I know nothing about Eviation other than what this article says. They're claiming 650 miles of range with nine passengers on batteries, and to that I will not say I'm merely skeptical. I'm saying they are flat-out liars selling bullshit, and I'll stake my engineering reputation on that statement.
The age of electric flight is finally upon us
201–210 of 272 posts
Re: The age of electric flight is finally upon us
#202Earlier quoted context omitted.
What’s the reasoning behind your statement? I think both are already being done, the economics are just not there yet. Digging up free energy from the ground is just too cheap.
The scale of co2 that would need to be sequestered is massive, I don't think anyone has a vaguely viable plan of how that would be done. Most attempts at biofuel are not even net positive on energy. if we did get there then the question is how much forest do we have to clear to grow biofuel AND eat, and what net effect does that have on co2. Hard problems all around.
> if we did get there then the question is how much forest do we have to clear to grow biofuel AND eat
Convert the beef/dairy farms. :D
Re: The age of electric flight is finally upon us
#203As 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…
One interesting idea but not likely workable, have an electric launch platform that simply has the actual passenger plane as its cargo and once sufficient speed is reached it drops off to circle back on its own for another go.
could work with either propulsion method of the plane being lifted.
Re: The age of electric flight is finally upon us
#204As 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…
Carbon sequestration and biofuels that are actually carbon neutral may be similarly implausible.
It's not necessary to do that. We could reserve use of hydrocarbon fuel to airplanes, and it would be fine. It's not necessary to go to zero.
Re: The age of electric flight is finally upon us
#205Earlier 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…
>New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg.
Depends if we're talking LHV or HHV. Additionally, we're talking smaller jet fueled vehicles which rarely have access to state-of-the-art efficiency.
>Beyond Mach 0.5, the efficiency degrades very rapidly.
In this case, we're talking Mach 0.5 or less.
>this can be done for any aircraft, not just the electric ones.
Didn't imply otherwise. The highest performance jet plane can fly literally around the world. But this is far more performance than anyone needs in an aircraft. And for whatever reason (partially because of aging fleets, at least for very small commuter aircraft), generally there have been efficiencies left on the table still, just the same as conventional car makers left efficiencies on the table which Tesla and the like have taken advantage of.
> Do you really believe there is a market for 1200km hops at Mach 0.5.
For domestic flights, yes. For transatlantic, no, not a large market. Not as long as jet planes aren't paying for their climate externalities.
>We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?
Because those have the same maintenance requirements and use the same fuel as jets, which are just as efficient and faster.
I don't think we'll do many transatlantic electric passenger flights until the climate externalities are priced-in for the cost of air travel or until lithium-air or similar. But now we've moved the goal posts to long-haul and transoceanic flight. Electric flight is clearly possible and for domestic flights it'll likely be cost-competitive even without fully accounting for climate externalities, particularly for these 9 passenger FAR-23 electric aircraft competing with fuel-guzzling and maintenance-heavy 40 year old fleets.
Re: The age of electric flight is finally upon us
#206As 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…
I think the biggest point that you and others that bring this up is missing, is not just how electric designs gives you higher efficiency and close the gap (as others have mentioned).
The main thing you're missing is that modern jet planes have absolutely ridiculous range, and a huge number of flights use only a fraction of that range. Electric planes don't need to match modern jet planes to be viable. They just have to compete on cost at a range that covers a significant amount of routes. And electric planes have a potential for huge cost advantages.
A related aspect is that electric planes are much more quiet. Being cheaper to operate and more quiet means you can fly smaller planes from smaller local airports to other small airports. You can create an entirely new market.
Electric planes are not going to take over transatlantic flights any time soon. But they don't have to in order to have a huge impact.
I do agree that carbon neutral fuels are important for long-haul flights for the coming decades. With batteries for land transport and short-range ships/ferries and planes and hydrogen for heavy trucks and ships, we might be able to sustainably make enough carbon-neutral fuels for long-haul planes.
Re: The age of electric flight is finally upon us
#207Earlier quoted context omitted.
I was just thinking about something autonomous. Basically a battery with wings. That way you don't need a plane with pilot.
Parachute not enough?
I don't think so. You cant steer a parachute well and you don't want some bypasser to get hit by a heavy battery on a parachute. The descent speed on a parachute is very high so it will hurt or more.
Re: The age of electric flight is finally upon us
#208I know nothing about Eviation other than what this article says. They're claiming 650 miles of range with nine passengers on batteries, and to that I will not say I'm merely skeptical. I'm saying they are flat-out liars selling bullshit, and I'll stake my engineering reputation on that statement.
> I'll stake my engineering reputation on that statement
Such forceful claims should not be made anonymously. I'm with you on the claim itself but feel that if you want to make that statement and stand by it that you should do so with your name and 'engineering reputation' attached to the claim itself.
Re: The age of electric flight is finally upon us
#209Earlier 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.
Dumb idea: If the weight of the batteries is significant, then dump out the empty ones with parachutes partway through the flight?
Re: The age of electric flight is finally upon us
#210Earlier quoted context omitted.
Better tell NASA, then, which is building a design (X-57) with the same kind of wing-tip propellers: https://www.youtube.com/watch?v=No9Rq3VE0FI The key is that the Alice aircraft is capable of take-off with just the rear propeller. That's possible because electric motors (unlike jet engines) can operate at much higher power for short periods of time. It was addressed recently at the Paris airshow Q&A for Eviation. I…
FWIW my thoughts: 1. Rear prop strikes. 2. Wing tip prop strikes. 3. Wing tip inertia 4. Prop wash over a wing is a good thing If (big if) this thing ever flies, it won't be in this form
Prop wash over a wing is good if you're lift-starved at take-off (which you aren't with this design). But otherwise it actually increases drag. Pusher configuration is superior in that you can ingest boundary layer air which has been slowed down by the fuselage and get an increase in efficiency. That efficiency gain is partially why pushers are often used in long-duration drones.