B-29 APU Pictures

Looks like some potential there for Steve's dream jet ski engine - although

3200 rpm might still be a bit too racey!

Nick H

It's interesting to note that nowadays everyone (last 25+ years at least) refers to such a device as an Auxiliary Power Unit.

Was this an airborne genny or for ground use only?

BTW I recognise the oil filler cap - it's still in use on Teleydyne Continentals today.

Julian.

At 175A it could possibly have started the engines, but I don't think it was used for that, rather it would have provided emergency power for the radio and navigation gear in the event of engine failure, and would have kept everything 'hot' while on the ground with the main engines off.

We used to have some thumping big ground-power generators at Gatwick which we had to plug into the DC-6's and other stuff to keep all their stuff working while the engines were shut down.

Modern APU's give hydraulic and compressed air services as well.

There is a Garret AIResearch APU at Pima, but I didn't see it, probably too small.... :-))

Peter Peter

-- Peter A Forbes Prepair Ltd, Rushden, UK snipped-for-privacy@easynet.co.uk

Small engines like this - there is an identical creature in the Spruce Goose Museum at McMinnville, OR

- used in aircraft were referred to as Auxiliary Power Units. Similar units used on the ground for a wider range of uses - in WW1, ABC twins were used to drive an airborne spotlight or (for instance) trench pumps: these were referred to as GPU's, variously "Ground" or "General" depending upon whom you believe!

They served various purposes, but almost every example was used to drive a generator in order to keep the on-board batteries charged. Some were very specialised and the ABC MkII APU fitted to Sunderland flying boats could be electrically started from the cockpit and then generate 300W at 24 volts. Alternatively, Bowden cable controls could engage a 2,500 gallon pump to empty both bilge and floats, a similar pump to raise petrol from a bowser to fill the fuel tanks. This done, further controls could engage air compressors that could charge air starting bottles to 400psi inside ten minutes. All this was achieved by a complicated air cooled OHV flat twin buried in the starboard wing root.

B17's had one too. A Homelite TS engine drove a generator & it swayed about noisily on four bed springs. The ground-based unit was inverted but I don't have a clue why - mine is painted white. The green Homelite flat twin is an example of a GPU, ex Canadian Army.

----------> +++

Various other examples exist & yes, they are my specialty, how did you guess???

Regards,

Kim Siddorn,

Prepair Ltd wrote:.

=== We had three Garrett AiResearch GTCP 85("Gas Turbine Compressor Power") and three 831 turbines at the Cooby Creek (Toowoomba) ATS Tracking Station in the 1960s. They were designed to deliver various combinations of shaft power and/or bleed air as required when used as APUs in BAC

1-11s and others in those days. Ours were used to drive Shrage alternators through reduction boxes for the funny American 60 Hz 120/208 electrickery where necessary.

Noisy little beggers (Hey? What did yer say? Speak up . . . that's me, ever since)

I have retained photographs and technical documentation if anyone requires info on same.

JW² ===

Julian,

Having spent a few years working on the B17 and occasionally the B29 at Duxford I can confirm as Kim has said that they would be an integral part of the aircraft and only used for running Avionics on the ground. Not enough grunt to spin a Wright Cyclone on a B17.

Not enough

No, for sure, unless they had inertial starters fitted. ( but I don't think they did) But it could probably be used to warm-up and augment the aircraft's main batteries during engine starts.

At a guess it wouldn't be used in the air because I suspect that at least two main engines (if not all 4) would have gennies fitted - you'd be unlucky if you lost the two in flight.

Julian.

Tell me about it. When I go for my annual medical the doctor always comments on my poor hearing, (just in the upper reaches) It's because I've spent too much time at the rear of 737's, and of course I was young then and knew better that the chaps who advised me to use ear defenders.

Julian.

Correct no inertial starters fitted to a Cyclone Engine

3200 rpm...now i know how they got 400 hertz.. never realised they ran them so fast. sammmm

Just in case you weren't joking Sam, they were 28V 175A DC.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

Max power of 15 bhp 2 3,200 rpm Interesting in that the APU was a Andover engine adopted by the USAF & Navy as a standard type, Fairchild in this case, just being a manufacturer. I have all the specs if anyone wants a scan

Tom

There have been a few for sale, looking at Google I found 2 or 3, but engines only.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

It will come as little surprise for anyone here to know that I'd like to add one of these to my collection. Anyone know of one for sale?

Regards,

J. Kim Siddorn,

Here's one that sold recently:

Bit of info on the APU use in a B-29 fron a website (FiFi - B-29)

"The APU on a B-29 must stay running while taxiing in order for the batteries to have enough "juice" to keep the electric/hydraulic pump pressured up for the brakes. The airplane has no direct nosewheel steering, as the nosewheel just freely casters. Steering is done solely by the brakes and alternate engine power. When the engines are at idle, their generators aren't turning fast enough for them to be "on line," so that is why the APU stays running.

As a matter of fact, the APU stays running until AFTER the gear is raised after takeoff, since it requires 460 amps to raise the gear. There are seven generators on a B-29. Two on each outboard engine and one on each inboard. Those are 300 amps each. The APU generator is 200 amps. If any of the engine driven generators aren't working properly, the APU will assist the gear and flap movements (the flaps require 270 amps to operate), along with any other electrical draw that is required of the airplane."

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

During the rebuild of Mary Alice we had her on stands and I'll tell you it took a lot of effort to hand crank the undercarriage up and down, one at a time!!!!!!!