Why battery-powered aircraft will never have significant range

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Jay Kempf

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One can market things in one sentence that can't go together.
Tesla has been doing it for quite a while now. You can have blistering acceleration, you can have long range, you can travel at high speeds, you can carry 4 adults and baggage, you can operate in winter: all the aforementioned are pretty much mutually exclusive. Operate the Tesla in cold weather and the range takes a hit, accelerate too much and the range takes a hit, carry bags and bodies... run at high speeds... mountainous terrain... lots of cornering...

Let the reader beware. Mission is context.
 

dog

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[QUOTE="Dan Thomas,I'm no physicist, but electrons tend to be pretty important, and no amount of current quantum mechanics jiggery-pokery will make more electrons.

The quantum state of the art is the ability to image and manipulate matter,one electron at a time.
Or to be slightly more precise, the term electron
as a concept has been superseded by "phonon"
where depending on conditions you have an electron or a photon,and these come with different energy levels.
The latest ability is to propose a desired property and then let a computer model millions of possible combinations of elements
and then test the suggestions.
One interesting recent breakthrough is the ability to image the atomic stucture of glass,
or rather one specific sample.
New tools new way of seeing matter,literaly.
There are results now and its just getting going.
Does that mean that I am ignoring the thread on hopping up n o-320,buddy of mine has a
Bintner 4 with a built 320,or the yamahaha 160.
No.
But physics is fun and the energy density inherant in all matter is far in excess of any possible utility.
The latest scheem from airbus is a blended wing,liquid hydrogen fuel celled super conducting electric power plant,uses liquid hydrogen for cooling to super conducting temp,
with a 50% weight reduction of the motor and electronics,plus allmost 100%eficiency.
The trick will be the fuel tank weight.
The thing that no one has brought up is that the same insights into materiels and phenominon at the quantum level also alow for
possibilities of useing chemical fuels much more efficiently.
Gasoline powered fuels cells for example,have been built but could not overcome the problem
of catilist poisoning due to sulfur.
A new teqnique for ultra pure hydrocarbons would solve this and refined efficiency is going to beat any ICE, hands down.
So who know which of the many many ideas bieng investigated will get to market first.
 

Bigshu

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I'm not sure hybrid would offer much improvement in economy for aircraft. When cars cruise on flat and level road, they require just 15 - 20% of the maximum available engine power. Aircraft cruise at airspeeds that cause significantly more drag, which requires much more energy to overcome, hence 55 - 75% power requirement for cruise. And having both the combustion engine, AND an electric motor, AND fuel tanks, AND batteries would incur such significant weight penalty that any possible savings in energy consumption would likely be wiped out by the significant increase in weight.
It'd be interesting to see the comparison of wetted surface and drag at cruise speed for cars and typical aircraft. Like everyone else, my SUV gets it's best gas mileage at highway speeds. In combined driving, the RPM stays between 1500 and 3500 RPM, with slightly less than 2000 RPM in final gear. Idle is around 600RPM. Highway driving is typically a judicious amount over the posted limit, so often around 80 MPH. This is for a 3500 pound + vehicle with another few hundred in passengers and gear in it. Drag effects designed into the vehicle for cooling or better handling ( ride height, air dams, etc) make the vehicle not awesomely slick, like a race car. So is it really that much less likely that hybrid electric aircraft could be successful? I'm not convinced, especially with the improvements in battery technology we've already seen, and other technology that for whatever reason got shelved ( Remember the Honda Clarity FCX?).
 

blane.c

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I'm not sure hybrid would offer much improvement in economy for aircraft. When cars cruise on flat and level road, they require just 15 - 20% of the maximum available engine power. Aircraft cruise at airspeeds that cause significantly more drag, which requires much more energy to overcome, hence 55 - 75% power requirement for cruise. And having both the combustion engine, AND an electric motor, AND fuel tanks, AND batteries would incur such significant weight penalty that any possible savings in energy consumption would likely be wiped out by the significant increase in weight.
Hybrid will be electric motors with battery and hydrogen fuel cell, the hydrogen fuel cell will replace the ICE.
 

Vigilant1

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With 1/5th of one percent of the population having a pilot license or permit of any sort, and the perception that pilots and owners are rich, it ain't gonna happen. It's not something necessary to the nation's transportation needs.
Right on time, as if to make your point, we get this news today:

Canada Moves Forward On Aircraft 'Luxury' Tax - AVweb

Canada's PM proposes a luxury tax of 10 percent on newly manufactured aircraft valued at 100kCAD (approx $80k US) and above. I guess a new Skyhawk is very luxurious.

There appears to be some possibility that used aircraft imported to Canada may also fall under this tax. I'm not sure if a kit, engine, avionics together will be taxed, it isn't hard at all to spend $80k building a nice E-AB.
 
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Vigilant1

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It'd be interesting to see the comparison of wetted surface and drag at cruise speed for cars and typical aircraft. Like everyone else, my SUV gets it's best gas mileage at highway speeds.
Only if folks on your highways drive a lot slower than I typically see. Fuel consumption goes up when driving faster than very moderate speed because aerodynamic drag is the major load on the engine on flat roads and constant speeds.

Natural Resources Canada puts the “sweet spot” for most cars, trucks, and SUVs even lower, between 30 mph (50 km/h) and 50 mph (80 km/h).
Note how quickly efficiency drops after 60 mph.

Fuel Efficient Graph
Link:Fuel Efficient Driving.

There aren't many folks who will risk driving 50 mph on an open highway, but if we wanted to squeek out max distance from a gallon of fuel, that's the way to do it. Best to put a ramp over the car before trying.

ETA: A calculator for fuel savings based on actual dynamometer tests for many vehicles and vehicle types. Save money and fuel by driving efficiently.

Example: A 2019 Ford Expedition 2wd 6 cyl turbo burns 30 percent more fuel per mile at 70 mph than at 50 mph.
 
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Rhino

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Only if folks on your highways drive a lot slower than I typically see. Fuel consumption goes up when driving faster than very moderate speed because aerodynamic drag is the major load on the engine on flat roads and constant speeds...
My pickup gets better mileage at highway speeds, but it isn't due to aerodynamic drag. It's because lower speeds are associated with areas that have stop and go conditions, mainly traffic lights and stop signs. The constant changes in speed are what accounts for the higher fuel use. You're both right, but trying to use automobiles and aircraft for comparing fuel efficiency doesn't really work very well, because the factors affecting their efficiency are very different.
 

Dan Thomas

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It'd be interesting to see the comparison of wetted surface and drag at cruise speed for cars and typical aircraft. Like everyone else, my SUV gets it's best gas mileage at highway speeds. In combined driving, the RPM stays between 1500 and 3500 RPM, with slightly less than 2000 RPM in final gear. Idle is around 600RPM. Highway driving is typically a judicious amount over the posted limit, so often around 80 MPH. This is for a 3500 pound + vehicle with another few hundred in passengers and gear in it. Drag effects designed into the vehicle for cooling or better handling ( ride height, air dams, etc) make the vehicle not awesomely slick, like a race car. So is it really that much less likely that hybrid electric aircraft could be successful? I'm not convinced, especially with the improvements in battery technology we've already seen, and other technology that for whatever reason got shelved ( Remember the Honda Clarity FCX?).
Generatng the lift to keep the airplane airborne creates a large amount of drag (induced drag) and there isn't much one can do to remove it. Your SUV doesn't have that problem.
 

Bigshu

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Generatng the lift to keep the airplane airborne creates a large amount of drag (induced drag) and there isn't much one can do to remove it. Your SUV doesn't have that problem.
Sure, and lift isn't something they are wanting from a car body, just the opposite, they want traction. But they also have big cross sections and blunt bodies, so the form drag is much worse than an aircraft. It's a trade off there. I'm just saying that a hybrid drive system isn't precluded by it being on an airplane. They're popular in all kinds of surface vehicles, and lots of auto makers are committing to getting out of the ICE as prime mover business by as early as 2025. It makes a lot of sense as the stop gap until battery technology gives the range/endurance/refueling speed that we want. There was an extended crossover period between horses and horseless carriages too. Until reliability and infrastructure improved, lots of people said cars would never replace horses. and yet more people own cars than ever owned horses. One side benefit nobody has mentioned is that generators are able to use the latest design and engineering advances so they don't need leaded, high octane fuel. So even if there isn't a weight, complexity, or cost advantage, you still gain by being able to fly on pump gas and potentially get fewer restrictions for noise abatement.
 

Bigshu

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There is also the potential for greater reliability, as modern engines have fuel and ignition systems that are way, way more reliable than any of the legacy aircraft piston engines. So, an electric prime mover, with batteries for high power needs, and a generator as range extender, could dramatically reduce the costs of maintenance and repair of the drivetrain/powerplant.
 

rdj

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Some HBA member had a post about the absolute limits of battery technology. It had to do with the finite number of molecules in a battery and the finite number of electrons that can be exchanged during the discharge process. I'm no physicist, but electrons tend to be pretty important, and no amount of current quantum mechanics jiggery-pokery will make more electrons. You would need some manmade elements at the far end of the periodic table, and the ones we have now have incredibly short half-lives.

Anyway, the current battery technology was approaching the atomic limits, according to that post. It would seem similar to approaching 100% efficiency in an engine; no amount of fooling further with it would get it past 100%.
I believe that would be the video in post #1 of this exact thread, by Autoreply. You don't seriously expect people to read from the beginning before arguing, do you? :)
 

EzyBuildWing

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Honda will be all electric by 2040 (just announced)....Tesla is already "all-electric" (has been for 20 years.)
If your first "electric-acceleration-experience" is in a Tesla, then you're sold....you never forget it!
Remember Jay Leno's first ride in a Tesla Roadster..... about 1.9 seconds into the acceleration-demo Leno was shouting: "I'll buy it, I'll buy it..."
Leno desperately wanted to "buy the sizzle" of course....right there, right then! The clip is on Youtube.
Check out the "sizzle" the test-pilot experiences in this e-Pipistrel..... 21kW cruise, 3kW whilst taxiing:
 

trimtab

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The power required to fly at a cruise speed is roughly the inverse of the L/D at cruise times the cruise speed times the weight of the aircraft. Incomparable to the needs of a car.

The energy density by mass or volume for electrochemical battery storage is orders of magnitude from equivalence to chemical energy.

Fuel cells make enormous sense for aircraft...and will still be very difficult to make popular safely.
 
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Marc Zeitlin

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The power required to fly at a cruise speed is roughly the inverse of the L/D at cruise times the cruise speed times the weight of the aircraft. Incomparable to the needs of a car.
Simplifying your description, since the inverse of L/D times the weight of the aircraft (L) is exactly (D), and P = D x V, then not only is this comparable to the needs of a car (at highway speeds), but it's in fact, identical, assuming that the vast majority of highway speed power requirement is to overcome aerodynamic drag.

Car: P = D x V​
Airplane: P = D x V​

what am I missing?

The energy density by mass or volume for electrochemical battery storage is orders of magnitude from equivalence to chemical energy.
Well, about 1.5 - 1.7 orders of magnitude, using gasoline and lithium ion batteries as a comparison. Gasoline at 47 MJ/kg, and lithium Ion at 1 and a bit MJ/kg.

The theoretical energy density of lithium air batteries is about 86% of gasoline's energy density (~40 MK/kg). Of course, the best that's been demonstrated so far is about 13% of gasoline's energy density (~6 MJ/kg). But since gasoline engines are only 35% efficient at best, while electric motors can be 90% - 95% efficient, there's another factor of ~2.5, so the current state of lithium-air batteries (hardly close to manufacturability, but still extant) gives gasoline with a delivered energy of 16 MJ/kg and l-a batteries at 5.4 MJ/kg, which leaves them at ~ a 3 : 1 disadvantage to gasoline. That's not an absurd ratio, and _IF_ the lithium air batteries can ever get to only 1/2 of their theoretical maximum energy density (say, 20 MJ/kg), then they'll be at about the same level as gasoline - maybe a bit better. Might be 30 years (or never) before that happens, but it's not beyond physics, and it's not cold fusion, whatever the statements in the video in post #1.

Fuel cells make enormous sense for aircraft...and will still be very difficult to make popular safely.
Yep - agree on both counts. Although fuel cell technology, right now, is NOT light...
 

trimtab

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]

what am I missing?
Just the critical takeaway that power required in flight is rather dependent on weight, and only very weakly dependent on weight for terrestrial vehicles. Mgh(dot).

Fuel cells need breakthroughs to be viable just as batteries need breakthroughs to be viable. There is no progression or Moore's law in either batteries or in fuel cells yet. But a fixed mass reactor with enormously energetic storage is a better bet than a fixed mass reactor with very weak energy storage in terms of mass. The only questions are at what scale and cost, and whether they can achieve an interesting niche for both in aviation.
 
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BBerson

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The lithium "battery" is an electrochemical cell. More like a fuel cell than a battery, me thinks.
 

John.Roo

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Honda will be all electric by 2040 (just announced)....Tesla is already "all-electric" (has been for 20 years.)
If your first "electric-acceleration-experience" is in a Tesla, then you're sold....you never forget it!
Remember Jay Leno's first ride in a Tesla Roadster..... about 1.9 seconds into the acceleration-demo Leno was shouting: "I'll buy it, I'll buy it..."
Leno desperately wanted to "buy the sizzle" of course....right there, right then! The clip is on Youtube.
Check out the "sizzle" the test-pilot experiences in this e-Pipistrel..... 21kW cruise, 3kW whilst taxiing:
I had opportunity to fly with Pipistrel Velis. And then I took pilot of Velis to a test flight in our electric Phoenix for comparizon. Velis had "cruise consumption" 17 kW. Phoenix with long wings is able to fly with 12 kW. Both planes were flying at MTOM 600 kg.
I will try to make a test with short wing extensions for comparizon.

Flying in formation with Velis

Flying with Phoenix with 15 m wing extensions

The same electric Phoenix only with short wing extensions (10,3 m wing span).
 

Marc Zeitlin

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Just the critical takeaway that power required in flight is rather dependent on weight, and only very weakly dependent on weight for terrestrial vehicles. Mgh(dot).
Well, yeah - that's true. And airplanes generally weigh less than a car carrying equivalent loads, and are more sensitive to weight. But the issue of the Power required being Drag X Velocity is the same for both.

In any case, I'll use my old car (2004 Subaru Outback wagon) and airplane (COZY MKIV) as examples. The Subaru had 5 seats and a luggage area, a 165 HP engine in it, and would get about 24 statute MPG on the highway at 70 mph. The COZY has four seats and no luggage area, a 180 HP O-360 in it, and would get about 22 statute MPG when cruising at 193 mph. The Subaru could carry more weight, for sure, and it wouldn't change the mpg much, unless I was in a very hilly area.

So my point is that it was taking about the same amount of energy to go 2.5X the speed over the same distance in these two relatively equivalent vehicles from a transportation (if not weight) standpoint. As of right now, my calculations show that if I put in ~400 lb. of batteries (a slight bit more than the gasoline capacity) with currently available 200 HP motors and controllers, the plane would be have a range of about 130 - 150 miles, give or take. Obviously that's not very useful for a cross-country cruising aircraft. But while I have flown a couple of 1K NM legs in the 18 years I've been flying the COZY, the vast majority of my flights (90% or more) have been 3 hours or less at my normal cruise speed, for distances of up to 500 NM. So it will only take a factor of about 3X - not orders of magnitude - for batteries to become a viable alternative for gasoline for my airplane (and for every training aircraft and "putter around in circles" aircraft out there, that fly for an hour or a couple at a time).

I was hoping, with 1700 hours on my engine, that 3X factor would have occurred a bit sooner, as I expect to have to rebuild the engine in 3 - 5 years, and was thinking I would go electric if the battery technology had gotten there. It won't in that time frame, so gasoline it will be for as long as I own the plane, as I don't expect to be around to rebuild it again in another 20 years :).

Fuel cells need breakthroughs to be viable just as batteries need breakthroughs to be viable. There is no progression or Moore's law in either batteries or in fuel cells yet. But a fixed mass reactor with enormously energetic storage is a better bet than a fixed mass reactor with very weak energy storage in terms of mass. The only questions are at what scale and cost, and whether they can achieve an interesting niche for both in aviation.
Agree with all that. Some breakthroughs are needed for either. But a factor of 3X can be seen on the horizon, whereas "orders of magnitude" are in the "there be monsters" region...
 

Rhino

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... the vast majority of my flights (90% or more) have been 3 hours or less at my normal cruise speed, for distances of up to 500 NM. So it will only take a factor of about 3X - not orders of magnitude - for batteries to become a viable alternative for gasoline for my airplane (and for every training aircraft and "putter around in circles" aircraft out there, that fly for an hour or a couple at a time)...
I'm curious what kind of market share they'd need to consider this not just operationally viable, but also financially viable. A lot of people want and/or need the ability to get back in the plane and putter around some more after that flight, without waiting for a recharge, so obviously they aren't going to be candidates for early adopters. I can see training aircraft benefitting as long as they aren't flying multiple missions a day, but I have to wonder how willing they'd be to jump on the bandwagon, and how soon. I've seen plenty of good ideas get shelved because there just wasn't enough of a market to support them. I'm curious about cost comparisons. Electric planes will obviously save money not having to buy fuel, but how long will it take for that savings to outweigh the initial cost? We don't even know for sure yet what the initial cost will be for most market segments. We've also seen how many pilots will steadfastly refuse to step into new or uncharted territory. Look how long it took so many to adopt ADS-B, and some still haven't. So investors in all this stuff are gambling with their money and banking on a certain degree of market acceptance within a certain timeframe to make it worth their while. I'm curious to see what level of cost and what level of market acceptance they'll need to make electric aircraft the next new, gotta have airplane. I don't think we can answer that yet, but I find it interesting to contemplate.

I also get a little snicker envisioning a salesman trying to convince some old codger that owns a plane with no electrical system whatsoever, to fork over bucks for a new plane that is nothing BUT an electrical system.
 
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