Shear Pins for Propellors?

Back when I was growing up on the farm, we used several powered
implements that received their power from the tractor through a power
take-off assembly. Somewhere on the device's power train, between the
PTO take-off and the "business end" of the apparatus, there was always
either a belt-drive or a coupling fitted with a "shear" pin. Both of
these systems were intended to protect that tractor (and the implement)
by failing if the implement bit off more than it could handle.

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.

Recognizing that this issue is driven as much by regulation as by
anything, I'm wondering if there would be any benefit to using shear
pins in these systems. Would it reduce the need for a complete (or
partial) tear-down after a prop strike? Would there be any benefit for
more complex propeller arrangements?

Any thoughts?

Rich Lemert

"Rich Lemert" wrote in message
link.net...
[...]
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.

Frankly, having the prop keep moving is so much more important than
protecting the engine in the event of a prop strike, I can't imagine anyone
accepting the additional potential failure mode of a bad shear pin. We seem
to have a hard enough time making the crankshafts right.

Note that in a tractor, you are much more likely to suffer a sudden
stoppage, and the consequences for the premature breaking of a shear pin are
dramatically less. It seems to make much more sense for that application.

My understanding is that the props on light singles (at least) are
connected directly to the engine's drive shaft.

That's true of almost every propeller driven airplane. There are
exceptions, of course, mostly related to geared engine installations (found
on singles and twins).

Pete

"Rich Lemert" wrote in message
link.net...

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.

I have also had shear pins fail for no good reason. Aviation thinks that
designing in another point of failure is a bad thing.
--
Jim in NC

"Morgans" wrote in message
...

"Rich Lemert" wrote in message
link.net...

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.

I have also had shear pins fail for no good reason. Aviation thinks that
designing in another point of failure is a bad thing.
--
Jim in NC


Don't some of the Rotax engines have a shear point to protect the engine? I
believe most vacum pumps have a Shear Wafer to protect the engine WHEN...
not IF the pump fails as well. But have ot agree that I'd rather have to
tear down an engine after a propstrike... than have the pin fail in
flight...

In article .net,
Rich Lemert wrote:

Recognizing that this issue is driven as much by regulation as by
anything, I'm wondering if there would be any benefit to using shear
pins in these systems. Would it reduce the need for a complete (or
partial) tear-down after a prop strike? Would there be any benefit for
more complex propeller arrangements?

Any thoughts?


I think the best protection for the engine would be to not land gearup,
taxi into super soft stuff, or do any of the other things that cause
prop strikes. G

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

"Rich Lemert" wrote in message
link.net...
Back when I was growing up on the farm, we used several powered
implements that received their power from the tractor through a power
take-off assembly. Somewhere on the device's power train, between the
PTO take-off and the "business end" of the apparatus, there was always
either a belt-drive or a coupling fitted with a "shear" pin. Both of
these systems were intended to protect that tractor (and the
implement)
by failing if the implement bit off more than it could handle.

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.

Recognizing that this issue is driven as much by regulation as by
anything, I'm wondering if there would be any benefit to using shear
pins in these systems. Would it reduce the need for a complete (or
partial) tear-down after a prop strike? Would there be any benefit for
more complex propeller arrangements?

Any thoughts?

Rich Lemert

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.

John Lowry
Flight Physics

"John T Lowry" wrote in message
k.net...

"Rich Lemert" wrote in message
link.net...
Back when I was growing up on the farm, we used several powered
implements that received their power from the tractor through a power
take-off assembly. Somewhere on the device's power train, between the
PTO take-off and the "business end" of the apparatus, there was always
either a belt-drive or a coupling fitted with a "shear" pin. Both of
these systems were intended to protect that tractor (and the
implement)
by failing if the implement bit off more than it could handle.

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.

Recognizing that this issue is driven as much by regulation as by
anything, I'm wondering if there would be any benefit to using shear
pins in these systems. Would it reduce the need for a complete (or
partial) tear-down after a prop strike? Would there be any benefit for
more complex propeller arrangements?

Any thoughts?

Rich Lemert

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.

John Lowry
Flight Physics


Now you have added two additional points of failure.

Now you have added two additional points of failure.

I'm sure Lycoming would be glad to pursue this, especially in light of their
recent failures in court.

Not.

Too bad, it's got merit.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

On 2005-04-01 04:32, Rich Lemert wrote:
Back when I was growing up on the farm, we used several powered
implements that received their power from the tractor through a power
take-off assembly. Somewhere on the device's power train, between the
PTO take-off and the "business end" of the apparatus, there was always
either a belt-drive or a coupling fitted with a "shear" pin. Both of
these systems were intended to protect that tractor (and the implement)
by failing if the implement bit off more than it could handle.

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.

Recognizing that this issue is driven as much by regulation as by
anything, I'm wondering if there would be any benefit to using shear
pins in these systems. Would it reduce the need for a complete (or
partial) tear-down after a prop strike? Would there be any benefit for
more complex propeller arrangements?

Any thoughts?

Rich Lemert


Hmm...I think this would mean a weakening of the shaft.
And how would it be inspected at preflight, as was suggested?

Maybe there could be a market for a protective skid, something like the
Avro 504K, if prop strikes are a common occurrence?

/Rolf

Rotax certified engines use a "slipper clutch" system to help protect the
crankshaft and gear box. It isn't a shear pin system, but rather a spring
loaded ramp-toothed afair that resets. Rotax has criteria for strikes that
still require teardown of the gearbox and/or the entire engine.

tom


I'm wondering if there would be any benefit to using shear
pins in these systems.
Rich Lemert