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 pounds lighter than it took off, meaning the landing gear, wing spar attachments, and brakes can all be lighter.)
Many airplanes are certified for a ramp, taxi, and takeoff weight higher than their approved landing weight. Electrics will be unable to take advantage of this and must confine their takeoff weight to their landing weight.
I love that such rapid progress is being made in automotive, and I'd love to see that adoption increase so we can reserve petro-based fuels for cases where their energy density provides a compelling operational benefit, such as in aviation.
There is little question that carbon-based flight power is here to stay for quite some time, but that isn't really the point - which is that electric flight is nevertheless a growth industry, and there are some markets where electric flight can make a lot of sense. If all you need to do is go up and fly for 2 hours or so, then an electric plane is a viable contender for the investment - maybe we're not at the tipping point, but we are approaching it, technologically at least, a few knots at a time.
It is a worthwhile goal, though. If we can somehow harness the suns' energy to get us around the world instead of using the world itself (and thus screwing it up), then we move closer to the cusp of a more viable long-term civilization. At the moment, every cheap flight to somewhere on a jet plane costs the Earth a great deal of survival potential...
Surely the landing gear, wing spar attachments, and brakes all have to be able to cope with an unexpected turnback and landing with most of the original weight? (not to mention heavy landings in adverse weather conditions)
They are only certified to the maximum landing weight which typically is lower than the maximum takeoff weight. When an overweight landing (ie. the weight is higher then maximum landing weight) occurs engineers have to perform a thorough inspection of the plane structure - landing gear, spars, wings, wingbox
> 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 of magnitude worse specific energy than petroleum fuels (Li-Ion or AgZn store 0.46 MJ/kg, kerosene stores 43 MJ/kg)
> 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.
I entered the Local Motors and ARPA-E contest for the Lightweight Sedan challenge and proposed a three part method to reduce weight: Revised chassis, bio-composite materials, and a hybrid drivetrain using micro-turbines to produce electricity to power the vehicle. The contest parameters stressed that the proposal should be "research for the next 10 years." So, I cited the efficiency and extremely light-weight of micro turbines to piston engines, and postulated that increasing technology in battery / KERS systems would compliment the real-world application in time.
Needless to say, I was ridiculously mad when I saw that the winning entries were 1) an aerodynamic proposal based on an exoskeleton, 2) replacing body panels with a new metallurgy compound, and some other thing that I can't recall right now. None of them really addressed the contest parameters. It basically made me swear off any more Local Motors participation.
Anyway, the bright side is that I get to maintain all rights to my entry / materials, so one day, I just might have a chance to develop a concept based on these principles and show ARPA-E and Local Motors what they missed. I guess this is how Ferruccio Lamborghini must have felt at first. Sigh.
No, I mean like the chassis components were on the outside of the car, like a bug. That was the crux of their entry, mollified by some talk of aerodynamic efficiency. From what I recall, the rendered images of their concept didn't even have a method of entry for the driver/passengers. No doors. It was...well, frustrating, as my tone probably conveyed.
Re: Monocoque - my entry cited that format to give additional strength to the chassis/panels mating. Bio-composites are approaching the tensile strength of carbon fiber, and could potentially be much easier to mass produce and at a lower price point. I thought the implication that in 10 years, with research, such an avenue would be viable. Instead, the second place entry was some proprietary kind of new metal that could be used to replace body panels...that's it. I remember calling that entry a "body kit" because that's what it reminded me of overall.
Thanks for being interested / opportunity to clarify. The rendering actually looked like I-Beams curved into some kind of egg-like shape. It was mathematically sound, sure, but at first glance coming up with an answer "Where can research go with this?" didn't seem apparent.
I tuned in to every Q&A session provided during the contest and time and again they reiterated certain principles for judging...when the results came in, yeah, pretty infuriating. Oh well...it did motivate me to finally meet with a Patent Attorney on a couple other ideas, so some lemonade did come out of it.
I think we might see gasoline/jet-A over electric airplanes, perhaps with or without battery storage. That would allow a few neat optimizations. You'd have more control over CG. You could have a smaller high efficiency engine that always ran at peak efficiency (or an IC engine with several modes). You could have more control over noise in urban areas. With a battery for peak/boost power, you could have a tiny engine which could supply cruise plus accessory power and use battery-backed boost for takeoff/climb. Engines that are replaceable in a few hours. All kinds of good things could happen.
>Many airplanes are certified for a ramp, taxi, and takeoff weight higher than their approved landing weight.
Is that common in G/A aircraft?
In any case, I'd love to see a tech. revolution in GA powerplants. I've grown tired of having quaint old 1950's era tractor engines be the dominant technology.
metal-air fuel cells are in many respects even better. And with metal content around 50% they become weight comparable or better than 30% efficient ICE.
In that case you have lithium oxide to take care of and you have heavier plane with each second (of course most of the fuel is wasted on lifting the plane, so it may be better)
the electric planes, at least at first, isn't about just swapping ICE for electric. It is about building different planes. The current planes have evolved significantly under the limitations of ICE. The electric planes, at least initially, is about short-hoppers ("flying car" like functionality) where ICE is a no-go because of cost and noise. The electrics are well suited to build STOL and VTOL (multi-copters). With years the electrification can make its way through various hybrid schemes into much more efficient long-haulers.
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) unleaded fuel available today. That's true, but paints an incomplete picture. That's 70% by aircraft, not 70% by flight hours or fuel consumed.
Cape Air and similar and other turbocharged piston aircraft are the ones that can't use the available unleaded "mogas". Those are also the aircraft that fly the most hours and thereby use the most fuel. Fixing the 172s and Cherokees doesn't move the needle much on TEL emissions.
I want to get rid of the lead from my aviation fuel, both for environmental reasons and for practical reasons. (Practically, it's a pain to deal with on the supply chain side, is expensive, there's only one manufacturer of TEL worldwide, it tends to gunk and foul plugs, etc.)
The FAA is the regulatory body that is presiding over this, much more than the EPA. End running the FAA to get the EPA to make another "lead is bad" proclamation won't do any good, IMO.
My engines can't burn any available and certified unleaded fuel.
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].
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.
If you could run cargo planes on beamed power, you wouldn't have to haul your power storage (fuel) to altitude. Also, given the extreme simplicity and reliability of electric motors, such an infrastructure would save huge amounts of money and also avoid externalities like atmospheric pollution.
The big question, of course, is the ability to build such an infrastructure with enough reliability.
Perhaps an orbiting network of solar powered satellites that can each manage large numbers of directed power beams. Though maybe that would be a non starter due to the large number of non-civilian applications.
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)
How old are you? 50 years from now the world will be a lot different. It'll probably change as much as it did in the last 100, which to put into perspective:
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:
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 cruising speed, and that's why planes have not got faster for the last 50 years. Go higher, as electrics could do, and you reduce the air pressure further and could fly faster and more efficiently. Who knows when battery technology will be advanced enough, but it sounds like a goal worth shooting for (as well as the other benefits of noise reduction and environment concerns)
> 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.
That's a meaningless/nonsensical assertion. If we're going to ignore basically everything we can also state that nuclear is the future of air travel (and that's actually a more sensible statement, nuclear fuel has ridiculous specific energy).
I'm not sure it's ignoring everything - as this article states, electric planes exist today, and are improving at a fast rate. Batteries are also improving (thanks to Musk and others), not that electric planes needs to be battery based - fuel cells could be the answer (though presumably these require oxygen so might have altitude issues). So whilst far away, it's an extrapolation from our current position.
Nuclear planes don't exist today in any form, and would have major safety concerns no doubt (any accident would be pretty catastrophic)
> 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 available today and bog-standard jet fuel) in any sort of interesting timescale. And that's before considering environmental issues, most batteries don't appreciates temperatures of -20C and below.
> thanks to Musk
That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing.
> So whilst far away, it's an extrapolation from our current position.
It's not extrapolation it's daydreaming based on what is basically magical thinking. It's less of an extrapolation than dyson spheres are.
"That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing"
That's exactly what brings costs down: economies of scale via efficient mass production. Whether we're talking about dramatically boosting the electric car market, or the giga factory.
Dyson spheres? Now who's exaggerating. Electric airplanes already exist, and will continue to improve for decades to come. Dyson spheres do not exist, and are not on the horizon.
The problem of batteries on airliners is not cost, it's that they don't store enough energy per mass. Even if your batteries are free, when your plane can't take off because its mass has increased >10 fold there's very little point, you're left with an expensive bus too wide to take roads.
> Dyson spheres? Now who's exaggerating.
Same as before.
> Electric airplanes already exist, and will continue to improve for decades to come.
The original assertion is that they're the future of air travel, not the future of small-scale hobbyists.
> Dyson spheres do not exist, and are not on the horizon.
Both of which apply equally to electric airliners. Electric airliners require a literal technological revolution, so do dyson spheres.
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 from the airfield rather than from the aircraft? What about hybrid - use gas to get to 30,000 feet, then turn on electric to go higher than that?
Yes battery energy density is miles away currently, but if we avoid batteries in part, and improve them too, where might things be in 50 years time?
The point is we are on the journey with electric planes, and the goal is a good one for reasons stated. Major problems to overcome - absolutely, but this is not a short or medium term prediction. But 'Magical thinking' required, more so than Dyson spheres? That's harsh.
I think Musk said he'd like this to be a far future project for him. He said he's driven by not wanting to go backwards - how space travel was worse than the 60s, as is air travel (no supersonic public aircraft any more). Electric planes - if possible - would be the solution to faster air travel. With Tesla and SpaceX under his belt, he'd certainly got the necessary chops to tackle it.
How is a turbofan/turboprop engine going to work in the thin air at these high altitudes? True jet engines work because of the combustion of jetfuel, but those are not really used much...
> 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.
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 battery.
This sounds ridiculous at first, but when you consider how cheap electricity is compared to jet fuel, as well as the other benefits the OP mentioned, there might be something to it (for short-haul flights.)
> 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 as a 747)
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.
> 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 battery.
Weight is the premium on planes, so the 10% of non-battery you're talking about is a full plane minus fuel tanks. An E-170 is 21t of empty plane, up to 9t of fuel and up to 36t total (MTOW). Given batteries have 1% the energy specificity of aviation fuel (so you need 100 times the weight in batteries for the same stored energy), the math doesn't quite work out.
> This sounds ridiculous at first
And at second, and at third.
> when you consider how cheap electricity is compared to jet fuel
Doesn't compensate the problem of needing a plane 10 times as heavy with 1/10th the payload.
> as well as the other benefits the OP mentioned
Which don't really make sense, lower air density means your turboprops have nothing to work with, there's no such thing as turbofans let alone turbojet so the gains in drag are killed by the inability to actually go forward.
At Airventure last week I listened to a talk on an electric motor glider (http://electricmotorglider.com). One of the takeaways that I had was that with current battery technology, for electric motors to make more sense than a gasoline powered motors you have to have a flight time of less than 23 minutes. Above that, the reduced weight of fuel beats out the weight of batteries. We need additional research in the battery technology space before it's going to make sense for aircraft to be electric.
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:
>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.
If this is true, wouldn't it make more sense to bring liquid oxygen up with you to burn with the fuel? That would only reduce your fuel energy density by a factor of 2 or 3, instead of the factor of 30-100 being claimed for batteries.
Of course that would not make sense, and rockets don't become the most efficient way to travel until you are a few times higher than 30,000 ft. But it's useful to put the idea of batteries in perspective.
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.
Reminds me of a german startup that designs a vertical takeoff and landing, two seated electric plane with an interesting form factor: http://lilium-aviation.com/
[Edit: no affiliation]
"In a statement, Pipistrel said Siemens prohibited the use of its motor for a flight over water."
I am not sure how that could happen? Surely if they bought the engines they could have done whatever they wanted with them? Unless they were leased from Siemens or something.
Maybe to get permission for your flight plan when using an experimental vehicle you have to be able to show that the manufacturers of the major components have confidence it will be able to complete the proposed route safely?
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[ 3.4 ms ] story [ 125 ms ] threadWhy? 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 pounds lighter than it took off, meaning the landing gear, wing spar attachments, and brakes can all be lighter.)
Many airplanes are certified for a ramp, taxi, and takeoff weight higher than their approved landing weight. Electrics will be unable to take advantage of this and must confine their takeoff weight to their landing weight.
I love that such rapid progress is being made in automotive, and I'd love to see that adoption increase so we can reserve petro-based fuels for cases where their energy density provides a compelling operational benefit, such as in aviation.
It is a worthwhile goal, though. If we can somehow harness the suns' energy to get us around the world instead of using the world itself (and thus screwing it up), then we move closer to the cusp of a more viable long-term civilization. At the moment, every cheap flight to somewhere on a jet plane costs the Earth a great deal of survival potential...
They are only certified to the maximum landing weight which typically is lower than the maximum takeoff weight. When an overweight landing (ie. the weight is higher then maximum landing weight) occurs engineers have to perform a thorough inspection of the plane structure - landing gear, spars, wings, wingbox
EDIT: thanks ForHackernews
I assume this was a typo and you mean that the max landing weight is typically less than the max takeoff weight.
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 of magnitude worse specific energy than petroleum fuels (Li-Ion or AgZn store 0.46 MJ/kg, kerosene stores 43 MJ/kg)
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.
Needless to say, I was ridiculously mad when I saw that the winning entries were 1) an aerodynamic proposal based on an exoskeleton, 2) replacing body panels with a new metallurgy compound, and some other thing that I can't recall right now. None of them really addressed the contest parameters. It basically made me swear off any more Local Motors participation.
Anyway, the bright side is that I get to maintain all rights to my entry / materials, so one day, I just might have a chance to develop a concept based on these principles and show ARPA-E and Local Motors what they missed. I guess this is how Ferruccio Lamborghini must have felt at first. Sigh.
Re: Monocoque - my entry cited that format to give additional strength to the chassis/panels mating. Bio-composites are approaching the tensile strength of carbon fiber, and could potentially be much easier to mass produce and at a lower price point. I thought the implication that in 10 years, with research, such an avenue would be viable. Instead, the second place entry was some proprietary kind of new metal that could be used to replace body panels...that's it. I remember calling that entry a "body kit" because that's what it reminded me of overall.
I tuned in to every Q&A session provided during the contest and time and again they reiterated certain principles for judging...when the results came in, yeah, pretty infuriating. Oh well...it did motivate me to finally meet with a Patent Attorney on a couple other ideas, so some lemonade did come out of it.
>Many airplanes are certified for a ramp, taxi, and takeoff weight higher than their approved landing weight.
Is that common in G/A aircraft?
In any case, I'd love to see a tech. revolution in GA powerplants. I've grown tired of having quaint old 1950's era tractor engines be the dominant technology.
I suspect all GA turbojets and most GA turboprops are in this situation.
Even the Beech Baron (a light twin) has a 100# (~16 gallons) difference in max takeoff vs max landing weight.
*the whole membrane degradation thing excluded
Toy planes (general aviation) are responsible for the majority of lead pollution:
www.emagazine.com/earth-talk/lead-in-aviation-fuel
The magazine article you reference says that 70% of aircraft could use (a lower octane) unleaded fuel available today. That's true, but paints an incomplete picture. That's 70% by aircraft, not 70% by flight hours or fuel consumed.
Cape Air and similar and other turbocharged piston aircraft are the ones that can't use the available unleaded "mogas". Those are also the aircraft that fly the most hours and thereby use the most fuel. Fixing the 172s and Cherokees doesn't move the needle much on TEL emissions.
I want to get rid of the lead from my aviation fuel, both for environmental reasons and for practical reasons. (Practically, it's a pain to deal with on the supply chain side, is expensive, there's only one manufacturer of TEL worldwide, it tends to gunk and foul plugs, etc.)
The FAA is the regulatory body that is presiding over this, much more than the EPA. End running the FAA to get the EPA to make another "lead is bad" proclamation won't do any good, IMO.
My engines can't burn any available and certified unleaded fuel.
[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
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.
The big question, of course, is the ability to build such an infrastructure with enough reliability.
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)
http://www.aerofiles.com/gallaudet-c2-1915.jpg
http://www.museumofflight.org/747
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/4/2014/10/...
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.
That's a meaningless/nonsensical assertion. If we're going to ignore basically everything we can also state that nuclear is the future of air travel (and that's actually a more sensible statement, nuclear fuel has ridiculous specific energy).
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 available today and bog-standard jet fuel) in any sort of interesting timescale. And that's before considering environmental issues, most batteries don't appreciates temperatures of -20C and below.
> thanks to Musk
That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing.
> So whilst far away, it's an extrapolation from our current position.
It's not extrapolation it's daydreaming based on what is basically magical thinking. It's less of an extrapolation than dyson spheres are.
> Nuclear planes don't exist today in any form
Nuclear planes were demonstrably feasible (if not necessarily smart) in the 60s: https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL
That's exactly what brings costs down: economies of scale via efficient mass production. Whether we're talking about dramatically boosting the electric car market, or the giga factory.
Dyson spheres? Now who's exaggerating. Electric airplanes already exist, and will continue to improve for decades to come. Dyson spheres do not exist, and are not on the horizon.
The problem of batteries on airliners is not cost, it's that they don't store enough energy per mass. Even if your batteries are free, when your plane can't take off because its mass has increased >10 fold there's very little point, you're left with an expensive bus too wide to take roads.
> Dyson spheres? Now who's exaggerating.
Same as before.
> Electric airplanes already exist, and will continue to improve for decades to come.
The original assertion is that they're the future of air travel, not the future of small-scale hobbyists.
> Dyson spheres do not exist, and are not on the horizon.
Both of which apply equally to electric airliners. Electric airliners require a literal technological revolution, so do dyson spheres.
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 from the airfield rather than from the aircraft? What about hybrid - use gas to get to 30,000 feet, then turn on electric to go higher than that? Yes battery energy density is miles away currently, but if we avoid batteries in part, and improve them too, where might things be in 50 years time? The point is we are on the journey with electric planes, and the goal is a good one for reasons stated. Major problems to overcome - absolutely, but this is not a short or medium term prediction. But 'Magical thinking' required, more so than Dyson spheres? That's harsh.
I think Musk said he'd like this to be a far future project for him. He said he's driven by not wanting to go backwards - how space travel was worse than the 60s, as is air travel (no supersonic public aircraft any more). Electric planes - if possible - would be the solution to faster air travel. With Tesla and SpaceX under his belt, he'd certainly got the necessary chops to tackle it.
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.
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 battery.
This sounds ridiculous at first, but when you consider how cheap electricity is compared to jet fuel, as well as the other benefits the OP mentioned, there might be something to it (for short-haul flights.)
Jet Fuel has about 128kBTU/gal and is available around $2/gal, so 64kBTU/$.
Electricity is about 3400BTU/kWhr and a kWhr is about $0.05, or about 68kBTU/$.
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...
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 as a 747)
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.
Weight is the premium on planes, so the 10% of non-battery you're talking about is a full plane minus fuel tanks. An E-170 is 21t of empty plane, up to 9t of fuel and up to 36t total (MTOW). Given batteries have 1% the energy specificity of aviation fuel (so you need 100 times the weight in batteries for the same stored energy), the math doesn't quite work out.
> This sounds ridiculous at first
And at second, and at third.
> when you consider how cheap electricity is compared to jet fuel
Doesn't compensate the problem of needing a plane 10 times as heavy with 1/10th the payload.
> as well as the other benefits the OP mentioned
Which don't really make sense, lower air density means your turboprops have nothing to work with, there's no such thing as turbofans let alone turbojet so the gains in drag are killed by the inability to actually go forward.
http://www.aviation.com/general-aviation/elon-musk-toying-de...
If this is true, wouldn't it make more sense to bring liquid oxygen up with you to burn with the fuel? That would only reduce your fuel energy density by a factor of 2 or 3, instead of the factor of 30-100 being claimed for batteries.
Of course that would not make sense, and rockets don't become the most efficient way to travel until you are a few times higher than 30,000 ft. But it's useful to put the idea of batteries in perspective.
https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft
I am not sure how that could happen? Surely if they bought the engines they could have done whatever they wanted with them? Unless they were leased from Siemens or something.
Additional info this thread: https://news.ycombinator.com/item?id=9850330
I think this says it all.