Dear Paul,
Do you have a machine drawing of the exact dimensions of the SAE 2
prop hub.
Can you possibly explain graphically to me, how a hydraulic constant
speed propeller works and how it is controlled via rpm of motor. Has
the thought ever crossed your mind to possibly look at running the
propeller out put shaft on a PSRU between white metal bearings being
oil lubricated from engine.
Regards
Craig
SA

Is the number 2 the constant prop speed hub (small) or the wood prop
hub (big)? I can never keep them stright. I have an unofficial drawing
of the wood prop hub.

Paul Lamar

Paul,
The SAE #2 prop hub has a 4.75" diameter bolt circle.  For wood props
the lugs are 3/4" diameter with a 1/2" diameter bolt and the O.D. of the
hub is about 7.25".  For metal props the lugs are 5/8" diameter with a
3/8" bolt and the hub O.D. is as you have shown about 6.25".  The lugs
are either threaded, type "B", or unthreaded, type "A".   The centering
boss for both wood and metal props is as your drawing shows, 2.25"
diameter.

Tracy's PSRU uses the smaller lugs and bolts.

BTW the difficult part of the constant speed prop is not getting the oil
to the prop hub, but mechanically driving the mechanical prop governor
from the PSRU.  Here is an idea to think about:  forget about the
mechanical governor and use a tachometer signal to control a pulse width
modulator circuit that controls a standard electro-hydraulic pressure
relief valve that controls the prop pitch.  We may need a small pump to
boost the pressure, but I think I would not be difficult to modify
Tracy's output shaft to provide engine oil through the shaft to the prop
hub.

Ed Anderson has done the preliminary design work for a digital prop
control with a very nice set of  features (stored set points, etc.).  A
PWM output could be added to this controller if we can work out the
details of the electro-hydraulic part of it.

Aubrey

www.legendaryaircraft.com
These guys make an adapter so you can drive the stock governor
with a cog belt drive off the front of the engine.

Paul Lamar

I wonder how much horsepower a governor takes to run..

Matt

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