Post by bob urzWith 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?
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
Forces 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."