Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Thu, 14 Nov 2002 10:50:40 -0500
Message-ID: <redirect-1870644@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: engine overrun conditions
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<<Yes it will Bob, but my mechanic tells me that technique is not  good for
the engine. Not sure exactly why. Sez that the engine should be turning the
prop, not the prop turning the engine. Something about de-tuning?  Anybody
have a better handle on this than I do?>>

As far as I can tell, this is another of those OPT's.  I can't see anything
in the design of the engine that suggests it is less able to handle rearward
thrust than forward thrust.  The prop blades will be held in place by
centrifugal force, so I don't see how the prop itself could care.  I have
heard people say that with the torque on the prop "neutral" the torsional
absorber weights flop around, damaging themselves - that just doesn't make
sense as it takes torsional excitation to do that and there are no
high-amplitude pulses at no power.  The key here would be to stay out of any
yellow arc, which is the rpm at which that could potentially occur, but even
then only with torque pulses.  Of course, to get the prop to "drive" the
engine the engine has to be producing no power.  It would be best to shut
the fuel off (not me, thank you) so that no fuel is going through the engine
to foul the plugs as most engines will cease to fire above maybe 1500 rpm
with the throttle closed.  With the fuel off the engine is turned into a
very good air compressor and will operate like that forever without damage.
(compressing the air absorbs very little power, though, since the air is
immediately expanded back to atmospheric pressure.  The power absorbed that
makes for a brake is really just the friction horsepower of the engine and
that will be lower at coarse pitch (low rpm) than it will be at fine pitch
(high rpm).  Let's see, I could put a Jake Brake on my engine and then.....

Gary Casey
ES project