RPM Gains
05-12-2004, 11:42 PM
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RE: RPM Gains
the 200-300 rpm gain is about right for a .40 power trainer or sport aerobatic type... the faster the aircraft can fly, and the higher the pitch of the prop, the more it can potentially unload the engine allowing the rpm to increase.
There are ways to measure the rpm of the engine while the airplane is flying. Extreme high speed photography for one. Take enough frames per second.. you can watch the prop move one frame at a time and calculate the rpm from the frame rate and angular change between frames. (not exactly a cheap way to do it...) There is a way to very closely estimate the increased rpm from the frequecy of the engine noise.
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http://www.ymec.com/hp/signal2/motor1.htm for one sound analysis that gives an electric motor's rpm. Same will work for a glow engine doing a high speed pass. (average the approach and retreat to eliminate the doppler shift effect)
There are ways to measure the rpm of the engine while the airplane is flying. Extreme high speed photography for one. Take enough frames per second.. you can watch the prop move one frame at a time and calculate the rpm from the frame rate and angular change between frames. (not exactly a cheap way to do it...) There is a way to very closely estimate the increased rpm from the frequecy of the engine noise.
**********
http://www.ymec.com/hp/signal2/motor1.htm for one sound analysis that gives an electric motor's rpm. Same will work for a glow engine doing a high speed pass. (average the approach and retreat to eliminate the doppler shift effect)
05-17-2004, 09:02 PM
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RE: RPM Gains
No physics no-it-alls out there? LOL
I'm being told at a few different clubs that there's a 12 - 1500 rpm increase at WOT in level flight over what tach readings are on the ground with the craft being held back! If this is true then my .61FX with a 12x6 Zinger is only running at 10,300rpm with a bisson pitts muffler on it. If Richard L. is correct in saying the average gain would be 200-300rpm, then is my engine sick?
I'm being told at a few different clubs that there's a 12 - 1500 rpm increase at WOT in level flight over what tach readings are on the ground with the craft being held back! If this is true then my .61FX with a 12x6 Zinger is only running at 10,300rpm with a bisson pitts muffler on it. If Richard L. is correct in saying the average gain would be 200-300rpm, then is my engine sick?
05-17-2004, 09:51 PM
#6
RE: RPM Gains
Both of my new ROTO engines 35 and 25 - have tattle tale tachs which record the highest rpm during any given run -
you simply point your optical el cheapo tach at the little LED and instantly it shows the rpm - (1/2 rpm)
so if it reads 4000- the engine turned 8000.
As far as "how much" from static to full speed ?
every case is different -and can vary from NONE (hover)
to thousands- full speed dive.
you simply point your optical el cheapo tach at the little LED and instantly it shows the rpm - (1/2 rpm)
so if it reads 4000- the engine turned 8000.
As far as "how much" from static to full speed ?
every case is different -and can vary from NONE (hover)
to thousands- full speed dive.
05-18-2004, 07:22 PM
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RE: RPM Gains
There must be a rule of thumb that veteran RCers use for rpm. If I want my 61FX to pull 13,500 - 14,000 rpm in straight and level WOT flight what would the tach reading be on the ground in the pits? I realize the rpm will climb significantly in a dive or fall off when climbing.
05-19-2004, 10:17 AM
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RE: RPM Gains
I don't guess I see the point of setting up for a particular RPM in flight. You might do that and still end up with a doggy flying plane if the prop/RPM/airspeed combination isn't right. I'd suggest testing a variety of props until you find the combination that gives the flying characteristics you want.
