Electric Planes Usher in the Second Great Age of Aviation • Hacker News Board

Re: Electric Planes Usher in the Second Great Age of Aviation

#61

Post by srb- » Tue, Jul 28, 2015, 6:08 PM UTC

masklinn wrote: post #32

coryrc wrote: post #27

Earlier quoted context omitted.

Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. Fuel costs are about 35%[1] of operating costs, so only a ~20% cost reduction is possible for fuel change, so your point is still mostly valid. [1] https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency [2] http://www.ajc.com/news/business/airlines-keep-adapting-to-h...

> Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. But then batteries store 1% the energy per mass fuel does so even assuming triple the efficiency, the energy storage is 30 times easier (assuming everything else stays constant which it can't because now your craft is an order of magnitude heavier and your short-haul plane is as heavy a…

Ah, thanks for putting some numbers out there everyone. Very interesting. That's why I love HN.

Musk has said several times that if he wasn't working on space and EVs, he'd be working on hyperloop or electric planes. Wonder what potential he sees in the latter.

Re: Electric Planes Usher in the Second Great Age of Aviation

#62

Post by sehugg » Tue, Jul 28, 2015, 6:13 PM UTC

simonsquiff wrote: post #5

I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to fly higher - increasing efficiency and speed. Apparently the normal 30,000 feet cruising altitude is not higher because the reduced oxygen levels at higher altitudes impact the gasoline combustion too much. Even at 30,000 feet the air is thick as soup at cruisi…

There are other considerations, like how stall speed and critical Mach intersect as you go higher (https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%...). So any plane that can fly above 60,000 feet is likely going to be a supersonic design. More drag, more heat, more complexity. Concorde had plenty of issues that had nothing to do with the power plant.

Re: Electric Planes Usher in the Second Great Age of Aviation

#63

Post by melling » Tue, Jul 28, 2015, 6:28 PM UTC

maxerickson wrote: post #60

melling wrote: post #58

Earlier quoted context omitted.

You probably should have gone with 46 years ago: https://upload.wikimedia.org/wikipedia/commons/1/11/Concorde... What was your point? Here's a computer from 1965: http://www.columbia.edu/cu/computinghistory/a10.jpg Not all technology is increasing at the same rate. Adoption is another problem. Take this bullet train from 1964. Still won't find that in America. http://cdn.gaijinpot.com/wp-content/uploads/sites/4/2014/…

Given your example, I thought you were talking about aircraft, so the diminishing returns in the recent 50 years seemed salient.

Nope, we were talking more about the ability to generate electricity for an electric plane, right? Battery technology, or something else that can deliver electricity.

Of course, 50 years from now we'll have commercial scramjets:

https://en.m.wikipedia.org/wiki/Scramjet

So, progress will be made on many fronts.

Re: Electric Planes Usher in the Second Great Age of Aviation

#64

Post by masklinn » Tue, Jul 28, 2015, 6:32 PM UTC

andrewla wrote: post #41

masklinn wrote: post #10

Earlier quoted context omitted.

> The energy density of batteries sadly lags the energy density of gasoline or kerosene Nitpick but the energy/mass density is usually called "specific energy" to differentiate it with the more usual energy/volume "energy density". And while a battery's energy density is pretty bad, they pretty universally have a higher density than petroleum fuels and thus even worse specific energy: the best batteries have 2 orders…

> And while a battery's energy density is pretty bad, they pretty universally have a higher density than petroleum fuels and thus even worse specific energy Is there a typo in there? Energy density (MJ/L) for batteries is lower than petroleum fuels by the same order of magnitude as the specific energy.

While batteries have very energy density compared to petroleum fuels, on average it's much better (compared to petroleum fuels) than their specific energy. Their energy density is 15 ~ 40 times lower than petroleum fuels whereas their energy density is 50 ~ >100 times lower.

Re: Electric Planes Usher in the Second Great Age of Aviation

#65

Post by mikeyouse » Tue, Jul 28, 2015, 6:48 PM UTC

srb- wrote: post #20

simonsquiff wrote: post #5

I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to fly higher - increasing efficiency and speed. Apparently the normal 30,000 feet cruising altitude is not higher because the reduced oxygen levels at higher altitudes impact the gasoline combustion too much. Even at 30,000 feet the air is thick as soup at cruisi…

Like most, I originally assumed that because batteries have poor specific energy compared to fossil fuels, there was no point in considering them for aircraft. But Musk's assertion has made me reconsider. Has anyone here done the math? What I think he's talking about is NOT a conventional plane with a battery simply replacing the gas tank, but instead essentially a flying battery, where 90% of the plane's mass is bat…

Just so people have a basis for his figures, Musk's calcs rely on 400wh/kg batteries and ~75% cell-mass fraction which he thinks will be sufficient for transcontinental flights. Another way to improve efficiency is be removing 'unneeded' components on the planes like tails, rudders, and elevators by just gimballing the electric fans for control. An article with a few embedded clips where he discusses his proposed VTOL supersonic electric plane:

http://www.aviation.com/general-aviation/elon-musk-toying-de...

Re: Electric Planes Usher in the Second Great Age of Aviation

#66

Post by masklinn » Tue, Jul 28, 2015, 6:53 PM UTC

simonsquiff wrote: post #47

masklinn wrote: post #16

Earlier quoted context omitted.

> I'm not sure it's ignoring everything - as this article states, electric planes exist today Prop toys exist, not "future of aviation" anything. Props being an other issue, electric planes means no turbofans. > Batteries are also improving Batteries are not improving at a rate which would increase their specific energy by 2 orders of magnitude (the difference between the specific energy of the best batteries availab…

The original supposition was that electric planes are the future - albeit a future very far way - because electric means no oxygen concerns, which means higher altitude, which increases efficiency and / or speed. Now, electric doesn't mean battery. Fuel cells, solar, or even hybrid might all play a part. I believe a large proportion of energy consumption is during takeoff - what if you could draw take off power needs…

> The original supposition was that electric planes are the future - albeit a future very far way - because electric means no oxygen concerns, which means higher altitude

But higher altitude means lower air density which means your turboprops windmill into nothingness and have no way to propel the plane forward (even ignoring the issue of staying up in the air at all, existing airliners already fly quite close to the limits of their flight envelopes in normal conditions).

> What about hybrid - use gas to get to 30,000 feet, then turn on electric to go higher than that?

And where would you get the energy to do that in-flight? Certainly not solar, Helios already had a larger wingspan than a 747-8.

> Major problems to overcome - absolutely, but this is not a short or medium term prediction.

Neither are dyson spheres, and at least we've got some idea about how to handle those.

> But 'Magical thinking' required, more so than Dyson spheres? That's harsh.

Is it now?

> no supersonic public aircraft any more

There is no supersonic "public" aircraft because people have decided it wasn't worth the cost and have gravitated towards cheap high-density flying instead, it's not like we're flying any less than in the 60s or less far (a 777LR can go halfway around the globe without stopping) so the comparison to space travel is bonkers.

> Electric planes - if possible - would be the solution to faster air travel.

That doesn't make a lick of sense, electric engines are the slowest thing you can find in the sky. The only way "electric planes" would be faster than turbojets — let alone ramjets or rocket engines — is for the plane itself to be a ballistic component launched by a gigantic railgun, and then — assuming you manage to build the thing in the first place — your passengers are literally paste on takeoff as they eat a few hundred Gs.

Re: Electric Planes Usher in the Second Great Age of Aviation

#67

Post by coryrc » Tue, Jul 28, 2015, 7:03 PM UTC

sokoloff wrote: post #53

coryrc wrote: post #28

Earlier quoted context omitted.

Electric planes could stop GA poisoning everyone with lead. You could also choose a different fuel. Toy planes (general aviation) are responsible for the majority of lead pollution: www.emagazine.com/earth-talk/lead-in-aviation-fuel

The FAA certification process is the largest limiting factor for bringing an unleaded fuel to the market. There are about 9 different formulations of unleaded fuels flying in experimental aircraft right now. I have my own "favorite", but it's unclear when, if ever, that will be available for sale to non-experimental aircraft. The magazine article you reference says that 70% of aircraft could use (a lower octane) unle…

AOPA lobbies to delay unleaded fuel at every opportunity [1] [2] [5]. Unleaded fuel is available now [3], but 10% of owners would have to spend some money to stop poisoning 3 million children [4].

[1] http://www.aopa.org/News-and-Video/All-News/2015/April/01/Bi...

[2] http://www.agairupdate.com/article_detail.php?_kp_serial=000...

[3] http://www.flyingmag.com/blogs/flying-time/transition-unlead...

[4] the link in my GP post

[5] http://blog.aopa.org/vfr/?p=870

Re: Electric Planes Usher in the Second Great Age of Aviation

#68

Post by masklinn » Tue, Jul 28, 2015, 7:14 PM UTC

elektromekatron wrote: post #46

sokoloff wrote: post #2

I drive an electric car and fly piston airplanes. I don't see electrics replacing internal combustion in aviation in my flying lifetime. Why? Weight. The specific energy (energy per kg, edited per masklinn) of batteries sadly lags the specific energy of gasoline or kerosene, and the airplane carries that weight for the whole flight for an electric airplane. (My gas airplane gets lighter and lands as much as 1000 poun…

It maybe isn't quite as bad as you think, as what really matters is the thrust for the combined weight of the engine and power source rather than just the energy density of the power source in joules per kilo. Combustion is generally pretty lousy, compared to electric, at converting joules into useful newtons.

Combustion is about 30% efficient, electric is about 95% efficient, so for the same energy input electric gets you 3 times (and a bit) the output.

Problem is, getting the same energy input via batteries weights 50~100 times as much as fuel does, and takes 15~40 times as much room. So your fuel still weighs 20~30 times as much, and takes 5~10 times as much room in your plane.

And while combustion is 30% efficient part of the energy loss can be used to heat up the cabin, because at 30000~40000ft you're not exactly at sauna temperatures outside, so now you need to spend part of your electricity to heat passengers and your batteries (because most of them don't like operating at 200K)

Re: Electric Planes Usher in the Second Great Age of Aviation

#69

Post by sokoloff » Tue, Jul 28, 2015, 7:40 PM UTC

coryrc wrote: post #67

sokoloff wrote: post #53

Earlier quoted context omitted.

The FAA certification process is the largest limiting factor for bringing an unleaded fuel to the market. There are about 9 different formulations of unleaded fuels flying in experimental aircraft right now. I have my own "favorite", but it's unclear when, if ever, that will be available for sale to non-experimental aircraft. The magazine article you reference says that 70% of aircraft could use (a lower octane) unle…

AOPA lobbies to delay unleaded fuel at every opportunity [1] [2] [5]. Unleaded fuel is available now [3], but 10% of owners would have to spend some money to stop poisoning 3 million children [4]. [1] http://www.aopa.org/News-and-Video/All-News/2015/April/01/Bi... [2] http://www.agairupdate.com/article_detail.php?_kp_serial=000... [3] http://www.flyingmag.com/blogs/flying-time/transition-unlead... [4] the link in my…

That UL fuel that's "available now" [3] is available now in Sweden only and doesn't work for the 10% of engines that require 100 octane fuel, those 10% of engines likely consuming >50% of the avgas sold.

If it was a matter of spending some reasonable (say mid 5 figure per airplane) sum of money to burn a readily available UL fuel, I'd do it. I literally can't do that.

There is no current path to certification for me to run that 91/96UL here in the US. It's a technical problem (maintaining adequate detonation margins on a high/hot takeoffs), a regulatory problem (getting the airframe and engine certified for the fuel), and a market problem (getting that fuel sold at airports here in the US). You have to solve the first to get to the second. I believe there are several viable compounds/blends now in testing and we're on to the second phase: getting one or more of them certified by the FAA. Only once that's done is it viable to talk about banning or curbing TEL use. If there's one clear winning fuel, the adoption by the industry will be swift (no pun intended, as SWIFT is one of the contenders, though I don't believe a leading contender).

I don't read any of those three AOPA links as AOPA trying to "delay unleaded fuel" in any way, shape, or form. One is an objection to an increase of tax on avgas (certainly one of the things I/we pay AOPA to lobby against), and the other two are presentations describing the technical reasons avgas contains lead now and the status of initiatives underway to create an alternative, unleaded fuel.

Re: Electric Planes Usher in the Second Great Age of Aviation

#70

Post by greedo » Wed, Jul 29, 2015, 10:52 PM UTC

melling wrote: post #63

maxerickson wrote: post #60

Earlier quoted context omitted.

Given your example, I thought you were talking about aircraft, so the diminishing returns in the recent 50 years seemed salient.

Nope, we were talking more about the ability to generate electricity for an electric plane, right? Battery technology, or something else that can deliver electricity. Of course, 50 years from now we'll have commercial scramjets: https://en.m.wikipedia.org/wiki/Scramjet So, progress will be made on many fronts.

Battery technology isn't progressing at anywhere near the rate of computer technology.