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From: George Braly <gwbraly@gami.com>
To: "'glcasey@gte.net'" <glcasey@gte.net>, lancair.list@olsusa.com
Subject: RE: Crankshaft certification
Date: Fri, 25 Jan 2002 18:56:46 -0600
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Reply-To: lancair.list@olsusa.com

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>

>>I am curious - what is the FAA requirement for crankshaft certification?
I
didn't know there was any as I thought the engine got certified as a unit
and folklore says that a run of 200 hours at full power is about all that is
required - and the TBO is whatever the manufacturer says it is.<<



Gary,

Good questions and thoughts about waiting on Charlie's engine tear down.
Looks like the crank is not an issue.

Re: How do you certify a crank?   

With great difficulty... and large sums of money! <ng>

You have to do a rather exhaustive survey
sweeping RPM, MP at almost every possible combination while the crank shaft
is
instrumented up with strain gages to determine at which RPM, MP combination,
the crank experiences the maximum strain reversals.   You have to do this
RPM sweep up through a 10% over speed condition.

One then has to operate the crank through 10^7 of those maximum strain
reversals.   If the max strain reversals happen only once every 720degrees,
it typically takes around 120 to 140 hours of operation at the specific
adverse RPM & MP combination to meet this requirement (depending upon the
exact RPM at which the peak strain reversals are happening.)

This is all outside the course of the rest of the engine certification...
although parts of the run times may overlap so that you can get credit for
some engine run time towards the crank certification... but don't hold your
breath.

If the crank doesn't break by 10^7 strain reversals, then, absent physical
damage to the crank, it will never break at that or any lower strain.

However,  I will mention, there are some serious issues, here, that are not
well explored in the current knowledgebase at the FAA.  

Have you noticed that TCM/FADEC ran into a serious torsional vibration
problem when they tried to run an IO-360 Lycoming on FADEC?   Totally
unanticipated, apparently.

Regards,  George


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