Shear Pins for Propellors?

wrote:

The shear pin would fail at idle.

How about this one. The prop would have a clutch plate on the front with a hole
in the center of both prop and plate large enough to fit over the end of the
crank. The prop/clutch assembly would slip over the end of the shaft and another
clutch plate assembly would bolt onto the end of the shaft. The latter would
have pivoting weights to increase pressure on the clutch as rpm rises (much like
some older CS props have to adjust blade angles). When the engine is producing
little power (as it would during landing), the prop would only be loosely
connected to the engine. Add power, and the clutch engages more and more
completely, both from the pressure added by the weight mechanism and by the
thrust pushing the prop forward.

This system would also allow the prop to windmill without attempting to turn the
engine in cases of engine failure.

You'd have to thread the inside of the crankshaft end and perhaps have to
rethink the current method of driving CS props with engine oil, but I doubt that
the problems are unsolvable.

George Patterson
Whosoever bloweth not his own horn, the same shall remain unblown.

On Fri, 1 Apr 2005 at 02:32:55 in message
.net, Rich Lemert
wrote:
This morning, while driving past the airport on my way to work, the
thought occured to me that a shear pin could be used to protect
airplane engines (at least partially) from prop strikes. My
understanding is that the props on light singles (at least) are
connected directly to the engine's drive shaft

It occurs to me that a shear pin could only work effectively against a
rotational stoppage. Since a normal prop either fits over a crankshaft
end or is bolted to a plate, a shear pin could do little or nothing.
What loading cases would you propose for the shear pin failure?

In a minor accident which way are the prop tips usual bent?

I somehow feel that the possibility of a prop detaching in flight should
not be encouraged. :-)

--
David CL Francis

On Fri, 1 Apr 2005 at 13:06:26 in message
t, John T Lowry
wrote:

Sounds to me like an idea worth pursuing. Could have two shear pins,
with visually checkable integrity during preflight inspection, to
counter the problem of one failing.

Good idea but when both were in place the shear failure load would be
twice as strong?
--
David CL Francis

This system would also allow the prop to windmill without attempting
to turn the
engine in cases of engine failure.

So what do we do for a flywheel?

Dan

wrote:
This system would also allow the prop to windmill without attempting

to turn the

engine in cases of engine failure.


So what do we do for a flywheel?

What about it? On my old Maule, it's attached to the crank just in front of the
engine case. The prop is attached to a flange that's located several inches in
front of the flywheel. I propose to replace the flange and rigid prop mounting
with a clutch arrangement. The flywheel location and method of attachment would
not change.

George Patterson
Whosoever bloweth not his own horn, the same shall remain unblown.

That isn't a flywheel. It a ring gear mount for the starter
that also drives belt for the alternator (if it's a Lyc). It's aluminum
and weighs about four pounds. An engine such as the O-320, with its
four huge cylinders (compared to a Chev 350's eight much smaller ones,
for instance) would need a wheel of about 50 pounds in that small
diameter.
In all direct-drive aircraft engines the prop is the
flywheel. In most geared certified engines, the prop is the flywheel.
Geared ultralight engines like the Rotax have a separate flywheel, as
do many of the converted and geared or belted auto engines. They have
other problems with resonance between the prop and flywheel that can
lead to belt or gear failures if not properly designed and operated.

Dan