3 ms·

While weight is very important in electric aircraft, I was hoping to see an efficiency advantage as well (batteries weigh more than motors). The top advantage

While weight is very important in electric aircraft, I was hoping to see an efficiency advantage as well (batteries weigh more than motors). The top advantage of electric motors for aircraft is that they can fly at much higher altitude, therefore much lower air resistance, reducing energy requirements. Fuel-burning jet engines require a certain oxygen density to operate[1]. Electric motors don't need oxygen, and propellers/fans can operate even with very low air pressure. [1] http://en.wikipedia.org/wiki/Jet_engine http://en.wikipedia.org/wiki/Jet_engine: "The limit on maximum altitude for engines is set by flammability- at very high altitudes the air becomes too thin to burn, or after compression, too hot. For turbojet engines altitudes of about 40 km appear to be possible, whereas for ramjet engines 55 km may be achievable. Scramjets may theoretically manage 75 km."

baddox 12y ago
> and propellers can operate even with very low air pressure How does that work exactly? Of course, my intuition is that lower air pressure means less to "push off of" but also less drag. And you've got certain constant overhead, like internal friction. Is there some sweet spot of air pressure where you'll get the best efficiency?
- krschultz 12y ago
  You change the pitch on the propellor. The steeper the pitch, the more air is grabbed on each revolution.
lotsofmangos 12y ago
There is far more benefit to be had by reducing the weight of the motor than increasing the conversion efficiency, given that modern motors are already generally over 95% efficient, so there is just not that much left to gain there.
thedrbrian 12y ago
Unfortunately one of the pilots disadvantages is that they don't work at high altitudes. Turbo prop and turbo jet planes get around this with PACKs and bleed air. To make a high altitude electric small plane you're going to have to make a mini Dreamliner PACK or carry tanks of liquid/gaseous oxygen.

baddox 12y ago

> and propellers can operate even with very low air pressure How does that work exactly? Of course, my intuition is that lower air pressure means less to "push off of" but also less drag. And you've got certain constant overhead, like internal friction. Is there some sweet spot of air pressure where you'll get the best efficiency?

krschultz 12y ago
You change the pitch on the propellor. The steeper the pitch, the more air is grabbed on each revolution.

lotsofmangos 12y ago

There is far more benefit to be had by reducing the weight of the motor than increasing the conversion efficiency, given that modern motors are already generally over 95% efficient, so there is just not that much left to gain there.

thedrbrian 12y ago

Unfortunately one of the pilots disadvantages is that they don't work at high altitudes. Turbo prop and turbo jet planes get around this with PACKs and bleed air. To make a high altitude electric small plane you're going to have to make a mini Dreamliner PACK or carry tanks of liquid/gaseous oxygen.