sharktail From United States of America, joined Feb 2012, 21 posts, RR: 0 Posted (10 months 2 weeks 6 days 16 hours ago) and read 2902 times:
In the last couple years an old technology, flywheels, has been used in motor sports. In Formula 1 and 24h of Le mans. The energy density with KERS is much higher than it is with batteries, allowing it to be used. The flywheel spins in a vacuum meaning there is minimal loss of energy. http://www.bbc.com/future/story/20120629-reinventing-the-wheel
So is there an application in aviation? Airplane engines most of the time spin at a relatively constant speed. But they are designed for the much higher thrust needed during take-off and subsequent climb.
The energy used to obtain a given height and speed is then burned off without it being re-used.
I can see 3 potential uses, but not convinced they all make sense yet:
A) During take-off, add energy from KERS to the engine, so the engine does not have to work as hard, or so we may even be able to use smaller turbines.
B) Allow engines to spool up quicker when power is re-applied or needed . This could allow idling to being more fuel efficient as the engine does not have to spin as fast during idle.
C) Power other airplane systems rather than using bleed air, or electricity generators(787).
The KERS system could be powered by the equivalent of braking in aviation This is now using flaps only, but it is possible to come up with a way to reuse that energy (like a RAT turbine). Or it could take surplus rotational energy from the engine at idle.
So does this make sense? Or is there a reason why it wouldn't work?
smws From Estonia, joined Jun 2012, 66 posts, RR: 0 Reply 1, posted (10 months 2 weeks 6 days 15 hours ago) and read 2826 times:
Interesting idea, but I do have a few thoughts.
1. Weight. Would the benefit if the stored energy be sufficient to counter the weight if the device?
2. Safety. KERS systems are insanely unreliable currently. A fire at the Williams box earlier this season was linked to a KERS unit.
3. Cost efficiency. Would developing such a system for planes be worth the investment and possible gains?
B777LRF From Luxembourg, joined Nov 2008, 1010 posts, RR: 3 Reply 2, posted (10 months 2 weeks 6 days 15 hours ago) and read 2799 times:
KERS is accepted in racing because the sport is somewhat risk tolerant. But apart from any technical issues, and the question of whether it would do any good at all, there's the issue of a 100.000 volt appliance being mounted in an airliner. This industry is inherently conservative and very, very, risk averse. You'd have to present a gold-plated business case, probably yielding the same savings as e.g. fitting APB winglets to a 737, to have a chance. Even with that you'd still have to convince the FAA, EASA et. al., and that is quite a formidable obstacle.
But why would you have the spinning engine drive a KERS, when it can drive a generator just as well and thereby create all the energy you need without the added complications? KERS derives it's energy from the braking action, i.e. it's converting kinetic energy into electricity. It therefore goes, that if you attach a KERS to the shaft of a jet engine, that engine needs to work harder to produce the same amount of thrust. So, what's the point?
From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
Coupling it into the gearbox would be tricky but possible; doing it in a weight efficient way is the part that I can't see with current technology.
Another way to look at is a KERS is basically a very fast moving rotor that holds a lot of rotational kinetic energy...which is an excellent description of a jet engine spool. I think you'd be better off trying to strap a driver/generator coil to the spool than to implement a separate KERS device.
sharktail From United States of America, joined Feb 2012, 21 posts, RR: 0 Reply 4, posted (10 months 2 weeks 6 days 8 hours ago) and read 2598 times:
Quoting B777LRF (Reply 2): But why would you have the spinning engine drive a KERS, when it can drive a generator just as well and thereby create all the energy you need without the added complications? KERS derives it's energy from the braking action, i.e. it's converting kinetic energy into electricity. It therefore goes, that if you attach a KERS to the shaft of a jet engine, that engine needs to work harder to produce the same amount of thrust. So, what's the point?
It's not so much that it replaces a generator. It replaces a battery as it is a way to store kinetic energy for a significant amount of time for later use. You can have solar cells generate electricity as well. The problem is where to store it more than getting the electricity.
Quoting tdscanuck (Reply 3): Another way to look at is a KERS is basically a very fast moving rotor that holds a lot of rotational kinetic energy...which is an excellent description of a jet engine spool. I think you'd be better off trying to strap a driver/generator coil to the spool than to implement a separate KERS device.
Good point. Thought that the fact that KERS was in a vacuum would allow a KERS device to maintain the energy for a significant amount of time while the friction in the spool means that it will lose it's energy a lot faster. Unless we can find a way to have the spool turn in a vacuum. But I don't know what an engine would look like if we managed to do that. Or the size of the magnets involved to transfer the energy.
The basic premise remains though: We convert a lot of energy to get an airplane in the air at a high speed. And then we burn it all off when landing instead of capturing it and reusing it for something else.
Thanks for the link. Guess I didn't look hard enough. So according to the link, on landing (not counting the descent) an A320 generates 3MW of peak power. Using that energy rather than burning it up in the brakes seems like it would be a good idea.
flipdewaf From United Kingdom, joined Jul 2006, 1525 posts, RR: 1 Reply 5, posted (10 months 2 weeks 6 days ago) and read 2498 times:
Maybe a kers system could be helpful in rediculously highly loaded cores that mean then 5 seconds spool up time (don't know if that is correct) to be able to gain the energy required quickly.
rwessel From United States of America, joined Jan 2007, 1991 posts, RR: 2 Reply 6, posted (10 months 2 weeks 5 days 16 hours ago) and read 2398 times:
Quoting sharktail (Reply 4): The basic premise remains though: We convert a lot of energy to get an airplane in the air at a high speed. And then we burn it all off when landing instead of capturing it and reusing it for something else.
Actually we don't. Sure some of it is just discarded that way, especially near the ground, but much of the descent happens without too much input from spoilers or such, and uses the recovered energy from the descent to compensate for the engines being at a lvery low power setting. A fuel saving measure is to try to align the descent with the engines-idle glide path of the aircraft - with has the advantage of not requiring a complex and heavy mechanism to be added to the aircraft).
It's different with a car - braking just converts the kinetic energy into heat, and is purely wasted - a recovery device (such as on a hybrid car), instead uses some of that energy to charge a storage device. If instead of braking, you just coasted to the stoplight (more similar to an aircrafts descent at the end of a flight), there would be no energy to recover, and hybrids would lose their main contributor to efficiency.
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