JONA4AERO wrote:
I heard rotary engine makes enough horsepower. what about the torque? Do you have a chart shows
rpm vs. torque and hp?

Torque does NOT make airplanes fly! HP makes airplanes fly!
HP is a force moving at a speed. One HP is 550 pounds of force
or drag or thrust moving at one foot per second. It is also
550 pounds of weight moving straight up at one foot per second.

Therefore HP is drag or force or weight or thrust... times speed.

An airplane flying at 300 feet per second (about 204 MPH) with
336 pounds of drag needs 183 HP out of the prop. Speed times
drag divided by 550. If the prop efficiency is 80% that means
you will need about 230 HP out of the engine.

Torque can be whatever you want it to be by gearing the engine down.
Torque at the prop equals the gear box ratio times the torque from engine.
Torque from any 200 HP engine running at 6000 RPM is 200 HP times 5252
divided by 6000 RPM or 175 foot pounds. 5252 is the magic constant.
Therefore if you have a HP curve you don't need a torque curve. If
you have a torque curve you don't need a HP curve. One is derived
mathematically from the other. All you need know is RPM in both cases.

175 foot pounds times a gear box ratio of 2.17:1 is 380 foot
pounds at 2765 RPM at the prop. The HP at the prop would be
the same as the engine.

If you use a 3:1 gear box you can use a larger dia. prop and the
torque would then be 175 X 3 or 525 foot pounds and the prop
RPM would be 2000 RPM while the engine was still running at
6000 RPM. The HP at the prop would still be the same as the engine.

Along these lines, for us pusher guys, a larger diameter prop isn't usually an option.  Seems that a
wider chord will have to be used if we are going to run at 6k engine rpm, and 2k prop rpm.
Any thoughts on how wide the chord can be in order to have an efficient prop using a clark y profile
with three blades?
BTW, anyone know which profile is the most efficient, clark-Y, or RAF-6? (pusher configuration)
Royce
(rest of message snipped)

I am not advocating that Royce. Run the engine at 7500 for takeoff
and the prop at 2700 with a 2.85:1 gear box. You are right on with the
wider cord. I think the jury is still out on what the best blade
airfoil is.

Paul Lamar
 
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