Look at this way, if you're up at 20,000 feet and the batteries go flat then the passengers could start peddling to recharge them!
EasyJet has given its blessing to a mildly bonkers plan to replace airliners with electrically propelled aircraft on short-haul flights. The low-cost airline is supporting American startup Wright Electric, which, judging by the picture on its homepage, wants to insert a large number of ducted fans into the wing-root area of …
No, the Captain flips a switch and the charging ports become de-charging ports and the airplane keeps flying for a few more minutes
Imagine the howls of complaint from the passenger cabin.
Captain: "Look, you idiots, you can either carry on posting your vapid nonsense on Twitter or we can carry on flying."
Captain: "Alright, you asked for it. Me and the co-pilot have parachutes."
Twitterer: "I neva knew freefall was so much f..."
I think large electric commercial carriers are a long way off.
However, I fly giiders and we are on the cusp of a move for motor-assisted aircraft to move from small IC (90 minute duration) to electric (currently 45 minute duration and rising, price is pretty similar). The same goes for launch systems (winches and tug aircraft).
So at the "small" end of commercial aviation it may well be that a ten year horizon for electric propulsion is feasible.
GIven the work that Renault et al are doing on 'in-motion" EV charge systems (car is charged as it passes over the road) it's not beyond reason to go for runways that provide initial takeoff power. That helps, as acceleration to flying speed is not an insignificant part of the overall energy budget of an aircraft.
A hybrid dirigible that uses aerodymanic lift as well as internal bouyancy would probably be feasible right now. Slower, but for the smaller/shorter routes that may not matter.
Or big electric catapults: might scare the punters :-)
For self launching gliders, where the mission requires relatively much power (in glider terms), but not much energy (just enough to get up into thermals, and then some to get home after you screwed up), electric propulsion beats infernal combustion today (even with regards to aircraft empty weight). HOWEVER, the energy density of today's batteries is two orders of magnitude less than hydrocarbons.
Anybody who projects battery powered airliners in the relatively near future either does not know what he or she is talking about, or has the need for some positive (although gullible) press. (for example, Boeing hyped the Sonic Cruiser when Airbus was about to roll out the A380)
What can be expected is varying degrees of hybridization, where energy production can take place on one location, while the propulsors are distributed where it is aerodyynamically advantageous.
So: Expect battery electric sailplanes, aerobatic machines, initial trainers, and maybe even intra city hoppers to dominate the future. Everything else needs a different energy storage solution.
and Keith.. try to guess what I do for a living :)..
Actual railgun launch is around 100 000g acceleration.
As for a carriage well the USN has got that EMALS thing working and that can throw about 27 tonnes of F35 into the air in 45 secs,
An Airbus A380 is about 575 tonnes, or 21x bigger.
As for a carriage well the USN has got that EMALS thing working and that can throw about 27 tonnes of F35 into the air in 45 secs,
An Airbus A380 is about 575 tonnes, or 21x bigger.
Looks like each airport would need its own power plant to launch and charge planes, doesn't it?
... That actually might work. Build a new airport? Include a power plant.
Build a new power plant? Include a new airport.
"Looks like each airport would need its own power plant to launch and charge planes, doesn't it?"
Well they could capture energy from landing planes to avoid all that wasted energy on brakes and retro thrust. Arrestor Hook on the back , cocks the catapult for next plane.
The force on the A380 front landing gear is designed to be in the opposite direction of an EMALS catapult. The first time they try to catapult an unmodified aircraft will be very exciting as the front gear is torn away and propelled miles into the next town.
An aircraft must have a safe rate of climb without external add-ons in order to cope with missed-approach situations That requirement would prevent fitting smaller "cruise only" engines.
In addition the aircraft will need at least enough charge in its battery to get to its intended destination, then execute a missed approach followed by a diversion to an alternate airport & landing (with the alternate being far enough away that it is unlikely to be experiencing the same shitty weather that caused the missed approach at the intended destination).
GIven the work that Renault et al are doing on 'in-motion" EV charge systems (car is charged as it passes over the road) it's not beyond reason to go for runways that provide initial takeoff power.
I'd have thought a passenger-friendly version of a steam catapult (ie just pull the aeroplane, not transfer energy for its own motors) would serve this purpose much more simply, no?
Since this isn't done already, I guess there's either some difficulty that can't be overcome or the benefit isn't enough to warrant it. *Shrugs*
Or go for JATO or RATO bottles on the aircraft. They've been mounting the military has been mounting them on various C-xxx aircraft for some time. Noisy, smoky, and the expended ones need to be dropped after use. The dropping part might clear the neighborhoods built at the end of runways, however.
The military has also been fitting them with more bottles than needed for a launch as a backup or for missed landings and requiring a go-around.
"A hybrid dirigible that uses aerodymanic lift as well as internal bouyancy would probably be feasible right now. Slower, but for the smaller/shorter routes that may not matter."
Wouldn't the problem be that going slowly DOESN'T generate much lift unless you have honking HUGE wings?
I was thinking exactly the same thing - I wonder if they could back in more passengers if everyone was on an exercise bike style contraption rather than a regular seat?
That would actually take up more room. The next obvious evolution in airline seating is standing through the whole trip.
" The next obvious evolution in airline seating is standing through the whole trip."
To me its lying down. Where you have 3 seats abreast i'd much rather have 3 bunks / tubes . like those things in japan . tak a nap , read a book , all the things you can do sitting , plus sleep .
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The whole concept is bonkers (unless they're in possession of some technology beyond the currently understood laws of physics). Electric cars work well (up to a point), but they're massively heavy because they're full of batteries. On a surface vehicle this isn't an insuperable obstacle, but aircraft designers grapple constantly with how to shed every excess pound. An aircraft (even a personal one*) with sufficient battery power for an hour's duration flight would be far too massive to get off the ground.
* Unless you're looking at something like the Gossamer Albatross or the Solar Impulse - but they're no-ones idea of a prototype airliner. A top speed of 75 kts would be a bit of a drawback, for a start.
Easy jet already prefer you not to bring hold luggage (or, well, charge a bloody fortune for it), so make that even more 'preferable' and use the space in the hold that would have suitcases in it, for freaking giant, easily removable, batteries.
During passenger loading / unloading, forklift comes and takes the old batteries out, shoves some new ones in.
Vulcan, Valiant, Victor - all wing root engines. Also DH Comet
Engines in the roots make for a noisier aircraft internally. Not so noticeable on military aircraft when crew all up front. Comet less of a problem because it was still much quieter (and smoother) than a piston engine aircraft.
I should also add that narrow turbojets (or low-bypass turbofans) take up less frontal area than high bypass turbofans hence they could fit them in wingroot.
According to Bill Gunston this was because the UK industry badly miscalculated the drag on podded engines.
Putting the engines in pods on the wings apparently stops the wings "waggling" about as much and definitely makes them a lot easier to service
And of course putting them next to the fuselage means the cabin is either much noisier or you have to increase sound insulation a lot.
That said the Victor and Vulcan looked stunning aircraft, despite neither being actually supersonic.
(1) increase the buoyancy of the plane by, say, having some hydrogen or helium filled bag on the top.
(2) supplementing the main engines by way of ducted turbo fans so that take-off and landing thrust is generated by burning kerosene, but they can be throttled way back during level flight.
(3) using some form of chemo-electrical reaction to create the electricity needed. No idea what, I'm not a chemist.
It sounds like a fantasy, but who are we if we are not the makers of dreams into reality? Once upon a time, saying that I could see and speak to an explorer on an antarctic plateau, hold a conversation with them, send them a photograph and a document and receive it back in a matter of seconds, one might have received a look of incredulity and a comment about training magic fairies as carrier pigeons.
Just don't let Samsung batteries near this.
Why not? It seems a perfect system, battery burns, generating hot gas which you then expel in a jet from the rear of the aircraft through some sort of nozzle.
It seems crazy but jet propelled aircraft without propellers might be the future
No problem if its their money. If on the other hand the chief ambition is to blag large quantities of venture capital cash and convert as much as possible into executive salaries while doing just enough press releases and "proof of concept" demonstrations to keep the taps flowing and hope they get lucky then that's another matter.
use sunlight as fairy dust. if the machines stuffed with tlighter than air gas , you can just get a little solar fan to push it along. Or sails - why didnt zeppeloins do that? oh wait , no centreboard - would only work downwind . dosent seem to stop Hot air balloners though.
> (3) using some form of chemo-electrical reaction to create the electricity needed. No idea what, I'm not a chemist.
Using some sort of magic fairly dust to keep the plane in the air for free. No idea what, I'm not a magician.
Innit obvious? Just stick a windmill on top of the plane! ☺☺☺
The hybrid electric. As airliners already run a small gas turbine at the rear to provide auxiliary electric power, and carry this in flight as a dead weight. Scale it up a bit, or add a second and use it to provide in flight electricity and use the exhaust for a little extra thrust.
I'm not going to downvote you, but analyze each of your ideas as simply as possible so you understand maybe why so many people are being 'negative':
1. That's called a blimp or a rigid airship, not a plane. H2/He is lighter than air, but metal, people, and batteries are far, far proportionally denser than air. Therefore you need a massive volume of lifting gas relative to the aircraft, which becomes a whole new set of engineering problems beyond an airplane.
2. This is at least a plausible idea, but I would guess that given the weight of two sets of engines this wouldn't be worthwhile. A jet engine that can run on both hydrocarbons and by electricity seems like it would be too much of a compromise in either direction. Ground-assist takeoffs for short transits may be more practical, such as the plane drawing electrical power from the runway until it gets airborne or maybe even a scaled-up carrier slingshot.
3. That's called a 'battery', electrochemistry is the principle behind batteries, lots of chemists are always working on better ones, and wanting batteries that can be recharged seems to impose some engineering restrictions on what chemicals can be used.
At last! A sensible discussion starts to take place.
(1) Yes, hybrid airships are already in use. A deltoid wing filled with, say, hydrogen that can generate contributory lift under forward propulsion, though air resistance becomes an issue. It's not going to be a direct competitor for the speedier traditional aircraft, but it would be faster than a ferry crossing - maybe the same speed as a rail crossing to Europe, but with a greater range of destinations. What about the use of aerogels filled with He/H? Create a rigid structure that's buoyant using that. Aircraft designers are already designing very lightweight fuselages through the use of carbon fibre composites, so technology advances.
(2) The hybrid engine sounds like a possibility, though they do mention that they wish to reduce the drag of an underslung engine. Possibly the old tri-star configuration could work - a tail mounted single jet engine with electrical engines in the wing root. Ground assisted take-off is another possibility, though that could require considerable alteration to runways which would be expensive.
(3) Yes, it is a battery, but what about some biomimetic technology to generate "artificial petrol"? That could be along in a few decades - using just as a guess say, sunlight directly to knock electrons off molecules, triggering the formation of less stable complex compounds. Developments in other areas of battery technology may produce a "liquid battery", unsuited as a replacement for the pastes, gels and powders of current batteries, but usable in cars, trains, even planes.
Be interesting to see what technologies develop from this.
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That is one hell of an informative xkcd!
It really hits the nail on the head as to why you cant invent or renewable your way out of trouble and of the extraordinary amount of energy held in a tiny amount of hydrocarbons and why we are truly fucked without them.
Also I'd like to point out once again that electricity does not grow on trees , like hydrocarbons. It is not a source of energy it is a transmission meduim. Something the public and media at large seem to be completely oblivious to. It might be more efficient if you generate the power elsewhere in bulk and use electricity all down the line , but you still have to find the energy . people forget that.
Chemical energy is stored in the batteries, and converted to other forms... e=mc^2, so by releasing energy you're reducing mass of the batteries.
Very, very, very, very slightly.
But you knew you could rely on some commentard to point this out. I decided to make it my job.
I am not a nuclear physicist, but as I recall, in the case of a battery, you're not converting matter into energy. That only happens in things like nuclear reactors. You're converting one form of matter into another (lead and sulfuric acid into some other mix of those elements that I can't remember offhand) and one form of energy (chemical potential) into another (electricity).
If you cause the battery to outgass, that could "make the plane lighter" in that some of the mass would not be carried by the aircraft, but in terms of the total system, the overall mass remains the same.
or did I miss an irony/joke icon?
It is targeted at sub-1.5h flights like Paris-London.
For that distance a propeller driven aircraft (especially in pusher config like Piaggio P.180 Avanti) has nearly identical door to door time as real or "fake" (like their design) turbojets.
While the design is quite cute, a scaled up pusher with a couple of electrics in the back is likely to beat it on all counts - up front cost, time to market, maintenance cost, etc. We have learned how to make relatively quiet propeller aircraft so the noise should not be an issue.
have you actually HEARD the P180? it is the loudest (and has very unique sonic signature) twin turboprop Ive ever witnessed coming in our out of SJ Mineta. Even the (also twin turboprop) Rutan Starship is quieter by a noticeable amount. Only seen that one twice.
turboshaft engines are light. electric motors can be close. But batteries still weigh more than kerosene. which means less cargo, higher wing loading, etc. Engineering challenges mostly but the biggest challenge is the bean counting. Not sure what technology is in the current or near state of the art that'll fix that. :(
You either need a highly-targeted and VERY dangerous beam with immense amounts of power, pointing towards an aircraft for the majority of its flight, covering pretty much the entire flightpath. fighting against the atmosphere which can block up anything if it's foggy, to a series of high-resilience devices capable of capturing and converting said energy with little to no loss, which need to weigh less than the battery to make it worthwhile, while also requiring all the same propulsion tech as these guys will need to develop anyway.
Or you could just stick a battery in a plane, refine the science, and hope that by the time you get anywhere close to success that just about ANY power transmission technology is viable. Hell, if you get that far, you'll plug it full of AA batteries if it works out cheaper and easier.
Yep, door to door electric for the Southampton/Edinburgh type route would, although slower, be near enough the same duration as a jet/turboprop as they don't really get a chance to stretch their legs on the short routes anyway.
I love the idea of ground based assistance too - sign me up for a EMALS launch from Gatwick :)
most commercial passenger craft have an Auxiliary Power Unit (APU) for providing power to air-con, lighting, entertainment systems, etc.
One presumes that a higher capacity APU could be part of the design, with the extra power provided to engines for takeoff/landing or topping up batteries in the air. As a result, the craft would still be burning SOME fossil fuel but orders of magnitude less, thereby reducing the carbon footprint to that of a smallish lorry.
That was my thought - the solution to drastically reducing car emissions was hybrid technology; could something similar not be made to work for aircraft? Have one (or two for safety/balance) small jet engines (say 20% size and 10% emissions of a standard airliner engine) whose primary purpose is to drive generators that provide power to the ducted fan engines, including batteries if necessary/optimal.
Working out the details would take more aircraft engineering skills than I have but I can't see why a solution based on that premise couldn't be operational in less than 10 years.
You'd have to make the attached generators and electric engines and batteries be
1) more efficient in conversion of fuel to motive power
2) lighter than having a suitable size jet engine to do the job.
Because unlike a hybrid car, an aircraft wouldn't get the benefit of regenerative braking to grab back some of the energy expended in getting it up to speed.
Now nuclear and steam turbines might work...
Hm... it could work you know. Coupled with a hybrid airship envelope, a solar array for a bit of a boost, an AI-pilot that can optimise a gliding route based on wide-field satellite observation of weather patterns, realising energy from a thermal gradient by making use of different temperatures in different layers of air, or even picking charge up by flying through proto-thunderstorm cloud layers.
Just dump passengers.
What's the problem? This is Ryanair.
"Ladies and gentlemen. This is your captain speaking. Due to a technical malfunction this aircraft will need to dump weight in order to safely carry out an emergency landing."
"Your cabin crew will shortly be going round the cabin with credit card readers. The 15 pasengers who pay the least, will be ejected from the emergency shutes in 5 minutes."
The other problem is that as a modern airliner flies, it gets lighter (you're burning off the fuel as you go) and thus the aircraft becomes slightly more efficient (same power output hauling less weight around). Battery-powered aircraft do not have this useful feature.
And this also means that the aircraft has a landing weight almost the same as its take-off weight, which makes it much harder to land safely.
No, it is not.
Batteries are heavy, and they store way less energy than petrol for the same volume.
Getting a plane off the ground, especially a commercial transport, costs a huge amount of energy. Without discussing any figures, lets just take this page as a reference. It concerns the A300-600. That plane has a range of 7500km and a maximum fuel load of 68150 litres.
The energy contained in 68150 litres of fuel is apparently in the order of 48MJ * 68150 = 3 271 200 MJ.
This page indicates that the best battery (as far as energy density is concerned) is the Lithium-Ion battery with 460000 J/Kg. So 0.46MJ/kg.
That means that we'd need 3271200 * 0.46 = 1 504 752 kg of Li-Io batteries to achieve the same energy availability. That's 1500 tons of battery and you don't have the plane, the passengers or the suitcases.
Oh, just FYI, the max takeoff load of the A300-600 is 171 tons.
P.S. : I'm sure I've made calculation mistakes, but I'm also pretty sure that I'm still right. Batteries are not going to be used to power planes any time soon. At least not until those famous carbon nanotube thingies with 80% solar panel efficiency wings are invented. And they won't fly at night.
And again, with anything about electrical transport, the 'I need to fly 7500 km so any plane that can'yt is useless' school of argument.
Take your calcs. Go for a range of 375 kms. Your A300 now presumably only needs 5% of the MJ, so with current Li_Ion technology a battery weighing 75 tons. (which is only just over a full full fuel load now). Maybe not a commercial proposition, but it would get you to Paris if you flew in a straight line.
But the chap they interviewed this morning said that they were developing on the basis of a doubling of battery efficiency - so now we are looking at being able to fly 750 kms, or with 35 ton batteries.
Maybe it's not going to happen tomorrow - but it's not impossible. And Westray to Papa Westray - probably doable now.
I never said it was impossible. I specifically stated that with a major overhaul of battery capacity, it would be doable.
So we agree.
Except for the fact that an A300 is not even going to get to lift-off on batteries at this point in time.
But one day, it might. Say 50 years from now. Like when we have AI.
Providing that someone doesn't strap an auto bomb to the landing gear, and the radiation shielding isn't the sacrificial sort that decays inside of 12 hours. Mind you, if it was then you could always get some sort of remote controlled elevator car with huge tyres for the plane to land on.
Who needs fusion. The US Navy's currently trying to do exactly that using the fission from their aircraft carriers, as it provides a double blessing for them: less need to take on fuel (you can now replenish on the fly) and the flexibility of potentially longer duty cycles since more stowage can be given to foodstuffs instead.
Indeed, some sci-fi visionaries picture this is how we will handle roving missions should we leave the solar system. A large powerhouse handles the mothership and produces portable fuel for the rovers.
> P.S. : I'm sure I've made calculation mistakes, but I'm also pretty sure that I'm still right. Batteries are not going to be used to power planes any time soon. At least not until those famous carbon nanotube thingies with 80% solar panel efficiency wings are invented. And they won't fly at night.
I absolutely agree with you. But that isn't the ultimate value proposition.
(a) aviation fuel jet engines are only going to get moderately more efficient.
(b) we've got to believe that battery tech is only going to to get ever more efficient (of course the rate of efficiency increase is important for ideas like electric planes)
(c) up to some range/distance batteries become viable (witness range anxiety in motor vehicles – we're talking triply so in non-ground vehicles I imagine)
(d) when the crossover happens you only need to recharge the batteries, and not buy a whole tank of non-replenish-able fuel. This part is predicated on your electricity coming from renewable sources which is a long-term overarching goal for humanity because if we run out of petrochemicals we don't get to fly any planes never mind the environmental consequences.
(e) ergo, we ought to explore this avenue
Thing is, you're making a VERY big assumption with (b), given that battery tech has been about as stuck in terms of innovation as hydrocarbon fuel for similarly long lengths of time. Point is that one cannot assume battery tech will continue to get better any more than one can assume fuel tech can get any better. There are even signs that we're hitting physical limitations regarding increasing energy capacity (burning Li-Ion batteries being a warning sign).
batteries do not hold the same amount of energy as aviation kerosene."
Well that is one way of putting about 60 times less.
Larger jumbos carry up to 193,000kg of fuel, lithium batteries with the same energy content would weigh
28 times more than the maximum take off weight of the same plane.
is the lack of a suitable battery.
The equations of flight are well known, and if and only if, a lithium air battery (which gets heavier as it gets exhausted, which is great for take-off) can be developed than prop and indeed ducted fan jet planes able to cross the Atlantic are possible.
As with all things electric in transport the world has been waiting for a suitable battery for well over 100 years.
I'm sure the smallprint says "where the next decade refers to 2020-2030 as opposed to 2027".
Even an extra 3 years is generous given we're talking about designing, prototyping, testing and building a large body passenger aircraft in an untested configuration. Not just the aircraft itself but all the construction facilities and all the infrastructure that airports would need to service and operate them.
Not to mention that fuel is often stored in the wings where exposure to the airflow cools it down below the ambient temp, hence fuel is used as a coolant. A battery powered plane would need an alternate cooling system.
Lithium batteries would be dangerous in an accident, particularly if the plane crash lands on water. They can vent toxic fumes when damaged, burst into flames when crushed and react explosively with water.
They would do better to spend their money researching carbon-neutral ways of producing kerosene fuel from natural / renewable sources.
It's practically impossible to be carbon-neutral when producing kerosene or any other hydrocarbon fuel because you NEED carbon to produce the fuel in the first place (hint: hydrocarbon). Unless you're using extra hydrocarbon fuel in the process (which then becomes a case of why bother), any desired process will by design be carbon-negative since it will be taking carbon out of the environment (like the US Navy experiment meant to pull it out of seawater).
That's why most turbojet engines are designed they way they are: they help compress the air in the combustion chamber to make it richer: allowing for a fuller burn in the thinner atmosphere. Indeed, most turbojet engines are deisgned to work best at high altitude and eating the transient inefficiencies of operating too rich at lower altitudes.
With super capacitors and batteries being installed in planes, wouldn't this allow a lot of the engine weight to be transferred out.
Imagine the fuel and engine weight you save on takeoff, it will be huge, but will cruising weight be a lot higher?
I would say the upshot to this being made now is that as battery density (and/or wireless energy transfer gets more efficient) then range will increase without the need to hugely change the designs.
Others say what about battery going flat, well, I have to wonder if the thing would still be okay landing without too much issues. I would imagine that you could recharge the caps (or battery) while slowing down, giving you the power needed to actually control the landing.
I cant see jet fuel going away any time soon, but I can imagine tons of hybrid builds coming along, and since this is not a car we are talking about then it should be a lot easier to get working than it has been for the auto industry.
The batteries are heavy, so the answer is to put a set of metal rails on the ground from A to B, on which will rest a trolley containing the batteries. A long cable will then go up to the aircraft, which will simply pull the trolley along.
It's obvious when you think about it.
@Voyna i Mor
Here's a thought. Dispense with the going up and coming down stuff (the difficult/expensive/dangerous bit) and create a carriage that runs on tracks and can travel 400-500 MPH. You wouldn't even need to carry 75t of battery as the power could be run above the track. PP
note they didn't say "they'll work great" or "they'll not require massive subsidy from the rest of our operations to function" or "they're mostly greenwashing for PR and subsidy/grant fishing" but that in the decade they'll simply "have them".
Like Tesla has "autopilot" but for some reason can't use that for materiel handling or security patrols at NUMMI. Having it and utilizing it to the fullest, are two different things apparently.
"A rough approximation is that, for a given weight, batteries do not hold the same amount of energy as aviation kerosene."
Rough approximation? That's nothing like proximate. It's a mealy-mouthed vagary at best. And in fact what we need is specific energy - energy per unit weight, rather than energy density - energy per unit volume. So look it up. Jet fuel has 42.8 MJ/kg, Li-ion batteries have 0.875 MJ/kg at best. As someone else pointed out, two orders of magnitude is your rough approximation. Near enough, kerosene has 50 times the specific energy of the best Li-ion batteries. If we're being precise, it's 48.9 times, but the best Li-ion batteries are varied, so 50 is a good figure to bandy about.
I have to applaud your efficiency in writing articles. Just put some blather in the body and wait for your pissed off readers to crowdsource the actual news in the comments. Your only problem is that a shitty AI could do it better but that gives you more time for downing pints so who cares, right?
Well if you are getting pedantic 2 orders of magnitude would be 100 not 50, and the 'best' batteries are now 2 to 3 Mj/kg, so all of a sudden we are in the 15 to 20 range. And Lithium air batteries - which aren't around yet, still more lab toys than reality, have theoretical energy densities right up with Kerosene.
And no one is mentioning the comparative efficiency of electric motors vs internal combustion. You will chuck away at least 50% of your Kerosene Mjs in heat losses (unless Carnot was wrong) - so in pedant mode you are playing with 21.4 Mj/kg of Kerosene, so we are already in 1 order of magnitude range, but who cares, right?
"Well if you are getting pedantic 2 orders of magnitude would be 100 not 50"
If you are getting really pedantic an order of magnitude is the fifth root of 100 - it was a prescientific classification of star brightness, and it turns out that's how the human eye seems to discriminate reliably.
It's why it's a term I prefer to avoid, whatever Wikipedia says. Orders of magnitude are only themselves within an order of magnitude.
Most passenger craft don't have stop-and-go issues because they tend to be placed on courses that allow them to operate very consistently, allowing them to basically cruise at an optimal position in terms of fuel efficiency. Given such an environment (especially one where the efficiency improves as the flight continues due to the decreasing weight), why do you need the engines to be electrical in the first place?
"electric motors are vastly more efficient, in power-in-power-out terms, than internal combustion engines of whatever type."
Mr Corfield makes the usual error of people pushing an opinion not backed by logic. Yes, the electric motor is efficient at power in- power out, but that power is derived by a process akin to the internal combustion engine, i.e., the conversion of Chemical Energy into Electrical Energy. The major, and unavoidable thermodynamic losses have already been made at the entry point of the electric motor. The further losses of the electric motor are added to the losses already made. There is no gain. Only a further loss, albeit a minor one
And you have made teh usual error of conflating the source of energy with the practicability of actually deploying it.
Namely the fact that an electric aircraft performs a lot better then than the megajoules in its battery would indicate by direct comparison with a fuel engine.
Oh and a ground based CCGT is about twice as efficient as the same turbine in the aircraft.
"Namely the fact that an electric aircraft performs a lot better then than the megajoules in its battery would indicate by direct comparison with a fuel engine."
By how much? Perhaps you can show us some actual numbers. Also for the reduction in drag using smaller pods for the electric motors versus turbofans.
"Oh and a ground based CCGT is about twice as efficient as the same turbine in the aircraft."
Also a lot bigger since you're basically using TWO powerplants. Given your physical restraints, size matters, and is there anything more efficient than a turbojet for its size and operational conditions?
Perhaps the answer is electric props powered by a hydrocarbon fuelled generrator mounted within the fuselage. Electric motors would be smaller than turbofans, causing less drag. You could also take advantage of more energy dense fuels like diesel - there are already drones powered by diesel for maximum endurance.
But how would the generator operate? Turbojets are designed for thin-air operation. Also, they're often used (via bleed-air extraction) to pressurize the cabin. Seems to me you end up trading two to four smaller turbine engines for one big one (because how else will you run the generator in thin-air conditions), making it a case of excessive complexity.
Hmm have a look at waveplate motors, over 90% efficient. You could use that to produce electricity from fuel. Turbine engines, I think can also go way efficient. I've looked into ideas for electric aircraft before. Energy density of batteries is the big issue. Even silicon nanowire with 10x the capacity of lithium ion is only a fraction.the capacity. In Cars the drive chain and motor produces major looses, so putting electric motors at the wheels is a major advantage. But on jets, the turbine by passes this already.
The big advantage is the electric version is probably much cheaper to maintain and build for short hauls.
So, starting with a hybrid until a suitable battery alternative is probably better.
Because fossil-fuel-powered aircraft never run out of fuel, ever. It's such an impossible event that no procedures are in place to account for this, like minimum fuel levels to account for delays and poor weather at the destination airport.
You forgot the Joke Alert icon.
You're basically going the roundabout route to the generator attached to the motor it's supposed to power: the classic Overunity Device.
Quick primer: any wind force used to power a windmill doesn't come out the other side. Breeze goes in, calm comes out. A ram air turbine adds drag because of the previous (similarly how it's harder to operate a crank charger when the phone's plugged into it than when it's not), which is why they're normally small and only used to charge essentials when necessary.
And stop being so defeatist!
If the windmills are inefficient, well, just turn them around - facing backward! (or is it forward?)
Periodically, the plane could do a steep dive, and thus use air-breaking to recharge its batteries. The same way electric cars do going down hills.
Sooner or later we'll solve this perpetual energy problem! Only a matter of time.
I don't think even the most optimistic predictions for battery development will get us to power densities even one order of magnitude that of JetA1, and there's the question of just how safe such batteries would be: arguably a complex next of microscopically layered fragile cells has more chance of going wrong than a tank of kerosene. Materials tech, especially for fan and HP turbine blades has come a long way to produce amazingly efficient and powerful high bypass turbofan engines: it's hard to envision a ducted fan using electricity alone producing 50,000-100,000lb static thrust.
So I'm very sceptical you'll see airliner-sized planes powered entirely by electricity in the next 30 years.
That said, I'm surprised more work hasn't gone into greater electrification of planes, particularly with respect to landing gear. Putting regenerative electric motors into the wheel hubs seems a reasonable first step. You save oodles of tyre wear by spinning up the wheels just before touchdown. You claw power back to the batteries during the rollout, braking regeneratively. You shut down the thirsty engines and taxi using electric power. Before take off, no tractor needed for pushback. Electric taxiing till you're within say 5 minutes of takeoff. Possibly even electric assist during the takeoff run. You have to carry electric motors and bigger batteries, but fuel and tyre wear savings will offset some of that, and since you've *got* bigger batteries, use them for more on-board and control functions instead of bleed air and hydraulics. The possibilities are interesting and this would seem a sensible incremental step towards greater use of electricity aboard planes.
"That said, I'm surprised more work hasn't gone into greater electrification of planes, particularly with respect to landing gear. "
This has of course been going on for some time with cars which nowadays have electric power steering, some have stop/start mechanisms, and the more efficient pusher belt CVT (compared to slushbox) has been made possible by computer control. But aircraft design, like big ship design, is very conservative and for very good reason.
I say power these things with simple AA batteries- thousands of them.
As each set of batteries go dead, you jettison (no pun intended) them, and the plane thus becomes lighter and more efficient!
Insecure passengers could bring thir own pile of batteries in their carry-on and receive a badly needed discount on this ripoff-charge.
If you wanna use rechargeable ones, pay people on the ground- kids or homeless people - a nickel for each AA turned in. They can combine it with their empty beer-can pickup.
And it will get these unhealthy city people out in the countryside! It's WIN-WIN!
There is a load of energy in a jug of Jet-A. Using a liquid fuel means that an aircraft gets lighter as it flies and can be short loaded for shorter trips. A battery powered airplane is going to weigh the same from start to finish and the weight isn't going to change if is isn't charged all the way up.
There are Lithium chemistry batteries that can be charged very rapidly, but they trade power density for the faster charge time. An aircraft would need the most power dense batteries on an energy/mass ratio which likely means a longer charge time. It would be very difficult to charge a plane rapidly enough to match the turn around time of using liquid fuel. Maybe somebody will come up with a hybrid that puts some batteries on the plane and a system of power beaming antennas that keep the plane topped up during the flight. For best results, the passengers should not be heated excessively.
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