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I am working on a school project of mine which involved testing the viability of a magnetically started jet engine. By magnetically started, I mean that there are magnets which accelerate the main shaft to speed to start the engine. The point of this is to remove the need for an APU, saving space and cost on airliners and military jets.

To provide intake air to the engine to allow it to start up without an APU, there would be a system on the bottom of the engine with small electric fans to push air to the wet section of the engine to start combustion. During the flight the electric fans would be turned off and the intake section would be used like a RAM air intake for the wet section of the engine. The magnets would be powered by the battery in the aircraft, and the small electric fans would be powered by a separate battery in the engine itself.

With all that in mind, would this be viable in a commercial or private environment? Or does the APU do its job too well to replace it?

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  • $\begingroup$ Even an electrical start system will take a lot of power, probably more suited to an APU than onboard batteries. And I'm having a hard time understanding how these electric fans and ram air intake work with a turbofan engine. $\endgroup$
    – fooot
    Aug 6, 2017 at 0:04
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    $\begingroup$ The APU does more than just start the engines... $\endgroup$
    – Ron Beyer
    Aug 6, 2017 at 0:09
  • $\begingroup$ Magnets start pushing the blades around, while fans in another section of the engine push air via a pipe to the compressor section. When I said RAM air intake, I mean that when inflight, the electric fans would be turned off, and the air flowing through that section would go into the compressor section. The design (so far) has it so that there is a soft 90 degree angle where the air comes in and is angled into the wet section of the engine. I probably misused the term RAM air intake, but that is the general idea. $\endgroup$
    – Aethoriago
    Aug 6, 2017 at 0:28
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    $\begingroup$ Would these "starting magnets" just be an electric motor? If not, what makes them different from an electric motor? $\endgroup$
    – Tanner Swett
    Aug 6, 2017 at 9:06
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    $\begingroup$ I thought I understood what you were asking when you were talking about the magnetics, but the "system on the bottom of the engine with small electric fans to push air to the wet section of the engine to start combustion" is not clear. I wonder if perhaps you have some misconception about how the APU starts an engine in current designs. Suggest to read this answer: aviation.stackexchange.com/questions/33597/… and then edit your question to clarify that section. Also I agree with all of points made by @Koyovis $\endgroup$
    – Daniel K
    Aug 6, 2017 at 12:21

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Three things come to mind:

Usually, new designs are implemented when they have clear advantages over previous solutions, but I cannot see what problem this would solve. The APU is a very versatile and lightweight piece of equipment that can power up all of the systems of an airplane. Not really anyone's prime target for replacement, I reckon that captain Sully would agree.

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