The main difference between the -7 and the -9 airframes is the longer wing of the 9. I'm wondering, all other things being equal, what the effect of this longer wing is on fuel economy. On the one hand, you have more lift, but on the other hand you have more drag. Of course the cruise speeds are different, so it's hard to compare. I'm not trying to start a 7 vs 9 debate, or even compare the two, I just don't understand airframes enough to know what the effect of wing size and aspect ratio is on fuel economy. For example, if you put an engine on a glider, would it be very efficient, or very inefficient from a fuel consumption point of view?
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long wing effect on fuel consumption?
- Thread starter prkaye
- Start date
mgomez
Well Known Member
Long wing->better low-speed L/D
At high speed (i.e. low angle of attack and low lift coefficient), the drag from a longer wing is higher. At low speed (high angle of attack and high lift coefficient), a long wing has lower drag.
That's why gliders have long wings and fighters have short wings.
The reason the -9 has a longer wing is so that it will climb better with a lower power/weight ratio. At climb speed, the long wing causes a lower drag, and therefore reduces the power required for level flight, so more power is available for climbing.
At cruise speed, there is a drag penalty for the longer wing.
To answer one of you questions: if you put an engine on a glider and tried to fly it at the lowest possible power (best endurance or minimum-sink speed) it would be very, very efficient. For example, an ASK-21 (a decent but not spectacular 2-seat glider) would require only 8 HP to stay aloft at 51 kts, its minimum sink speed.
For the curious, I assumed a gross weight of 1250 lbs, and a minimum sink rate of 160 ft/min, and an 80% efficient prop.
At high speed (i.e. low angle of attack and low lift coefficient), the drag from a longer wing is higher. At low speed (high angle of attack and high lift coefficient), a long wing has lower drag.
That's why gliders have long wings and fighters have short wings.
The reason the -9 has a longer wing is so that it will climb better with a lower power/weight ratio. At climb speed, the long wing causes a lower drag, and therefore reduces the power required for level flight, so more power is available for climbing.
At cruise speed, there is a drag penalty for the longer wing.
To answer one of you questions: if you put an engine on a glider and tried to fly it at the lowest possible power (best endurance or minimum-sink speed) it would be very, very efficient. For example, an ASK-21 (a decent but not spectacular 2-seat glider) would require only 8 HP to stay aloft at 51 kts, its minimum sink speed.
For the curious, I assumed a gross weight of 1250 lbs, and a minimum sink rate of 160 ft/min, and an 80% efficient prop.
Chickenlips
Active Member
It is a great question and I don't have enough knowledge to fully answer... but a couple of toughts that came to mind are this:
1. I doubt the -7 is faster than the -9 if you use comparable power plants. I think the differences you hear of are not apples for apples comparisons.
2. The wing span is greater on the -9 than the -7 but the wing cord is larger on the -7 than the -9.... thus total wing area is not that different.... if this is so then parasitic drag between the two cannot be very different. Induced drag may be a different story. I am only guessing but I seem to remember that it can be demonstrated that a longer wing may have lower induced drag at higher altitudes?? Aspect ratio effects?? So maybe with everything considered, the -9 at high altitudes may be potentially faster than the -7?
Some of the gurus on this site will probably clarify this contention...
1. I doubt the -7 is faster than the -9 if you use comparable power plants. I think the differences you hear of are not apples for apples comparisons.
2. The wing span is greater on the -9 than the -7 but the wing cord is larger on the -7 than the -9.... thus total wing area is not that different.... if this is so then parasitic drag between the two cannot be very different. Induced drag may be a different story. I am only guessing but I seem to remember that it can be demonstrated that a longer wing may have lower induced drag at higher altitudes?? Aspect ratio effects?? So maybe with everything considered, the -9 at high altitudes may be potentially faster than the -7?
Some of the gurus on this site will probably clarify this contention...
gmcjetpilot
Well Known Member
It's way more than span
Different airfoil and control surface design. Its hard to apples and apples but the RV-9 is very efficient but tuned for a little lower speed range but also is more efficient at those ranges.
Just take Van's 160 hp numbers (note RV-7A solo/gross is 1400/1800 lbs; RV-9A solo/gross is 1350/1750 lbs):
SOLO
.....................RV-7A........RV-9A:
top speed......200 mph.......195 mph
75% cruise.....190 mph.......187 mph
stall................51 mph.......44 mph
takeoff...........300 ft.........300 ft
landing...........350 ft.........300 ft
rate climb.....1,800 fpm...1,900 fpm
ceiling........20,000 ft.....24,500 ft
75% range......825 sm........700 sm (RV7A/42 gal; RV9A/36 gal)
75% mpg......19.64 mpg....19.44 mpg (75%)
55% range.....1025 sm.......850 sm
55% mpg......24.40 mpg....23.61 mpg (55%)
Gross
.....................RV-7A........RV-9A:
top speed......199 mph.......194 mph
75% cruise.....189 mph.......186 mph
stall................58 mph.......50 mph
takeoff...........600 ft.........475 ft
landing...........650 ft.........400 ft
rate climb.....1,350 fpm...1,400 fpm
ceiling.........17,500 ft.....18,500 ft
You can see the difference. the RV9A has:
lower top speed (5 mph)
lower cruise speed (3 mph)
lower stall speed (7-8 mph)
shorter landing length especially @ gross (125 ft)
shorter landing length especially @ gross (150 ft)
slightly higher climb rate (50-100 fpm)
higher ceiling especially solo (4,500 ft)
miles per gal: about the same, but small edge goes to the RV7A
The RV7 is designed for Acro, the RV9 is not. The RV7 is designed for up to 200 hp and about 220 mph top speed, the RV9 is 160HP and 197 mph top speed. That should tell you the difference. If you make the the RV7 non aerobatic you could make it lighter, which would haved a positive effect on takeoff/landing/celing.
Span is related to Aspect ratio. Aerodynamisist have longed known what a good thing high aspect ratio is. A glider is a high aspect ratio wing. It tends to lower "induced drag", thus the better climb on same HP, however there is a 50 lb weight difference 7 v. 9, not large but affects the #'s. However at higher speeds long wings works against you, unless you fly higher. The term higher speed is relative, but the RV7 is faster on the same HP.
To make the RV9 suitable for Acro or more HP and more speed, the structure needs to strengthened. This would results in heavier structure and higher stall. This would mean longer takeoff/landing distance and lower ceiling. Its a trade off. To make the RV9 optimal or suitable for 180-200 HP engine it would basically become a RV7. They both are surprisingly efficient planes. The RV9 is clearly more efficient at low speed and lower HP.We don't have performance for the RV7 with 120-140 HP but suspect the RV9 would be better than the RV7.
Even though the RV7 got slightly better gas milage, if you flew the RV-9 at higher altitudes, w/ a high aspect ratio wing, efficiency (mpg) increases.
My choice to build the RV7 was the fact I had a 180HP engine, wanted to do Acro, like the extra 6 gal of fuel and really did not care about the slower stall speed. As far as takeoff/landing/rate-of-climb/ceiling with 180HP the RV7 will outperform the RV9 easily in flight, but the lighter RV9 will still land slower and shorter. Of course fuel economy for the higher HP RV7's goes down a little and the RV9 has the edge in econ.
There is the deal. You want to use 160 HP or less the RV9 can be real efficient. If you want to use a bigger engine than 160HP, the RV7 wing is the only way to go. THERE AIN'T NO REPLACEMENT FOR DISPLACMENT. A RV7 with a 180 HP or 200 HP would of course exceed the RV9 speed and rate of climb performance even more (at more fuel).
If you don't want to do Acro and have a 160 HP or less engine to use, the RV9 is a real nice wing.
Vans TO/Ldg distance are ground roll; I'm not sure how they got them. TO/Ldg distance is skill related as well as prop related. A C/S prop gives more thrust on TO and less idle thrust on landing, which has a big effect on takeoff and landing distance. So how Van figures them I don't know.
This may not be the answer but study the performance numbers and a relationship will be exposed.
Different airfoil and control surface design. Its hard to apples and apples but the RV-9 is very efficient but tuned for a little lower speed range but also is more efficient at those ranges.
Just take Van's 160 hp numbers (note RV-7A solo/gross is 1400/1800 lbs; RV-9A solo/gross is 1350/1750 lbs):
SOLO
.....................RV-7A........RV-9A:
top speed......200 mph.......195 mph
75% cruise.....190 mph.......187 mph
stall................51 mph.......44 mph
takeoff...........300 ft.........300 ft
landing...........350 ft.........300 ft
rate climb.....1,800 fpm...1,900 fpm
ceiling........20,000 ft.....24,500 ft
75% range......825 sm........700 sm (RV7A/42 gal; RV9A/36 gal)
75% mpg......19.64 mpg....19.44 mpg (75%)
55% range.....1025 sm.......850 sm
55% mpg......24.40 mpg....23.61 mpg (55%)
Gross
.....................RV-7A........RV-9A:
top speed......199 mph.......194 mph
75% cruise.....189 mph.......186 mph
stall................58 mph.......50 mph
takeoff...........600 ft.........475 ft
landing...........650 ft.........400 ft
rate climb.....1,350 fpm...1,400 fpm
ceiling.........17,500 ft.....18,500 ft
You can see the difference. the RV9A has:
lower top speed (5 mph)
lower cruise speed (3 mph)
lower stall speed (7-8 mph)
shorter landing length especially @ gross (125 ft)
shorter landing length especially @ gross (150 ft)
slightly higher climb rate (50-100 fpm)
higher ceiling especially solo (4,500 ft)
miles per gal: about the same, but small edge goes to the RV7A
The RV7 is designed for Acro, the RV9 is not. The RV7 is designed for up to 200 hp and about 220 mph top speed, the RV9 is 160HP and 197 mph top speed. That should tell you the difference. If you make the the RV7 non aerobatic you could make it lighter, which would haved a positive effect on takeoff/landing/celing.
Span is related to Aspect ratio. Aerodynamisist have longed known what a good thing high aspect ratio is. A glider is a high aspect ratio wing. It tends to lower "induced drag", thus the better climb on same HP, however there is a 50 lb weight difference 7 v. 9, not large but affects the #'s. However at higher speeds long wings works against you, unless you fly higher. The term higher speed is relative, but the RV7 is faster on the same HP.
To make the RV9 suitable for Acro or more HP and more speed, the structure needs to strengthened. This would results in heavier structure and higher stall. This would mean longer takeoff/landing distance and lower ceiling. Its a trade off. To make the RV9 optimal or suitable for 180-200 HP engine it would basically become a RV7. They both are surprisingly efficient planes. The RV9 is clearly more efficient at low speed and lower HP.We don't have performance for the RV7 with 120-140 HP but suspect the RV9 would be better than the RV7.
Even though the RV7 got slightly better gas milage, if you flew the RV-9 at higher altitudes, w/ a high aspect ratio wing, efficiency (mpg) increases.
My choice to build the RV7 was the fact I had a 180HP engine, wanted to do Acro, like the extra 6 gal of fuel and really did not care about the slower stall speed. As far as takeoff/landing/rate-of-climb/ceiling with 180HP the RV7 will outperform the RV9 easily in flight, but the lighter RV9 will still land slower and shorter. Of course fuel economy for the higher HP RV7's goes down a little and the RV9 has the edge in econ.
There is the deal. You want to use 160 HP or less the RV9 can be real efficient. If you want to use a bigger engine than 160HP, the RV7 wing is the only way to go. THERE AIN'T NO REPLACEMENT FOR DISPLACMENT. A RV7 with a 180 HP or 200 HP would of course exceed the RV9 speed and rate of climb performance even more (at more fuel).
If you don't want to do Acro and have a 160 HP or less engine to use, the RV9 is a real nice wing.
Vans TO/Ldg distance are ground roll; I'm not sure how they got them. TO/Ldg distance is skill related as well as prop related. A C/S prop gives more thrust on TO and less idle thrust on landing, which has a big effect on takeoff and landing distance. So how Van figures them I don't know.
This may not be the answer but study the performance numbers and a relationship will be exposed.
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Bryan Wood
Well Known Member
I know the question is regarding the seven vs. the nine but I'll throw this out anyway. Having never traveled with a 7 I can't make this statement or even guess about it, but I have traveled with numerous 6's many times. What I notice is that 6500' and below I almost have to wring my 0-320's neck to stay with them and their powered back 0-360's. If we get up to around 8500' I can get out of the power a little bit which is simply turning the prop a little bit slower. If we are at 10,500 or higher the six's start to work a little bit. I don't mean the nine is overcoming the displacement of the six's, but the advantage that they enjoy is dwindling. The benefits of the wing do start to show in the thinner air. I'd be curious if this transition is noticable with the nine and the seven like it is with the nine and the six. I'm guessing that it would, but in the low to mid teens.
What I'm seeing here agrees with my thinking on my decision to pick the 9, with another aspect I'd like to add. I really want to use a turbodiesel engine in my bird, which would increase efficiency no matter which plane it was mounted on. The key difference is that all the turbodiesels on the market (or about to be on the market) are not rated for acro. If I put a non-acro engine on a 9, I've a got a terrific XC plane. If I put that same engine on a 7, I've got an aerobatic plane that can't do acro, with a lowered resale value unless I change engines.
That, and most of my trips will be 3-hour XC and I like flying high, where the 9 wing is as happy as the turbocharged engine.
That, and most of my trips will be 3-hour XC and I like flying high, where the 9 wing is as happy as the turbocharged engine.
Lift = Weight
I picked up a common misconception in your initial post that often confuses people when they are comparing aircraft designs:
Two aircraft of the same weight are flying in straight and level flight. The lift of both aircraft is the same regardless of speed, altitude, or wing design. This is because in level unaccelerated flight, lift equals weight.
Hope that helps.
Alex
I picked up a common misconception in your initial post that often confuses people when they are comparing aircraft designs:
Two aircraft of the same weight are flying in straight and level flight. The lift of both aircraft is the same regardless of speed, altitude, or wing design. This is because in level unaccelerated flight, lift equals weight.
Hope that helps.
Alex
GMC- great comparison of the 7 and 9, the best Ive seen so far, a keeper. Ive always thought the differences between the two are less than most believe them to be. Based on some reports, I believe 160 hp MIGHT be a little underpowered for the 9's, since they seem to have a problem maintaining the 180 mph designed cruise speed, assuming the commonly used O-320 Lycs provide full rated power.
Prkaye- Keep In mind that you will lose about 25% of the sea-level rated hp by ~8000 ft. due to the reduced O2 content and related leaner mixtures (less fuel, less power). That expected loss is one of the reasons I decided on the Mazda Renesis motor (rated 200 hp @ ~350 lbs); I live at the base of the Rocky mountains @5000' elevation w/ 12000' peaks in 3 directions.
The way I see it, your options are either to figure out the various problems involved with a turbocharger installation, to maintain nearly the same rated power, or start with a more powerful engine and plan on losing some of the rated HP at altitude. It all boils down to a compromse of cost, weight, heat generation/cooling, fuel burn, and utility.
Prkaye- Keep In mind that you will lose about 25% of the sea-level rated hp by ~8000 ft. due to the reduced O2 content and related leaner mixtures (less fuel, less power). That expected loss is one of the reasons I decided on the Mazda Renesis motor (rated 200 hp @ ~350 lbs); I live at the base of the Rocky mountains @5000' elevation w/ 12000' peaks in 3 directions.
The way I see it, your options are either to figure out the various problems involved with a turbocharger installation, to maintain nearly the same rated power, or start with a more powerful engine and plan on losing some of the rated HP at altitude. It all boils down to a compromse of cost, weight, heat generation/cooling, fuel burn, and utility.
prkaye said:
A normally aspirated engine will get you up there just fine - Vans published performance numbers use NA engines and show a solo-weight ceiling of 24,500 for a 9A at 160 hp. Your power will of course drop off as you climb, so performance will drop as you climb, but efficiency will also rise in the thin air. The turbo buys you increased climb rate, increased ceiling, and higher TAS at cruise altitude thanks to higher manifold pressure and correspondingly higher HP - but you still have to watch Vne (corrected for altitude) due to flutter. The turbo also adds weight, complexity, price, and cooling issues. It's all a tradeoff.
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gmcjetpilot
Well Known Member
Does not compute
From my O320 RV-4 experience, at max gross/aft CG, fuel fuel, passenger, bags, 9-10,500 ft was all I could get and where it still felt good. Trying to get to 12.5 or higher was just not pleasant. Solo and light, sure 12,500 ft in the RV-4 and higher was fine. Decked out w/ O2 I few some trips as an experiment in the + 16,000 ft range. My fuel burn down and spacific miles per gal up, but I was going slow. It took a lot longer to get there, but than I skipped a few gas pumps. The RV-4 is not slouch. A 160 HP RV-4 has 1,000 ft higher service ceiling than a 160 HP RV-9A. Of course the RV-9A's gross is higher by 200 lbs than the RV-4. That just shows you how important weight is. KEEP IT LIGHT.
I suspect a O320 RV9A is similar but may be able to pull off a few more thousand feet with the longer wing and still have a sold feel, so the first thing I would say is experiment!! You need to fly it near service ceiling light and heavy. Take data and find out what the plane likes. I have no RV9A time, but I can speak to the basic principles of altitude flight and turbo charges.
So lets assume a 160 hp RV9A, Sensenich prop with proper pitch, standard day and zero wings. My common advice for VFR normally aspirated engine GA planes is 8,500-12,500 ft for practical and efficiency reasons. Why do you want to fly at 18,000 ft? There is no real reason. Trying to TOP convective weather in a single engine plane is not a good idea.
Do you need a turbo? NO. Turbo charging was covered in a recent thread; the bottom line it's: heavy, expensive, does not fit under a RV cowl easily. Also Vne speed goes down with altitude. It would be easy to exceed Vne with a turbo at altitudes above 10,000-13,000 ft, so the benifit on the RV airframe is limited, unless you increased Vne and added more fuel. Turbo charging maintains power at altitude. Yes you go faster but you burn more fuel, no free lunch. I talked to a turbo RV pilot, it flew high and fast, but not that fast and drank lots of fuel. You have to pay to go fast. You want to go fast in a RV, stay on the deck and leave it wide open. You will get there in a hurry, just try not to cry like a little girl at the gas pump.
Looking at Vans ** service ceiling numbers for the RV-9A for 160 HP:
Solo:....24,500 ft
Gross:..18,500 ft
The answer is, it it practical? Of course you can physically fly up to 18,000 ft without a turbo in a RV9(A), but read the definition of ** service ceiling below.
The practical part is sucking O2 thru a mask, staying warm and going real slow, I mean slow. Nothing wrong with going slow; you will get great miles per gallon if the wind is favorable. Depending on time to climb and trip length; Even solo, I would say 18,000 feet is not real practical or efficient, but 13,500-15,500 ft may be practical at lower weights and standard or better day's (cool). Flying high means going slow, but you will be nearing you best miles per gallon.
Most people don't have the patients to fly that slow, but with a good tail wind, its like free lunch. The problem is knowing the real winds aloft. Often you don't know until you are there. Learn the ATC freqs and see if they can ask any higher flyers what the winds are. Almost all planes have ADC's (airdata computers) and can give you winds. So plan on a lower altitude and then step up as you burn fuel or if you think there is more winds to be had. Bottom line 8,500-9,500 ft is your everyday get there, 75% X-C altitude. You want to fly near 55% climb up to 11,500-12,500 ft. You don't need O2, good econ and decent true airspeed. Now if you are one of those fire breathing 180 hp and 200 hp RV lone eagle jockey's, than fly even higher, but break the O2 bottle out. I don't care for O2 myself, unless I have to; some times its nice to have the option to climb up into strong tailwinds. Higher HP gives you more altitude capability even if its not a turbo. So the RV-7/8 with a large engine can make up for the shorter wing with raw power. That's why I went with the 180HP RV7 and the acro/fuel range.
In general for any GA plane RV (non-turbo), HP drops, lift drops, speed drops but MPG's increase to a point. As you get near your ** "service ceiling" you are start to get below best range or long range cruise speed and nearing the bucket, backside of the power curve. Before that the plane's feel is not pleasant, mushy. Some Jets do the same thing when you get high: lift is down, thrust is down and they start to mush along. The old B737 was not real happy heavy and high up, but the newer "long wing" or "new gen" B737-700's flys nice high up w/ a higher aspect ratio wing. However keep in mind HP on piston engines drops off way more than a Jet engine does. Jets have tons of sea level reserve power for single engine performance and altitude performance; also jet engines benefited and increase in efficiency from colder temps and higher speeds. Pistons don't work that way, temps and aircraft forward speed has minor or nil affect on engine efficiency.
Yes you could turbo the RV-9A and fly at 18,000 ft but structurally the wing and controls are not designed for high speed flight at extream altitudes, i.e., Vne. Where a jet wing is made to fly high. YES THAT'S IT a sweep-ed wing RV9A with a jet engine.
Also what speed do you want to fly? Our RV's will fly 100-110 mph, but we also want to get there today! You can just fly at 500 ft and throttle back and get good gas milage and a great view. There's is max range, max endurance, long range cruise, min trip time and so on.... At some altitude, speed and power setting for the weight and condtions there is an optimal balance of speed, economy and practicality. You are the PIC, so you decide. In general for normally aspirated engine planes like the RV its under 12,500 ft, giving good speed, econ and got to get there today time.
Hot and heavy best alt may be as low as 8,500 ft. If there are head winds, 1,000 ft may be best. Its a question that can't be answered completely but you do NOT need a turbo.
** Service Ceiling: This by definition means hanging on the prop, with a handful of MPH above stall and max climb rate of 100 fpm by definition (and no down drafts). I arbitrarily subtract 6,000 ft off these numbers for max semi-practical cruise for 18,500 ft or 13,500 ft for solo/gross. Of course you will need O2 to breath. At night you should be on O2 before 12,500 ft.
Trick question, what are the winds and atmospheric conditions (temp/pressure). What's your gross weight? How far is the trip? What kind of prop? (carb has nothing to do with it)prkaye said:
From my O320 RV-4 experience, at max gross/aft CG, fuel fuel, passenger, bags, 9-10,500 ft was all I could get and where it still felt good. Trying to get to 12.5 or higher was just not pleasant. Solo and light, sure 12,500 ft in the RV-4 and higher was fine. Decked out w/ O2 I few some trips as an experiment in the + 16,000 ft range. My fuel burn down and spacific miles per gal up, but I was going slow. It took a lot longer to get there, but than I skipped a few gas pumps. The RV-4 is not slouch. A 160 HP RV-4 has 1,000 ft higher service ceiling than a 160 HP RV-9A. Of course the RV-9A's gross is higher by 200 lbs than the RV-4. That just shows you how important weight is. KEEP IT LIGHT.
I suspect a O320 RV9A is similar but may be able to pull off a few more thousand feet with the longer wing and still have a sold feel, so the first thing I would say is experiment!!
You need to fly it near service ceiling light and heavy. Take data and find out what the plane likes. I have no RV9A time, but I can speak to the basic principles of altitude flight and turbo charges.So lets assume a 160 hp RV9A, Sensenich prop with proper pitch, standard day and zero wings. My common advice for VFR normally aspirated engine GA planes is 8,500-12,500 ft for practical and efficiency reasons. Why do you want to fly at 18,000 ft? There is no real reason. Trying to TOP convective weather in a single engine plane is not a good idea.
Do you need a turbo? NO. Turbo charging was covered in a recent thread; the bottom line it's: heavy, expensive, does not fit under a RV cowl easily. Also Vne speed goes down with altitude. It would be easy to exceed Vne with a turbo at altitudes above 10,000-13,000 ft, so the benifit on the RV airframe is limited, unless you increased Vne and added more fuel. Turbo charging maintains power at altitude. Yes you go faster but you burn more fuel, no free lunch. I talked to a turbo RV pilot, it flew high and fast, but not that fast and drank lots of fuel. You have to pay to go fast. You want to go fast in a RV, stay on the deck and leave it wide open. You will get there in a hurry, just try not to cry like a little girl at the gas pump.
Looking at Vans ** service ceiling numbers for the RV-9A for 160 HP:
Solo:....24,500 ft
Gross:..18,500 ft
The answer is, it it practical? Of course you can physically fly up to 18,000 ft without a turbo in a RV9(A), but read the definition of ** service ceiling below.
The practical part is sucking O2 thru a mask, staying warm and going real slow, I mean slow. Nothing wrong with going slow; you will get great miles per gallon if the wind is favorable. Depending on time to climb and trip length; Even solo, I would say 18,000 feet is not real practical or efficient, but 13,500-15,500 ft may be practical at lower weights and standard or better day's (cool). Flying high means going slow, but you will be nearing you best miles per gallon.
Most people don't have the patients to fly that slow, but with a good tail wind, its like free lunch. The problem is knowing the real winds aloft. Often you don't know until you are there. Learn the ATC freqs and see if they can ask any higher flyers what the winds are. Almost all planes have ADC's (airdata computers) and can give you winds. So plan on a lower altitude and then step up as you burn fuel or if you think there is more winds to be had. Bottom line 8,500-9,500 ft is your everyday get there, 75% X-C altitude. You want to fly near 55% climb up to 11,500-12,500 ft. You don't need O2, good econ and decent true airspeed. Now if you are one of those fire breathing 180 hp and 200 hp RV lone eagle jockey's, than fly even higher, but break the O2 bottle out. I don't care for O2 myself, unless I have to; some times its nice to have the option to climb up into strong tailwinds. Higher HP gives you more altitude capability even if its not a turbo. So the RV-7/8 with a large engine can make up for the shorter wing with raw power. That's why I went with the 180HP RV7 and the acro/fuel range.
In general for any GA plane RV (non-turbo), HP drops, lift drops, speed drops but MPG's increase to a point. As you get near your ** "service ceiling" you are start to get below best range or long range cruise speed and nearing the bucket, backside of the power curve. Before that the plane's feel is not pleasant, mushy. Some Jets do the same thing when you get high: lift is down, thrust is down and they start to mush along. The old B737 was not real happy heavy and high up, but the newer "long wing" or "new gen" B737-700's flys nice high up w/ a higher aspect ratio wing. However keep in mind HP on piston engines drops off way more than a Jet engine does. Jets have tons of sea level reserve power for single engine performance and altitude performance; also jet engines benefited and increase in efficiency from colder temps and higher speeds. Pistons don't work that way, temps and aircraft forward speed has minor or nil affect on engine efficiency.
Yes you could turbo the RV-9A and fly at 18,000 ft but structurally the wing and controls are not designed for high speed flight at extream altitudes, i.e., Vne. Where a jet wing is made to fly high. YES THAT'S IT a sweep-ed wing RV9A with a jet engine.
Also what speed do you want to fly? Our RV's will fly 100-110 mph, but we also want to get there today! You can just fly at 500 ft and throttle back and get good gas milage and a great view. There's is max range, max endurance, long range cruise, min trip time and so on.... At some altitude, speed and power setting for the weight and condtions there is an optimal balance of speed, economy and practicality. You are the PIC, so you decide. In general for normally aspirated engine planes like the RV its under 12,500 ft, giving good speed, econ and got to get there today time.
Hot and heavy best alt may be as low as 8,500 ft. If there are head winds, 1,000 ft may be best.
Its a question that can't be answered completely but you do NOT need a turbo. ** Service Ceiling: This by definition means hanging on the prop, with a handful of MPH above stall and max climb rate of 100 fpm by definition (and no down drafts). I arbitrarily subtract 6,000 ft off these numbers for max semi-practical cruise for 18,500 ft or 13,500 ft for solo/gross. Of course you will need O2 to breath. At night you should be on O2 before 12,500 ft.
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Bryan Wood
Well Known Member
Link to an old post
This post reminded me of one from a while back with great photos attached. As they say pictures are worth a thousand words... Roger Ping took his nine up to 17,900 at a takeoff weight of around 1700lbs with two people. Still climbing at 500fpm when he reached altitude, indicated of 108 knots when level which is 60 knots over the clean stall speed. I've only flown mine up to 16500 but it still felt pretty solid. This wing likes to fly high! Once you go up high though it isn't likely you will repeat it to often as George points out. It gets frigid cold and thawing out takes hours or a good dunk in the hot tub.
Edit... I think Dan Checkoway posted similar pictures of his 7 way back when and his plane was still climbing at 1000fpm at 20k"with his cheater engine. Does anybody recall this? Dan?
http://www.vansairforce.com/community/showthread.php?t=4632
Regards,
This post reminded me of one from a while back with great photos attached. As they say pictures are worth a thousand words... Roger Ping took his nine up to 17,900 at a takeoff weight of around 1700lbs with two people. Still climbing at 500fpm when he reached altitude, indicated of 108 knots when level which is 60 knots over the clean stall speed. I've only flown mine up to 16500 but it still felt pretty solid. This wing likes to fly high! Once you go up high though it isn't likely you will repeat it to often as George points out. It gets frigid cold and thawing out takes hours or a good dunk in the hot tub.
Edit... I think Dan Checkoway posted similar pictures of his 7 way back when and his plane was still climbing at 1000fpm at 20k"with his cheater engine. Does anybody recall this? Dan?
http://www.vansairforce.com/community/showthread.php?t=4632
Regards,
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