Is a Battery-Powered Plane the Future of Air Travel?

[mgb_phys]

They call it the first Battery-Powered Plane (but thst's only because they don't know any better)

http://blog.wired.com/cars/2008/08/the-company-cla.html

70Mph, 2hour endurance and a 2hour 60cent recharge!
It's also silent, low vibration and of course pollution free.

Amazing - I want one (except I can't fly and have nowhere to put it!)

 

[Redbelly98]

Neat. I wonder how easy it is to change batteries? You have a 2nd battery on the recharger while you fly around. 2 hours later you land, exchange batteries, and off you go again!

 

[FredGarvin]

I guess it was just a matter of time. It makes sense. The reliability goes way up. I would also redundancy would be much easier to design in. Very neat.

 

[dlgoff]

How about the Trike?
http://electraflyer.com/"

 

[mgb_phys]

I guess it was just a matter of time.

Surprised the power/weight for batteries is good enough - it looks like the lightweight low speed prop is the real breakthrough.

I wonder if you could put a few m² of solar panels on the wings and give the range a boost.

 

[russ_watters]

That calculation is relatively easy: A good solar panel can generate 140 w/m^2 at noon. The batteries on that plane hold 5.6 kWh and can power the plane for up to 2 hours (2.8 kW). If the wing area is 10 m^2 (it is probably less), in 2 hours, it would generate enough energy to keep the plane flying another hour.

This, of course, assumes the sun is high in the sky and doesn't take into account the weight of the panels or electronics, which would be substantial...

 

[mgb_phys]

I thought (it's too early here for calculations) it was impractical because the solarplanes are ultra-light NASA carbon fibre things. So I was surprised that the battery on this worked.

Although - this is likely to be mainly used in areas with nice weather (SW USA). It might be worth having a m^2 of solar panels just to re-charge on the ground, so it's charged for the next days flying.

 

[charith]

Hey,

Out of interest, how much does a small aircraft such as this normally cost?
And how much runway do these need to take off and land?

Thanks,
Charith

 

[Topher925]

Out of interest, how much does a small aircraft such as this normally cost?

This the right question to ask. Electrical power trains can achieve much higher power to weight ratios than any internal combustion engine can. Designing an electric airplane that will perform is easy. Doing so at a practical cost isn't.

I would guess that this plane is going to be a lot more expensive than its gasoline powered counterpart.

As for take distance, I'd guess around 100-200 yards. Can't really tell just by looking at it.

 

[charith]

Hmm, how much would a gasoline aircraft cost?

Also, they might be able to fix the cost of the lithium battery packs by using something such as this: http://en.wikipedia.org/wiki/EEStor

Its claimed to have a higher energy density and lasts much longer than the lithium packs used on this aircraft.

Do you guys believe this technology is actually real and viable anytime soon?

 

[mgb_phys]

Cost is apparently $16-21k. I don't know how much an equivalent piston engined aircraft costs but in terms of SUVs that seems like a bargain!
The recharge may only be 60c, but the battery pack is $6K and has a 1000 cycle life so $6/flight in depreceation.
I suppose by the time you have worn out one pack some better technology might be available.

 

[berkeman]

Although - this is likely to be mainly used in areas with nice weather (SW USA). It might be worth having a m^2 of solar panels just to re-charge on the ground, so it's charged for the next days flying.

You mean the next night's flying. Sorry, I couldn't resist

 

[russ_watters]

Electrical power trains can achieve much higher power to weight ratios than any internal combustion engine can. Designing an electric airplane that will perform is easy. Doing so at a practical cost isn't.

While that is true, it is incomplete. The energy density of the "fuel" is also pretty important and the energy density of batteries is almost two orders of magnitude below that of conventional fuel. And, range is a component of "performance". As such, making such an aircraft practical is not really a matter of cost, it is a matter of performance. Electric planes (with batteries) can come nowhere close to the performance of conventionall powered planes.

 

[russ_watters]

Do you guys believe this technology is actually real and viable anytime soon?

There isn't really any new technology here. It is most certainly real. But as I pointed out in my previous post, there is a serious and probably impenetrable performance barrier to viability. Battery powered electric planes will amost certainly never be anything more than a novelty.

Hydrogen fuel cell powered planes, however, stand a fighting chance of viability.

 

[mgb_phys]

TBattery powered electric planes will amost certainly never be anything more than a novelty.

I suppose general aviation flying is itself a bit of a novelty. I'm very impressed that they made this work with a relatively conventional aircraft given the disadvantages of batteries.

Without a pilot your could triple the range ( the battery pack weighs about 80lbs) so the same airframe could be a 6-8 hour endurance RPV for 1/100 the cost of a predator.

 

[Topher925]

While that is true, it is incomplete.

Indeed. Battery technology does allow greater power to weight ratios but not necessarily greater energy to weight. In some applications it does and in other it doesn't.

I'm very impressed that they made this work with a relatively conventional aircraft given the disadvantages of batteries.

This is not the first time someone has done this although the article says it is. People have been building electric planes for years now, especially ultralights.

http://www.airventure.org/2007/4wed25/sonex.html
http://www.treehugger.com/files/2008/01/first_conventio.php

 

[russ_watters]

I suppose general aviation flying is itself a bit of a novelty.

Very true. When you're building something as a hobby, often you do it just to prove you can, not to meet a performance spec.

Without a pilot your could triple the range ( the battery pack weighs about 80lbs) so the same airframe could be a 6-8 hour endurance RPV for 1/100 the cost of a predator.

It would have very little in common with the Predator, so that doesn't really mean a whole lot. Also, a pilot isn't all that heavy of a flight control system. Taking him, his seat, and his instrument panel out doesn't mean saving 200 lb when you have to put back in a lot of electronics and controls to turn the plane into a UAV.

 

[mgb_phys]

It would have very little in common with the Predator, so that doesn't really mean a whole lot.

There are a lot of less demanding UAV roles; LIDAR, power line surveys, forest fire wathc, animal research that would be nice to do with something that cost as much as a bit of lab kit instead of as much as a building!

I don't know if the FAA/CAA rules for UAVs are relaxed if you are in the middle of nowhere.

 

[charith]

There isn't really any new technology here. It is most certainly real. But as I pointed out in my previous post, there is a serious and probably impenetrable performance barrier to viability. Battery powered electric planes will amost certainly never be anything more than a novelty.

Hydrogen fuel cell powered planes, however, stand a fighting chance of viability.

Oh, the technology I was referring to was the EEStore batteries, they claim to have an energy density 3 to 5 times greater than the Li-Ion batteries and offer almost unlimited charges before the battery pack dies off.

To be this seems like a dream battery for this sort of purpose and for transport.

I am referring to http://en.wikipedia.org/wiki/EEStor or just google up EEStor.

Does this technology seem possible to you guys?

 

[russ_watters]

There are a lot of less demanding UAV roles...

Well, fair enough, and the military has dozens of other UAVs:
http://www.globalsecurity.org/intell/systems/uav.htm

I would think it might be worth considering a solar powered one for the high altitude-long endurance type.

 

[russ_watters]

Oh, the technology I was referring to was the EEStore batteries, they claim to have an energy density 3 to 5 times greater than the Li-Ion batteries and offer almost unlimited charges before the battery pack dies off.

To be this seems like a dream battery for this sort of purpose and for transport.

I am referring to http://en.wikipedia.org/wiki/EEStor or just google up EEStor.

Does this technology seem possible to you guys?

They claim a 2 order of magnitude improvement in energy density over other supercapacitors. That's tough to swallow, but they apparently did get Lockheed to take notice. So there might be something to it. We'll probably know more in a few months (according to the Wiki, that partnership started very recently).

 

[Redbelly98]

Oh, the technology I was referring to was the EEStore batteries ...

Thanks for the info & link. If everything in the Wiki article is true (or, ahem, "reasonably true") these things should easily be able to replace lead acid batteries as soon as they are available. The 0.1 %/month self-discharge rate is impressive.

 

[FredGarvin]

There are a lot of less demanding UAV roles; LIDAR, power line surveys, forest fire wathc, animal research that would be nice to do with something that cost as much as a bit of lab kit instead of as much as a building!

I don't know if the FAA/CAA rules for UAVs are relaxed if you are in the middle of nowhere.

I just read an article in Sound and Vibration about engineers anylizing bridge deflections using RC helicopters as a remote power source and data bucket. I can see general business applications along those lines as well. Electric would be very sexy for something like that.

http://www.sandv.com/downloads/0804masc.pdf

 

[mheslep]

Also, a pilot isn't all that heavy of a flight control system. Taking him, his seat, and his instrument panel out doesn't mean saving 200 lb when you have to put back in a lot of electronics and controls to turn the plane into a UAV.

That's a little light on pilot overhead. Also add : canopy and extra fuselage, additional airframe drag for same, heating/cooling/atmosphere environmental gear and APU for same, voice radio electronics, etc.

 

[mheslep]

Oh, the technology I was referring to was the EEStore batteries, they claim to have an energy density 3 to 5 times greater than the Li-Ion batteries and offer almost unlimited charges before the battery pack dies off.

To be this seems like a dream battery for this sort of purpose and for transport.

I am referring to http://en.wikipedia.org/wiki/EEStor or just google up EEStor.

Does this technology seem possible to you guys?

That 1 MJ/kg claim is 30-40x over any existing ultracap. EEStor was talking the talk 1-2 years ago. We'll see.
http://en.wikipedia.org/wiki/Image:Supercapacitors_chart.svg

 

[russ_watters]

That's a little light on pilot overhead.

I don't think so...

Also add : canopy and extra fuselage, additional airframe drag for same,

True, but minimal. I'm thinking 10 or 20 lb. Part of that is because, the plane needs a certain weight distribution which means a long fuselage. The engine isn't where it is just to make room for the pilot - it needs to be that far forward to bring the COG forward of the center of lift.

heating/cooling/atmosphere environmental gear and APU for same,

Not on that plane. It's a motor glider: it doesn't go high enough to need or have enough weight carring capacity to lift such things.

voice radio electronics, etc.

Minimal on a plane like that. 10 lb. Max. We're talking a small VHF radio (maybe handheld) and a handheld GPS. Not much more than that.

Remember, that's just a motor glider we're talking about. Before conversion to electric, it had an empty weight of 260 lb and a gross takeoff weight of 500 lb. Don't know yet what the specs and performance of the electric version is.

 

[mheslep]

I don't think so... True, but minimal. I'm thinking 10 or 20 lb. Part of that is because, the plane needs a certain weight distribution which means a long fuselage. The engine isn't where it is just to make room for the pilot - it needs to be that far forward to bring the COG forward of the center of lift. Not on that plane. It's a motor glider: it doesn't go high enough to need or have enough weight carring capacity to lift such things. Minimal on a plane like that. 10 lb. Max. We're talking a small VHF radio (maybe handheld) and a handheld GPS. Not much more than that.

Remember, that's just a motor glider we're talking about. Before conversion to electric, it had an empty weight of 260 lb and a gross takeoff weight of 500 lb. Don't know yet what the specs and performance of the electric version is.

ok, I was thinking manned vs unmanned predator sized aircraft which is off topic.

 

[mheslep]

They call it the first Battery-Powered Plane (but thst's only because they don't know any better)

http://blog.wired.com/cars/2008/08/the-company-cla.html

70Mph, 2hour endurance and a 2hour 60cent recharge!...

1 hour charge if you have a high power electrical facility. Alternatively, it should be possible to swap out batteries in minutes.

 

[mheslep]

After watching the video I caught something I've never heard of before in aviation: on descent, under control of the pilot, the prop/motor can act as a generator recharging the batteries, in effect recapturing a chunk of the energy required for the ascent to cruise altitude. The Li-Poly batteries in this thing are about 160Wh/kg. I wonder what amount of energy density improvement is needed to make commercial prop aircraft viable?

 

[russ_watters]

That doesn't seem very useful to me: efficiency-wise, you could do better by starting your decent sooner and making it shallower.

 

[mheslep]

That doesn't seem very useful to me: efficiency-wise, you could do better by starting your decent sooner and making it shallower.

I don't follow. On descent, the aircraft stands to recover energy that would just otherwise be bled off in drag by bringing on the flaps or even airbrakes. Instead prop drag slows the aircraft with electric. Are you describing a method that would entail less time in the air?

 

[mgb_phys]

I don't follow. On descent, the aircraft stands to recover energy that would just otherwise be bled off in drag by bringing on the flaps or even airbrakes. Instead prop drag slows the aircraft with electric. Are you describing a method that would entail less time in the air?

I think the idea is less time with the engine on full power. Instead of flying at full power to the runway an diving steeply while recovering some energy you are better off reducing engine power early and losing altitude gradually.
A bit like taking your foot off the gas well before a red light and cruising to a stop rather than driving at full speed and using regenerative braking at the end.

 

[mheslep]

I think the idea is less time with the engine on full power. Instead of flying at full power to the runway an diving steeply while recovering some energy you are better off reducing engine power early and losing altitude gradually.
A bit like taking your foot off the gas well before a red light and cruising to a stop rather than driving at full speed and using regenerative braking at the end.

Ok I follow, the idea there is to approximate killing power and using the accumulated potential energy to glide all the way in, and I expect that to the extent that is possible it represents the lowest energy profile. But that is not typical (or practical), energy must be bled off (wasted) in drag via turns, flap extensions, air brakes to accommodate the descent.

 

[RonL]

Ok I follow, the idea there is to approximate killing power and using the accumulated potential energy to glide all the way in, and I expect that to the extent that is possible it represents the lowest energy profile. But that is not typical (or practical), energy must be bled off (wasted) in drag via turns, flap extensions, air brakes to accommodate the descent.

I think the prop profile will change a bit as more use of electric power develops, as a plane flies the prop is pulling and when desending you are in essence pushing a wind turbine.

 

[mgb_phys]

It still depends on the amount of power lost by aerodynamic drag.
If when you turn off the engine you lose speed fast enough due to drag then using a regenerative propeller to slow even more isn't possible. It would only be worth it if with no engine you still had to use flaps to dump speed.

I think we covered this in another thread with regenerative braking on bicycles - since most of the power is lost to aerodynamics it isn't worth it.

 

[mheslep]

It still depends on the amount of power lost by aerodynamic drag.
If when you turn off the engine you lose speed fast enough due to drag then using a regenerative propeller to slow even more isn't possible. It would only be worth it if with no engine you still had to use flaps to dump speed...

Flaps are part of it, but I suspect a larger part is bled off in approach turns, which are in part required to do just that.

 

[mgb_phys]

Flaps are part of it, but I suspect a larger part is bled off in approach turns, which are in part required to do just that.

If you have to use active means to lose speed then regenerative braking is in theory worth it - wether it would be worth it in terms of added weight, complexity, reliability etc .

On a similair note the ski resort here now charges you to go down on their cable car - after you hike the 900m up the mountain. That is definitely not fair, with my more than ample mass I am significantly contributing to their power bill.

 

[russ_watters]

Flaps aren't used to bleed speed, they are used to allow the plane to fly at a lower speed. The only thing this would replace is an airbrake.

If I were less lazy, I'd figure out how much kinetic and potential energy is lost in dropping 1000 feet and from 120 to 100 mph...

 

[mheslep]

Flaps aren't used to bleed speed, they are used to allow the plane to fly at a lower speed.

They increase lift and drag.

 

[FredGarvin]

Drag is increased as a byproduct of lift. The purpose of flaps is to increase the angle of attack of the wing while maintaining a constant fuselage orientation and thus lift. This allows the aircraft to maintain the same amount of lift at lower speeds while maintaining a somewhat constant attitude.

 

[mheslep]

Last month in Zurich a Swiss crew unveiled another shot at a pure solar-battery-electric that they plan fly across the Atlantic and then circumnavigate.
http://www.solarimpulse.com/unveiling/documents/unveiling_user.php".
Specs:
Wingspan: 63,40 m
Length: 21,85 m
Height: 6,40 m
Weight: 1 600 Kg
Motor power: 4 x 10 HP electric engines
Solar cells: 11 628 (10 748 on the wing, 880 on the horizontal stabilizer)
Average flying speed: 70 km/h
Take-off speed: 35 km/h
Maximum altitude: 8 500 m (27 900 ft)

Which is 1.4x more power than the old Gossamer whatever.

This is an interesting challenge (the crossing) for a manned aircraft, and a bit risky. But why not just ditch the pilot? Without the pilot and support the problem must be an order of magnitude easier, not to mention that an essentially indefinitely orbiting high altitude aircraft has practical value, but as a transportation device its just a gimmick.

 

[mgb_phys]

not to mention that an essentially indefinitely orbiting high altitude aircraft has practical value,

There have been a bunch of Nasa and secret projects to make a long endurance UAV as a sort of mini-satelite.
If you want to fly in cloud or at night you also need batteries (or fuel cells) and these aren't quite there yet in power/weight. The sunsailor team estimate that you need about 40% efficency panels to fly indefinitely in good conditions (they are in sunny Israel) which is still a little way off.

 

[FredGarvin]

One of the big things the Solar Impulse is relying on is that they gain altitude during the day when they don't have to draw off the batteries. At sunset, they initiate a slight decent and try to extend that for as long as possible to some low altitude point. From then until sunrise, they are on batteries. Kind of risky especially when you have to also think about having to possibly avoid weather issues.

 

[mgb_phys]

I suppose if the aim is just to stay 'up there' then you could hunt for thermals and soar - only using the engine to get to the next thermal.
But if you want to stay over a city to relay TV signals or loiter over a battlefield you are going to need a lot more power.

 

[mheslep]

There have been a bunch of Nasa and secret projects to make a long endurance UAV as a sort of mini-satelite.

Yes, thanks for the NASA reminder: Pathfinder-'95, PF+-'98, Helios (solar+ fuel cells)-'01.

If you want to fly in cloud or at night you also need batteries (or fuel cells) and these aren't quite there yet in power/weight. The sunsailor team estimate that you need about 40% efficency panels to fly indefinitely in good conditions (they are in sunny Israel) which is still a little way off.

Apparently the Solar Impulse crew believes the batteries are there if they are to fly across at 70km/h. Regards energy requirements, I expect a better metric is solar efficiency divided by battery energy density greater than a constant for indefinite flight, so progress in either one gets you there.

Yes here - the 40% referred to manned aircraft.

Q: Commercial Photovoltaic cells still have fairly low efficiency (typically >20%). At what level of efficiency do you believe they will start proving to be more useful in commercial aviation (both manned and unmanned)?
A: Truthfully, Solar cells low efficiency is only half of the problem. The means of energy storage such as rechargeable batteries or fuel cells is the other half. But solar cells for large scale commercial aviation will have to go a long way before they can supply the power that is needed. Even a 40% solar cell covered wing on a sunny day will barely be enough for the cruise power requirements of a small manned aircraft

.
http://thefutureofthings.com/articles/51/solar-uav-to-set-a-new-world-record.html
If 20% panels can now carry a person across the Atlantic w/ good batteries, then I expect 20% panels can keep up a UAV indefinately.

 

[mgb_phys]

If 20% panels can now carry a person across the Atlantic w/ good batteries, then I expect 20% panels can keep up a UAV indefinately.

The solarimpulse is intending to fly to very high altitudes during the day and slowly descend during the night. So the battery just has to generate enough power to reduce the descent rate.
The 40% figure for the UAV is (I think) to give the same performance on battery as during the day - so slightly more than half your solar power goes to charging the battery.

 

[mheslep]

One of the big things the Solar Impulse is relying on is that they gain altitude during the day when they don't have to draw off the batteries. At sunset, they initiate a slight decent and try to extend that for as long as possible to some low altitude point. From then until sunrise, they are on batteries. Kind of risky especially when you have to also think about having to possibly avoid weather issues.

Yes I saw the day/night altitude plan. I don't see that flying at night by itself is risky. The battery energy is definite, the sunrise time is definite. Weather is another issue, though they can fly above most cloud cover ascending during the day, and they don't care about cloud cover when flying lower at night. Otherwise they have the option to simply avoid the more intense weather. I did notice they were concerned about head winds at night. This must mean they intend to chase the sun rise and gain an ~hour of sunlight. If things are that tight then they are certainly at the margin.

 

[mheslep]

I suppose if the aim is just to stay 'up there' then you could hunt for thermals and soar - only using the engine to get to the next thermal.
But if you want to stay over a city to relay TV signals or loiter over a battlefield you are going to need a lot more power.

Why? Based on the energy - time profile claimed for this manned vehicle, then a UAV should weigh ~200kg less without a cabin, have less drag, require no cabin environmental power. Thus I would think a fuel-less loitering UAV immediately possible w/ the same technology. It might have other undesirables, such being slow to move on-off station, or forced off station by weather.

 

[mgb_phys]

and they don't care about cloud cover when flying lower at night. Otherwise they have the option to simply avoid the more intense weather.

They don't have much leeway to avoid weather at night, they are going to descend to a certain altitude by a certain time however bad weather is down there. They also don't have the energy reserves at night to fly a few hundred miles around a large storm system.

Most of these solar powered aircraft also look pretty flimsy to be flying into turbulence.

 

[mheslep]

They don't have much leeway to avoid weather at night, they are going to descend to a certain altitude by a certain time however bad weather is down there. They also don't have the energy reserves at night to fly a few hundred miles around a large storm system.

? They have essentially infinite reserves. Unlike a fueled aircraft, they can afford to fly in any direction they care to. They only need to avoid weather for the night and can choose any compass point w/ out regard for the nearest airport. Granted some 1000 mile wide severe front will cause problems.

Most of these solar powered aircraft also look pretty flimsy to be flying into turbulence.

Agreed, though I wouldn't underestimate. Given the budget one can build very strongly w/ carbon fiber. Edit: yes its carbon fiber honeycomb. Expensive and very strong. And they claim 220Wh/kg in the batteries. That's almost double what's cited for the new EV car batteries. Twice as expensive too I believe.