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The age of electric flight is finally upon us

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Re: The age of electric flight is finally upon us

#191

Post by inflatableDodo »

tristanb wrote: post #183
Robotbeat wrote: post #149

Earlier quoted context omitted.

Yeah, I see this kind of thing repeated any time Eviation comes up. I don't believe them. The design is sound, if radical in the decision to be mostly-battery. And I think that's partly why people are so skeptical: it definitely goes counter to the industry grain. But it IS the right way to build a serious electric aircraft for regional/commuter passenger travel. Pressurized, extremely high lift-to-drag ratio, very h…

The design is "sound" ? It is ridiculous! Those engines are at each end of a wing. That is a 100% no no. They are feet from the ground, and would make one engine out operation impossible. Even someone with a cursory understanding of aerodynamic could see this is a ridiculous design.

>Those engines are at each end of a wing. That is a 100% no no.

I assume they are at the end of the wings on purpose to deliberately interact with the wingtip vortices. The back prop is power, those wingtips are for drag reduction.

Re: The age of electric flight is finally upon us

#192

Post by namirez »

Robotbeat wrote: post #160
namirez wrote: post #106

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries: Gas and jet fuel specific energy density ~= 45 MJ/kg; Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is aro…

This is constantly repeated, but it's not true. I work in the field of electric motors for electric aircraft, and the amount of nonsense constantly repeated on the Internet about how electric flight cannot be done without a breakthrough is breathtaking. Electric motors can achieve FAR greater than 1kW/kg. Here's one used sometimes on electric aircraft capable of 10kW/kg, same as a jet engine: https://emrax.com/produc…

Your numbers are not quite right.

> jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned.

New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine.

> more glider-like L/D of 25-35 (the best gliders can do 70).

This is not limited to electric planes. The reason no one has done it so far is the aeroelastic divergence.

> improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy

Again, this can be done for any aircraft, not just the electric ones.

> as low as 1200km is the minimum range needed for transatlantic flights

Do you really believe there is a market for 1200km hops at Mach 0.5. We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?

Re: The age of electric flight is finally upon us

#193

Post by _ph_ »

frenchyatwork wrote: post #161
zdragnar wrote: post #133

Earlier quoted context omitted.

Or a dry forest, or grassland. Burning lithium probably can't be all that good for ponds, rivers or lakes either.

Burning lithium in a pond sounds awfully spectacular, with an emphasis on the awful.

One is actually supposed to use water for large lithium battery fires, Tesla recommends this. The lithium in batteries isn't elemental and thus does not react strongly with the water.

Re: The age of electric flight is finally upon us

#194

Post by stcredzero »

0xffff2 wrote: post #118
stcredzero wrote: post #109

Earlier quoted context omitted.

Electric motors can enable something which jet fuel and gasoline cannot: beamed power. There could be a new class of vehicles which only have a small onboard power store for emergency purposes. The weight savings would be about 20%.

Is this something that someone has actually fleshed out with real numbers? The infrastructure and efficiency problems involved seem at first glance to be extremely challenging.

I've seen numbers for microwave power transmission efficiency ranging from 75% to 84%.

http://large.stanford.edu/courses/2011/ph240/shu2/

Re: The age of electric flight is finally upon us

#195

Post by dredmorbius »

emanuensis wrote: post #162
ginko wrote: post #2

I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene. The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.

How 'bout Ammonia fuel cells?

Very bad news in event of loss of fuel containment.

Re: The age of electric flight is finally upon us

#196

Post by darkpuma »

base698 wrote: post #40
taf2 wrote: post #22

I wonder if with electric we can fly higher like much higher maybe 80k to 90k since we don’t have to worry about the engine stalling. Could this also make the flight times comparable or faster? For sure less turbulence. As someone who lives on a flight path I’m eager for the change in noise pollution too- though I’m worried the transition will take decades...

Engines don't stall, planes do. Plane stalls are about aerodynamics, and nothing to do with the engine. Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout

Turbine compressors can also 'stall': https://en.wikipedia.org/wiki/Compressor_stall

Re: The age of electric flight is finally upon us

#197

Post by FabHK »

namirez wrote: post #192
Robotbeat wrote: post #160

Earlier quoted context omitted.

This is constantly repeated, but it's not true. I work in the field of electric motors for electric aircraft, and the amount of nonsense constantly repeated on the Internet about how electric flight cannot be done without a breakthrough is breathtaking. Electric motors can achieve FAR greater than 1kW/kg. Here's one used sometimes on electric aircraft capable of 10kW/kg, same as a jet engine: https://emrax.com/produc…

Your numbers are not quite right. > jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine. > more glider-like L/D of 25-35 (the best gl…

> > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy

> Again, this can be done for any aircraft, not just the electric ones.

Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.

Re: The age of electric flight is finally upon us

#198

Post by newnewpdro »

Johnny555 wrote: post #169

Would it make sense to jettison the discharged batteries shortly after takeoff to reduce cruising weight? The "takeoff battery pack" could be in some sort of autonomous drone that pilots itself back to the airport so it could be jettisoned after reaching cruising altitude. Does weight make a significant difference once the aircraft is at cruising altitude?

Yes, planes for ages jettisoned any fuel before landing because of the weight. Keeping the landing weight down to a minimum does wonders for the airframe design.

Nowadays they just do a better job of loading only the fuel necessary, and circle pointlessly to burn excess fuel before landing. It's still an issue, they just don't dump the fuel on the neighborhood below like they used to.

Re: The age of electric flight is finally upon us

#199

Post by namirez »

FabHK wrote: post #197
namirez wrote: post #192

Earlier quoted context omitted.

Your numbers are not quite right. > jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine. > more glider-like L/D of 25-35 (the best gl…

> > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy > Again, this can be done for any aircraft, not just the electric ones. Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.

True! Actually airplanes are loaded with just enough fuel to finish their mission safely. It's not like a 777 always taking off with maximum fuel.

Re: The age of electric flight is finally upon us

#200

Post by dreamcompiler »

markab21 wrote: post #11

As someone who regularly pilots a piston-single, I'm looking forward to what hybrid or full electric can do for us little guys. The takeoff phase of flight is a high-risk situation in events such as fuel contamination which could prove fatal. Having a small buffer, even a few minutes of battery power to rely on while trying to get back to the field to land the "impossible turn" [1] would make me feel a lot better and…

I've seen the Pipistrel at EAA a few times. It seems to be a real product, but flight time is quite short, even though it's basically a sailplane with an engine. That's why they're billing it as a trainer.
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