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Electric Planes

Gord_in_Toronto

Penultimate Amazing
Gord_in_Toronto
Joined
Jul 22, 2006
Messages
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I seem to remember this being discussed in another hread but it probably deserves one of its own anyway.

It looks as if the reality of planes powered by electric motors (and thus mostly batteries) is getting closer. Here is one example of such progress:

Future of Aviation? NASA and U.S. Air Force Testing Joby’s Electric Vertical Takeoff and Landing (eVTOL) Aircraft

You can follow along the progress here:
ADVANCED AIR MOBILITY REALITY INDEX

IMHO there's probably another leap in battery technology required before EPs become mainstream but promoters are promoting really hard.
 
Well, electrically powered aircraft are already a reality, in the form of drones. Multirotor drone lay-outs are quite scalable, control software is already well developed, so we shall no doubt soon see them as short range VTOL craft, capable of carrying passengers and smaller loads.

Otherwise, for both rotor and fixed wing configurations, range and weight/load ratio is a big hurdle. So I agree that energy storage (I avoid the term 'battery' on purpose) is a main issue.

Hans
 
Well, we already have electric training aircraft here in NZ, the Pipistrel Alpha Electro run by ElectricAIr Flight School

https://www.electricair.nz/

They are very cheap to run. Typical price for flying lessons in, say, a Piper Tomahawk, a Piper Cherokee or a Cessna 172 runs at about NZ$250 to $275 per hr. ElectricAir are charging about 190 per hr

 
MRC_Hans said:
Well, electrically powered aircraft are already a reality, in the form of drones. Multirotor drone lay-outs are quite scalable, control software is already well developed, so we shall no doubt soon see them as short range VTOL craft, capable of carrying passengers and smaller loads.
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Carrying passengers is not so easy. The larger you scale a multirotor, the harder you stress the rotor components, meaning that reliability becomes more difficult. Yeah, we are able to scale them to large sizes, but what happens if a rotor fails? For a small drone, that's not such a big deal. Even for larger drones, that's still OK as long as you don't hit anyone on the ground. You can tolerate failure rates that no passenger aircraft could ever last with. But you can't tolerate failure rates with passengers that you could with small cargo. We aren't close to having an established safety record for copter drones capable of carrying passengers that would make this commercially feasible. It's not an impossible task, but it's a really, really big one, and it's probably going to take a long time (as in decade+) to solve.

Otherwise, for both rotor and fixed wing configurations, range and weight/load ratio is a big hurdle. So I agree that energy storage (I avoid the term 'battery' on purpose) is a main issue.
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It's either a battery or a fuel cell. Nothing else is going to give you electricity directly, and a hybrid engine plane isn't an electric plane.
 
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One thing I realized, looking at drone use in Ukraine, is that larger payloads means larger batteries, and unlike fuel tanks batteries don't get lighter over the duration of the flight. It seems that above a certain payload size, the dead weight of depleted batteries tends to offset the benefit of an electric drone, and you're better off going back to ICE.

Also, VTOL is ridiculously energy-expensive, compared to other forms of powered flight. It's a niche application, for when you are putting a very high premium on being able to land and take off from anywhere, without a runway. Military applications, of course, where winning is more important than mere fuel efficiency. Ostentatious executives, who have money to burn. Etc.
 
As a follow-up to my notes above about human safety. For planes (electric or not), you can survive an engine failure by gliding to the ground. Helicopters can actually do something similar with autorotation. Not as simple a maneuver, but helicopter pilots train for it. But it requires being able to adjust the pitch of the blades.

Quad copters and the like have fixed pitch blades. They adjust lift by changing rotation speed of the blades. But that also means that you cannot do autorotation. And they can't glide either. Basically, if you have an engine failure in a quad copter style design, you're going to crash. With passengers, that means engine failures are not really survivable events. There's no way in hell that gets widespread adoption.

And if you want to add blade pitch capability, then there's really little point in using a quad copter style design rather than a traditional helicopter.
 
Ranb said:
This looks interesting. https://www.eviation.com/

Ranb
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Which brings up a point.

The vast, and I mean VAST majority of airliner flights are short range commuter flights with small passenger numbers. They have the greatest impact on the environment as regards emissions, so much so that some countries are banning them. But electric aircraft could fill replace many conventional fuel-powered aircraft on short-haul flights and there are technical reasons why that could be a good thing.

One of the greatest impacts on the life of an aircraft is not, as you might expect, the number of flight hours, but the number of "pressurization cycles". Each cycle involves a takeoff, a pressurization sequence and a landing. Aircraft on short-haul services undergo a lot of pressurization cycles, but the reason they need to do this is because the engines are more efficient at higher altitudes, so they need to fly higher to be at their most economical.

However, electric aircraft have no such constraint. There are no efficiency gains to be had by flying at 20,000 ft instead of 2,000 feet so - in fact, it is probably more efficient for electric aircraft to fly lower. Consequently, there is no need for a pressurization system. Short haul electric aircraft could fly much lower, meaning no need to waste battery power climbing to high altitudes. I can easily see a small commuter airliner like the one shown in RanB's link flying a 500km flight from one airport to another at 1,000 ft AGL instead of the usual 20,000 ft by something like a Citation or a Gulfstream.
 
smartcooky said:
Aircraft on short-haul services undergo a lot of pressurization cycles, but the reason they need to do this is because the engines are more efficient at higher altitudes, so they need to fly higher to be at their most economical.

However, electric aircraft have no such constraint. There are no efficiency gains to be had by flying at 20,000 ft instead of 2,000 feet
Click to expand...

That's not quite true. The engine efficiency might not change, but drag efficiency does. Drag at 20,000 feet is a lot lower than at 2,000 feet.

in fact, it is probably more efficient for electric aircraft to fly lower.
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Only if you also go slower. Which has significant downsides in terms of what people want.

The overall balance might still allow for economic short range electric flights, but I don't think the case is as obvious as you suggest.
 
Ziggurat said:
Why does it have an air intake for its motors? Does it really need that much cooling?
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Yes. They are the air intakes of the motors' Thermal Management Systems (TMS). Electric and Hybrid-Electric Aircraft propulsion systems rely on high-power electrical equipment, electric motors, voltage/current converters, power electronics and batteries. These items dissipate heat at a much higher rate than conventional propulsion aircraft systems.

The Eviation Alice uses a though-flow ventilation system for the the TMS - you can see the exit holes at the rear of the engine nacelles.
 
Ziggurat said:
That's not quite true. The engine efficiency might not change, but drag efficiency does. Drag at 20,000 feet is a lot lower than at 2,000 feet.
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True, but it is a much smaller part of the equation. Over 80% of the efficiency gains from flying at altitude come from greater engine efficiency

Flying at altitude might give you better drag efficiency, but you have to get there first. Most of those gains are eaten up by the losses incurred in using battery power. It costs more power to climb than it does to fly level, and in the case I am making, short haul, very little of the flight time is spent at high altitude.

Ziggurat said:
Only if you also go slower. Which has significant downsides in terms of what people want.
Click to expand...

The Eviation Alice has a cruising speed of 481 km/hr. The type of aircraft it would be competing against are

ATR72 - 510 km/h
Cessna Skycourier - 389 km/h
Piper PA31 Navajo - 383 km/h

That's not a lot of difference
 
Ranb said:
This looks interesting. https://www.eviation.com/

Ranb
Click to expand...

Ziggurat said:
Why does it have an air intake for its motors? Does it really need that much cooling?
Click to expand...

smartcooky said:
Yes. They are the air intakes of the motors' Thermal Management Systems (TMS). Electric and Hybrid-Electric Aircraft propulsion systems rely on high-power electrical equipment, electric motors, voltage/current converters, power electronics and batteries. These items dissipate heat at a much higher rate than conventional propulsion aircraft systems.

The Eviation Alice uses a though-flow ventilation system for the the TMS - you can see the exit holes at the rear of the engine nacelles.
Click to expand...

Huh. I assumed it was just the usual turboprop intake. Use electrical power to suck in the air, compress it, then use the compression to drive the propeller.
 
theprestige said:
Huh. I assumed it was just the usual turboprop intake. Use electrical power to suck in the air, compress it, then use the compression to drive the propeller.
Click to expand...

No, the motors are not turboprops, they are electric motors.

(fast forward to 3:16 if the link doesn't take you there automatically)

ETA: https://youtu.be/ZCTQiuHAFSQ?t=196
 
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smartcooky said:
No, the motors are not turboprops, they are electric motors.

(fast forward to 3:16 if the link doesn't take you there automatically)

ETA: https://youtu.be/ZCTQiuHAFSQ?t=196
Click to expand...

Huh. I assumed that the "turbo" in "turboprop" came from adding energy by compressing the air and then using that energy to drive something. And that electricity rather than combustible fuel could be used to add energy in the compression step. I.e., one could use an electric motor to drive a turboprop.
 
Ziggurat said:
Carrying passengers is not so easy. The larger you scale a multirotor, the harder you stress the rotor components, meaning that reliability becomes more difficult. Yeah, we are able to scale them to large sizes, but what happens if a rotor fails? For a small drone, that's not such a big deal. Even for larger drones, that's still OK as long as you don't hit anyone on the ground. You can tolerate failure rates that no passenger aircraft could ever last with. But you can't tolerate failure rates with passengers that you could with small cargo. We aren't close to having an established safety record for copter drones capable of carrying passengers that would make this commercially feasible. It's not an impossible task, but it's a really, really big one, and it's probably going to take a long time (as in decade+) to solve.



It's either a battery or a fuel cell. Nothing else is going to give you electricity directly, and a hybrid engine plane isn't an electric plane.
Click to expand...

The inability to perform an autorotor landing is a problem for a quad/hex/whatever number -rotor drone-style craft, when manned. Or perhaps it can be dimensioned to land with one engine out. Electric motors are potentially far more reliable than fuel engines.

So far, battery or fuel cell, yes.

There are also hydrogen-burning engines, but off topic.

Hans
 
theprestige said:
Huh. I assumed that the "turbo" in "turboprop" came from adding energy by compressing the air and then using that energy to drive something. And that electricity rather than combustible fuel could be used to add energy in the compression step. I.e., one could use an electric motor to drive a turboprop.
Click to expand...

Nope. The "turbo" comes from "turbine" - a turboprop is essentially a turbine engine that drives a propeller instead of using jet thrust for propulsion.

https://aerospaceweb.org/question/propulsion/q0135b.shtml

Both turboprops and turbofans use the same fuel... usually Jet A1 (sometimes called AvTur in the military) which is essentially high-quality aviation grade kerosene.
 
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smartcooky said:
Nope. The "turbo" comes from "turbine" - a turboprop is essentially a turbine engine that drives a propeller instead of using jet thrust for propulsion.

https://aerospaceweb.org/question/propulsion/q0135b.shtml

Both turboprops and turbofans use the same fuel... usually Jet A1 (sometimes called AvTur in the military) which is essentially high-quality aviation grade kerosene.
Click to expand...

Yes, the energy in the compressed air is used to spin the turbine. I know all this. I had just sort of assumed that the compression stage could be electrically driven.
 
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