"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