Ground Power Units

OK, ground equipment isn’t glamorous but it is part of aviation history – right?

When I was serving in the RAAF at Darwin back in the early 1960s, we looked after transit aircraft as well as our own base squadron Lincoln and Dakota. Because of the international scope of things in a transit base such as Darwin, we used three different GPUs. One Australian, one British and one American. The variety of these machines was quite marked, and may be of interest.

Our RAAF GPU was a yellow, towable, unit and had a three-cylinder Deutz diesel, which was easy to start but almost impossible to stop! Let me explain. To stop this engine one had to pull a valve lifter, which was in an awkward position inside and hard to hold open.

The diesel ran slowly and made a comfortable ‘b-dum’ noise. So you held the valve lifter to stop it until you thought you heard the last ‘b-dum’ – only for it to start up again ‘b-dum, b-dum, b-dum’! Sometimes it took two or three attempts to get it stop.

The British GPU, supplied by the RAF for use with anything from the Comet and Britannia to all three versions of V-bomber was an air force blue, towed, monster with an amazing eight-cylinder Rolls Royce B80 petrol engine. When the engine was idling, you couldn’t hear a thing – it being a Rolls Royce.

The only indication you had that it was running was that the rev counter was hovering around 500rpm. I listened to the engine once with a stethoscope, and could hear nothing but a slight murmur. Sometimes other ground crew came along and pressed the starter button – only to get a loud screech from the starter ring!

Starting Vulcan engines with this GPU was an experience. The Olympus had an electric starter which used an awful lot of current (if I remember aright more than 1000A). The Rolls would be happily whining away at top speed until the pilot pressed a starter button (can’t use the preferred term here!) when the whine from the Rolls turned to an anguished low-pitched howl as it reduced speed!

The American-made GPU was a yellow, self-propelled and fairly compact unit, with a very well silenced Continental flat six aircraft engine inside it! That was all high-tech, as you would expect from the days of the SAC. We plugged these into our RAAF Hercules which, of course, used their APUs to start the engines.

The self-propelled feature was useful but a little awkward, because you had to use the towing handle held low down near the ground and press a couple of buttons on it to move forward or back. This machine didn’t last long, and went caput maybe because it was too high-tech. Anyway, it was taken away and we never saw it again. Back to ‘b-dum, b-dum’!

bri 🙂

PS: Those Deutz engines would make good replacements for an old ‘thumper’ on a narrowboat!