b29 ENGINE FAILURES

[bob urz]

With some casual research on the B29, its seems they were plagued from
day 1 with engine issues and fires. I saw some info about you wanted to
get a 29 off the ground and fast as soon as possible to keep the engines
cool so they would not fail. It seems a fair number of 29's were
destroyed and crashed due to engine fires. I can see engine fires
causing issues, but it seems many 29's were lost because of it.
what was so special about a B29 that would cause an engine fire
to result in loss of aircraft? You see many images of shot up B17's
coming home on a couple of engines. Was it because of gas tank in wing
issues or?

bob

[Orval Fairbairn]

In article <jdij8u$mi3$1...@speranza.aioe.org>,

They used a lot of magnesium in the engine, to keep weight down. Once
magnesium catches fire, few chemicals will douse it.

[Steve Hix]

In article <orfairbairn-A3BE...@70-3-168-216.pools.spcsdns.net>,

It's even worse; try putting out a magnesium fire with water, and you just make
things worse, as the fire is hot enough to disassociate the water into hydrogen
and oxygen, which then recombines explosively.

But the lure of reduced airframe weight kept magnesium in the toolbox for other
designs, such as the B-36.

The B-29 wasn't the only heavy to have engine fire issues around that time;
Heinkel was, with somewhat less ultimate success, working similar issues with
the He-177 series of bombers.

My father spent 30+ years working for the L.A. county air pollution control
district as an industrial/refinery inspector. One day he was eating lunch in his
parked car, on the side of a four-lane road across from a manufacturing plant
that worked on magnesium products, when some lit off accidentally.

He said the initial flare up was like late summer sun through the closed window,
and fighting the fire took crews quite a while, using foam, not water.

[George]

The problem was partly the very tight cowling (poor cooling at
low airspeeds) and partly the reliability of the early model
R-3350s. As others have noted here, get a magnesium alloy hot
enough to burn, and it'll burn through damn near anything.

From http://en.wikipedia.org/wiki/Boeing_B-29_Superfortress

"The most common cause of maintenance headaches and catastrophic
failures was the engine.[17] Although the Wright R-3350 later
became a trustworthy workhorse in large piston-engined aircraft,
early models were beset with dangerous reliability problems. This
problem was not fully cured until the aircraft was fitted with
the more powerful Pratt & Whitney R-4360 "Wasp Major" in the
B-29D/B-50 program, which arrived too late for World War II.
Interim measures included cuffs placed on propeller blades to
divert a greater flow of cooling air into the intakes, which had
baffles installed to direct a stream of air onto the exhaust
valves. Oil flow to the valves was also increased, asbestos
baffles installed around rubber push rod fittings to prevent oil
loss, thorough pre-flight inspections made to detect unseated
valves, and frequent replacement of the uppermost five cylinders
(every 25 hours of engine time) and the entire engines (every 75
hours).[N 1][17]

Pilots, including the present day pilots of the Commemorative Air
Force’s Fifi, the last remaining flying B-29, describe flight
after takeoff as being an urgent struggle for airspeed
(generally, flight after takeoff should consist of striving for
altitude). Radial engines need airflow to keep them cool, and
failure to get up to speed as soon as possible could result in an
engine failure and risk of fire. One useful technique was to
check the magnetos while already rolling rather than from a
"braked" start.[19]"

From http://en.wikipedia.org/wiki/Wright_R-3350

"By 1943 the ultimate development of the new bomber program, the
B-29, was flying. However the engines remained temperamental, and
showed an alarming tendency of the rear cylinders to overheat,
partially due to minimal clearance between the cylinder baffles
and the cowl. A number of changes were introduced into the
aircraft production line in order to provide more cooling at low
speeds, with the aircraft rushed into operational use in the
Pacific in 1944. This proved unwise, as the early B-29 tactics of
maximum weights combined with high temperature airfields produced
overheating problems that were not completely solved, and the
engines had a tendency to swallow their own valves. Because of a
high magnesium content in the crankcase alloy, the resulting
engine fires were often so intense the main spar could burn
through in seconds, resulting in catastrophic wing failure.[1]

Early versions of the R-3350 were equipped with carburetors,
though the poorly designed elbow entrance to the supercharger led
to serious problems with inconsistent fuel/air distribution. Near
the end of World War II, the system was changed to use direct
injection where fuel was injected directly into the combustion
chamber. This change improved engine reliability. After the war
the engine was redesigned, and became a favorite for large
aircraft, notably the Lockheed Constellation and Douglas DC-7."

[Orval Fairbairn]

In article <kt2qf7hpl52vmki5d...@4ax.com>,

An old friend, since deceased, worked in the Curtiss factory in
Nashville. He said that, as a trick, they would drop a small block of
magnesium into a bucket of water and then pot a lighted acetylene torch
into the bucket and light the magnesium. It would leach the oxygen out
of the water and provide some fireworks!

[Eunometic]

1 the cowling was to tight and had inadquete flow; early cowlings
lacked access doors which meant the prop and the cowling had to be
removed to change spark plugs.
2 the tightness of bends around exahust manifolds caused hot spots and
pitting.
3 because the R-3350 didn't use fuel injection the fuel distribution
was uneven leading to hot spots in some parts of the engine.
4 the 5 upper cylinders of the second row needed replacement every 25
hours on early engines due to poor cooling; one effect was discharged
valves.
5 B-29's were opperated with very high fuel and bombloads which
combined with climbs to high altitudes leading to stress on the
engines
6 a counter productive and fairly pointless habbit of some crews
reving their engines while stationary to build up revs and prior to
brake release.

[Orval Fairbairn]

In article
<2c756ec6-502e-4022...@u10g2000prl.googlegroups.com>,

Some of the WW-II pictures show mountains of broken R-3350s on the
island bases.

[fgdu...@bellsouth.net]

My understanding was that the engine mounts were made of magnesium and when the exhaust collector ring got a hole burned in it, the exhaust would set the engine mount on fire. Magnesium burns very hot, but in addition, CO2 made it burn hotter so the extinguisher couldn't put out the fire! The magnesium would take the oxygen away from the CO2. The fire would then burn through the wing spar and/or set the wing tank just behind the spar on fire.
The story I was told was that the flight engineer would watch the speed of each engine, looking for a slow increase and decrease in speed. This variation was supposed to be from when the exhaust had burned through the collector ring. This variation lasted about a minute, and if the flight engineer caught it in time, and shut the engine down, then all would be well. At least as well as a '29 flew on three engines, anyway. After about 1 minute, the exhaust would set the engine mounts on fire, and you had about 1 more minute to bail out before the plane blew up.
That is the story as related to me about 40 or so years ago.

[Jim Wilkins]

<fgdu...@bellsouth.net> wrote in message
news:bb31e7fa-71f4-467f...@googlegroups.com...

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https://www.historynet.com/superbombers-achilles-heel.htm

The crew of the CAF's B-29 "Fifi" told me the engines are now very
reliable. They custom-built them as hybrids of the best
late-production parts from the various models. They treat it very
gently and don't exceed 10,000 feet.

When my father was CO of an Air Corps ordnance company on Okinawa he
took his Jeep out to pick up the crew of a B-29 that had diverted
there to land and for some reason couldn't taxi in. He said he had
never seen an uninjured aircrew so shocked and silent. I think it may
have been Bock's Car, the Nagasaki bomber.