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Date: Fri, 10 Jun 2011 09:01:32 -0400
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From: Ted Noel <tednoel@cfl.rr.com>
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Subject: Re: L-IV Choice of Engine
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Brent,

Let me distill a couple of your comments.

Resonant frequencies. Obviously unknown at present, but a question 
arises as to measurement. Is there an instrument that can be attached to 
the engine somewhere that will measure frequencies to assess likely 
nodes of "don't run there?"

The fatigue limit for steel vs aluminum. Given that the major aluminum 
item in my setup is the engine block, with a secondary unit (PSRU case) 
of aluminum, it would seem that the fatigue life for steel is best 
tested at 50+ hours, and that's the major concern for me.

Helical thrust loading: That's why Timken helicopter experts were 
involved in designing the gearbox. As for cooling, we haven't been able 
to get the PSRU oil temperature above 120 degrees on the ground, even 
during a 5 minute full power run. That doesn't seem to be a high 
probability failure area. Fatigue failure in that unit? That seems to be 
the most likely, if at all, aluminum failure possibility, and that would 
be case cracking. Something I'll have to keep inspecting for a while.

Ted Noel