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

tommayer wrote:

Paul,
    Would you explain people are not using the higher ratio planetary
reduction gear on airplanes, and only on gyros?  From past posts it

sounds

like the higher ratio has fewer inherent weak links.  Tom Mayer

Conventional wisdom has it we should keep down the RPM for cruise. Gyro

guys

rarely cruise. They get up there and go berserk for a half hour or so :-)

I think we could cruise over 6000 RPM no problem. Probably a bit higher
fuel consumption.

Paul Lamar

tommayer wrote:

Paul:

    What if you had a constant speed prop and a turbo?  Climb at 2450 prop
rpm--just under 7000 on the engine, right?  Cruise at 1800 to 2000 prop rpm,
like a radial, with way oversquare manifold pressure, again like a
supercharged radial,  to get the hp.  You'd be under 6000 engine rpm.  What
would be the dangers in that?   Is the lack of a suitable C/S prop what has
kept people from going that way?  Tom Mayer 

I think that is a good way to go. We were working on a constant speed
design but I think John Moran got diverted to the higher priority
six pin planet carriers for Ross and Tracy's redrives with good reason. 
We need a light weight planetary redrive for turbo 13B's and 20B's. Of course 
you could always pop for a $10K bucks German electric constant speed prop.  

BTW As Vance says, larger dia., slower turning props are better.
Trouble is you need to start with a lot of ground clearance and most kit planes
landing gears are designed up for the 68 to 72 inch diameter props.

Paul Lamar

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