Mark,
"I'm not aware of THE published method."
John A. Gard "An Experimental Method to Determine Rubber Powered Airplane
and Propeller Efficiencies" 1981 NFFS Sympo, pp 21-24.
The method assumes the plane flies at the same attack angle in glide and
under power. When I read this article, I went back in my notes to review my
measurements where I found that, although I got "reasonable" numbers for prop
efficiency, I also calculated other coefficients and found discrepancies. The
discrepancies were such as to suggest that the airspeed over the wing was
greater than the airspeed determined by the distance flown in the time observed.
I interpreted this to mean one or both of two things. First, the prop slip
stream made the average speed over the wings greater than the flight speed,
and second, the attack angle was not the same in power and in glide, due to
the effect of thrust line location on pitch trim. I do not use those prop
efficiency measurements in my flight performance calculations.
"I have some 2/99 also, so I'll use that if that's what you plan to use. It
used to be the breakiest rubber I own, so I may not be able to wind as hard
I am used to. No matter!"
Use the best rubber you have. You will be competing against other people
who will be using their best. You may also make flights with the 2/99 for
comparison purposes. And when we're done, I can tell you what fixed prop and
thin motor size to use to beat your time. ;-)
Gary Hinze
************************************** AOL now offers free email to everyone.
Find out more about what's free from AOL at
http://www.aol.com.
[Non-text portions of this message have been removed]
Received on Sat Mar 24 2007 - 17:43:52 CET