5 ms·

Let's do a quick comparison. A candidate plane for this engine would be the Cesna Turbo Stationair. -It is a six passenger plane with a base operating weight

by beloch 12y ago

Let's do a quick comparison. A candidate plane for this engine would be the Cesna Turbo Stationair. -It is a six passenger plane with a base operating weight of about a ton. -It's engine delivers 231 kW, which is slightly less than Siemens electric engine. It's mass is approx. 200 kg, so the Siemens engine frees up 150 kg of weight. -It's fuel capacity is 237 kg of 100LL avgas. With an energy density of 44.0 MJ/kg, this gives the plane a stored energy of 10.4 GJ. The plane's max range is 1300 km. -Tesla's best battery (the Smart) has an energy density of 132 WH/kg, which is 475.2 kJ/kg. That means you'd need 21.9 thousand kilograms of battery to store the same energy that's in the Cesna's tank when full. -If we assume the plane's range is linearly related to it's stored fuel (an approximation not really accounting for take-offs), 237 kg plus the 150 kg saved in engine weight gives 0.051 GJ of stored energy, which would reduce the plane's range to 5% of normal, or about 63 km. Based on this, don't expect an EV passenger plane anytime soon. Battery technology just isn't good enough yet. A hybrid with a gas-turbine generator is much more likely in the near future. This engine may also have applications where range is not important, such as training, stunt and racing planes.

nether 12y ago
> If we assume the plane's range is linearly related to it's stored fuel it's not btw: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node98.html http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/...
- mikeash 12y ago
  Ah, but it is if you're running on batteries! Unlike fuel tanks, batteries don't get lighter (at least, not measurably; e=mc^2 tells us that there will be a little change) as you drain them.
tlb 12y ago
Piston engines are only about 30% efficient in converting gasoline to mechanical energy. While battery/electric can be around 90%. So you may be off by a factor of 3.
- beloch 12y ago
  My intention was just to get ballpark close. 15% of normal range is still not very good. Battery's may get there eventually, but not yet. As stated in the article, they're going after hybrid applications and this is probably why.
transfire 12y ago
Did you forget to take the engines efficiency into account? I think the electric engine is going to be in the 90 percentiles. The fuel engine in the 30s. You also failed to read the word "hybrid". But not to worry, battery tech will continue to improve too. Fossil fuel efficiency? Not so much.
deleted 12y ago
[deleted]
RobotCaleb 12y ago
What about all the square footage present for solar panels?
- mikeash 12y ago
  It's irrelevantly small. You can build solar-powered aircraft, but they have to be extremely light, huge, extremely slow, and carry almost no payload. Insolation is approximately 1hp per square meter. The Cessna in question has about 16m^2 of wing, so that's 16hp of incoming sunlight. Solar cells are maybe 20% efficient, so that's about 3hp of actual electricity generated. That's not even counting cosine error, which will hurt you badly any time you're not flying at high noon in the tropics.
  - RobotCaleb 12y ago
    Great answer. Thanks.
  - hyperpallium 12y ago
    converting to OP units: 1 hp is about .75 kW, so 3 hp is 2.25 kW, compared with the 231 kW used by the engine. 1/100. But apart from drones, perhaps a specifically designed aircraft to target this could help: lighter, smaller, larger surface area, slower cruising speed would reduce air-friction so increasing efficiency. Mightn't be practical to get down to self-fueling, but at least make a significant contribution to range. NB: longer flights collect more fuel. Human-powered flight is possible using only 0.35 hp (0.26 kW), though superslow at 18km/hr. See Gossamer Condor http://wikipedia.org/wiki/Human-powered_aircraft http://wikipedia.org/wiki/Human-powered_aircraft EDIT: here's the real deal: human flight, pure-solar, no batteries at all http://wikipedia.org/wiki/Solar_Challenger http://wikipedia.org/wiki/Solar_Challenger EDIT2 Solar Impulse 2 is currently on a circumnavigation of the globe (they store power to continue to fly at night) http://wikipedia.org/wiki/Solar_Impulse http://wikipedia.org/wiki/Solar_Impulse At the moment waiting for ideal weather in the China leg
    - mikeash 12y ago
      Solar aircraft can definitely be done (what with the existence proofs you provided) but they're not very practical. Power consumption is roughly proportional to the cube of speed, so to get the Solar Impulse 2's cruise speed up to, say, 150kts instead of the 49kts it actually does would require 27x more solar collection surface area. If you want to carry two people instead of one, it'll need to be about twice again as big. You'll hit annoying scaling laws since larger structures are proportionally weaker so it'll get even worse.
D_Alex 12y ago
Well, to begin with, you are off by a factor of 3 on useable energy, and perhaps by a factor of 2 on the energy density of best batteries of today (Wikipedia stated 0.95 MJ/KG for best Li batteries), so achievable range should be ~380 km to begin with. I'll also note that the fuel tank itself has weight (though I do not know how much it is). Next, the Stationair is a really old airplane, the basic design is over 50 years old. If we take the 2004-ish Cessna 400 instead, which has a 60% greater maximum range than the Stationair... perhaps we can claim that 500km+ is achievable, without calling upon radical new designs or further technology improvements. And an airplane with ~500 km range is pretty sensible. (frankly, long trips in small planes are a bit of a trial, though probably less so in a smooth and quiet electric plane). OTOH, you do need to consider reserve range, that does not work in favour of electrically powered aircraft. But the effect might be limited to having to add some battery capacity, sacrificing some performance along the way. In conclusion... It does not even matter if the first commercially available electric airplane matches the petrol airplane on range. It would be nice to have a useable range, but ~500 km is enough for many applications. The electric airplane does not need to dominate the market from the start... just enter it.
tsotha 12y ago
Seems like you'd use fuel cells instead of batteries.

by beloch 12y ago

nether 12y ago

> If we assume the plane's range is linearly related to it's stored fuel it's not btw: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node98.html http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/...

mikeash 12y ago
Ah, but it is if you're running on batteries! Unlike fuel tanks, batteries don't get lighter (at least, not measurably; e=mc^2 tells us that there will be a little change) as you drain them.

tlb 12y ago

Piston engines are only about 30% efficient in converting gasoline to mechanical energy. While battery/electric can be around 90%. So you may be off by a factor of 3.

beloch 12y ago
My intention was just to get ballpark close. 15% of normal range is still not very good. Battery's may get there eventually, but not yet. As stated in the article, they're going after hybrid applications and this is probably why.

transfire 12y ago

Did you forget to take the engines efficiency into account? I think the electric engine is going to be in the 90 percentiles. The fuel engine in the 30s. You also failed to read the word "hybrid". But not to worry, battery tech will continue to improve too. Fossil fuel efficiency? Not so much.

deleted 12y ago

[deleted]

RobotCaleb 12y ago

What about all the square footage present for solar panels?

mikeash 12y ago
It's irrelevantly small. You can build solar-powered aircraft, but they have to be extremely light, huge, extremely slow, and carry almost no payload. Insolation is approximately 1hp per square meter. The Cessna in question has about 16m^2 of wing, so that's 16hp of incoming sunlight. Solar cells are maybe 20% efficient, so that's about 3hp of actual electricity generated. That's not even counting cosine error, which will hurt you badly any time you're not flying at high noon in the tropics.
- RobotCaleb 12y ago
  Great answer. Thanks.
- hyperpallium 12y ago
  converting to OP units: 1 hp is about .75 kW, so 3 hp is 2.25 kW, compared with the 231 kW used by the engine. 1/100. But apart from drones, perhaps a specifically designed aircraft to target this could help: lighter, smaller, larger surface area, slower cruising speed would reduce air-friction so increasing efficiency. Mightn't be practical to get down to self-fueling, but at least make a significant contribution to range. NB: longer flights collect more fuel. Human-powered flight is possible using only 0.35 hp (0.26 kW), though superslow at 18km/hr. See Gossamer Condor http://wikipedia.org/wiki/Human-powered_aircraft http://wikipedia.org/wiki/Human-powered_aircraft EDIT: here's the real deal: human flight, pure-solar, no batteries at all http://wikipedia.org/wiki/Solar_Challenger http://wikipedia.org/wiki/Solar_Challenger EDIT2 Solar Impulse 2 is currently on a circumnavigation of the globe (they store power to continue to fly at night) http://wikipedia.org/wiki/Solar_Impulse http://wikipedia.org/wiki/Solar_Impulse At the moment waiting for ideal weather in the China leg
  - mikeash 12y ago
    Solar aircraft can definitely be done (what with the existence proofs you provided) but they're not very practical. Power consumption is roughly proportional to the cube of speed, so to get the Solar Impulse 2's cruise speed up to, say, 150kts instead of the 49kts it actually does would require 27x more solar collection surface area. If you want to carry two people instead of one, it'll need to be about twice again as big. You'll hit annoying scaling laws since larger structures are proportionally weaker so it'll get even worse.

D_Alex 12y ago

Well, to begin with, you are off by a factor of 3 on useable energy, and perhaps by a factor of 2 on the energy density of best batteries of today (Wikipedia stated 0.95 MJ/KG for best Li batteries), so achievable range should be ~380 km to begin with. I'll also note that the fuel tank itself has weight (though I do not know how much it is). Next, the Stationair is a really old airplane, the basic design is over 50 years old. If we take the 2004-ish Cessna 400 instead, which has a 60% greater maximum range than the Stationair... perhaps we can claim that 500km+ is achievable, without calling upon radical new designs or further technology improvements. And an airplane with ~500 km range is pretty sensible. (frankly, long trips in small planes are a bit of a trial, though probably less so in a smooth and quiet electric plane). OTOH, you do need to consider reserve range, that does not work in favour of electrically powered aircraft. But the effect might be limited to having to add some battery capacity, sacrificing some performance along the way. In conclusion... It does not even matter if the first commercially available electric airplane matches the petrol airplane on range. It would be nice to have a useable range, but ~500 km is enough for many applications. The electric airplane does not need to dominate the market from the start... just enter it.

tsotha 12y ago

Seems like you'd use fuel cells instead of batteries.