Why battery-powered aircraft will never have significant range

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tspear

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I like the concept of Beta. But like a lot of others, I feel they are doing to many things. I think the incremental approach of Pipistrel is much smarter, and more likely to lead to success.

The more I have learned about electric planes, the more complicated I think it really is. I used to figure it was pretty simple, battery, motor and a rheostat to control power. To actually have any useful range, battery life, you need to temp control the battery and the motor. The wires are also a consideration, how do you control the power, burst capacity....

There is a lot of systems design work here that needs to be done to make the aircraft actually useful. And trying to do all of it at once, introduces a lot of complexity.

Tim
 

dwalker

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Wish him well and good luck for me.
Wonder when the ladys start complaining about the smell of ozone and testosterone.
Will do!

I have two concerns, that I expressed to Mike and his people, about the electric racecars, especially on the mountain. Battery temp control is the thing they are struggling with the most, every time they think they have it down, something new comes up.
My biggest concern is the weight of the cars. The battery packs alone weigh more than some of the gas cars, total vehicle weights are on the high side, and this is concerning for tires, handling, and of course, what happens if you fly off the side of the mountain. These guys are smart, and seem to have it figured out, but other than the minor off last year with a Tesla, there has been no real emergencies involving the electrics. Obviously, no one wants one, but we have to prepare for it and I hope they have it covered. Like I said, these are pretty smart people.

In an aircraft, the weight of the batteries and motor and how strong the structure will have to support them is concerning from a "what if it crashes" standpoint, along with fire/explosion mitigation.
 

BJC

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My understanding of grid losses is that the nature of the grid means that it is horribly inificient off peak,as there is no way to throtle
the monster sized generators and that the current MUST go somewhere,so they burm it in resistance air heaters.
Generation systems continually change output to match generation (both real and reactive power) to the load. A well-designed system will have a mix of sources (generating units) that can change output quickly enough to maintain system stability. Many (probably most or all, I don’t have any current statistics) systems have the ability to shift loads to off peak times and to change system capitance to minimize reactive current flow. Another technique used when to topography permits, is pumped storage hydroelectric. Nukes don’t change generation well, and are typically base loaded. Large coal units change load better than nukes, but not as easily as smaller coal, oil, or gas steam units. Combined cycle units can change generation fairly easily, but frequently don’t for system economics. Simple cycle combustion turbines can start quickly and change output quickly, but are inefficient and maintenance intensive. Hydroelectric generation in the south east is more frequently dispatched to meet lake level and minimum stream flow criteria or reactive control, with short spurts to support rapid system load increases. I have no experience with wind or solar, but other “renewable” sources and qualifying (industrial co-generation) sources are a real PITA when designing and operating a system. Another dispatch consideration is the transmission system’s capacity and losses. Those factors are very specific to the system.

Note that public utilities operate to comply with the dispatch criteria defined by the state utility commission, which is a political entity. You would be dismayed to learn of the technical ignorance of many commissioners. The same, in my experience, applied (probably still does, because they are political appointees) to the top Department of Energy leadership for electric generation.

Utility commissions typically dictate that the generation system be operated to minimize the cost of generation after first taking the “renewal” generation, which typically costs more that the utility’s base load generation. That means that customers are subsidizing “renewable” generation.

Contrary to your understanding, the highest generation cost occurs on peak.


BJC
 

tspear

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@BJC

I am years out of date, it has been almost a decade since I was working with building control systems.
However, part of the proof of concept system we developed for a Federal agency was to smooth out and reduce peak load for a large campus location. It involved managing the compressor cycles across multiple A/C and refrigeration units, this was just one example of demand management and load shifting.
This kind of "end user" intelligence while bleeding edge ten years ago, is getting to be more common, and will be needed to reduce spinning reserve.

Thinking of reducing spinning reserve, I wonder how the PAD based peak load reserve batteries worked out in CA. Assuming I recall correctly it was a Siemens and PGE project where they would put 25 kwh batteries on each PAD to handle transient loads in the afternoon, such as the start power for an A/C (each PAD served 10 homes if I recall correctly in the PGE model). If it worked, and the theory was to be able to eventually reduce spinning reserve down to 1%. The math "proving" the theory was to complex for me to follow :)

Tim
 

BJC

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I am years out of date, it has been almost a decade since I was working with building control systems.
However, part of the proof of concept system we developed for a Federal agency was to smooth out and reduce peak load for a large campus location. It involved managing the compressor cycles across multiple A/C and refrigeration units, this was just one example of demand management and load shifting.
This kind of "end user" intelligence while bleeding edge ten years ago, is getting to be more common, and will be needed to reduce spinning reserve.
Yes, those types of systems were (are?) popular among users who had a peak charge and or time-of-day rates. The first digital control system that I designed was for a 600,000 square foot sub zero F refrigerated warehouse complex, plus a 4,000HP waste water COD/BOD aeration system in central Florida, circa 1974. Used a (gasp) IBM System 7. The primary goal was reducing the charge for peak energy. It did that, but returned much more saving by reducing consumption via better control.

Load shifting via switching off residential water heaters and A/C systems by the utility (mostly to mollify the utility commission) was popular in Florida in the 1980's, but was later abandoned due to its minimal effectiveness.

PS for those not familiar with the vagaries of regulated utility finance, note that the utility does not earn a profit on the purchase and subsequent sale of fuel, but fuel purchases are continually monitored by the utility commission.


BJC
 

FarmBoy

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While we won't know the end unit production specs of the new (Panasonic/Tesla) 4680 batteries, they are based on a 380Wh/Kg chemistry, are already in production, and will be going into all Tesla Model Y and Cybertrucks being built at the Texas Gigfactory this year. Of course an integrated pack will shave off a few percent, though conservative estimates indicate the new Tesla modules will carry around 307 Wh/Kg (a 16% increase from the current 265Wh/Kg modules in my 2020 Model Y).

I don't see this slowing down any time soon either - a tremendous amount of capital is being invested in these technologies and there are already chemistries in various phases of proof of production upwards of 600 Wh/Kg (and LiS has a theoretical limit of ~2,600) . While 600 Wh/Kg would only reflect a ~4x increase over the currently contested Pipistrel use case, 4+ hours in the air is probably the average desired amount of time before a pee break (or other form of rest) is desired while traveling and certainly meets almost any training use case. I have no doubt that other aerodynamic and systems design improvements will add to potential time aloft. I believe we will be seeing some air worthy news items this year that will surprise quite a few folks. :)
I should have been more specific in reference to energy density of cells vs. modules vs. fully integrated packs. BFE_Duke and PiperCruisin rightly remind us all that the Pipestrel 144 Wh/kg reference is for the integrated pack (based on BMW i3 cells if my calculations were correct). As a reference, the battery pack in my previous 2019 Tesla Model 3 was about 180 Wh/kg. While changes to my 2020 model Y battery pack were modest, I believe that slight reductions in pack weight and small increases in cell energy density place current production Tesla packs at or above BFE_Duke's 181 Wh/kg.

The new Texas Gigafactory packs will utilize the newly produced tabless 4680 cells. Using conservative esimates based only on the packing density increases provided by this new cell should put it at a cell level of 307 Wh/kg and a pack level energy density of about 210 Wh/kg. The near term target for this cell is 340 Wh/kg which should see full Tesla packs with nearly 233 Wh/kg within a year or two.

It has been prognosticated that at least 450 Wh/kg, at the cell level, is needed to make commercial air passenger service viable. We're actually not very far off from this goal. More than one company is working on commercially scalable battery production of Li based cells with >400 Wh/kg today with targets over 700 Wh/kg (https://www.nasa.gov/sites/default/files/atoms/files/650_whkg_1400_whl_recharg_batt_new_era_elect_mobility_ymikhaylik_0.pdf). Based on prototypes from more than one manufacturer that I have seen, I believe that commercial scale availability of >450 Wh/kg is all but certain within 3-4 years and I personally see no roadblocks to high discharge rate, transportation capable cells with >500Wh/kg which would allow a > 342 Wh/kg fully integrated pack level battery. So, if it were me, I would be working very hard optimizing my air frames for the absolute greatest efficiency so that I would be ready to run with a portion of the coming all electric aviation market.

To reduce flames (literally and from trolls) it should also be noted that many new cell chemistries are in the works that will both increase energy density and allow physical destruction of a cell without it blowing up (or doing much at all really). Stay tuned!
 

tspear

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@BJC

In 74, I was barley out of diapers :)
What I liked about the project I did with the refrig and a/c systems was it was managing across multiple buildings on a campus, controlling stuff in locations a thousands miles away from the HQ. The rules engine ran locally onsite, but the rules were setup and managed remotely, we integrated local weather intelligence, demand information from the utility, fuel prices, local cogen/backup sources.

Tim
 
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Aesquire

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So, if it were me, I would be working very hard optimizing my air frames for the absolute greatest efficiency so that I would be ready to run with a portion of the coming all electric aviation market.
That's a necessity when your power is limited, no matter the fuel. And an ongoing trend in glider/powered glider type craft. If Pt 103 wasn't so weight limited, the evolution would be toward Stemme 80 foot span luxury motorgliders, ( but with cheaper engines and airframes, ) Towards, meaning a continuum from paramotors through wooden motor gliders and Windward Osprey carbon wonders, to the yachting class...

There's a reason motor gliders are the working pattern for limited range/power engines. Squeeze the most out of what's available. Then low performance trainers.

Those of us that like soaring are by definition willing to accept limitations & use skill and natural renewable pure green ( stacking buzzwords... ) energy to fly longer and further. ( though it you've ever caught a thermal from a cow pasture, pure & green have a distinctive smell ) Soaring folk are a minority in GA. Hence the increasing popularity of cruising motor gliders, for a variety of reasons, from Medical regulations to Electric power limitations.


The title of this thread is technically wrong. Electric just won't have the same range per pound & power, until some future featherweight breakthrough approximates the power density of IC & turbines. Don't hold your breath.

But you can have "significant" range for values of the word, if you accept compromises like low speed, limited cargo, and, today, using natural lift to stretch your power storage. And reduced expectations.

My example mission is a roughly 45 mile straight line ( one way ) trip from my house to the airport at my buddy's town. I might make it round trip on the same battery/fuel tank if I hug the ridges and stop to circle from time to time which might make the total distance covered closer to 200 miles, and a few extra hours. That's not acceptable for a normal commute. But might be perfection if hearing a variometer chirp and airtime is your goal.
 

PiperCruisin

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They could make an order of magnitude reduction in vehicle complexity and COST for the whole urban air mobility thing, by accepting E-STOL instead of E-VTOL.

The small "distributed" motors on the leading edge, plus large double-slot fowler DeHavilland style flaps ("blown" by the distributed propeller flow), would allow a 6 place conventional airplane commuter vehicle (something the size of a fat 207 or Caravan, 125-150 MPH cruise, 40 MPH Vso) to operate in 500 feet of runway, leaving a 100% margin for density altitude and gusts and what-not. Heck, the guys in Alaska almost do that with a stock 206 or 207 right now.
Agree. Wondering why there is so little interest in eVSTOL vs simply vertical. Rather than blown/distributed (which has obvious advantages) not sure why no one pursues this: ch8 (see figure 106).
Adding a rotating cylinder at the elevator as well as the flaps would not add a ton of complexity. Might have to have blown flow over the vertical or a fan at slow speeds for directional control.
 
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tspear

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Simple VTOL can be foreseen to eventually have no pilot. STOL will pretty much always require a pilot, and is much more limiting in terms of locations.
My driveway at roughly 105 ft would work perfectly for a VTOL. However, no STOL plane will be able to get over the trees at either end that are approaching 75ft or taller.

Tim
 

BFE_Duke

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The new Texas Gigafactory packs will utilize the newly produced tabless 4680 cells. Using conservative esimates based only on the packing density increases provided by this new cell should put it at a cell level of 307 Wh/kg and a pack level energy density of about 210 Wh/kg. The near term target for this cell is 340 Wh/kg which should see full Tesla packs with nearly 233 Wh/kg within a year or two.
I'll have to be on the lookout for a crashed Cybertruck at the insurance auctions once they start making deliveries. I think Tesla is also achieving better pack-level weight by double-stacking. Kinda like how a big mac only needs 3 buns to support 2 patties.
 

Sockmonkey

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Agree. Wondering why there is so little interest in eVSTOL vs simply vertical. Rather than blown/distributed (which has obvious advantages) not sure why no one pursues this: ch8 (see figure 106).
Adding a rotating cylinder at the elevator as well as the flaps would not add a ton of complexity. Might have to have blown flow over the vertical or a fan at slow speeds for directional control.
If I were going STOL, I'd want something with a few fiddly bits as possible.

This bad boy uses the delta wing landing struts for vortex lift for high AOA STOL landings.
Symmetrical with a neutral pitch they don't make induced drag during cruise.
Junkers flaperons for full roll control at high AOA.
There ya go. No extra mechanical complexity like slats and stuff.
 

Rhino

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...Symmetrical with a neutral pitch they don't make induced drag during cruise...
You mean effectively no induced drag. Nothing in the airstream produces no drag at all.

Out of curiosity, wouldn't those make boarding a real pain?
 

Sockmonkey

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A vortex generator, appropriately sized and placed, can keep the ailerons effective through an un-flapped stall in my Sportsman.
Yes, but for a STOL bird you would still want the flaps.
A vortex generator on it might be a good idea though.


You mean effectively no induced drag. Nothing in the airstream produces no drag at all.

Out of curiosity, wouldn't those make boarding a real pain?
Yep, the gear struts were gonna be in the airstream producing a certain amount of form drag anyhow, so shaping them to do something during takeoff and landing isn't going to significantly impact drag during cruise.

If a patch on top of the delta is slightly reinforced, you can use it as a step. They only angle down around 30 degrees.
 

dog

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Will do!

I have two concerns, that I expressed to Mike and his people, about the electric racecars, especially on the mountain. Battery temp control is the thing they are struggling with the most, every time they think they have it down, something new comes up.
My biggest concern is the weight of the cars. The battery packs alone weigh more than some of the gas cars, total vehicle weights are on the high side, and this is concerning for tires, handling, and of course, what happens if you fly off the side of the mountain. These guys are smart, and seem to have it figured out, but other than the minor off last year with a Tesla, there has been no real emergencies involving the electrics. Obviously, no one wants one, but we have to prepare for it and I hope they have it covered. Like I said, these are pretty smart people.

In an aircraft, the weight of the batteries and motor and how strong the structure will have to support them is concerning from a "what if it crashes" standpoint, along with fire/explosion mitigation.
One counterintuitive aproach to battery temp
management is to HEAT the battery before discharge and charge cycles,going from memory here ,but recent work published this year.The gist of it is that there is a best performance temp and getting it there first reduced the resistance,therefore current, and therefor heat.
And luckily for us ,all of the issues around weight,power density,reliability,saftey,and cost,
apply to all mobile aplications.
An ultra fast charge battery that lasts two weeks in a big phone is gona fly just fine.
 

BJC

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Junkers flaperons for full roll control at high AOA.
I’ve never flown with Junkers flaperons, but they look like they would lose roll power at high alpha.
Yes, but for a STOL bird you would still want the flaps.
Agree, but with Junkers deflected, do they provide adequate roll control?
A vortex generator on it might be a good idea though.
They work on my airplane; I have aileron roll control even stalled with flaps retracted. They seem to help maintain aileron roll control up to the stall with 30 degrees (full deflection) flaps.

Perhaps someone here has tested a vortex generator with lowered Junkers.


BJC
 

Saville

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One counterintuitive aproach to battery temp
management is to HEAT the battery before discharge and charge cycles,.....

Which takes energy and therefore must be added to the "cost"/energy utilization etc.
 

dog

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Which takes energy and therefore must be added to the "cost"/energy utilization etc.
Wrong.It is counterintuitive.The "cost" is more than paid back in reduced resistance and therefor heat,which is proof of increased overall efficiency.
Pick up your game.
 
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