Aircraft Auxiliary Power Unit  


I found this engine on Ebay, and purchased it. It is an auxiliary power unit from a Boeing KC-135 StratoTanker. The KC-135 is the military version of the Boeing 707, a large commercial jet liner powered by four turbofan engines. The StratoTanker, as its name implies, is a flying tanker, used for aerial refueling of other military aircraft.


The APU sits in the tail of the aircraft and is used to provide auxiliary power in the form of electricity, pressurized air, and hot air. The APU is usually activated when the aircraft is on the ground and the main engines are shut off. The APU consists of a gas turbine engine, an electric generator, a heat exchanger to provide hot service air for the cabin air conditioning system, a control panel, a fuel tank, and a frame with rolling casters to make the unit easier to move around.

Here is what the APU looked like right after we unloaded it from the trailer. A big plus is that the unit is in completely running condition. I have already spooled up the starter a couple of times. As soon as we get an opportunity, we will do a test firing of the engine and post a video clip.

Once we have run the APU a few times, we will probably remove the unnecessary items such as the heat exchanger and the generator, and see what we can do with the engine. It may be a little more difficult to use it in a project because of the fixed shaft arrangement.

The gas turbine engine that powers this APU is a Solar T41-M9A. It is a 50 shaft horsepower, single spool, simple cycle engine. To learn more about the Solar T41, click here.

As we continue to explore this APU, we will add more photos and information. We will also add a video clip, so be sure to keep checking back.

Be sure to check out the engine running video clip HERE

UPDATE 3/08/04-

Tired of staring at the monstrous APU sitting dormant in the corner while taking up significant amounts of precious real estate, we decided to tear down the unit to its bare essentials. We figured that, if we're lucky, we may even find a gas turbine engine in there somewhere...

Before and After

So, after cracking open a couple of cold Heinekens, the wrecking crew went to work...

Before we knew it, we found the engine in there. We pulled off the control panel box, which I will probably save for the gauges and switches and stuff for when we make our own instrument panel. The heat exchanger came off, which I really have no use for, so I'll probably scrap it, unless someone is interested in buying it from me; All of the steel cabinets, the insulation, and all the other junk came off to reveal a neat little engine which doesn't look much different than some of the turbocharger based DIY engines that my friends Chris Krug and Mark Nye, among others, are known for building.

The next step will be to clean up the grease and grime from the engine, clean up the wiring, and then wire up a new control panel. We are also going to need to rework the engine's rolling base, now that it is carrying less stuff. Once that is complete we hope to do a test fire of the newly liberated engine. Stay tuned for more updates...


Please drink responsibly; especially when playing with large quantities of flammable liquids. Thank you.


UPDATE 3/30/04-

After we finished cutting apart the base frame, and relocating one of the casters, we now have a smaller, more manageable package. Then, I stripped off all of the wiring so I could start my new instrument panel. We are currently in the process of wiring the panel and should have it completed by the end of the week. After that we will do another test firing of the engine and get a video clip of it. We hope to be able to connect something up to the generator to see if the generator works properly.

The engine and uncompleted control panel


UPDATE 4/15/04-

With our T41 control panel and wiring completed, we are now ready to test fire the engine. This will be first time that the engine will be run outside of its cabinet. We will run up the engine this weekend and shoot a video clip of it. We will also try to connect a lightbulb to the generator to see if produces current. Once it is complete, we may think of using it in a project, or we may just sell it. If anyone is interested, please email me.

The completed panel


Update 4/19/04-

This past weekend the Solar T41 lives again, this time in a new, sleek form (sort of). After ripping all the wiring off and making a new control panel with a more entertaining manual start, we wheeled it out to the same familiar deserted road to some old military fort, and we spooled it up. Once again the wonderfully deafening roar of a 1950's era gas turbine filled the air. Check the videos section to see a video clip of it in action.

We don't know what the future holds for this little machine, but we sure think it's pretty cool...


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