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Feathered Props

     The B-29 engines normally used a couple gallons of oil on a ten-hour flight. Sometimes a new oil leak would deplete the 70 quarts of oil from the engine oil tank before the flight was over.  When this happened, it was necessary to feather the prop while a couple gallons of oil remained so the engine could safely be restarted in case of an emergency. On three of my flights I had to shut down an engine while in flight because of oil depletion.  Two of those feathering operations worked according to the book.  On the third time I had to shut down an engine in flight, a dangerous condition surfaced.  On the B-29s with hydromatic props, there was a small tank of hydraulic fluid in the engine nacelle specifically for the purpose of feathering that engine.  Normal RPM control was done by metering engine oil pressure to the piston inside the propeller hub to set the blade angle.  A sudden loss of oil pressure in flight would make it impossible to control engine speed.  The feathering oil tank held only enough fluid to feather the prop 2 times.  The pilot had the feathering button (switch).  To feather an engine the pilot and engineer worked together.  The engineer retarded the throttle and cut off the fuel as the pilot reduced RPM and pushed the feathering button.
       We were about seven hours into our flight when engine no. 2 lost all but a required reserve of oil.  After the shutdown, power was adjusted in the other three engines and for about an hour the flight was uneventful.  Suddenly I noticed that the engine we had feathered was showing 350 RPM on the tachometer, and oil pressure had come up.  I informed the pilot, and we repeated the feathering procedure.  Realizing that the incident could repeat, I kept an eye on the engine.  It was the inboard engine on the right side of the airplane, so I could stretch my neck and see the propeller through the only small window near the engineer's seat. After about a half hour, I could see that the engine was very slowly rotating.  Initially it would rotate through a compression stroke and stop, creep through another compression stroke and stop. Fifteen minutes later the prop was turning slowly and slight oil pressure was registering on the gauge.  The engine oil pressure on the inside of the propeller hub is the mechanism that brings the propeller out of feather, so it was assumed that the engine was going to continue increasing in RPM.  The danger was that if the engine could not be held in feather it would continue to use oil. When the oil was completely depleted, the engine could overheat, catch fire, seize, and cast off the propeller.  When the RPM reached 200, we attempted to again feather the prop with the remaining feathering oil.  Again the engine stopped for a while before resuming its slow revolution. There was still an hour and a half of flight time before reaching Travis AFB. On this occasion, I had no comforting words for the pilot or crew.
     By the time we arrived back at Travis, the engine was wind milling at 350 RPM and we had no way to stop it. As it turned out, there was still enough engine oil in the tank to keep the engine lubricated, and there was no damage to the engine.