Van's Air Force
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Fuel burn
- Thread starter ARJAY
- Start date
Beancounter
Well Known Member
At that RPM and a low MP, I am closer to 6gph. If you did a number of circuits your total fuel consumption would be reasonable.
Don
Well Known Member
I'd expect just a bit higher burn than 6 gph. Probably closer to 5.5 gph?but, I did a 1.2 hr flight with a tail wind, doing 150kts or a bit more, and I took 5.9 gallons of fuel when I arrived (4.9 gph). I have not duplicated those numbers and I tend to fly faster now. My memory is my IAS was just over 130.
Unequivocally, V-man has an iron arse. Three tankfuls of gas in one day? A 9A holds 36 gallons of fuel. If he keeps an hour reserve @ 6 gph, then a tank full = 30 gallons (if he cuts it to a 30 minute reserve add 1.5 hours to my calculation). 3 tankfuls = 90 gallons. 90 gallons at 6 gph = 15 hours of flying. I'm stunned - The most I've flown is literally half that long and felt like it was a long day. 15 hours! Wow. I'm not completely sure I could extract myself from the cockpit after 15 hours.
Unequivocally, V-man has an iron arse. Three tankfuls of gas in one day? A 9A holds 36 gallons of fuel. If he keeps an hour reserve @ 6 gph, then a tank full = 30 gallons (if he cuts it to a 30 minute reserve add 1.5 hours to my calculation). 3 tankfuls = 90 gallons. 90 gallons at 6 gph = 15 hours of flying. I'm stunned - The most I've flown is literally half that long and felt like it was a long day. 15 hours! Wow. I'm not completely sure I could extract myself from the cockpit after 15 hours.
RVbySDI
Well Known Member
Don, are you sure you are not talking MPH instead of KNOTS? 150kts is 172-173MPH. If this is true then I am stunned at the difference in fuel burn compared to my 9a. In my 9A it will easily cruise at 172MPH but I am burning 8-8.5gph in doing so. No way I can get down to 5.9/1.2 = 4.92gph at that speed.
Don
Well Known Member
I am positive its knots. Everything I have is calibrated in knots. The 150 kt figure is GS, not IAS, and I noted a tailwind in my post. I'm not positive but my memory is I had about a 20 knot tailwind, which sure helped. At 150 IAS I'd be burning around 8 gph?if I could get there.
FWIW, I regularly see fuel burns of less than 5.5 gph @ when I'm cruising around 130 knots IAS (2200-2250 RPM).
Another data point: I normally/consistently cruise @ 145 KTAS, 4500ft / 5500ft MSL with throttle set to about 2400 RPM fuel burn is 6.8 to 7.2 gph. This is with O-320, fixed pitch Sensenich carbon fiber ground adj prop with #4 pin which is very close to the numbers I would get with the Van's standard recommended metal Sensenich prop.
YMMV
Bill
YMMV
Bill
RVbySDI
Well Known Member
Aw, Don, now that makes much more sense!
Because of the great variability of wind conditions (head, tail, cross winds) I never think of discussions associating speed readings as they relate to fuel burn in terms of ground speed.
Yes 5.5gph @ 130kts IAS does indeed sound very reasonable for the 9A.
Indicated Airspeed (IAS), True Airspeed (TAS), Calibrated Indicated Airspeed (CIAS), Ground Speed (GS) all have their place when discussing the performance of an aircraft. However, each has their purpose and usually is more meaningful in some discussions, less meaningful in others. I think it wise to define the TYPE of speed being discussed before hand anytime we are making comparisons.
In my case I typically use TAS when discussing cruise performance and fuel burn. In my opinion it is a much more accurate depiction of the true performance of the aircraft. Granted I have a nice GRT EFIS that constantly displays that information and am aware that many may not have instrumentation that will give them that information readily. In the absence of TAS information I think it would be better to discuss speed in terms of IAS when dealing with fuel burn. There are too many variables associated with wind and altitude for GS to be a good tool for that purpose.
As for my 9A, I typically cruise at 165mph TAS (143kts). Depending on the altitude I cruise I can typically see anywhere from 6.9 to 8.5 gph at that speed. Down lower equates to higher fuel burns (2000 to 6000 Mean Sea Level (MSL)). Up Higher I can see much lower burns (8000+ MSL).
petehowell
Well Known Member
go lean......up high
It can be done........
130KTAS 4.9-5.1GPH down low
150KTAS 6.0-6.1 GPH up high
The Van's plane did even better at the CAFE Foundation!!!
http://www.vansairforce.com/community/showpost.php?p=735857&postcount=20
It can be done........
130KTAS 4.9-5.1GPH down low
150KTAS 6.0-6.1 GPH up high
The Van's plane did even better at the CAFE Foundation!!!
http://www.vansairforce.com/community/showpost.php?p=735857&postcount=20
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Don
Well Known Member
In my case I ignored the gauges and it's what the meter at the pump said. Are you actually burning 6-7 gph at 130 kts IAS?
RVbySDI
Well Known Member
Pete,
I appreciate your input but again I have not been able to see those numbers with my 9A. I routinely cruise at higher altitudes, 8000' or higher, on long cross country flights unless the winds are just not cooperating. There is absolutely no way I can burn less than 7.5 gph at the absolute leanest I can get LOP running anything faster than 143kts TAS. Yes, I always run LOP.
I can only surmise that if your numbers and others are accurate, my prop pitch is hurting me much more than I previously thought it was. I have been discussing my speed/economy performance situation with Craig Catto for 1.5 years now. I have been trying to see about getting a different pitch on my 3-blade prop. I have received a glimmer of hope from Catto's shop last week when they informed me they would ship me a new prop in about 3 weeks. Whenever I do get the new prop I will run some numbers and perhaps see what you are showing but I am most definitely not seeing it now.
For reference I am running a forward facing cold air induction, 4-straight pipe exhaust, fuel injected 180HP IO-340 with 68x72 Catto 3-blade.
I appreciate your input but again I have not been able to see those numbers with my 9A. I routinely cruise at higher altitudes, 8000' or higher, on long cross country flights unless the winds are just not cooperating. There is absolutely no way I can burn less than 7.5 gph at the absolute leanest I can get LOP running anything faster than 143kts TAS. Yes, I always run LOP.
I can only surmise that if your numbers and others are accurate, my prop pitch is hurting me much more than I previously thought it was. I have been discussing my speed/economy performance situation with Craig Catto for 1.5 years now. I have been trying to see about getting a different pitch on my 3-blade prop. I have received a glimmer of hope from Catto's shop last week when they informed me they would ship me a new prop in about 3 weeks. Whenever I do get the new prop I will run some numbers and perhaps see what you are showing but I am most definitely not seeing it now.
For reference I am running a forward facing cold air induction, 4-straight pipe exhaust, fuel injected 180HP IO-340 with 68x72 Catto 3-blade.
N941WR
Legacy Member
Slightly different setup.
Yesterday I flew from Greenville, SC to Houston, TX and was seeing 150 KTAS while burning 7.1 GPH at 6500 MSL (about 10K DA). (Ground speeds were down to 110 Kts, due to the winds aloft. OUCH!)
That is with a FP Catto being spun by an O-360 LOP.
I used to run my O-290 at 140 KTAS while burning the same amount ROP.
The O-290 just didn't like to run LOP but the O-360 does it just fine.
Yesterday I flew from Greenville, SC to Houston, TX and was seeing 150 KTAS while burning 7.1 GPH at 6500 MSL (about 10K DA). (Ground speeds were down to 110 Kts, due to the winds aloft. OUCH!)
That is with a FP Catto being spun by an O-360 LOP.
I used to run my O-290 at 140 KTAS while burning the same amount ROP.
The O-290 just didn't like to run LOP but the O-360 does it just fine.
Houston
Bill,
Are you still in Houston?
Would enjoy meeting you and seeing your plane. I am in Katy.
Just so I do not hijack the thread, I have a Lycoming 150 hp O-320 swinging a Sensenich FP with 2600 max rpm blade. At 181 mph (that is all I can muster at 2600 rpm), I am burning 9.5 gph. At 2250 rpm, 152-155 mph am burning around 6 gph. I have to go to 2200 rpm to get to 5.5 gph.
Pat Garboden
RV9A N942PT
Katy, TX
Flying Phase I complete
2014 dues paid
Bill,
Are you still in Houston?
Would enjoy meeting you and seeing your plane. I am in Katy.
Just so I do not hijack the thread, I have a Lycoming 150 hp O-320 swinging a Sensenich FP with 2600 max rpm blade. At 181 mph (that is all I can muster at 2600 rpm), I am burning 9.5 gph. At 2250 rpm, 152-155 mph am burning around 6 gph. I have to go to 2200 rpm to get to 5.5 gph.
Pat Garboden
RV9A N942PT
Katy, TX
Flying Phase I complete
2014 dues paid
RetiredRacer
Well Known Member
Here's a different setup again
Our 9a with a 115 hp 0-235 C2C. With duel PMags RotecTBI and 1 1/2" Vetterman pipes. Two blade 78"x 62" Catto.
Between 4500" & 8500" 2400 RPM = 120 - 125kts IAS (138 - 145 kts TAS), 5.3 GPH by Dynon fuel flow. Fuel tank top up shows 5 GPH. ROP.
Bob
Our 9a with a 115 hp 0-235 C2C. With duel PMags RotecTBI and 1 1/2" Vetterman pipes. Two blade 78"x 62" Catto.
Between 4500" & 8500" 2400 RPM = 120 - 125kts IAS (138 - 145 kts TAS), 5.3 GPH by Dynon fuel flow. Fuel tank top up shows 5 GPH. ROP.
Bob
N941WR
Legacy Member
Yep, brought the plane down on Monday. I'm at Pearland and will be out there on Saturday working on the plane. That is if the weather is nice. Check your PM's.
If you're relatively sure that your engine is making good power, and your prop is hooking it up (or getting changed and on it's way to hooking it up) then the only other variable to consider is drag. Start looking at what is causing drag on the airplane - it makes a lot more difference than you might think.
petehowell
Well Known Member
Ignition?
Hi Steve,
What are you running for ignition? I have dual EI and I think it helps quite a bit. Mix in 1/2 carb heat to see if you can get her to run a little leaner in cruise, it helps me. The higher compression O-340 should be a bit more efficient than the 160HP O-320.
Specs say Van's RV-9A at Cafe was running 2 mags and a MT 3 blade prop - the fuel burn they saw was really amazing!
Hi Steve,
What are you running for ignition? I have dual EI and I think it helps quite a bit. Mix in 1/2 carb heat to see if you can get her to run a little leaner in cruise, it helps me. The higher compression O-340 should be a bit more efficient than the 160HP O-320.
Specs say Van's RV-9A at Cafe was running 2 mags and a MT 3 blade prop - the fuel burn they saw was really amazing!
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RVbySDI
Well Known Member
not sure where any extra drag would be coming from. Other than the engine changes the airframe was built as a standard 9A.
i am running a Slick mag with impulse coupling on the left. A Lightspeed Plasma III on the right. I have the IO-340 not the carbed O-340. Since no carb, no carb heat. I run LOP most every flight especially on X-country flights. Oh, and just to hit this topic, my CHT's are running within 10 deg of each other at all times. The engine is a smooth running machine.
I really think the 68 x 72 3-blade is just not the right prop for this engine. I have been waiting for a long time for Craig to build me a 68 x 74 3-blade to see how it will perform with that pitch.
With my current configuration I have done many GPS speed tests at 8K DA. At wide open throttle I can spin the prop to 2950 RPM. I have done quite a few tests at various settings, I have done some side by side flight comparisons with friend's RV 7's with 180 hp engines to compare speeds, rpm, MP, fuel burns, etc. At comparable true air speeds I am spinning the prop approximately 200 rpm faster and MP approx. 2in more than they are.
As I said I am hoping Craig Catto will be getting me a prop with a different pitch soon to try.
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simpkinsona
Well Known Member
If you have a higher RPM and MP, you are producing more power than your friends. You must either have a less efficient prop or more drag/weight.
-Andy
RVbySDI
Well Known Member
I understand and agree. Now the difference in my friend's plane(s) and mine is basically 7 vs 9A, tail vs nose wheel, carbed 360 with standard Van's snout lower cowl on the 7 vs FI forward facing cold air induction with Van's smooth cowl and snorkel on the 9A, standard Vetterman cross-over exhaust for the 7 vs Vetterman 4-straight pipes clogging up the exit area with the nose gear on the 9A (most assuredly creating more drag that one day I am going to try to address). Maybe there are some rigging issues that could possibly be creating more drag but I do know my plane does not have any adverse flight characteristics.
For the past year and a half I have been communicating with Craig about possible prop inefficiencies with my configuration. If I ever get the prop in my hands and on the plane I will be better able to determine if that is going to make a difference. Just as another point of information, I can run up to around 2300 to 2350 with this prop on the ground. Another reason I am leaning toward a different pitched prop.
