vance wrote:

Frank Wrote> My guess is that props are made to turn at about 3000 RPM max
because 50

years ago that was about the max that a Lycont could turn.

If you check out WW1 airacrft powered by rotories, some of these had
performance approaching an RV-6, and ran huge propellors below 1500 rpm.
(Cleget 1200rpm, Le Rhone 1400rpm). GA aircraft turn 2500-2800rpm as the
best compromise between prop effiency and engine efficiency. If you are
going to a reduction drive you are freed from this compromise. Looking at
most prop driven aircraft with out this compromise, they mostly run a lower
prop RPM. If you are fitting a 13b to an existing design design, you still
have the prop diameter limitation.  Is it more efficient to run a two blader
at lycon design speed, or a three blader of the same diameter slower?

Mark Wrathall

All other things being equal - propeller diameter is the driving factor
for propeller efficiency. However, if you are limited to a fixed pitch
prop, the steep pitch for cruise with the slower turning prop, will be a
higher loss at take off and climb. With proper blade area, and
controllable pitch, the efficiency would be essentially the same tho the
slower prop would be quieter.
Vance

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org