Why battery-powered aircraft will never have significant range

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tspear

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I wonder how the hydraulic clutch handles TV.
From previous discussions, I have come to the conclusion that TV is one of the harder issues to address for a hybrid system.

Tim
 

AJLiberatore

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Let me add some real numbers from the world of electric motorcycles!

Instead of electric cars, IMHO electric motorcycle development in past 5 years show how battery capacity has changed without liquid cooling as they need to keep volume, weight, and cost down.

Here is a snapshot of the 2013 Zero powertrain battery specification.
View attachment 66860

The 2013 battery with BMS is 42 lbs and 2.8KWhr (132Whr/Kg)
The new 2018 battery with BMS is 42 lbs and 3.6KWhr (188 Whr/Kg)
The volume & weight of the battery pack is the same year over year as the frame remained the same. This is a 42% increase over 5 years.

I have yet to see an aircraft using a Nissan Leaf or BMW i3 powertrain but the egull and its derivatives have flown with the 2013 Zero powertrain. Also the Windward Goshawk will use the new Zero powertrain. There is a Belite here on HBA that is using zero too.

Saini flyer,

So, do we take this Zero Battery and send it to Romeo Power and can they tweak it like they did the BMW Battery....

From the Article:
“If you look at the BMW i3 with 114-mile range, we're over 220-mile range with our technology in the vehicle on an equal-weight basis,” Porter said, citing test versions the company has built."

Go here: https://www.forbes.com/sites/alanohnsman/2017/08/24/elon-musk-has-a-new-battery-rival-packed-with-his-ex-employees/#12e9f7e66f88

I get that Battery Chemistry etc is not like bolt-ons massive net HP increases you see w/ your SBC or SBF. However an almost doubling from where an existing pack is? That 42 lb Zero Battery Pack would have what for KWhr - Whr/Kg? Imagine at that point something like a Hummel H5 / Onex with said battery pack or 2 of them and 2 Zero Motors in Series ( 40 hp / per is where they are at if my memory is correct ), or a specific 80hp-ish E-Motor. At that point is our Electric "$100 Hamburger" Special here? I think we are closer than were dare to think...

My best, Anthony
 

autoreply

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I just watched the video, and they really phrase things in the worst possible way to make the energy densities look low. But if you just keep track of the statements it makes, it really should have the complete opposite conclusion for batteries.

Statements on the left are from the video, the right is the equivalent statement about density:
Lithium ion with the same energy can theoretically be 50% of the weight of current batteries = Lithium ion can have 2x the density of current batteries
Lithium sulfur can weigh 30% of the Lithium ion = Lithium sulfur is 3x the density of the theoretical maximum of lithium ion (6x current batteries).
Lithium oxygen is 25% weight of lithium sulfur = 4x the density (24x current batteries).
Lithium fluorine (if possible) is 5% weight of lithium oxygen = 10 x the density (240x current batteries).

So the theoretical limit of batteries, using the video's own numbers, is 60,000 Wh/kg. Even ignoring lithium fluorine, you'd still get 6,000 Wh/kg as the theoretical maximum. I have no idea how he gets the 5% number at the end of the comparisons, it's not consistent with the comparisons before that. That's still 20x current, or 5,000 Wh/kg.

With the most pessimistic, out of nowhere 5% current figure, the Hummelbird that needs 20kW to fly for an hour? That's 8.8 lbs of battery, or 3.2 lbs less than the gasoline that would be needed.

Even if the development only got as far as lithium sulfur, at 1,500 Wh/kg, the Hummelbird would need 29 lbs. of batteries for an hour. Assuming a 25 lb electric motor plus 10 lbs of controller and wiring replaces the 85 lb 1/2 VW plus full 6 gallon tank, you would have 2.7 hours with batteries instead of 3 hours with gas at the exact same weight.

I can't vouch for these figures, I got them from the video and they didn't list sources. The video is inconsistent, and uses percentages in a way that supports the most pessimistic view of batteries in a biased way at best. And his math sucks. But the end result is that batteries theoretical limits are well in the range that will be useful.

It's likely to be a long wait to get to these limits, but his conclusion isn't consistent with his data in any way.
A few remarks:
Battery energy density will be about half of the batteries number. You need a BMS, protection, barriers etc. These are actual numbers from real airframes.

If we ignore Lithium Fluorine (which only raison d'être is to prove that Darwinism will extinguish the fearless and stupid) we get roughly this:
24 times current battery density, which leads to:
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 at a modest 70 kts or so. 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.
I wouldn't quality either as practical (for going the distance). Did I screw up the math? If not, would you qualify the best theoretical possible as practical?
 

BBerson

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Are you talking about a rechargeable lithium oxygen battery?
Or one than converts lithium metal into lithium oxide and needs to be removed and recycled?
 

12notes

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A few remarks:
Battery energy density will be about half of the batteries number. You need a BMS, protection, barriers etc. These are actual numbers from real airframes.

If we ignore Lithium Fluorine (which only raison d'être is to prove that Darwinism will extinguish the fearless and stupid) we get roughly this:
24 times current battery density, which leads to:

I wouldn't quality either as practical (for going the distance). Did I screw up the math? If not, would you qualify the best theoretical possible as practical?
24x todays capacity is still 6000 Wh/kg, which is more than the effective energy density of gasoline when you take motor efficiency into question.

Gasoline has specific energy of 46MJ/kg. At the 30% efficiency of internal combustion engines, that's 13.8 MJ/kg. The theoretical Lithium-Oxygen battery, assuming we halve the energy density as you suggested, would have a density of 3,000 Wh/kg, or 10.8 MJ/kg. At 90% efficiency produces 9.7 MJ/kg. That's still 70% the energy density of gasoline. I would be suspicious of the calculation that resulted in the SR22 having 15% of the range at 100 mph slower cruise.

This doesn't take into account the weight savings from using a much, much lighter electric motor. Conservatively, you'd save 300 lbs in the motor, weight that would equate in these batteries (at 70% energy density) to 35 gallons of avgas. There's more than an hour and a half at maximum cruise speed (~300 miles at 200 mph) at the same weight as the gasoline engine plane with completely empty fuel tanks. There is a tipping point where gasoline overcomes that disadvantage and provides maximum energy, but it's at 116 gallons, well over the Cirrus' 92 gallon tank.

I used performance data for the Cirrus SR22-G3 with the IO-550-N engine (300hp, 460 lbs) printed in Plane and Pilot and Flying magazines. I used Tesla's 362 hp electric motor as an equivalent, it weighs 70 lbs. For round numbers I added another 90 lbs for controller, wiring, and deep fryer for fresh en route donuts (we're not savages).
 
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Aesquire

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Thanks I was off by one Sea, language, culture, and history.

Tomorrow I will discuss the use of air power to battle Canadian Poncho Via. Or Spanish Queen Elizabeth III. ;)
 

blane.c

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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).

Bottomline; for range hybrids will be the future :)
Lets assume that batteries alone cannot make up for the power demands of a practical cruising aircraft at this time.

(1) Is it practical to use battery powered aircraft such as the EMG-6 as trainer aircraft? (Considering that in practice you would have several battery packs to enable you to swap and go)

(2) For cruising two seat aircraft would a electric motor powered hybrid glider be practical?

(3) Is it better to have a fossil fuel propeller driven auxiliary engine to supplement the electric motors or is it better to use on-board electrical generation to supplement battery power?

(4) Batteries and solar?
 

tspear

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A while ago, I recall a concept vehicle which the battery was part of the frame.
Now some Li polymer's might be a little to volatile for this concept; but could it be viable to use graphene capacitors inside a tube frame? Or thin battery like in new laptops as the wing skins?

Tim
 

pictsidhe

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I've seen ebike batteries dropped into frame tubes, but they were small. Wing skin storage seems unwise, they'd compromise the structure and be vulnerable. Packs that fit between ribs make more sense to me.
 

RJW

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So gas at about 30% efficiency gives about 16.5MJ/Kg. Current tech chemical batter at 90% efficiency gives about 1.8MJ/Kg. Better but very difficult (not yet built) chemical battery at 90% efficiency gives about 2.7MJ/Kg. Best but not at all practical (almost certainly will never be built) chemical battery at 90% efficiency gives about 4.5MJ/Kg.

So best but almost certainly never to be built chemical battery installation would have to weigh about one fifth the equivalent ICE installation.

Very good but not yet built chemical battery installation would have to weigh about one sixth the equivalent ICE installation.

Current tech chemical battery installation would have to weigh about on ninth the equivalent ICE installation.

We can rearrange these ideas, change the units, and pound the ideas into a hundred different shapes but no matter how it is presented, it doesn’t look good for chemical batteries.

Wondering if Jarno isn’t just having us on a bit with this thread?

Rob
 

12notes

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So gas at about 30% efficiency gives about 16.5MJ/Kg. Current tech chemical batter at 90% efficiency gives about 1.8MJ/Kg. Better but very difficult (not yet built) chemical battery at 90% efficiency gives about 2.7MJ/Kg. Best but not at all practical (almost certainly will never be built) chemical battery at 90% efficiency gives about 4.5MJ/Kg.
Check you math and sources. For gas as in Methane (55.5 MJ/kg) you would be correct. But gas as in gasoline (46.4 MJ/kg), which at 30% efficiency is 13.8MJ/kg. At 90%, current batteries (252 Wh/kg) provide 0.8MJ/kg. The rest of the numbers I covered in my other posts.
 

Jambo

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Jambo

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Lets assume that batteries alone cannot make up for the power demands of a practical cruising aircraft at this time.

(1) Is it practical to use battery powered aircraft such as the EMG-6 as trainer aircraft? (Considering that in practice you would have several battery packs to enable you to swap and go)

(2) For cruising two seat aircraft would a electric motor powered hybrid glider be practical?

(3) Is it better to have a fossil fuel propeller driven auxiliary engine to supplement the electric motors or is it better to use on-board electrical generation to supplement battery power?

(4) Batteries and solar?
(1) yes, given pipistrel is already doing this. Although I feel that it is the noise/gas price issue specifically in europe that's driving it. In the USA, I still think ICE has the edge.

(2) For a motorglider, hybrid might very well be an ideal powerplant, though haven't done any work on such a design

(3) I would strongly argue the former

(4) maybe for charging a battery aircraft with no grid. But solar during flight just isn't going to offer much, if any useful power(besides avionics)
 

pictsidhe

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A solar/battery aircraft managed to fly around the world, so it has some potential. The usefulness of solar power depends on the cruise speed. To get lots of solar power, you need a lot of area. To fly efficiently with a lot of wing, you need to go slowly. If L/D is fixed, power is proportional to speed. The better gliders get around 50:1.
My 103 project is currently looking very slippery. I'd like at least 4x the cruise power for a decent climb rate, so a hybrid boost is one possibility. 10 minutes should be plenty to get over things. I could even add solar cells and get 1/2 the cruise power, but it's a lot of hassle and range isn't an issue.
I want to fly for longer than my battery budget will allow, so a constantly running IC engine is for me. i don't see much point is using it to run a generator which runs a motor should I go hybrid.
If I do go hybrid, I'll have a dual speed gearing to a motor/generator. The IC would be mechanically connected to the prop. In generator mode, the mogen turns slowly for lower losses. In motor mode, it spins faster to get high power. 2 belt drives and 2 overruning clutches does this automagically.
 
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