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1. 08:24 AM - Re: Re: Re: Hydraulic Lock (Bitterlich, Mark G CIV NAVAIR, WD)
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| Subject: | Re: Re: Hydraulic Lock |
Actually this is very good information to keep in mind, and I am going
to chew on the physics of that answer for a day or two. It poses a very
interesting study in the stresses involved and should make for a rather
intense dinner table debate! :-) (Not you, my engineering friends!)
Thanks for writing back Jill.
So given this information, what is the advice of M14P.com regarding prop
strikes and what should be done to the engine afterwards?
Mark
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Jill Gernetzke
Sent: Tuesday, April 23, 2013 16:56
Subject: Yak-List: Re: Re: Hydraulic Lock
Good feedback, Mark.
Most prop strikes occur with wood composite or carbon fiber blades. (We
haven't had a prop strike teardown with a metal prop, yet.) The inertia
of
energy is absorbed by the blades disintegrating or being shaved off.
I agree with your assessment of a hydraulic lock on startup, but not
when
the engine fires and it pulls fuel or oil in from the intake tubes. If
it
fires, there is a good likelihood that the accessory shaft will twist.
At landing speed, the aircraft travels 3.5 feet for each blade in
contact
with the ground at initial point of contact. As the engine slows, this
increases. Consequently, the rearward deflection of a very thin blade
exceeds the rotational shearing. Additionally, the reduction of blade
length per rotation with a normal flare landing is less than a tenth of
an
inch. In other words, the wood fails well before any engine parts are
stressed to the +400 foot/lbs of torque design load.
Jill
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