Electric planes

[daniel]

That's their 1/3 scale test launcher. They've achieved about 1% of the energy the full-size version will need. IIRC they've accelerated a projectile one-tenth the mass of the planned real thing to about one-tenth of the speed the real thing will need. I probably have those numbers wrong. This really is just a toy slingshot, useful for conning investors into giving them money.

Oh, and note that when a rocket launch fails and blows up you lose the rocket and its payload. When this thing fails they'll lose the entire launch system. I think everybody stays about a mile away when they run a test launch. They've run ten test launches so far.

 

[Electroman]

Yup, I find this Slingshot thing more in the realm of perpetual machines. The ejection speed should be much more than the orbital speed of 24K km/hr. Because it will lose a lot of energy to air friction at sea pressure. Throwing a projectile at say 50K km/hr (or even more) at seal level is insane.. Maybe they can try this from atop Mt. Everest

 

[daniel]

Yup, I find this Slingshot thing more in the realm of perpetual machines. The ejection speed should be much more than the orbital speed of 24K km/hr. Because it will lose a lot of energy to air friction at sea pressure. Throwing a projectile at say 50K km/hr (or even more) at seal level is insane.. Maybe they can try this from atop Mt. Everest

To be fair to them, they're not throwing the projectile all the way to orbit. It's a rocket. Basically the "slingshot" takes the place of the first stage and the projectile contains the second stage which would put it into orbit. The idea is that they save the weight of a first stage with all its fuel.

However, there are still so many failure points, and they've achieved such a minuscule percentage of the energy needed, and the whole contraption is so vulnerable to any small mishap, that I regard it as a pipe dream. And if it did work it would only be for small cubesats.

I don't think they've yet tested the rocket part of the projectile. They've just done ten tests, flinging a giant dart up into the air, including with instrumentation to monitor the forces involved, and to try to determine if satellite components could survive those forces. The G forces of the centrifuge are immense.

 

[wwu123]

A VERY big one.

You don't need a catapult, if we're talking about a hybrid aircraft that has a electric motor for takeoff. You need some durable releaseable tether that can transfer power while along the length of the runway, so that the energy comes from a ground source rather than in batteries on board, that then are empty the entire flight.

Still an engineering challenge to make reliable and durable, but doesn't require much more on the aircraft side of the equation

 

[daniel]

A tether to launch a commercial passenger plane would provide so little energy that it would be pretty much useless. Gliders can do it this way because they are ultra-light and typically have just one person (the pilot) on board, and only need to get high enough to begin to catch thermals. Ain't gonna happen with commercial planes.

 

[SalisburySam]

A tether to launch a commercial passenger plane would provide so little energy that it would be pretty much useless. Gliders can do it this way because they are ultra-light and typically have just one person (the pilot) on board, and only need to get high enough to begin to catch thermals. Ain't gonna happen with commercial planes.

On a more humorous path, how about an A380 with very beefed-up undercarriage launched by a 25mW rail gun? I think the physics should work, and be just a delightful ride for the 500 passengers, though there may be a bit of a clean up issue in many seats.

 

[daniel]

On a more humorous path, how about an A380 with very beefed-up undercarriage launched by a 25mW rail gun? I think the physics should work, and be just a delightful ride for the 500 passengers, though there may be a bit of a clean up issue in many seats.

Didn't you mean 25 MW? 25 milliwatts isn't going to even move that plane. Note, however, that an aircraft carrier's catapult delivers 95 MJ over about two seconds, to launch a much lighter airplane than an A380. Somebody with better math skills than I have might be able to calculate how much energy a catapult would need to launch an A380. I suspect that the FAA would not approve.

 

[swaltner]

While it would be fun, cool, <insert adjective>, using a catapult or whatever is pointless in the grand scheme of things for the total energy budget required for air travel. The energy to accelerate a vehicle to flying speed is nothing compared to the energy required to climb to cruising speed. Everyone that drives an EV intuitively knows this already. We don't estimate energy loss to do a one-time acceleration to highway speed, but we do plan for elevation gain required to cross a mountain pass.

Putting actual numbers to it. The formula for kinetic energy is "1/2 m v^2" and the formula for potential energy due to gravity is "m g h". In both cases, m is mass so the relative scale of the numbers doesn't change if we're talking about a small business jet or an Airbus A380.

In the kinetic energy formula, v is velocity in m/s. An airline lifting off at 200 mph is traveling at just shy of 90 m/s. Square that and take 1/2 and you get roughly 4,000 as the number to multiply by the mass for getting the kinetic energy.

An airline flying at 32,800' above ground is 10,000m above the ground, which is h in the potential energy formula. g is gravity, which on earth 9.8 m/s^2 - call it 10 to make the math easy. That means that potential energy for an airline in cruising flight is 100,000 times the mass.

This means that it takes 25 times as much energy for an airline to climb to cruising altitude as it does to accelerate to flying speed on the ground. You could accelerate to a higher speed, but you're still not even within the same order of magnitude compared to the energy required to climb to altitude. I understand that this probably should be an integral of some sort to figure out the true energy required as fuel is burned off in the climb, but this simple calculation gets you in the right ballpark and the two energy buckets aren't even in the same order of magnitude, so everything else is probably inconsequential.

This difference in energy input requirements is also intuitive in that an airplane can accelerate to flying speed in a minute, but it takes 10-20 minutes to climb to flying altitude.

Kinetic Energy Calculator - Kinetic Energy Calculator
Gravitational Potential Energy Calculator - Gravitational Potential Energy Calculator

 

[daniel]

@swaltner: Thanks for that. As I said, a catapult is pointless for a passenger plane. Which, of course, is why they don't use them. On an aircraft carrier the planes need to reach take-off speed in a very short distance. Thus the catapult.

 

[SalisburySam]

Didn't you mean 25 MW? 25 milliwatts isn't going to even move that plane. Note, however, that an aircraft carrier's catapult delivers 95 MJ over about two seconds, to launch a much lighter airplane than an A380. Somebody with better math skills than I have might be able to calculate how much energy a catapult would need to launch an A380. I suspect that the FAA would not approve.

Yup, megawatts, not milliwatts, thanks for the subtle but important correction! And I agree, I cannot see any licensing agency like our FAA approving anything remotely like this. I can only imagine the aircraft frame requirements would turn an A380 into a plane that could only carry one or two passengers, likely not very profitable for carriers. But a heck of a ride for sure.

 

[daniel]

Yup, megawatts, not milliwatts, thanks for the subtle but important correction! And I agree, I cannot see any licensing agency like our FAA approving anything remotely like this. I can only imagine the aircraft frame requirements would turn an A380 into a plane that could only carry one or two passengers, likely not very profitable for carriers. But a heck of a ride for sure.

I'm pretty sure there are amusement park rides that mimic that sort of experience without affecting commercial aviation.

 

[ggr]

On a more humorous path, how about an A380 with very beefed-up undercarriage launched by a 25mW rail gun? I think the physics should work, and be just a delightful ride for the 500 passengers, though there may be a bit of a clean up issue in many seats.

I don't think 25 milliWatts will do much of anything.

 

[SalisburySam]

I don't think 25 milliWatts will do much of anything.

Yup, already pointed out and corrected in a follow-up response. Can no longer edit original post.

 

[JRP3]

Sandy takes a look at an electric VTOL

 

[ecarfan]

ZeroAvia nears takeoff with its 19-passenger hydrogen-electric plane

Hydrogen-electric plane developer ZeroAvia has come one step closer to performing the first test flight of its hydrogen electric plane equipped with a 600kW powertrain. The company has received a permit from the UK’s Civil Aviation Authority (CAA) to takeoff soon.

ZeroAvia is a zero-emission aviation company that develops planes that utilize hydrogen-electric propulsion. The company currently operates in the US and UK and previously snagged experimental certificates for prototype aircraft from both the CAA and FAA.

The company wants to scale up its technology to planes with 200+ seats and 5,00 Nm range by 2040.

Probably more feasible than pure BEV planes for the foreseeable future.

 

[EVer Hopeful]

This means that it takes 25 times as much energy for an airline to climb to cruising altitude as it does to accelerate to flying speed on the ground.

but not if it took off from a conveyor belt

 

[daniel]

ZeroAvia nears takeoff with its 19-passenger hydrogen-electric plane

The company wants to scale up its technology to planes with 200+ seats and 5,00 Nm range by 2040.

Probably more feasible than pure BEV planes for the foreseeable future.

They're calling it zero-emission, but of course they're just moving the emissions from the plane itself to the plant that's producing the H2, probably from natural gas. H2 CAN be produced cleanly by electrolysis from water using sustainable energy (solar, wind, etc.) but in the real world it's not.

Doing the same for cars can be justified if the H2 plant is away from population centers, because car exhaust in cities is a serious health issue. Moving it away does nothing for the climate crisis, but at least reduces smog in cities. But aircraft spend most of their time far from population centers, so the same argument does not apply.

 

[EVer Hopeful]

yes but . . .

One difference between emissions taking place at one central place as opposed to spread out in several million vehicles is that it might be more feasible to create some form of emission control at that one place than it would be in a distributed setting, or at least a better one

Everything we do creates an impact, even wind and solar as they reduce the energy available behind the extraction points. I think focusing on emissions (etc) is only half the story and that usage and efficiency are equally important. I think these two get overlooked

 

[Etna]

They're calling it zero-emission, but of course they're just moving the emissions from the plane itself to the plant that's producing the H2, probably from natural gas. H2 CAN be produced cleanly by electrolysis from water using sustainable energy (solar, wind, etc.) but in the real world it's not.

Doing the same for cars can be justified if the H2 plant is away from population centers, because car exhaust in cities is a serious health issue. Moving it away does nothing for the climate crisis, but at least reduces smog in cities. But aircraft spend most of their time far from population centers, so the same argument does not apply.

This is a moot point. None of these H2 projects intends to use anything else than green H2 since that is the whole idea.

Airbus has specifically repeated that as long as there is no green H2 infrastructure in place, none of their H2 plane projects will start production. Accordingly, they have taken steps to get involved in such infrastructure, for example through the Hy24 investment fund, the largest of its kind.

 

[daniel]

yes but . . .

One difference between emissions taking place at one central place as opposed to spread out in several million vehicles is that it might be more feasible to create some form of emission control at that one place than it would be in a distributed setting, or at least a better one

Everything we do creates an impact, even wind and solar as they reduce the energy available behind the extraction points. I think focusing on emissions (etc) is only half the story and that usage and efficiency are equally important. I think these two get overlooked

Agreed. But H2 is not efficient unless it's green. And there isn't any significant amount of green H2 at present. And due to the inefficiencies of H2, we should not be wasting green energy to make inefficient H2 until we have enough green energy to meet other needs that use it more efficiently

This is a moot point. None of these H2 projects intends to use anything else than green H2 since that is the whole idea.

Airbus has specifically repeated that as long as there is no green H2 infrastructure in place, none of their H2 plane projects will start production. Accordingly, they have taken steps to get involved in such infrastructure, for example through the Hy24 investment fund, the largest of its kind.

In that case, Airbus won't have any H2 airplanes for a decade or three. As noted above, H2 is a very inefficient use of energy. And even though H2 has a weight advantage over batteries (everything has a weight advantage over batteries) the tanks needed to hold it will be very heavy once they exist (tanks suitable for carrying H2 in an airplane will be an engineering problem in themselves, as they need to contain great pressure and maintain very cold temperature.)

As for the Hy24 investment fund, it looks like a lot of hype to me. And if they're legit they have their work cut out for them. H2 cars have been a big failure, with H2 filling stations going on the fritz constantly, due to the myriad difficulties of handling the stuff.

Note that if you're going to use clean energy to make H2, you could just as easily use that same clean energy to make liquid fuels that are a thousand times easier to handle. Hydrogen is really hard to handle.