit, from a spreadsheet I wrote to calculate the power required for an RV-7. I started with Van's numbers for a 200 HP RV-7 at 1800 lbs gross weight.
Assumptions: prop efficiency of 80%, and Oswald efficiency number of 0.8, and tweaked Cdo (the drag at zero lift) until I made the top speed come out to Van's numbers.
Weight (lbs) Speed (mph)
1450 217.15*
1700 216.36
1800 216.00
1900 215.62
* The speed at 1450 lbs is also the result of my spreadsheet, to check it. It agree with Van's "Solo Weight" number, at least to the resolution they give us.
As you can see, weight makes a small difference in top speed, because the drag there is dominated by parasite drag. The induced drag at high speed is small, because the wing is at a small CL.
Even a 200 lbs difference in weight (say due to carrying a passenger, or due to a heavier engine and prop) makes a difference of of less than 1 mph.
Another way to look at it is Lift/Drag ratio. Here is the drag produced by an RV-7 at top speed, with various engines (data again taken from Van's Web site) at 1800 lbs gross:
Power (HP) 160 180 200
Top Spd (mph) 201 209 216
75% 8000' crz (mph) 191 199 206
Drag Force (lbs) 239 258 278
L/D @ top speed 7.54 6.97 6.48
This says that an increase in weight is "derated" by a factor of 6 or 7, i.e. adding 6 or 7 lbs of weight adds only 1 lb of drag.
I'll post these spreadsheets if anyone is interested.
Regards,
Martin
I have read this thread with interest. I just wanted to add this little tidbit, from a spreadsheet I wrote to calculate the power required for an RV-7. I started with Van's numbers for a 200 HP RV-7 at 1800 lbs gross weight.
Assumptions: prop efficiency of 80%, and Oswald efficiency number of 0.8, and tweaked Cdo (the drag at zero lift) until I made the top speed come out to Van's numbers.
Weight (lbs) Speed (mph)
1450 217.15*
1700 216.36
1800 216.00
1900 215.62
* The speed at 1450 lbs is also the result of my spreadsheet, to check it. It agree with Van's "Solo Weight" number, at least to the resolution they give us.
As you can see, weight makes a small difference in top speed, because the drag there is dominated by parasite drag. The induced drag at high speed is small, because the wing is at a small CL.
Even a 200 lbs difference in weight (say due to carrying a passenger, or due to a heavier engine and prop) makes a difference of of less than 1 mph.
Another way to look at it is Lift/Drag ratio. Here is the drag produced by an RV-7 at top speed, with various engines (data again taken from Van's Web site) at 1800 lbs gross:
Power (HP) 160 180 200
Top Spd (mph) 201 209 216
75% 8000' crz (mph) 191 199 206
Drag Force (lbs) 239 258 278
L/D @ top speed 7.54 6.97 6.48
This says that an increase in weight is "derated" by a factor of 6 or 7, i.e. adding 6 or 7 lbs of weight adds only 1 lb of drag.
I'll post these spreadsheets if anyone is interested.
Regards,
Martin
