I read here and there that the C-124 was the first airplane to have an on-board APU. I assume this means a true turbine APU that could provide power for engine starts and to run lot of electrical systems, since plenty of older airplanes had small gasoline-engine "auxiliary power units."
Can anybody confirm that this is so--that the C-124 had a "true" APU and that it was the first?
Interestingly, somebody on the WIX forum, where I also asked this question, said the C-124's APU was a pair of 50-hp V-twin recips in the two outboard nacelles, and he was quoting from the three-page section on APU operation in his father's C-124A POH, which he had saved. So I guess the answer is that SOME C-124s had turbine APUs...
I was a crew chief on both C-124A and C-124C models back in the 1960s. The C-124A had the gasoline putt-putts in the #1 and #4 nacelles. These A models with the gasoline 2 cylinder power units also had over the wing fueling where you had to service each tank seperate. I think there were six tanks. The later C models had a turbine APU in P compartment which is forward of the wing below the cargo floor. This compartment also had the access doors for the wing crawlway. These C models had single point refueling I think twelve tanks. The fuel access panel was on the left side of the fuselage down low forward of the leading edge of the wing. Not all C-124s with single point refueling had the turbine APU.
To further complicate this it is possible that the later A models that were converted to C models may have been retro-fitted with the turbine APU. I was on C models but do not recall if they were true C or converted A models but they had the turbine APU. That was a long time ago and my memory is not what it was.
One further point. The WRM (war readiness material) kit was also in P compartment and carried all the spares (exhaust stacks, W clamps, generators, hydraulic pumps etc etc.)
Last edited by Patrick Dean; 25th Feb 2013 at 03:44.
First with a turbine APU maybe, but nothing says an APU has to be a turbine of course. The name "Auxiliary Power Unit" contains no implication of power source. What's a "true turbine APU"? Putt-putts (and they didn't, they made a very healthy clamour) provided power for engine starts and what's more powered all electrical systems, not just "a lot of them"(!). They were therefore "true"APUs.
Last edited by Agaricus bisporus; 30th May 2012 at 10:13.
These A models with the gasoline 2 cylinder power units also had over the wing fueling where you had to service each tank seperate.
I travelled in one from McGuire AFB, New Jersey to Europe in 1961. My log book shows McGuire to Harmon AFB, Newfoundland 4 hours 25m, Harmon to Lajes 7 hours 40m, Lajes to Wiesbaden 9 hours 10m.
Apart from size and the spaciousness of the cockpit the only thing that really impressed me was the Flight Engineer's station and the engine analyser that constantly monitored the health of the engines.
I shot some 8mm cine film of this trip and the screen-grab below gives some idea of how far it was from the top of the fuselage to the top of the wing, with a further drop to the gound below.
Could the engineer in my screen grab have been refuelling or otherwise attending to the APU?
What's a "true turbine APU"? Putt-putts (and they didn't, they made a very healthy clamour) provided power for engine starts and what's more powered all electrical systems, not just "a lot of them"(!).
That's not accurate.
What I meant by "a true turbine APU" is an engine and generator that can reliably power ALL of a relatively complex airplane's electrical systems simultaneously and start the engines. No reciprocating APU could do that, unless perhaps there was some extremely simple 1930s/'40s airplane that might have been an exception. In fact, many in the U. S. industry refer to the simple power units a GPUs and the stand-alone, powerful ones as APUs.
The Lockheed C-130 was the first airplane designed from the outset to have a "true turbine APU" rather than just a GPU.
I think it is more likely that the mechanic is checking the oil level in the # 1 engine. To refuel, the caps would normally be in the highest point of each tank in the top surface of the wing. If you were doing this in very hot weather you felt like a burger as the wings top surface would be very hot in the sun. If it was raining your biggest worry was slipping on the wet top surface of the wing as it was a long way to the ground especially on the wings outer tanks. Under wing refuelling was much more safer
Now the C-124 might have been the first to have a turbine APU butthe Super Connie also had a turbine APU whereas the ordinary  Connie had a piston engine APU, which could though supply aircraft electrics and engine start at same time, but it is true that aircraft electric demand was a lot less then, than on modern aircraft.
What is really attractive about modern APU,s is the amount of air they can produce for both engine starts [some aircraft] and airconditioning
Regarding APU, the B29 that was first recovered and then lost to fire in Greenland had an APU, pistn type fitted. I believe it was a leaky fuel line to the APU that fed the fire.
I worked a lot of Constellations at Lockheed New York. Never saw an APU on any L049 or L749 models, piston or turbine including the VC-121A (L749) of SAMFLEET. Did see a few turbine APU on some special purpose C121 Super Connies. They were all added as modifications.
Lockheed New York also installed an APU in a VC-118 in the forward baggage. Had a special shroud around it as it was not pressurized inside the shroud as there were cooling air intakes and exhausts.
I also believe most Navy flying boats had an APU as you couldn't roll up a GPU.
B727 had a turbine APU but it was for ground use only. B707 and DC-8 had no APU (unless modded as some were) but as an option for international service had provision for stored compressed air (3000 psi) which blew down into a combustor and fed the resulting hot air to the starter on No. 3 engine. Always danger of a hung start when using it.
L188 Electras had no APU. Eastern Air Lines however modded one with a turbine APU. It proved to be too noisy in the cabin and was removed.
If memory serves, I also believe the prototype DC-4 with the triple tail had an APU fitted. It certaily would have been a piston powered one.
The HARS C121C ( military eqiv of an L1049G) manual refers to a gas turbine APU. Our manual is a generic C121C and C121G manual. Our aircraft APU was removed during its storage in Pima and we have not been able to find a replacement so far. The manual says that on the C121C, the APU can be used inflight in an emergency.The rating is 500amps. The unit was fitted in the rear of the fuselage. The controll panel is at the top of the FEs panel and certainly looks like it was fitted at the time of manufacture in 1955.It would be hard to understand why a blank panel area is there if an APU was not planned during construction.
We also have a Catalina which was originally fitted witha single cylinder petrol APU. The generator is at one end of the crankshaft and a bilge pump at the other. It seems to have been fitted in the area below the flight engineer's station, lwr left hand side with both exhaust and bilge water into the L/H wheel well area ( for those that had wheels).