# Electric Airplanes?

Discussion in 'Hangar Talk' started by Stephen Poole, Jul 19, 2019.

1. ### Stephen PoolePre-takeoff checklist

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I know there are plenty of engineering/techie types here, and I wondered what all y'all thought. I know that some of you will see the latest Gee-Whiz electric aircraft at Oshkosh. That got me thinking.

Most objections to electric aircraft in particular involve the batteries. They're too heavy, they're expensive, they don't have enough range.

But assume that someone works a miracle and develops a battery that can store gobs and gobs of juice, that will be lightweight, and (biggest miracle of all), reasonably-priced. The way I see it, there's still a BIG problem: physics ... as in, you can't cheat 'im. You have to fill the batteries with energy before you can pull watt #1 from it.

Just to have some numbers to play with, ignoring losses and just doing some back-of-napkin math: 100 HP is 75KW. If you want to fly for 5 hours, you will need 375 kilowatt hours (5 x 75) of juice put in the batteries. (That's a bare minimum; ignoring losses and assuming that a boost circuit could play "joule thief" and drag every available drop from the batteries later.)

Tesla has some numbers for their cars that illustrate the problem. Charging at 240 V, the draw (depending on model) ranges from 30 to 40 amperes. Charge time is several hours.

Now: consider the average FBO. If he/she only has to charge one plane every now and then, meh, maybe it's not a big deal. But if there are several planes on the ramp, each needing a 240V, 40A service to charge in any rational amount of time, that's going to require some very expensive electrical work (and probably a major upgrade to the utility service).

Tesla owners could pipe in here, too. Remember, I'm talking about the real world, where more than one person might want to fly this New Miracle Airplane(tm). In the real world, there are going to be lots of people who want to draw that 240V/40A for hours on end to top off their batteries.

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2. ### LndwarriorPre-takeoff checklist

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You make a very good point. Very few facilities have over- sized electrical services and adding a number of high amperage outlets will be a problem.

Pulling in a new service is very costly as well.

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3. ### mwagg737Pre-takeoff checklist

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I think they are a cool toy, but a long way from mainstream. Lots of torque could turn a big prop slowly making it efficient.
Of course, infrastructure is a big deal. on a side note, I just got a quote for a solar installation for my house. my total out-of-pocket expense (with incentives) is around \$4,000 and it saves me \$1900 a year in utilities. In addition, I can charge my electric car for free. That's a pretty good return on investment.
With this kind of incentive and small investment, any FBO would be able to add this to their place. Effectively making charging aircraft free. The airfraft owner would of course be charged, but for the FBO it would be almost an infinite return on investment.
Picture this: pull into the FBO, plug in, grab a courtesy car and go get food, come back in the plane is full.
Who knows, maybe it's not so far off in the future after all.

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4. ### RyanShort1En-Route

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There’s an awful lot of solar farms being built in some parts of the country...

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5. ### Stephen PoolePre-takeoff checklist

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The Sun will give you, on a clear sunny day, at most about 150 watts of power per square meter. (Going from memory; but anyway, it's not nearly as much as some people think.) So, even with 100% conversion of sunlight to electricity, you still need a LOT of square meters of solar cells to come up with enough energy to charge a plane (or car) at 240V, 40A for several hours.

The math is relentless. If you can charge in 10 hours at 240V, 40A and want to cut that to 1 hour, you'll need 240V at 400 amps (or higher voltage -- watts = volts x current, say, 2400V at 40A). (Yes, I'm being fast and loose with joules vs watts, but you get the drift.) If you need to put X energy into your batteries, you can do it quickly with lots of energy, or more modestly with lower voltage and current. It's inescapable.

What I'm saying is, going electric is not a panacea. Right now, we're obtaining the needed horsepower to move an airplane by pumping fossil fuels out of the ground. If we replace that oil/gas with electric power, the energy has to come from somewhere. There's no free lunch.

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6. ### Stephen PoolePre-takeoff checklist

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Good for you, but see above. The math for large-scale applications still doesn't work. (That's the key: large scale. Lots and lots, vs. a single home with modest needs.) To repeat: you can't cheat physics. If you want to make 100 HP for five hours, you need to store enough energy to supply 375 kilowatt hours.

(In the case of your car, I'm guessing that you're probably "topping it off" with the solar stuff. I can't imagine that you're using it to charge the batteries from dead-flat empty to full juice.)

Now multiply that by many electric airplanes and you see the problem. You could cover every available piece of real estate with the most efficient solar panels and/or windmills known to man and you'd still come up way short.

I originally did all of this math for electric cars; the Ford Fusion I was driving at the time required about 22 HP to maintain 60MPH on a level surface. After I ran the Big Numbers for large-scale conversion to electric, I concluded that a lot of it is hype, smoke and mirrors. Most of our electricity is still produced from fossil fuels, so all we've done is to move the emissions from our tailpipes to a power plant somewhere else.

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7. ### Cap'n JackFinal Approach

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The sun gives 1000 watts per meter square. Current solar cells produce 150-200 watts/m2. I was in California a couple of weeks back and thought the sun shades they built over parking lots was interesting. I noticed they not only shaded the cars, but produced electricity, too.

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8. ### Old97Pre-takeoff checklist

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Charging is an inconvenience. Energy density of the batteries is what is killing it now, which is obvious if you put pencil to paper like you have here. It is cool that the electric motor is way lighter, and simpler than a piston engine. You would probably move most of your maintenance costs from the motor to the fuel source.

But i think if they magically get a leap in energy density there will be motorgliders and trainers first. Not quadcopters like all the magazines seems to think.

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9. ### JOhnHTouchdown! Greaser!PoA Supporter

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There are a few very promising things going on in battery research these days. Lithium Oxygen for one. They are still a few years away, but getting closer. I don't think it will be like hydrogen fuel cells; "still 10 years away and always will be".

10. ### Blatham489Pre-takeoff checklist

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Doesn’t all of this make a good case for hybrids? The energy density of gas or diesel and existing infrastructure, reduced noise and increased reliability of the main propulsion motor, regeneration on descent, . . .

Somebody do the napkin math on that.

11. ### saranganLine Up and Wait

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A better way to think about it is, what would it take to fly an electric airplane if it was attached to an outlet with a very long cord. A modern home may have a total capacity of 20kW. You would need the equivalent of three or four homes, all running at their max capacity and powering nothing else, to fly a Cessna 150. Now translate that to a Boeing 777, or an Airbus 340.

People under-appreciate the energy content of a gallon of gasoline.

I am not saying electric power can never be used to fly airplanes. But in its current form, using copper wires and lithium batteries, its more fiction than reality.

12. ### Kenny PhillipsEn-Route

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Not that it would make much difference, but you cannot even build a modern home in most places without 200 amp 220/240 volt service, so more or less 45 kW, enough to underpower a small plane.

13. ### Kenny PhillipsEn-Route

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They have those at the Cincinnati Zoo, as well. I don't know what they power with the juice, which would be negligible in winter.

14. ### kylebFinal ApproachPoA Supporter

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My opinion is that right now, what I'll call "boost hybrids" make the most sense. Enough combustion power for all normal operations, but an electrical boost system for takeoff, go around, and other situations where you need extra HP for a few minutes. For instance, you could put a boosted 140 HP Rotax in a C-172, which would offer good high altitude performance, great cruise efficiency, but would be a slug in the runway environment. Add a 60 HP electric motor and enough battery to power it for 10 minutes for takeoff, initial climb, and maybe a couple of go-arounds, and now you have a higher performance airplane that uses less fuel. Quieter too... That's kind of the Prius model where (among other things) you use the battery power to hide the deficiencies of the engine they chose for it.

15. ### SoonerAviatorFinal ApproachPoA Supporter

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That’s an even worse case for hybrids. Then you’re lugging around a heavy battery, an electric motor, gas, AND an engine. Useful load is already minuscule with electric aircraft, much less adding a hybrid setup. It makes more sense just to use the weight as extra battery capacity instead of storing fuel and an engine.

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16. ### SoonerAviatorFinal ApproachPoA Supporter

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If someone manages to make batteries with much higher energy density (like triple current energy density), then they will probably have a place in aviation. Right now, it’s not useful for anything other than circling the pattern for 30 minutes and landing to recharge for several hours. Not exactly helpful, and too narrow a use case to be marketable. Even in quad copter form like an Uber taxi service, you’d have to have a huge fleet of them to be able to have enough charged up at any one time.

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17. ### tspearPattern AltitudePoA Supporter

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The only answer will be storage systems. Same way gulf courses store water during the day in ponds to use at night for irrigation. The water pipes to the courses just are not big enough to handle the night time demands.

Tim

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18. ### Velocity173Touchdown! Greaser!

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19. ### RyanShort1En-Route

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Of course not, but it IS an option that's already becoming viable for SOME uses. Personally, I could see a rancher that wants to go for a spin being able to top off his batteries and being ready to run the plane most any time and he might also be able to occasionally commute to town with it. I'm already thinking an electric motorglider would be awesome.

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20. ### Stephen PoolePre-takeoff checklist

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Wow, I was WAY off. That's what I get for going on memory. Next time, I'll google it.

Even so, let's do the math: still using 100HP/75KW as the working number, I'd need roughly 75 square meters, or about 800 square feet. At 200 watts per square meter (assuming current efficiencies), you're going to need about 4,000 square feet of solar panel(s).

Remember: I was talking about large scale. Dozens of airplanes and/or cars (or whatever) charging at the same time. You need to multiply the number of square feet needed times the max number of people who want to charge at the same time. I still say it doesn't work out on the large scale.

21. ### Stephen PoolePre-takeoff checklist

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Yeah, that's probably what will end up happening. I look at it the opposite from you: I'd use the energy density of petroleum for takeoff power, then cruise with electric.

The way my crazy mind works, one of the first things that impressed me here is how pilots are in tune with the energy usage in flight. "I cruise at 55%, using X gallons per hour." Think that if you could cruise on electric at that 55% or 70%, you're using less.

Ah, my mind is warped, anyway. Always has been.

Even worse, I truly enjoy it. Not really proud of it, though.

22. ### Stephen PoolePre-takeoff checklist

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But we need mass production to get the economies of scale to bring the prices down. One rancher isn't going to change the world.

Oh, agreed on the electric motorglider, by the way.

Yeah, I know -- GA hasn't had economies of scale for a long, long time.

23. ### Stephen PoolePre-takeoff checklist

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Or lots of spare battery packs that can be swapped in quickly. Pipistrel offers something like that on their Alpha Trainer.

24. ### Old97Pre-takeoff checklist

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Hybrids work for cars because they can generate power from regenerative braking that can be stored in the battery. The more continuous your power needs are (airplane) the less two different power sources make sense. In my feeble opinion.

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25. ### Stephen PoolePre-takeoff checklist

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Mo' napkin math: 900KWH battery bank, to charge in 5 hours (again, at perfect efficiency) would require 180,000 watts per hour. VoltsxAmps, diddle it around, even at 2,000 volts (which is becoming a serious employee hazard), you'll be drawing 90 amperes. For five straight hours.

It's cheaper than gas, but if you start seeing a lot of these, the power companies are going to flip. They'll have to build generating facilities to meet the demand.

26. ### Dan ThomasFinal Approach

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And added a bunch of losses at each stage, too.

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27. ### mwagg737Pre-takeoff checklist

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The car is a Volt, so the battery is 17.4 KW and it is charged from dead usually. A vast majority of the driving is local in nature and the engine rarely runs. The home system is 13.8KWA. It's all about power in vs power out. When my energy usage is low, the panels run the meter backward. Comed gives a credit equal to their charge. Right now, the credit is \$.12/KW. This stores up. When I pull from the grid, it comes out at the same rate. The net effect is a zero sum game.

It takes very little light to produce electricity with modern solar cells... they will produce when the panels are covered with snow (albeit not as much), regardless, the only time they are not producing is at night.

From a pure investment standpoint:

System cost: \$26446
Illinois incentive: \$15323
Federal Tax CREDIT: \$7933
Total OOP: \$3190

My present annual electric bills average: \$1986

Total return on investment: 62%/yr Call it 50% return to account for errors and variances. Not a bad return by anybodies metric.

Now... electric airplanes??? It's always impossible until someone does it.

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28. ### Dan ThomasFinal Approach

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The engine and generator PLUS the batteries and electric motor just add up to make a heavy, heavy airplane. Every ounce matters. And it adds cost, as if airplanes weren't out of reach now.

The airplanes converts its altitude to distance in the descent. regeneration would require a much steeper descent, and the propeller, being designed to drive air, does not efficiently let air drive it. Its camber is all backwards for that. It's not symmetrical like a helicopter rotor.

Last edited: Jul 20, 2019
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29. ### Old97Pre-takeoff checklist

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Yes
Its been possible for 100+ years. Its only now approaching practical.

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30. ### Dan ThomasFinal Approach

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The Illinois Incentive and Federal tax credit both come out of the taxpayer's pockets, right? How long do you think that will last once half the people start installing these things and applying for those rebates?

We have to look at REAL costs here, not costs that are simply dumped on other people that can't afford this stuff.

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31. ### 3393RPEn-Route

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Dan, didn't you know those rebates are free money?

There are many twists made to bake the pretzel that justifies electric airplanes. Everything will work out someday in the Panglossian world of believers.

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32. ### mwagg737Pre-takeoff checklist

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The Illinois invective is part of everyone's electric bill.
Yes, it will go away eventually, but the cost will come down as well.
With no incentives, it works to 7.5% yearly ROI. Not awesome, but compared to most long-term investments, not bad. Compare to the BEST bank CD "safe investment" you can find.
Regardless, this is what's available now. Take advantage or don't... There will always be those jump on a deal and there will always be those that don't. As an investor, i look for investments where i can find them. Sometimes they show up in the most unique of places.

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33. ### RyanShort1En-Route

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[QUOTE="Dan Thomas, post: 2761914, member: ]We have to look at REAL costs here, not costs that are simply dumped on other people that can't afford this stuff.[/QUOTE]
Don’t forget that there are “real” costs and tax incentives in the oil business, too. I have problems with both, but you’re kind of ignorant if you don’t see real problems with the oil and gas industry, too. The long term effects are going to be felt in the future.

Last edited: Jul 20, 2019
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34. ### Cap'n JackFinal Approach

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You'd be surprised, I think. Certainly less power than in summer, but far from negligible.

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35. ### Dan ThomasFinal Approach

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Yup, there are tax breaks for some energy companies, but we can't simply replace subsidized fossil fuels with more-heavily subsidized electricity and figure we have progressed. The economy is unforgiving that way.

We need sensible electricity, and sensible ways to store it. Solar is fine where there are no baseball-sized hailstones like we had a few days ago not far from here. Wind is fine where there's lots of consistent wind and we don't have to cut down massive areas of forest and bulldoze endless roads for access and powerlines like my home province of BC would have to do. It takes nearly 1800 windmills to replace a major hydro dam, and 1800 mills take a LOT of room, and a lot of wind, which might be ideal 10% of the time, while water runs year-round through those dams. And BC will need 15 more dams (on top of the 28 they have now) to meet the needs of electric cars if every BCer buys ONE electric car. Getting one new dam built now would involve many years of litigation and compromises and concessions with numerous groups, making it financially and politically impossible. The greenies simply don't know where energy comes from, and don't want to know, and some other groups just want to milk the process for all it's worth.

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36. ### ZeldmanTouchdown! Greaser!

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I can see it now.

I am flying up in the cool, crisp air just enjoying life in my electric plane, then on the ground some fool pulls the plug to plug in their phone charger....

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37. ### Old97Pre-takeoff checklist

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Nuclear, baby. It’s time for a comeback.

38. ### CharlieD3Line Up and Wait

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Dilithium crystals.

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39. ### Dan ThomasFinal Approach

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40. ### mwagg737Pre-takeoff checklist

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Dang.... Looks like a warranty claim to me.

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