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If the front fan on a gas turbine had a blade, or some of its blades extending into the surrounding housing, where there was a maglev ring of electromagnets, could fuel use be reduced by the engine? While still providing similar levels of thrust? Perhaps at the expense of electricity in the cabin.

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    $\begingroup$ What makes you think this would work? What principles are you looking to use to improve efficiency? There's plenty of ways to put together technologies, but the thing which distinguishes the snake oil perpetual motion machines from the elegant solutions to improve fuel efficiency is that the latter is assembled using tried and true principles. $\endgroup$ – Cort Ammon - Reinstate Monica Dec 12 '16 at 18:50
  • $\begingroup$ I don't know if it would work that's why I asked the question, there are many variables on aircraft, this is not perpetual motion, and neither is the Maglev train. This is about whether electromagnets could making a jet engine spin, using power from the axillary power unit on-board an aircraft. Also whether the results would be anywhere near as good as a conventional gas turbine engine. $\endgroup$ – Jameson Dennelly Dec 12 '16 at 20:24
  • $\begingroup$ Ahh, those details help. So you are looking at using energy from another engine (i.e. the APU) to spin the compressor blades, so that the jet can use more of its output for useful thrust rather than spinning the compressor? $\endgroup$ – Cort Ammon - Reinstate Monica Dec 12 '16 at 21:16
  • $\begingroup$ @CortAmmon the APU will overheat if it is run too long, as it is buried way in the back. It starts the engines, then they turn it off. $\endgroup$ – user108787 Dec 12 '16 at 23:20
  • $\begingroup$ Hi Jameson, your post needs to explain how a magnetic system would actually push air backwards, to duplicate what modern engines already ready do with pretty good efficiency. I an 99% sure you will never see commercial aircraft power by electromagnets, possibly it will work with smaller glider sized aircraft, variations of the [Solar Impulse]( solarimpulse.com). Diesel trains do run the system like you describe though, using a diesel engine that than runs a generator with electric motors on the wheels, to provide better performance and braking, but it would not work on planes $\endgroup$ – user108787 Dec 12 '16 at 23:36
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There's a few layers to this question, each with its own answer. However, fortunately, the answers for each layer are the same: no. You cannot improve your fuel economy by adding a maglev system to an engine.

The first layer is easy -- conservation of energy. Any energy that you put into the compressor blades from the maglev system must come from somewhere. That "somewhere" is another engine, such as the APU. All you do in this case is rob Peter to pay Paul. However, it's even worse in this case. Jet engines are tremendously optimized beasts. A 1/10th of a percent improvement in fuel economy translates to somewhere around $500 in savings per plane, per flight! I hand waved the distances there... math is based on a 10 hour flight and 36,000 gallons of gas consumed. You should get the idea for just how much money there is in this business.

What does this mean? Well, it means that the engines are already optimized to do exactly what they need to do. Using an APU and bulky maglev system would consume far more energy than it cost to keep the compressors spinning the normal way. Yes, your main engine may be slightly more efficient, but you more than pay for those enhancements by running a less efficient engine.

Worse, you might not get any benefit at all! Maglev equipment doesn't exactly come without costs. It takes space to put that equipment into the engine space, and it brings mass. You may not be able to use the most ideal materials for compressor blades because they need to have good magnetic properties now... that can decrease efficiency. You may find that not only does the maglev equipment require a separate power source, but that it actually decreases the efficiency of the engine by applying new requirements to the design!

I hate to use an appeal to authority on Physics.SE, but truthfully, if there was a solution like this, the engineers who pour hundreds of thousands of hours into these devices would probably have found it. Airplane manufacturing is a multi-billion dollar industry feeding an even more massive air travel industry. There's a lot of eyes on efficiency of planes. Lots of sharp eyes.

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  • $\begingroup$ Yes that makes sense, which is why I'm here. Common sense shows that this would already have been done, but I couldn't help but check just in case, as I wanted to know the reason. It stands that this is nothing more than using the same amount of energy, to do the same thing, even with a loss of energy in the process of doing that. Thanks for your answer, I wanted this debunked, because it has been annoying me for weeks! $\endgroup$ – Jameson Dennelly Dec 13 '16 at 0:19
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No is the quick answer

If the front fan on a gas turbine had a blade, or some of its blades extending into the surrounding housing, where there was a maglev ring of electromagnets,

This is an engineering question. The thrust from a Rolls-Royce_Trent, for example, is 420 kN and a lot of that comes from the high by pass ratio. We know exactly how fan blades thrust air backwards and that fan housing is vital to performance.

It's a double whammy, you take power from the engine core to power the maglev, (if they can provide it), then you block off the very point of the high pass systems but without giving an explanation for how magnets would have sufficient power to drive enough air to rip off the top layer of a badly maintained runway, which a modern turbine engine is perfectly capable of doing, if the aircraft rotates too quickly on takeoff.

From Power of High Bypass Engines

The airplane was positioned for the run with asphalt extending from close to the wing trailing edges to beyond the empennage. During the high-power part of the run, asphalt lifted from behind the left engine and broke into pieces, sending large fragments into the aft fuselage and outboard horizontal stabilizer.

Or am I misunderstanding you, if I am, my sincere apologies.

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  • $\begingroup$ Yes you have understood correctly. I was concerned about the level of torque such a system would produce, and I honestly did have thoughts of it paling in comparison to combusting fuel. However, when there are magnets that can lift up cars, I began to get confused. Thanks for your answer! $\endgroup$ – Jameson Dennelly Dec 13 '16 at 0:21

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