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Comment by gambiting | Hacker News Reader

Yep - and as you use up fuel, your plane gets lighter, saving more fuel the longer you fly. With batteries, you have to carry the same weight for the duration of the flight. Which actually is a huge problem, because on most airplanes maximum take-off weight is higher than maximum landing weight.

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I have the stupidest idea. As energyless state fuel is released in the air, just drop 'depleted' battery modules and have them collected.

still the energy/weight ratio is > 60 times worse than gasoline. If you're not going to recharge them, then there's no remaining advantage to batteries

Collect, centralize, recharge, reuse. Maybe have a solarimpulse battery carrier to distribute them while flying.

Mechanical simplicity. If your going to use fly by wire it's nice to have stored power to land without losing control in the event of total loss of fuel or massive mechanical failure. Though this is something like 1/10,000th of total energy used in flight it's really important.

Better yet, design the battery so that air forms one side of the chemical reaction, with waste products that can be dumped overboard. Oh, wait!

(I'm making a dumb reference to ICE engines here, but actual batteries where air participates in the reaction are a promising area of research that could greatly improve battery energy density.)

> batteries where air participates in the reaction

Wouldn't that just be a fuel cell?

Or a combustion engine, yes. That's the joke.

Yes, lithium-air batteries have some promise. They approach gasoline energy/weight by better than half as good. So that's a possibility.

Another stupid idea: use aircraft catapults[1] to reduce the onboard energy requirements. Takeoff seems to be the most energy demanding stage of the flight.

Obviously a drawback is that existing airfields' or airports' runways would have to be retrofitted, but if the fuel and maintenance savings were enough, it might make sense.

[1] used on aircraft carriers: https://en.wikipedia.org/wiki/Aircraft_catapult

A cable winch like they use with sailplanes would work really well for this.

You just need to carry energy into the airplane, with coils for example. No need for a catapult.

The catapult is a proven technology for aircraft though, with decades of development.

Or with a reusable launcher. Somebody get Elon on the line.

Huh...that's actually a great idea. I never thought about it for commercial liners.

I'm sure Boeing or Airbus could create prototype liners and only have a few airports with catapults built into the airstrips. You could save a considerable amount of energy if it's designed correctly. Plus airplane tires have to be replaced very frequently. It could reduce takeoff wear as well.

There's research going on about that [1], in fact going a step farther by removing the entire undercarriage of the plane. It's safer too -- partially extended landing gear is more dangerous than belly landing because struts and hydraulic systems are a lot more fragile than solid ribs of metal.

[1] https://en.wikipedia.org/wiki/Ground_carriage

Air to air refueling where the refueling is fast charging lithium batteries and the tanker is formation of drones not KC-135 full of jet fuel.

Probably not the craziest idea ever.

While the "refueling drones" are circling overhead waiting to charge up a transport jet, may as well use them as five mile high wifi access points for internet, and divebomb amazon deliveries. I mean they're up there, may as well make use of them when they aren't charging jets.

Think of the FAA madness WRT flight plans and mandatory minimum "fuel" and alternatives/diverts. The paperwork alone for aerial refueling on plain old passenger service is likely to get weird.

Meanwhile if solar panels get cheap and durable enough, or safe enough in a crash to plow thru, charge the drones off panels laying around the airfield.

In theory you could have 100% solar powered high speed aircraft transportation using this weird system.

Note that you can cross the ocean if you have a dense enough fleet of charger drones. By dense "enough" I have no idea what to say here.

You need enough battery power to get "up there" and to cruise between drone hookups (which might only be a couple seconds if the drone comes along with you, or if you have dual charging ports I guess that means zero...)

Note that every airframe full of people requiring 2 or 3 smaller airframes full of batteries will be an interesting capital cost to work around.

Here's a riff on that idea.. Have midair recharging drones fly up to meet the plane along its route. Just like the military uses to extend range, except small and automated.

Unless you use a hybrid approach, like a super efficient turbine generator + solar cells, so your battery doesn't need to be nearly as big.

I am not seeing how a jet turbofan is going to be less efficient than a turbine engine driving a generator driving an electric motor driving a propeller or fan.

I don't think there's enough surface area on an airplane to gather significant solar power. And that doesn't help at night or in clouds.

Jet turbofans have an efficiency curve related to the velocity of the aircraft. They are least efficient when the aircraft is stationary, and most efficient when the aircraft is moving at the same velocity as the exhaust.

A jet turbine generator can run at near-constant efficiency.

Or using diesel electric hybrids. That's how train engines work. They're still way more efficient that using combustibles directly because you can run at lower RPMs and buffer the energy (trains run at like 1k ~ 2k RPM).

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