Since a big chunk of the power is expended on takeoff, the ideal would be to drop part of your battery then rather then waiting until after landing. But either way, you're stuck with the significant complexity and expense of having to prepare a parachute and landing gear specifically for the battery on each flight, plus having to collect and charge those batteries.
Accepting that we're just throwing out interesting-sounding ideas, I wonder if having a powered runway rail (or something of the sort) to provide takeoff power could work. With that you wouldn't have to worry about dropping anything.
But I do wonder how much power is actually expended at takeoff versus climbing or cruising flight. According to [1], only ~19% is used for both takeoff and climb, so electrifying the runway to save the fraction of the 19% used while in contact with the ground is probably not worth it.
SupersonicScrub's comment (a sibling to yours) says that the engine can be significantly more efficient if it doesn't have to meet the power demands of take-off. Their link says "at least 30%" fuel savings on a one-hour flight (although "the fuel savings will partly come from the latest gas turbine technology"). So maybe the rail system you propose isn't such a crazy idea. Also, it's not totally different in concept from an aircraft carrier's catapult; hopefully gentler...
>Also, it's not totally different in concept from an aircraft carrier's catapult; hopefully gentler...
Nah. If someone can't handle a few g's in takeoff, maybe they shouldn't be flying, and should should stay home, or maybe in a nursing home. I know it sounds mean, but seriously, think about it: aircraft transport isn't always comfortable. Turbulence happens, and it can be extremely rough at times, even injuring people severely if they're not belted in. If someone is too frail to handle being launched by an aircraft carrier catapult (which, remember, also launch those big AWACS planes, not just small fighter jets), then they're not suited for handling turbulence either.
Also, don't forget, the latest generation of catapult technology is actually pretty gentle. The USS Ford's "EMALS" catapults are electromagnetic, rather than steam, and one of the big stated benefits of this is that it's gentler on the airframes than the old steam catapults. It's still going to subject the pilots/passengers to several g's, but probably lower peak acceleration than the older technology did.
There's a better electrically driven solution that takes advantage of the fact that take-off and climb-out requires the most power.
Maximum power requirements come from take-off and climb-out, so the engine size is designed around the max take-off power. This means that the engine is over-designed and less-efficient for the majority of the flight.
By implementing a hybrid engine, the gas-powered component and the electric powered component work together to provide take-off power requirements. By the time the aircraft reaches cruising altitude, the batteries are dead, and the gas-powered component works alone. This allows the engine to be designed for the cruise power requirements, which results in a much more efficient engine. UTC is currently experimenting with this concept.
Not just for take-off, but for the possibility of finishing the take-off with one engine failure. That's quite a bit of spare capacity.
However I also wonder why, if electric motors are a solution here, there hasn't been a comparable fuel-powered extra-takeoff-engine. Why would this not have the same benefits? Or are extra engines simply too complicated mechanically unless they are motors?
(The liked article is about modifying a Dash 8, which is a turboprop, and perhaps it's easy to have oversize propellers for takeoff, and just connect a motor to the same gearbox.)
Probably because a jet engine costs like $30MM. It may well be that the incremental cost ($, weight, complexity) of adding an electric booster to an existing engine design is much more practical than just adding more engines.
You still need enough power to make a late go-around at the destination, in case of problems due to weather on final approach, arrival spacing, or a problem on the runway. I've been on planes that had to go around from low altitude three times, so it's not even that rare. Either the engine needs to be large enough to generate full take-off power, or you need a large margin of battery power that will never be used on an uneventful flight.
Wouldn't this also mean that full engine power is unavailable in the event of an emergency? Seems like this solution makes edge cases more likely to be fatal.
Heck, it might be doable to just lay the power cable in a permanent route on the ground and use electricity to propel the craft along that route! You wouldn't even need wings!
Aircraft carrier catapults do that. When launching the aircraft, all the energy is expended from the ground. Looking forward to such gigantic machines on airports, how much they would charge per flight, and problems like terrain slowly moving due to the gigantic forces at play.
Catapults accelerate aircraft to the point of generating enough lift for powered flight. They allow you to take off from a short runway like a carrier but don't get you to altitude. You can get a sense of how much power is being used to reach cruising altitude by listening to the engines on take-off. They don't fully throttle back until you reach a high enough altitude to permit level flight.
>Catapults accelerate aircraft to the point of generating enough lift for powered flight.
Yes, but the reason they're used is because it's infeasible or too expensive to build an aircraft carrier long enough to have jets reliably take off from them without this extra boost. Even so, those catapults are fairly short: notice they're only a fraction of the length of the carrier.
They're not used in regular airports because they're not absolutely necessary, the way they are on aircraft carriers. It's more expense, and planes can do without them. However, there's a cost to this: the planes need bigger engines and more fuel to take off reliably. And bigger engines are less efficient overall (as in cruising). So there would be a significant fuel savings if you could count on having catapults on the ground to help get the plane to takeoff speed: you could downsize the engines, and carry less fuel, saving a lot of money overall per flight (not to mention all the carbon pollution).
Finally, the extra g-forces shouldn't be a big deal. There's high g-forces in a carrier launch because the catapults are very short. And until recently, they were steam powered. This needn't be the case with commercial aviation: they can use modern electromagnetic launchers, and they can make the catapults very long (as long as much of the runway), to have lower peak acceleration. Basically, the planes and passengers would not need to experience higher g-forces than they already do; they'd just be getting them from the catapult instead of solely from the engines.
Good point - if you watch carrier launches, the planes actually fall a little as they go off the end of runway because they aren’t lifting yet. But presumably with a longer runway like you have at an airport, you could get to higher speed and truly liftoff.
But having also launched from a carrier myself, I wouldnt want that g force everytime I fly commercially.
> Looking forward to such gigantic machines on airports, how much they would charge per flight
It's actually an interesting supposition, because whether it's gasoline or electric, it should be cheaper and more reliable to run a ground operation than to pack fuel that is expelled before anything meaningful has happened.
> What happens when the plane mechanically fails? Having 600 tons of metal raining down on a population sounds quite dangerous
Simply put, that's just not how aviation works.
Mechanical failures aren't uncommon in aviation, but for an aircraft to not be able to divert and return to the ground, a lot has to go wrong all at once. It's infinitesimally rare for all systems to fail at once on an airliner. There simply isn't a problem of airliners dropping out of the sky, ever. They're incredibly robust machines.
However, with your idea, we'd be relying on a single system to prevent catastrophic failure. That's a massive step backwards for aviation.
That doesn't even begin covering the problems with delivering enough electricity over this cable to power an airliner at takeoff... That cable would need to be a very thick gauge of wire and very heavy - causing all sorts of it's own problems.
It wouldn't be viable for flights over oceans but I wonder if having batteries that eject at 95% exhaustion and then fly/glide themselves to a collection point with the last 5% of energy would work. There are too many variables for me to even do cocktail napkin math on it but with ever increasing drone tech, perhaps it would be possible.
Hard to say if giving the battery its own avionics is better or worse than equipping it with a parachute or steerable glider. Either way, it's the kind of thing that SpaceX decided was worth trying for the sake of fairings worth a few million apiece. Asking them how it went is probably a good place to start.
Regardless of the specifics, it's obvious that any of these schemes is a logistical and technical nightmare compared to "taxi up to the terminal, plug in the refueling hose while people and cargo are loaded onto the plane." It's unlikely that the private sector will be too enthusiastic about investing in anything like this without heavy incentives.
The liquid is gasoline, and you can make it carbon neutral. This whole effort toward battery powered aircraft is misguided: technically, hydrocarbon fuels work better than anything else. What you want to do is make carbon neutral hydrocarbon fuels.
The real advantage of electric airplanes is simplicity of electric motors, better aerodynamical properties of a plane using many small propellers, and possibility of vertical takeoff.
Ideally when we have kerosene based fuel cells we could have small electic aeroplanes that will be much easier to control, and would allow more frequent direct flights, instead of having to collect 100s of people together make them wait several hours, and drop them at an inconvenient location.
Sure. I have no objection to electric power trains for aircraft. But at that point, we're not talking about eliminating carbon emissions anymore, so the climate angle in this article ceases to be relevant.
