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wild.blue(at)verizon.net
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 Posted: Tue May 06, 2008 10:17 am Post subject: Engines, props |
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Walt et al--
What unusual, if any, failure/wear modes you see in round/geared engines?
The usual valve/ring/cylinder stuff or do you see gearbox or bearing
problems?
Jim--what kind of failures in the 1830/20's etc. do you guys see on the
bombers? Or are you just being prudent? Were short engine lives in the
USAAF bearing lubrication related as described? You can imagine what combat
engines being operated off dirt, maintained in the mud, parts shortages etc
would do.
The reliability of auto racing engines is pretty amazing. I think Ferrari
F1 cars went several years between engine failures recently.
I've read some military engines had very short lives, like 4 or 5 hours,
Napier Sabre etc--way complex, lots of failure opportunities. First
airplane I owned was a '46 Bellanca with a Franklin 150. Interesting to
read factory bulletins upping the TBO every few years, beginning, I think,
with 400 hr TBO, increases usually attributed to incremental oil
improvements. We know Doug's HS6 failure was the gearbox, maybe a prop
strike lurking? Anybody had any similar problems? Been quite a few prop
strikes. I've been involved with these things for a while now myself and
with others, some with extreme abuse like you describe, Mark, and have yet
to see any reliable reports here or elsewhere about real world engine life
or weaknesses other than the usual and usually piddly stuff (that's a
scientific term sometimes used in nanobiologyurology as well as aeronautics)
and usually maintenance related, not wear or design weakness. And as for
piston speed/forces, think about all that mass flailing (another scientific
term) around in a 4360 compared to an M14, which has pistons about the same
size as in your 150's O-200, 2700 RPM redline, thank you very much. I think
4360's turn some pretty good RPM, too. Listen to them, 3350's, Merlins etc.
go by at Reno, all tightly wound, mucho boosto. Love it. Bearings, rings,
pistons sometimes fail, no surprise there.
Supercharger compression/combustion "cushion" also probably helps keep the
piston pin/rod bearing forces kinda sorta (more science) in the same
direction, too, so reverse loading could affect that, yes? I know of a few
HS6/M14 failures resulting from hydro lock damage, and have flown a few
myself with obviously bent rods and pretty severe vibration etc., but really
have never heard about any unusual problems/failures or even reliable
wear/TBO data. Most of what is described on this list is just usual
maintenance or lack thereof, not failure or even clapped out. Inquiring
people ask me about M14/HS6 real-world TBO and I have no idea.
I know guys who have run 470's etc. To more than triple TBO, got nervous so
tore them down and found everything within tolerance. I've read of a 135
freight operation, supervised carefully by the feds, going nearly 9000 hours
in tests, got nervous, tear down, all within tolerance, now run 4500 hours
or something routinely. The key to all this, of course, being continuous
use, careful monitoring, maintenance etc. Not ol' Joe who flies once in a
blue moon, 40 year TBO kinda stuff.
Doug--
Did the gearbox pack up or did the prop freewheel?
Elmar--
There are several gas and spring operated full feathering props, Hartzell
comes to mind, no accumulator required (gas/spring in the hub), don't know
if any would be suitable for M14/HS6's. Whirlwinds use a McCauley hub
designed to go to high pitch with loss of oil pressure, but not feathering,
one reason I like them, they make beautiful V530 blades, too. Don't know
about the usual others, but many/most props go flat with lost oil pressure.
Jerry Painter
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cjpilot710(at)aol.com
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| Posted: Tue May 06, 2008 12:31 pm Post subject: Engines, props |
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In a message dated 5/6/2008 2:19:11 P.M. Eastern Daylight Time, wild.blue(at)verizon.net writes:
| Quote: | Jim--what kind of failures in the 1830/20's etc. do you guys see on the
bombers? Or are you just being prudent? Were short engine lives in the
USAAF bearing lubrication related as described? You can imagine what combat
engines being operated off dirt, maintained in the mud, parts shortages etc
would do.
|
The main failures we see in the 1830/20 are thrust bearings and main bearings. Almost without fail, it usually goes "TU" soon after first power reduction. First we get a chip light, than an oil filter bypass light. Right after that we get an oil pressure drop than a oil temp rise. That is an "automatic feather" for us. Just a chip light or just a bypass light only makes us watch that engine until the flight done. We than go to the chip detector or oil filter, open them up for a look see.
"Dead cylinders" are the next most common problem. During the war, squadron level maintenance never change cylinders. They would just yank the whole engine and replace with a "QEC" which usually took just 4 hours to do. The engine was than sent back to a depot. The most they would do is change out a mag, starter, any of the pumps or generator. Many engine didn't last 100 or 200 hours. It was just the way they were operated. . Unbelievable time spent at "max continuous power" in climbs that lasted hours. Constant power changes trying to stay in formation. Plus all the imaginable climates they operated in. Starting and stopping these takes its toll. I've been told and seen written here, M14p used on ground generators and pumps will run CONTINUOUSLY for some 20,000 hours.
Jill Grenetzke has a very good article on M-14 failures in the last issue of the "Red Alert". For us pilot types it even has pictures of the different failures. BTW all RPA members automatically get the magazine which has a lot of pictures.
The picture above is of #3 piston removed my engine with 438 hours fresh purchased from Aerostar. I got a chip light and found lots of metal in the 10 micron filter. You can see that either a scraper or compression ring was put in the oil groove instead of an oil ring. The ring was broken in about 4 or 5 pieces. A compression test found the cylinder. You can see where the ends of the ring jammed over each end. Note too how the lands have broken down. This same engine now has 1300 plus hours with #3 cylinder in the mid 70's. This piston sits in a prominent spot on my hangar desk. NO I don't use as an ash tray.
Jim "Pappy" Goolsby
Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.
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