Van's Air Force
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RV-9A TOLD w/IO-240
- Thread starter 2Texians
- Start date
Kyle Boatright
Well Known Member
Rough calcs say it should climb at about 475 FPM at max power at 10K'. However, the prop would need to be under-pitched to turn full rpm, which would hurt cruise performance. The old fixed pitch compromise. Every 100 rpm you lose is ~ 4 hp, so if you're down 200 RPM, that's 8 hp and a loss of another `130 fpm once prop efficiency figures in.
Thanks for your reply! If I left the prop set for better cruise, what's the approximate fpm in these conditions?
Use the performance specs listed here for the 9A equipped with a Lyc O-235.
www.vansaircraft.com
The performance with the IO-240 would likely be nearly identical.
I flew the original prototype some and it performed very well in the context of a light airplane with a low HP engine.
It was way faster than a C-152 or Piper Tomahawk, which both used the same engine, but in higher density altitudes
the degradation in performance was very noticeable and required careful consideration, though it still did better than the Cessna or Piper would have in the same situation.
This could be improved with a finer pitch prop but at a big compromise in speed.
To me the only reason that makes sense to install the small engine in an RV-9(A) is if someone already has one that they know to be perfectly good.
Even then, I think the better plan would be sell that engine and put the funds towards an O-320.
Hopefully you are not considering this because of fuel economy benefits. That is a hunt for a unicorn.
An O-320 RV-9A flying beside an IO-240 RV-9A at its best cruise, will have close to exactly the same burn rate as the smaller engine.
When local flying, I fly my RV-6A a lot at power settings that produce a fuel flow that is the same as an RV-12 but at speeds 10-15 Kts faster than the RV-12.
RV-9 / 9A - Van's Aircraft Total Performance RV Kit Planes
www.vansaircraft.com
The performance with the IO-240 would likely be nearly identical.
I flew the original prototype some and it performed very well in the context of a light airplane with a low HP engine.
It was way faster than a C-152 or Piper Tomahawk, which both used the same engine, but in higher density altitudes
the degradation in performance was very noticeable and required careful consideration, though it still did better than the Cessna or Piper would have in the same situation.
This could be improved with a finer pitch prop but at a big compromise in speed.
To me the only reason that makes sense to install the small engine in an RV-9(A) is if someone already has one that they know to be perfectly good.
Even then, I think the better plan would be sell that engine and put the funds towards an O-320.
Hopefully you are not considering this because of fuel economy benefits. That is a hunt for a unicorn.
An O-320 RV-9A flying beside an IO-240 RV-9A at its best cruise, will have close to exactly the same burn rate as the smaller engine.
When local flying, I fly my RV-6A a lot at power settings that produce a fuel flow that is the same as an RV-12 but at speeds 10-15 Kts faster than the RV-12.
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