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Auxilliary Power Unit (A.P.U.) aka 'Putt-Putt' The Auxiliary Power Unit (A.P.U.) was fondly referred to as the "Putt-Putt". These were small gasoline engines that were aboard every B-29 aircraft. The "Putt-Putt" provided electrical power to run electronics before the No. 3 engine was started. Once No. 3 was started that would provide sufficient power to start up the other three engines, also the alternator on No. 3 would provide power to the instruments needed to check the reading on all the various controls.
Prior to take-off one of the gunners would pull the crank and fire this up just like you would an old lawn mower. (She apparently sounded just like a lawn mower engine). The APU would continue to run during taxi and takeoffs as well as landings in the event of an engine/generator failure. Once safely in the air, it would be shut down. 
In these two photos you can clearly
see the fuel tank on the left hand side of the photo with the vent leading
out, and the exhaust for the APU on the right-hand side leading to the
exterior of the aircraft. (as seen below) 
Here are the controls showing amperage, fuel level and RPM's. |
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This site was last updated 06/282004
