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Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft.

What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money?

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    $\begingroup$ Too heavy too produce meaningful amount of power. $\endgroup$ – user3528438 May 25 '18 at 5:47
  • $\begingroup$ What is too heavy? If you mean the airframe, then what about using them as an auxiliary source to drive smaller electronic components like servos maybe? $\endgroup$ – user31222 May 25 '18 at 5:54
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    $\begingroup$ Any form of energy harvester in general. You can recover heat from engine exhaust, or you can cover the wings with solar panels. The energy harvested in a few hours simply doesn't worth carrying the harvester around. $\endgroup$ – user3528438 May 25 '18 at 6:10
  • $\begingroup$ Seems like this would conflict with another goal: Minimizing vibration. $\endgroup$ – Steve May 25 '18 at 17:51
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Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft.

Ok, think about this: in a perfect airplane, there would be no vibration. Every erg of energy being used would go into the propulsion. Any vibrations are, by definition, wasted energy.

Think about a specific example. You know the vibrations in a turboprop plane that make it sort of "buzz" inside the fuselage? That's caused by air off the props that hits the fuselage. That air is being pushed by the engine, yet it's not pushing the aircraft forward. That is the definition of wasted energy.

Ok, so real aircraft waste some energy, big deal. But how much? Obviously, the thing is flying, right? So it can't be that much. I mean, if it was 50%, that would be 2000 hp of wind smacking into the fuse - you'd need a parachute, not ear protection! So we're talking about what, 1%? 3%

So that's why we don't use piezos to recuperate. You're trying to collect this tiny bit of power. Even at 100% efficiency, and I'd say 10% is more likely, we're still talking about a tiny fraction of the power you need to do anything.

In fact, the only use of piezos in this role is the exact opposite. The Q400 (and others I assume) power a set of piezos on the fuselage that provide the opposite vibration to the air off the props, and thereby lower cabin noise.

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What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money?

It's not worth the weight.

The power that can be extracted from piezoelectronics is on the order of microwatts (100 uW in the above article). In contrast, light aircraft have their power measured in kilowatts and commercial aircraft reach a megawatt of electrical power.

In other words, it would take 8-16 million of piezoelectronic harvesters to replace the alternator on a small aircraft, and 3-10 billion on a modern airliner. Drones use more power than small aircraft as they've got a lot of electronics.

Piezo harvesting is being developed to power completely unattended tiny sensors that won't have access to any other power source for years. All aircraft, including drones, already have their own power source - the engine - with fuel tanks that get refilled each flight. So power's cheap and available.

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the quantity of power (volts times current) produced by flexure of piezoelectrics is very small. You would need a very large number of them to produce useful amounts of power from airframe vibrations.

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