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Can this be done military style refueling but with an electric wire boom supplying current from tanker aircraft to electric aircraft mid air in flight? Electricity from the tanker craft can be generated from its engines and/or an on board diesel generator. And utilising fast charging technology for quicker refuel times to recharge the electric aircraft's batteries.

Is a technology demonstrator already available? Or is Google not showing me any results?

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    $\begingroup$ Not exactly the same thing, but perhaps pertinent. Some work is being done charging drones with ground-based stations: newatlas.com/in-air-drone-charging-unlimited-range/56363 $\endgroup$ – Fred Larson Jan 28 '20 at 17:43
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    $\begingroup$ Yes, drones or other light aircraft can be used as research for a start, but the whole idea is to do mid air refuelling to increase the electric aircraft's range $\endgroup$ – Nederealm Jan 28 '20 at 17:47
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    $\begingroup$ Considering that a Tesla Supercharger takes over an hour to fully charge a car's batteries. it would seem fairly pointless, since you'd have to have the refueling aircraft connected to the electric one for more time than it's not connected. $\endgroup$ – jamesqf Jan 28 '20 at 17:48
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    $\begingroup$ Charging an electric aircraft with a diesel generator - sorry, a flying diesel generator - sounds like an awesome environmental breakthrough! Just the kind the geniuses on Top Gear come up with all the time. Greta would approve. $\endgroup$ – Therac Jan 28 '20 at 19:29
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    $\begingroup$ How about using an extension cord? $\endgroup$ – Koyovis Jan 28 '20 at 19:37
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An automotive analogy is found in Formula E racing. It never considered "refueling" through a power cable, instead opting for swapping entire cars mid-race. Its parent company is now trying battery-swap stations for consumers, if not yet for the race cars.

So, replacing an airplane's depleted batteries with fully charged ones from the "tanker" might work. Although I shudder at how to engineer an airborne two-way conveyor belt, aerospace history is full of even more audacious challenges that have been overcome.

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  • $\begingroup$ I hope battery swap in mid air were developed. It would provide noce pictures $\endgroup$ – Manu H Jan 30 '20 at 7:17
  • $\begingroup$ I don't mind losing the accepted answer here, but how on earth is this one better @Nederealm Sorry CamilleGoudeseune , nothing personal against you ;) $\endgroup$ – Jpe61 Jan 31 '20 at 18:51
  • $\begingroup$ Please note the pun is intended in the comment above :) $\endgroup$ – Jpe61 Jan 31 '20 at 19:10
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    $\begingroup$ If munitions can be dropped from aircraft, then shouldn't be to much of a problem. The aircraft have to be in position belly facing top. The charged battery pack will be dropped into the electric aircraft. The empty battery bank can be returned to the tanker aircraft via some sort of propulsion system firing the cartridge upwards into the tanker craft. A switchgear should be able to disconnect the low battery and reconnect connect the new pack almost instantly $\endgroup$ – Nederealm Feb 4 '20 at 5:29
  • $\begingroup$ Dropping is easy, but catching is hard. Once that's figured out, then after refueling, the tanker moves below the other airplane, which drops the empty battery into the tanker! (You just need room, temporarily, for both batteries.) $\endgroup$ – Camille Goudeseune Feb 4 '20 at 17:58
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This would certainly be possible, but the current status (pun intended) of the battery technology makes it pretty much pointless.

The charging would simply take too long: for example, Eviation Alice has a battery capacity of 900kWh. If we were to charge, say, 75% of this (because you would need to have some reserve capacity in case charging does not work out) it would take about 10 hours to charge if the charge time was comparable to Tesla Superchager (85kWh battery charges in about 75minutes =1.13 kwh/minute). Even if the battery was charged in ten parallel segments, charging would still take an hour.

Alice has an endurance of about two hours, so to double that, you'd have to spend at least an hour, most probably more charging.

Then, there's of course the sillyness of charging an electric aircraft with electricity made from jet fuel (or diesel)... it would be far more efficient to use that fuel to propel the aircraft without the engine-alternator-charger-battery-motor -detour.

For further reading, please see this Aviation Stack Exchange question regarding aerial refueling, many of the points raised in the answers also apply to aerial recharge.

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    $\begingroup$ Charging any battery takes about one hour. Larger batteries have more cells but they all charge simultaneously so it doesn't matter. $\endgroup$ – Rainer P. Jan 29 '20 at 18:52
  • $\begingroup$ Well not any battery, but I have to say your point might very well be correct for most battery systems that would be feasible in aviation @RainerP. $\endgroup$ – Jpe61 Jan 29 '20 at 19:10
  • $\begingroup$ If 70% charged is enough, then some batteries can reach that in ten minutes. batteryuniversity.com/learn/article/ultra_fast_chargers $\endgroup$ – Camille Goudeseune Jan 31 '20 at 21:27
  • $\begingroup$ @CamilleGoudeseune a very good article, which also discusses alot about the limitations of ultra fast charging. As such, I do not see it matchin the ultra high safety standards of aviation :) $\endgroup$ – Jpe61 Jan 31 '20 at 21:36
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Tesla now has batteries to the point where you can recoup energy for a 4-hour drive in 30 minutes. That's in full-on production, you can buy it and do it at retail today. The biggest challenge Tesla has is keeping the batteries cool during this slam charging; and in an airplane we have a huge surface area being blown by a slipstream. Have the battery pack be a thin layer bonded to the underside of the wing, and you got that licked!

So I think we can safely say woth emerging tech, you could recoup energy for 40 minutes of flying in 5 minutes of tanking.

The problem is, this defeats the entire purpose.

You are spending between 4 and 10 times the fossil fuel to get the tanker airborne, on station and generating the recharge power, than if you just ran the e-plane on a gas engine in the first place. And wasting a whole second crew, and having to build the second airplane with positively ginormous auxiliary generators... The whole thing beomes an exercise in futility.

Use fuel for that mission. Offset fuel burn elsewhere.

So you want an e-plane? OK, build a gas plane and buy the Postal Service ten electric jeeps. Not only will it work better, with proven COTS tech, it'll be cheaper to boot.

The realistic picture for green aviation is to beat the Cessna 182 into feeder wires for high speed rail. Let the electric truck deliver the epoxy, rolls of carbon fiber cloth, electric motors and battery modules. Then, build something totally new, with new design factors from prop(s) to rudder.

Honestly, given the numbers Tesla is proving in production, I am optimistic about electrifying all sorts of things previously thought to be un-electrify-able. I see 1200 mile flights with an electric plane to be perfectly feasible: fly for 4 hours, land, supercharge while you get breakfast, fly for 4 more hours, lunch, 4 more hours and home.

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This question shows the fallacy of electric propulsion in its current state. The electricity needs to be generated using non-environmentally friendly means. Even solar power is unfriendly due to the process for making the current panels. Hydro and geothermal power would not work in this scenario. Even the production and disposal of the batteries have environmental consequences. All we are doing is shifting the environmental impact. At best, we are benefiting our immediate environment at the expense/ detriment of someone else’s in another place or time.

A better question is how do we use renewable energy to power a plane already in flight without the use of fossil fuels to create, transmit, or transport that power. Maybe with better, more environmentally friendly, and more efficient batteries, motors and solar panels, we could make the plane entirely self-sustaining.

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