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Why battery-powered aircraft will never have significant range

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autoreply

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We've seen more and more discussion on HBA about battery-powered aircraft and hybrids. I've been arguing that it's fundamentally impossible to get range up enough for a practical airframe to be solely powered by batteries, necessitating hybrid aircraft powered by chemical means (piston generator, fuel cell).

This video neatly sums up the fundamental limits:

Current aircraft-rated battery systems do about 100 Wh/kg. That is the whole system weight, so BMS, insulation, packing structure etc.

Let's talk numbers. 100 Wh/kg is 360 kJ/kg. Specific height is the amount of altitude you can gain by using all the energy to climb. This is about 36 kilometers for such a battery. If we factor in drag, propulsive efficiency and prop efficiency, we see that existing planes (Antares 20, FES) obtain about half that rate.

Of course, a plane can't have 100% of it's take-off mass in batteries. If we look at the best possible today, say the Binder EB29 and we assume 50% of it's take-off mass is batteries, it can climb to about 9 km of altitude, for an equivalent mission range of 450 km (assuming a climb to 2 km altitude).

100 ft of span and 50% batteries might not be terribly practical. If we assume an SR22-like airframe with 30% battery mass and cruising at 80 kts or so, range gets down to 41 km, or about the length of a marathon.

Even with the currently non-existing Li-O batteries, that SR22-like airframe would only have a range of 235 km, or about 145 miles. While the Binder EB29 with half it's TOW in batteries would do a mighty 2200 km (1380 miles), that would be a flight of over 24 hours, cruising at a comfy 50 mph if there is no wind.

Bottomline; for range hybrids will be the future :)
 
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tspear

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Years ago Chevron renamed itself the Energy Company. They tried to distance themselves from being oil only. As part of this effort, they bought a couple of solar companies, a battery company...
I have no idea of the success or if it persisted.
But the basic concept is the same to me, stop thinking about batteries per se, or gas engines... They all are part of an energy storage system.
So it does not matter if it is LI, or gas, or Jet-A. What matters is I can get more, makes the plane useful, and is not made from unobtanium.

Tim
 

Topaz

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It's a bold man that says, "Never...", especially when most such predictions are eventually proven to be wrong.

We're nowhere near a "practical" cruising all-battery airplane, for all the reasons Autoreply lists, and it's likely to be a very long time before energy-storage technology advances to the point where we can. But "never" say "never".
 

blane.c

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(1) Gliders are not necessarily practical, they are fun machines or for me the idea of them is fun. It is conceivably practical to have a self launch electric motor with battery power glider that can extend it's range with solar power, I think I've seen a video recently, it is fun. The elemental principal behind ultralights is a lightweight motor glider, that is their roots, and they are arguably solely for fun.
(2) We need to show some responsibility, at least try to use a non carbon foot print machine especially for activity's related to fun. If we try who knows what may become of our efforts, but to shrug it off as impossible ... why even get up in the morning then?

http://www.solar-flight.com/projects/sunseeker-duo/
 
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lathropdad

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One advantage I can see for liquid fueled airplanes is that as you expend the energy you during a flight, you reduce the weight of the aircraft. With batteries, your take off weight and landing weight will be very similar. Now with solar plus batteries you may be able to help this power to weight equation over the length of a flight.

I am familiar with a fuel efficiency contest for automobiles that ended with a liquid fuel powered car winning by an embarrassing margin. The designer of that car said that weight was the down fall of all the electric powered cars. Batteries have weight that is always present throughout a journey.
 

proppastie

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(1) Gliders are not necessarily practical, they are fun machines or for me the idea of them is fun. It is conceivably practical to have a self launch electric motor with battery power glider that can extend it's range with solar power, I think I've seen a video recently, it is fun. The elemental principal behind ultralights is a lightweight motor glider, that is their roots, and they are arguably solely for fun.
(2) We need to show some responsibility, at least try to use a non carbon foot print machine especially for activity's related to fun. If we try who knows what may become of our efforts, but to shrug it off as impossible ... why even get up in the morning then?

http://www.solar-flight.com/projects/sunseeker-duo/
Personally I think as a power launch glider, the electric/solar, is potentially here now and very practical. It should be much more reliable than any small gas engine, and landing out would be history if there was any lift and not much juice was used. Someone might just make some money in aviation with an off the shelf system (or plans for same) at a reasonable price, (equal to a gas engine price). With all the electric bicycles and motorcycles coming out it might be just around the corner.
 

pictsidhe

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I just added a solar powered calculation to my spreadsheet. it's quite feasible.
A quick look on ebay turned up some 125mm mono cells putting out 3.4W. They are 165um thick; about 2 sheets of paper. Silicon that thin will bend a bit, such as over the top surface of a wing... I came up with a weight of 6grams each. 1hp of cells is going to weigh 1.3kg. The current best commercial flexible frontsheet is 3M ultrabarrier, 204um thick. That'll be a bit lighter than the cells, say 1kg for 1hp Then we need to encapsulate the cells in EVA and add a backsheet. Lets say, with some encapsulating experiments and relying on a carbon substrate for strength (wing skin), 1hp of cells weighs 5kg. How much power does a modest glider need to stay up? How much ballast is it carrying? Batteries are not be there yet, but solar is on!
My 103 design currently has 15m2 of wing area. With 80% cell coverage, that'd be a free 3.6hp, for about 20kg extra weight. More span, Igor!
 

tspear

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I am familiar with a fuel efficiency contest for automobiles that ended with a liquid fuel powered car winning by an embarrassing margin. The designer of that car said that weight was the down fall of all the electric powered cars. Batteries have weight that is always present throughout a journey.
Every one of those tests I have seen is funny, but is also crap. Having a Prius go to a race track and try and outrun a BMW? (Most common Top Gear episode to demonstrate this).
Or the other side, have a Civic Hybrid sit in NYC traffic compared to a Porsche?

If you want to compare, compare two vehicles which are designed for the same mission.

Tim
 

lathropdad

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Every one of those tests I have seen is funny, but is also crap. Having a Prius go to a race track and try and outrun a BMW? (Most common Top Gear episode to demonstrate this).
Or the other side, have a Civic Hybrid sit in NYC traffic compared to a Porsche?

If you want to compare, compare two vehicles which are designed for the same mission.

Tim
The test I was referring to was not what you describe. In that test the rules were written and contestants built vehicles for the competition. There was a very substantial prize for the winner.

Your criticism is way off base. Sorry that I was not more specific about the test I was referring to.
 

pictsidhe

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Hybrid is the current best efficiency for cars. The early hypermiling vehicles would use vehicle inertia to store energy, they accelerate at peak engine efficiency, then shut the engine off and coast down. Now, you can just go buy a hybrid battery car tat cycles the engine without varying forward speed. Aircraft don't need a huge surfeit of power like cars do, so hybrid is a lot less benefit. In fact, aircraft engines maximise efficiency at around cruise power. Yes, extra takeoff power is useful, but making the added complexity of hybrid worthwhile is a lot harder. Has anyone else considered JATOs?
 

DonEstenan

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... Aircraft don't need a huge surfeit of power like cars do, so hybrid is a lot less benefit. In fact, aircraft engines maximise efficiency at around cruise power. Yes, extra takeoff power is useful, but making the added complexity of hybrid worthwhile is a lot harder.
Uhmmm, that is true for 'standard' aircraft, designed around standard engines, operated in a standard way.

Not so much the case for motorgliders which might want decent power for takeoff and climb, but can cruise on a very small fraction of that power.

Hybrid has other potential advantages:
- much better reliability/safety (electric motors/controllers much simpler than IC engines/fuel systems, greatly reducing risk of engine failure in critical phases of flight)
- possibility of novel/more efficient configurations (e.g. distributed electric propulsion)
- reduced cost of (short) flights (if just going for short flight, it might be mostly covered by batteries...)

One would hope that the mechanical simplicity of electric motors would also put a downward pressure on engine/motor prices ... if the volume climbs ... one can hope
 

choppergirl

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Not so much the case for motorgliders which might want decent power for takeoff and climb, but can cruise on a very small fraction of that power.
(Solid) Rocket assisted motor glider take off; battery sustained flight...

Never say never. If mankind can invent god, mankind can invent anything....

I do at least 150 things every day that 200 years ago, were absolutely impossible and absurd to even conjecture.

I do at least 6 impossible things before breakfast...
 

Arthur Brown

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Two considerations;
1/ "never" is a very long time and things may change. I remember lead batteries being wet and very spillable but now they are sealed and about 10x the capacity for mass. I remember torch batteries that eat through the zinc container and rotted the contacts -now it's alkaline batteries with more power and almost leak proof.

2/ Probably half the privately owned aircraft do a maximum of an hour of flight time per week which is probably rechargeable from solar power in the other six days of the week. Solar and Batteries and motors may well improve in performance meaning that a moderate solar panel would provide 2+ hours of flight during one week in the summer -when flying is usually nicer.

The only significant time when flight energy could be returned to the battery would be a prolonged descent, but while airliners have to "spoil" lift and speed to descend to land most GA aircraft do not cruise at a suitable height to have a worthwhile amount of recoverable energy. ALSO a blade to extract power from wind is very different from a blade to turn power into thrust so I'd doubt the value of a less than optimum for flight prop just for very little recoverable power in the descent phase of flight.
 

Jambo

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An interesting link, for quick calcs

http://web.mit.edu/lochie/www/erange/main.html

This youtube video has the electric range formula at 51:10 for pencil pushers
https://www.youtube.com/watch?v=-yo820YZWqU&list=PL98EozRZbPbECY5dnWyZVrM4aj4qf7-Pz&index=32

My general conclusion is that, for 'GA' distances about 400 miles(w/o reserves) you need about 400 Wh/kg. Tesla batt, without all the support equipment, are running around 250ish

In short, batteries need to come a rather long way, similar to the leap from lead acid to lithium. It's hardly impossible, indeed likely inevitable, but hard enough that predicting the future availability of such batteries is rather elusive.

Also, as I'm sure many of you have found out, the 'cost' of adding range to a ICE aircraft is rather low, so it comes down more often to how long you want to sit. With any electric aircraft, determining the 'range' of your mission is going to become far far more critical.
 

ScaleBirdsScott

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Well physics can only allow so much. So there will be some limits to practical power availability on simple chemicals as the video points out, just by looking at the periodic table. But, maybe there's unseen advancements in deriving energy from nuclear forces or other means than a traditional chem battery. That'll be the interesting bit. Will there be means of energy transmission? Get your energy wirelessly from a satellite or ground based network? Who knows what workarounds exist. But traditional batts as we consider them, only so much juice to squeeze in theory.
 

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