2

Why can’t electric motors be used in aviation? Is it a problem with batteries, torque, or what? From what I’m aware motors at high torque are expensive and need a massive footprint, than a high rpm low torque motor. Is the issue the weight and size of a motor to lift 500,000 pounds off the ground? We have motors right now that can spin a turbo fan at a high speed and compute a comparable thrust, but is that thrust under load a different story? Is the energy required way too much for a realistic battery size?

AndroidSmoker74
  • 287
  • 3
  • 12
Useruuu
  • 341
  • 1
  • 2
  • 4
  • 3
    It's not the motor, it's the weight of the batteries. There are some electric aircraft, but their endurance is quite limited, or they have impractical for general use wingspans &c: https://en.wikipedia.org/wiki/Electric_aircraft – jamesqf May 25 '19 at 03:22
  • @jamesqf that's good enough to be an answer. You should maybe expand it a bit and post it. – John K May 25 '19 at 04:02
  • Electric power does not need to be delivered by batteries, fuel cells or a generator work as well. – Koyovis May 25 '19 at 05:49
  • @John K: There are already several questions with answers saying essentially the same thing. – jamesqf May 25 '19 at 18:03
  • @Koyovis: Fuel cells need to carry fuel, and AFAIK are fairly rate-limited. Using a generator to produce electricity to run an electric motor that drives your propellor would be stupidly inefficient. Though one might consider solar power, as with the Solar Impulse https://en.wikipedia.org/wiki/Solar_Impulse to be a sort of generator. But again, it's hardly suited to practical uses. – jamesqf May 25 '19 at 18:08
  • @jamesqf Hydrogen in fuel cells does not weigh very much. Hybrid cars are stupidly inefficient? – Koyovis May 26 '19 at 01:05
  • Electric motors most certainly are used for propulsion in aviation in the present day. An ideal application is a self-launching sailplane with some amount of long-duration sustainer/ cruise capability. Examples-- https://www.icaro2000.com/Products/Swift/Swift.htm and http://www.alisport.com/?product=silent-2-electro-2 . I would like to be able to add this comment as an actual answer but apparently I cannot since the question has been ruled to be a duplicate that has already been answered. – quiet flyer May 26 '19 at 13:43
  • Moderators, the question is not a duplicate, see my comment/ answer above, it does not appear to be an applicable answer to the other questions to which this question is supposedly a duplicate of. – quiet flyer May 26 '19 at 13:46
  • Added to second comment above this one-- obviously, the reliability of starting/ ease of starting an electric motor is a huge asset in this application as it is expected to be started in flight if soaring conditions deteriorate. – quiet flyer May 26 '19 at 14:09
  • @Koyovis: 1) Enough hydrogen to propel a plane does weigh quite a bit, but the real problem is the containers. You either need high-strength tanks for gas (ever hauled around scuba tanks?), or you need insulation and/or refrigeration equipment to keep it liquid. 2) Hybrid cars do not use generators, they use regenerative braking. Their efficiency is principally a reflection that it takes a lot more power to accelerate than to maintain steady speed, so the electric assist allows a smaller, more efficient engine. Airplanes fly at close to full power, and seldom brake :-) – jamesqf May 26 '19 at 19:02
  • They can, but it's a nascent field. Harbour Air and magniX Announce Successful Flight of World’s First Commercial Electric Airplane – Ian W Dec 21 '19 at 11:03

1 Answers1

2

Electric motors can be and are used in aviation - there's hundreds of them on any airliner you fly on.

As for using them for main propulsion, let's first look at the power/weight ratios. The highest number for Tesla's car motors is 8.5 kW/kg. The electric-aircraft-specific Emrax 268 delivers about 12 kW/kg.

In comparison, the Trent XWB delivers 430 kN of thrust at 300m/s flow rate, which equates to 64.5 MW of power, in a 7,550 kg package - a power/weight ratio of 8.5 kW/kg. However this isn't apples to oranges: this ratio is for the whole package, engine and fan, and measures useful output, like wheel power for a car.

In short, turbine engines are still lighter than electric motors, but the difference is not dramatic. Where all-electric powerplants fail to stack up is range. I've elaborated on it in response to another question - Are there any hybrid electric planes?. The short version is that the maximum possible range of an electric aircraft is 10 nmi for every % of its weight dedicated to the battery. This limits the range of electric aircraft to 300-450 nmi, if sticking with the fuel fractions of known airliners.

But there are aviation applications where this is enough. The most important non-renewable resource consumed by modern aviation - the supply of 1960s Cessnas and Pipers, without which no one could afford to become a pilot - will not last forever. Should authorities permit it, mass-produced Tesla powerplants could power trainers and GA planes at a fraction of the ownership cost of a certified avgas engine.

Therac
  • 26,835
  • 2
  • 73
  • 110