Subject: Re: Hydraulic Lock
Author: GaryS
Date: May 6, 2005, 9:12 AM
Post ID: 1718822917
Joe, that was damn interesting!! I always wondered why they were turning the props, I thought they were maybe priming the cylinders
with fuel or something?
I am now educated and have one less mystery in my life. :)
GaryS
----- Original Message -----
From: "joe jump" <jum-@hotmail.com>
To: <Loopfram-@topica.com>
Sent: Friday, May 06, 2005 7:56 AM
Subject: Hydraulic Lock
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Hydraulic lock got its reputation for engine damage from the huge task
of starting aircraft radial engines. They were "dry sump" like a British
twin, but residual oil could run down into the lowest cylinders & leak
past the rings into the combustion chamber. When starting, if one of the
other (6,8,13,17, or 27) cylinders would happen to light off while the
oil filled cylinder was beginning its compression stroke, the
rod/piston/cylinder could loose the battle against all the inertia
carried by the mass of the machinery. Also a number of those engines
used what was known as an inertia starter, where a relatively small
electric starter motor would spin up a massive starter flywheel to a
high rpm. Once up to speed the flywheel would be engaged to the
crankshaft through a planetary gear set to set the engine into motion -
I'm sure you can imagine the damage that could be done to this starter
system with a hydraulic lock. Ever wonder why, when watching the History
Channel, you see the whole aircrew lined up taking turns pushing the
prop through on a B-29? Now you know the rest of the story.
Another problem encountered with starting these behemoths was
the friction encountered with cold 50 wt oil. One method used to help
out was thinning of the oil with gasoline. The gas was actually pumped
into the oil tank to thin out the viscocity. Once started the gas would
evaporate from the heat of the engine & oil. As others have suggested, I
don't think this would be a good thing on our Loop engines because they
use plain bearings throuought whereas the raidials were all roller
bearings.
Just some useless trivia I had to learn for my A&P certificate back in
the '70s.
Joe in St Louis
850T-Powered Ambo
"Junkyard"
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