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Airbus and Boeing are exploring the viability of electric planes

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Re: Airbus and Boeing are exploring the viability of electric planes

#131

Post by ajross »

toomanybeersies wrote: post #122

Airbus actually made a prototype electric ducted fan plane: https://en.wikipedia.org/wiki/Airbus_E-Fan The core problem with it though was the poor energy density of batteries. Hopefully electric cars will drive more innovation in this area, although the aviation industry is usually at least 20-30 years behind the automotive industry as far as engine technology goes, so we're probably 40 years away from getting wides…

> so we're probably 40 years away

Batteries will never get there, even in four decades. There's no known battery chemistry, even in theory, that even comes close. Fuel cells would have to be the power source, though fuel cells are like fusion in that they're always a few decades out.

Frankly if the real goal is having aircraft flying on renewable power, I'd put my money on using that clean energy at sea level to synthesize fuel to burn at altitude. Aviation just isn't a meaningful application of electric motors IMHO.

Re: Airbus and Boeing are exploring the viability of electric planes

#132

Post by bigiain »

skookumchuck wrote: post #86
GuB-42 wrote: post #77

Earlier quoted context omitted.

There is more than that. Planes become lighter as they burn fuel, batteries don't become lighter as they drain. Lighter planes are more efficient, and most airliners are not designed to land with their tanks full. They have a option to jettison their fuel in case of emergency. It means that just matching the energy density of fuel is not enough, batteries must exceed it. Jet engines are also quite efficient: around 4…

> batteries don't become lighter as they drain. Right, but they can be thrown overboard :-)

I wonder if you could split the battery pack into thirds - each with a modern steerable parachute type glide-return system?

You climb out to cruise altitude - then drop off the "climb battery" which would autonomously return to your takeoff point (somewhere nearby where if can easily/safely land, be retrieved, and recharged for the next flight). You'd cruise to your destination on the "cruise battery", which you'd jettison near the landing point, so it could fly itself there for charging. You'd land with just the "landing battery" which'd have sufficient capacity for go-arounds and/or diversions, just like your fuel reserve in a conventional dinosaur-burning aircraft.

Dropping batteries off and moving the remaining ones around while maintaining safe centre of gravity might be tricker than just pumping liquid fuel around, but surely not insurmountable (the military seem to be able to jettison stunning weights of munitions while flying...) Perhaps youd got for batteries divided into six spread equally for and aft from the cog - and drop them in matched pairs?

Re: Airbus and Boeing are exploring the viability of electric planes

#133

Post by voodooranger »

bigiain wrote: post #123
GuB-42 wrote: post #77

Earlier quoted context omitted.

There is more than that. Planes become lighter as they burn fuel, batteries don't become lighter as they drain. Lighter planes are more efficient, and most airliners are not designed to land with their tanks full. They have a option to jettison their fuel in case of emergency. It means that just matching the energy density of fuel is not enough, batteries must exceed it. Jet engines are also quite efficient: around 4…

I'm pretty sure the "emergency fuel jettison" is for "I'd rather it not splash about everywhere and catch fire in the case that I put this plane down hard enough to split the tanks open" rather than "It's impossible to land this plane safely at the same weight as it took off". (Not that I'd want to be hurtling at the ground barely in control with many tons of fully charged LiPo battery on board either...)

If the landing speeds are the same, a heavier aircraft requires a longer landing roll. But a heavier aircraft also requires a higher landing speed. Those two phenomena compound.

Re: Airbus and Boeing are exploring the viability of electric planes

#134

Post by taneq »

Infernal wrote: post #84
cm2187 wrote: post #24

As a first step, they could make at least the take off and landing electric, that would help a lot with the noise and pollution around cities, i.e. where people live. I guess the batteries could be recharged during the flight for landing.

If you compare to hybrid cars, landing is more like braking to a stop light (unless you need to gun it again to abort the landing). Takeoff is like accelerating from a stoplight (where you need the most power). If electric could take over at any point, it would be in the steady cruise at altitude (akin to overdrive on the highway).

Going by your hybrid car analogy, electric would make most sense as a brief power boost on takeoff, allowing the aircraft to use smaller, lighter engines to cover cruising power requirements more efficiently.

Re: Airbus and Boeing are exploring the viability of electric planes

#135

Post by Merad »

skookumchuck wrote: post #118
Merad wrote: post #110

Earlier quoted context omitted.

Actually the aux tank wasn't added to the Mustang purely for range. A big factor was helping to balance out the heavier Merlin engine. Pilots would typically leave about 1/3 of the tank to keep ideal balance and have an emergency fuel reserve. Typically by the time they had taken off and made the climb to altitude they had burned enough fuel from the aux tank (about half) to be in reasonable "fighting trim". Would've…

Interesting. I was told this by a former P51 pilot. He also said sometimes lone Ju-88s would sneak in at low altitude and pick off B-17s taking off or landing when they thought they were safe.

I’m sure the Ju-88 thing probably happened. IIRC there were at least a couple instances of caputured B-17s trying to slip into formations and shoot at damaged bombers, and there were definitely a few cases of captured allied fighters being used on bombers.

Re: Airbus and Boeing are exploring the viability of electric planes

#136

Post by hueving »

bigiain wrote: post #123
GuB-42 wrote: post #77

Earlier quoted context omitted.

There is more than that. Planes become lighter as they burn fuel, batteries don't become lighter as they drain. Lighter planes are more efficient, and most airliners are not designed to land with their tanks full. They have a option to jettison their fuel in case of emergency. It means that just matching the energy density of fuel is not enough, batteries must exceed it. Jet engines are also quite efficient: around 4…

I'm pretty sure the "emergency fuel jettison" is for "I'd rather it not splash about everywhere and catch fire in the case that I put this plane down hard enough to split the tanks open" rather than "It's impossible to land this plane safely at the same weight as it took off". (Not that I'd want to be hurtling at the ground barely in control with many tons of fully charged LiPo battery on board either...)

Nope, look at the difference between the MTOW and MLW columns here: https://en.m.wikipedia.org/wiki/List_of_airliners_by_maximum...

The issue is the brakes overheating and the impact on the landing gear.

Re: Airbus and Boeing are exploring the viability of electric planes

#137

Post by bigiain »

hueving wrote: post #136
bigiain wrote: post #123

Earlier quoted context omitted.

I'm pretty sure the "emergency fuel jettison" is for "I'd rather it not splash about everywhere and catch fire in the case that I put this plane down hard enough to split the tanks open" rather than "It's impossible to land this plane safely at the same weight as it took off". (Not that I'd want to be hurtling at the ground barely in control with many tons of fully charged LiPo battery on board either...)

Nope, look at the difference between the MTOW and MLW columns here: https://en.m.wikipedia.org/wiki/List_of_airliners_by_maximum... The issue is the brakes overheating and the impact on the landing gear.

Thanks! Yet another thing to add to "the list of stuff I'm wrong about"... :-)

Re: Airbus and Boeing are exploring the viability of electric planes

#138

Post by philwelch »

GuB-42 wrote: post #77
savrajsingh wrote: post #25

It’s just a question of the energy density of batteries vs. fuel. We need a couple more battery breakthroughs before we get a fully electric commercial airliner.

There is more than that. Planes become lighter as they burn fuel, batteries don't become lighter as they drain. Lighter planes are more efficient, and most airliners are not designed to land with their tanks full. They have a option to jettison their fuel in case of emergency. It means that just matching the energy density of fuel is not enough, batteries must exceed it. Jet engines are also quite efficient: around 4…

It's possible to turn atmospheric CO2 and water back into hydrocarbons, which would make for a carbon-neutral, closed-loop fuel system. It takes extraordinary amounts of energy to do that, but improvements in that process, and/or the ability to generate energy more efficiently than we can now, would help.

Re: Airbus and Boeing are exploring the viability of electric planes

#139

Post by Hextinium »

TheSpiceIsLife wrote: post #119
ShorsHammer wrote: post #94

Earlier quoted context omitted.

Another SE link of interest, how much electrical power needed to run a 747 engine: https://aviation.stackexchange.com/questions/19569/how-many-... The consensus is ~90 MW. That's a lot of energy, electric air travel is certainly possible, but it will likely come at a severe cost to speed and endurance. If we are going to travel slowly would personally prefer autonomous airships.

Megawatts is a power unit. To sustain 90MW for a 4hr flight you need a battery that can provide 360MWh of energy. Anyone care to do the numbers on how much a lithium ion battery would weigh to be able to deliver 360MWh, and remember if you want to use it more than once you can full charge no discharge it.

A standard lithium ion battery has between 100-265 Wh/kg if you need 360 thousand to 135 thousand kg of lithium ion batteries plus probably a few thousand for charging equipment. A a 747 has capacity for about 45k kg of fuel so a factor of 4 improvement is needed before that is comparable.

Re: Airbus and Boeing are exploring the viability of electric planes

#140

Post by CalRobert »

patrickaljord wrote: post #16
amelius wrote: post #4

Earlier quoted context omitted.

Or add a large tax to flying that pays for the development of green solutions.

This way only the super rich will be able to fly.

How do you propose keeping something cheap while ensuring only a small amount is used? Rationing?

I remember when Obama said "Gas under a buck ain't bad" (paraphrased) and was dismayed - you cannot pursue the goal of making something cheaper and reducing it's consumption without something like rationing (or, I suppose, simply making an alternative which is profoundly superior and cheaper, but we haven't got that)

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