[HN Gopher] Skeptical About Electrical
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Skeptical About Electrical
Author : prostoalex
Score : 15 points
Date : 2021-11-11 16:41 UTC (6 hours ago)
(HTM) web link (www.planeandpilotmag.com)
(TXT) w3m dump (www.planeandpilotmag.com)
| bklyn11201 wrote:
| For anyone else like me wondering why hydrogen is difficult for
| airplanes (not mentioned in the OP article):
|
| from https://www.bbc.com/future/article/20210401-the-worlds-
| first... --------------
|
| Hydrogen has higher energy by mass than jet fuel, but it has
| lower energy by volume. This lower energy density is because it
| is a gas at typical atmospheric pressure and temperature. The gas
| needs to be compressed or turned into a liquid by cooling it to
| extremely low temperatures (-253C) if it is to be stored in
| sufficient quantities. "Storage tanks for the compressed gas or
| liquid are complex and heavy," says Finlay Asher, a former
| aircraft engine designer at Rolls-Royce and founder of Green Sky
| Thinking, a platform exploring sustainable aviation.
|
| And there are other challenges. The energy density of liquid
| hydrogen is only about a quarter of that of jet fuel.
| ncmncm wrote:
| Probably you will want liquified H2. So, we need volume
| manufacturing of aerogel, for the tanks. If we don't go to
| wholly new airframes, we will need to sling the LH2 tanks in
| nacelles under the wings, like the engines, because the needed
| tankage volume won't fit inside normal wings. (With a new
| airframe with more internal space, the tanks could be inboard,
| but maybe you don't really want big tanks of LH2 inboard.)
|
| The LH2 would be electrolyzed on demand at the airport, using
| power delivered by transmission lines from all over, banking
| LH2 when the sun is out or the wind is blowing, when it is
| cheapest.
|
| Once these planes start flying, it will become impossible to
| compete with them, because the smaller mass of fuel needed
| translates to substantially more freight, both total capacity
| per flight, and per unit-cost of fuel. But there are still
| things to work out, so there will be an interim need to
| synthesize jet fuel from atmospheric CO2 and H2, which should
| soon get cheaper than extraction.
|
| It would be helpful if somebody were to come up with a good use
| for all the waste oxygen everyone is going to be producing.
| PostThisTooFast wrote:
| Not to mention that compressing or liquifying gas takes a
| shitload of energy to begin with.
| aplummer wrote:
| This is an industry we will be trying to improve for several
| hundred years from now at least. Very good chance electric
| airplanes are not feasible today, or tomorrow, but this is a long
| game. Maybe it won't be typical batteries, and very likely not
| lithium ion batteries.
| PostThisTooFast wrote:
| I think it'll age pretty well. I want electric airplanes to be
| viable, but come on.
| thehappypm wrote:
| I don't really buy the main counter arguments here.
|
| First, the current tech as stated in the article is short
| flights, like an hour. That's actually a niche that's already
| marketed--luxury flights to Martha's Vineyard, Tahoe, Bar Harbor.
| People are already paying for these flights today.
|
| Second, the heat issue. Batteries do suffer from cold weather but
| if it's an hour flight, with the batteries dumping their full
| charge, between thermal heating and simply insulating your
| battery it can stay warm.
| sokoloff wrote:
| I likewise don't get the breathless exuberance over the prospect
| of electric airplanes. Weight matters a little bit in cars.
| Weight matters one hell of a lot in light airplanes.
| kurthr wrote:
| Fuel and Maintenance costs, they're about 10-20% and 30% of
| total costs (flight/ground crew, landing/taxes, and
| amortization make up much of the rest) respectively. Combined
| they are a huge portion of potential cost reduction.
| LittlePeter wrote:
| I have mostly questions...
|
| Are we at the theoretical limit of energy density in current
| batteries? How much more progress can we make, in theory? Could
| it be that in 20 years we find drastically better materials for
| batteries? Materials which would make electrical flight feasible.
|
| Assuming high energy-density batteries are coming, shouldn't you
| start now with developing electrical airplanes to be one step
| ahead of competition?
| evandijk70 wrote:
| Assuming that higher energy-density batteries are possible is
| an extremely big ask. Yet somehow, plane companies are valued
| as if there is a commercial business case. I think long-range
| (over 2000 km), big airplanes are as far away as fusion power
| plants. Maybe even further, as fusion does not require any
| theoretical breakthroughs. You don't see big valuations for
| companies purporting fusion power generators, but for some
| reason, you do for electric planes..
| jareklupinski wrote:
| jumping on with one more question: would there be an advantage
| to lining the wings/flat surfaces with solar cells and patching
| them into the powertrain, helping drive even higher efficiency
| gains during optimal weather?
| dsign wrote:
| I did the math for that one, though not exactly for an
| airplane, but for a boring land vehicle (think Ford Traffic).
| I assumed futuristic photovoltaics with 40% efficiency, a
| factor of 0.7 to account for angle-of-incidence
| inefficiencies, pretty much all of of the van covered in
| panels, for an area of about 16 square meters, similar to the
| wing area of a glider Schleicher ASW 22 (I couldn't find the
| wing area of a Cessna 172).
|
| The result I get is somewhere from 3 to 8 kilowatts. A quick
| search in the Internet shows that a typical car has engine
| power starting at 130 horsepowers, which is 95 kilowatts. A
| van the size of a Ford traffic probably uses twice as much,
| and the Cessna uses 132 kilowatts.
|
| So, no, I don't think we are getting aviation as it exists
| today with solar panels and batteries, but one hour twenty
| minutes in good weather will be enough for some recreational
| pursuits.
|
| I also did the math for sailplanes with solar panels. That
| looks better, if all you are looking for is activating the
| propeller for a small fraction of the total flight time, or
| having an aircraft that can go very slow (that, in fact, has
| been done). I'm just an amateur, but my opinion is that,
| without solving the energy density issue, about 98% of the
| aviation we enjoy today will be gone.
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