ORIGINAL: dick Hanson
"It is all about load and the speed where the max possible motor/engine POWER is desired
for example:
To go fast I prop up to where max watts hit at about the speed I am shooting for
then -ready for this?
I hope I guessed right.
Then I change props and try again
Anyone who thinks they can accurately compute the speed and load is kidding themselves
They may (read that MAYBE), get in the right ballpark but that's all."
Thats the rub.. All the tweaking and tuning and taching doesn't mean squat as soon as the plane begins to roll down the runway. I'm frustrated that the IC engine manufacturers will not publish torque/power curves for their engines (I think Fuji does but thats it). We can't even iterate like Dick described because we don't know where to target for maximum power at target airspeed.
If we had a reliable engine dynamometer we could plot torque/power vs. rpm. With that information we might then "estimate" the rpm's difference between static and maximum airspeed. (On board rpm readings in-flight would make this a piece of cake and cheaper than renting windtunnel time!)
As it stands now, the glow guys have to iterate between at least 3 different unknowns (power curve, rpm, airspeed) to get at maximum speed in the air - which is darn near impossible.