The age of electric flight is finally upon us
bbc.com
bbc.com
https://twitter.com/BenBrelje_says/status/106485722028904038...
https://twitter.com/BenBrelje_says/status/106491195862390374...
To recap, based on financial statements the company:
used to be a "waste management" company that failed and was sold as a "public shell" to enable the formerly private company to go public and sell shares (the waste management business it was engaged in was an effort to commercialize a process to treat low-level nuclear waste developed by Russian scientists)
has $64 mil in debt apparently unrelated to aviation
has spent $3.8 mil on R&D for this project
has 8 R&D employees
only 2 of those 8 have any evident experience related to designing aircraft (pretty apparent from the "design").
I don't believe them. The design is sound, if radical in the decision to be mostly-battery. And I think that's partly why people are so skeptical: it definitely goes counter to the industry grain. But it IS the right way to build a serious electric aircraft for regional/commuter passenger travel. Pressurized, extremely high lift-to-drag ratio, very high battery mass fraction, focus on high propulsive efficiency by ingesting boundary layer with the pusher propeller and countering wing-tip vortices with wing-tip propeller. The passenger count is also right, at the limit of FAR-23, allowing you to use a single pilot.
The only thing I would do differently is probably have a higher cruise altitude and higher aspect ratio wings (and probably counter-rotating dual-motor pusher propellers) instead of using wing-tip propellers and gettin, but theirs is a valid design choice as well.
So much group-think especially with the larger aerospace companies. They insist on hybrids for flight (notice how whenever Airbus or Boeing buy one of these exciting electric flight startups, they all of a sudden switch to hybrid?), which ends up compromising the design and adding a whole new propulsion system to validate and certify. Others have a valid approach of retrofitting electric onto older airframes, but that is not going to get anywhere near the operational efficiencies of a clean-sheet design. And still others insist on VTOL, but I have my doubts as to whether the focus on VTOL by so many of these electric flight startups is going to really be worth it in the end except for niche cases.
The key is that the Alice aircraft is capable of take-off with just the rear propeller. That's possible because electric motors (unlike jet engines) can operate at much higher power for short periods of time. It was addressed recently at the Paris airshow Q&A for Eviation. If a wingtip motor (not engine) fails, the other side is designed to immediately stop (electric motors such as these respond immediately to input) and flight continues with the remaining tail motor.
Additionally, electric motors are fundamentally more reliable than jet engines.
1. Rear prop strikes. 2. Wing tip prop strikes. 3. Wing tip inertia 4. Prop wash over a wing is a good thing If (big if) this thing ever flies, it won't be in this form
A puller takes advantage of the volume behind the prop taken up by the body of the aircraft to offset the loss of air volume caused by accelerating the air (Bernoulli's theorem). A pusher can't do that.
Being able to take off with one engine that’s rapidly overheating, does not mean is safe to continue a flight with a single engine. Electric aircraft don’t get lighter in flight because they don’t burn fuel.
A motor that would overheat at takeoff power won't necessarily overheat at cruise and would be designed not to overheat in an aircraft application.
Motor control is not just on or off.
I assume they are at the end of the wings on purpose to deliberately interact with the wingtip vortices. The back prop is power, those wingtips are for drag reduction.
I believe tristanb cut & paste his own post from six months ago on this same topic, and it broke the links.
Having a small buffer, even a few minutes of battery power to rely on while trying to get back to the field to land the "impossible turn" [1] would make me feel a lot better and could be the difference between life and death.
There are various groups (Pipstrel[2], Diamond[3]) that I'm aware of that are working on electric GA aircraft. For young pilots that are looking to train, the cost of jumping in a Cessna 172, the gold standard in GA trainers will cost at best $120-200/hr. Electric costs should be 1/5 (or better) of that in reality due to the absolute bargain of replacing a TBO electric engine, scheduled maintenance and relatively low level of complexity.
[1] https://www.aopa.org/training-and-safety/air-safety-institut...
[2] https://www.pipistrel-usa.com/electric-propulsion/
[3] https://www.flyingmag.com/diamond-da40-hybrid-electric-proto...
Gas and jet fuel specific energy density ~= 45 MJ/kg;
Lithium-ion specific energy density < 1 MJ/kg
Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is around 1 kW/kg.
In short we need much better batteries and much lighter motors. This is not going to happen anytime soon. A more reasonable option is to create carbon-neutral fuels (biofuels, carbon sequestration, etc.).
Most attempts at biofuel are not even net positive on energy. if we did get there then the question is how much forest do we have to clear to grow biofuel AND eat, and what net effect does that have on co2.
Hard problems all around.
Convert the beef/dairy farms. :D
Also, where/how is all that electricity getting generated/transmitted to the emitter, and what complications does that introduce? What about environmental conditions? How does that effect the efficiency? Does a storm front blowing through suddenly make regular ICE planes a better idea again?
Oh, yeah, don't forget the security aspect. Those emitters are more than 'interesting' enough to be weaponized in the wrong hands.
I mean, beamed power sounds cool and all, but you actually have to take into account a heck of a lot of variables first.
Compare that to the 800kW that the APU in the tail supplies to keep electric and hydraulics running if the main engines fail or the well above 200 MW that the main engines put out.
I've found a statement that some version of their motors with 270 kW weigh 31 kg (70 pounds). Which amounts to 8.7 kW/kg and isn't far off from your 10 kW/kg estimate for modern turbofan engines. Also it's probably not the latest number for an electric motors, and newest motors have better power-to-weight ratio.
[1] https://newatlas.com/siemens-world-record-electric-motor-air...
Edit: I think I met the guy behind these. But I'm not sure, for lack of having asked for the name of the company. I certainly have seen a prototype that could have been the 348.
Electric motors can achieve FAR greater than 1kW/kg. Here's one used sometimes on electric aircraft capable of 10kW/kg, same as a jet engine: https://emrax.com/products/emrax-268/
The specific energy of lithium-ion is poor, but jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. There's also some efficiency improvement possible, i.e. from airliner lift-to-drag of 16-20 (and like 8-10 for a Cessna) to a more glider-like L/D of 25-35 (the best gliders can do 70). Additionally, improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy (general aviation craft are only like 10-15% fuel, but 777s can be almost 50% fuel, and electric aircraft could be 60% battery).
So if you combine efficiency improvements and high battery mass, sure, electric planes still may have a tenth the range of jet liners. But jets like the 777 have a range of 10,000 to 15,000km. A tenth of that is still over 1000km! Quite doable for a very large portion of domestic flights. Since domestic flights often involve multiple hops anyway (due to hub and spoke model), you could fly basically anywhere up and down the eastern seaboard in just the typical two hops. And faster than high speed rail.
But of course, there are already better lithium batteries that are available in small quantities, like lithium-sulfur, metal electrode lithium batteries, solid-state batteries, or batteries that combine those various features. ~1.5MJ/kg cells are already demonstrated and you can buy them on an evaluation basis. ~2MJ/kg is feasible as well, enabling single-hop flights all over the eastern seaboard and enabling multi-hop transatlantic flights (as low as 1200km is the minimum range needed for transatlantic flights if you really wanted to do it).
...Transpacific (i.e. reaching Asia from North America) wouldn't be too hard as you can hop along Alaska and the Aleutians, but reaching Hawaii is a major challenge. To get to Hawaii from LA takes 3800km (at the edge of what you can do with L/D of ~40-50 and 500Wh/kg batteries). Taking the long way from the Aleutians to Midway cuts that down to 2600km for the minimum hop distance, which is perhaps feasible with a sailplane-like L/D and the next-generation lithium-metal and/or lithium-sulfur batteries (that are already demonstrated at the lab scale).
Lithium-air is the breakthrough in battery tech people want, which will enable much easier transpacific flights at transonic speeds (rather than the ~Mach 0.50 speeds you'd be limited to for the most extreme high performance airfoils), like what people are used to already. Lithium-air would also potentially enable long distance supersonic electric passenger aircraft.
Look, we all want electric aircraft. I can't wait for them. But to say that it doesn't require a major (honestly several major) breakthrough (s) is an extreme understatement and does not requisite the hostility you are giving.
Batteries don't need to equal jet fuel in order for electric air travel to be viable.
We have airplanes capable of 15,000km trips. But we were making transatlantic flights back when our aircraft could only do about 2000km range reliably. Going from from Labrador, Canada to Greenland to Iceland to England, the minimum hop distance is about 1200km. https://en.wikipedia.org/wiki/Transatlantic_flight#/media/Fi...
I don't expect electric air travel to operate Transatlantic flights with 1.5MJ/kg batteries as major competitor to jet travel unless there's a very hard clampdown on greenhouse gas emissions. The logistics of adding major stops in Greenland and northern Canada to enable transAtlantic electric flight just likely won't be worth it. But for domestic flights (which are the majority of flights), electric air travel will be common.
Source for ~1.5MJ/kg batteries:
But still, until we get into that efficiency range of batteries vs direct power of jet fuel, it is far from solved. But like you mention with greenhouse gasses, it does have to be solved. I have yet to see anyone here that is doubtful that electric aircraft will exist. I just see people (at least on HN) that are either bearish or bullish. But don't be hostile to people that are being bearish. We need both camps.
Also -- it's pretty easy to be negative. "That's dumb, it's not going to work", etc... I really appreciate this poster remaining positive in the face of OVERWHELMING negative feedback on this thread.
And I don't think you should take my comments as "that's dumb, it's not going to work." You should take them more as "we still got a way to go but we've made a lot of progress. But don't bet all your money on this horse."
> jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned.
New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine.
> more glider-like L/D of 25-35 (the best gliders can do 70).
This is not limited to electric planes. The reason no one has done it so far is the aeroelastic divergence.
> improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy
Again, this can be done for any aircraft, not just the electric ones.
> as low as 1200km is the minimum range needed for transatlantic flights
Do you really believe there is a market for 1200km hops at Mach 0.5. We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?
> Again, this can be done for any aircraft, not just the electric ones.
Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.
It'd be fun to try, though.
Would electric towplanes be doable for passenger aircraft? (Long or short haul, electric or otherwise).
If one of the downside of electric planes is the range, while fuel is cheap, making them cheaper to operate, and take-off uses a significant portion of the total energy, I could see very powerful electric towplanes as a way to reduce the amount of fuel needed for takeoff. This would:
* Allow to travel longer distances with the same amount of fuel (enabling electric airplanes to fly longer distances). Alternatively, allow planes to fill up with less fuel for the same distance.
* Improve fuel efficiency of big airliners, and their carbon footprint if you consider regular ones.
One last question: aircraft that fly shorter routes typically embark less fuel, but would that be doable with electric planes?
Depends if we're talking LHV or HHV. Additionally, we're talking smaller jet fueled vehicles which rarely have access to state-of-the-art efficiency.
>Beyond Mach 0.5, the efficiency degrades very rapidly.
In this case, we're talking Mach 0.5 or less.
>this can be done for any aircraft, not just the electric ones.
Didn't imply otherwise. The highest performance jet plane can fly literally around the world. But this is far more performance than anyone needs in an aircraft. And for whatever reason (partially because of aging fleets, at least for very small commuter aircraft), generally there have been efficiencies left on the table still, just the same as conventional car makers left efficiencies on the table which Tesla and the like have taken advantage of.
> Do you really believe there is a market for 1200km hops at Mach 0.5.
For domestic flights, yes. For transatlantic, no, not a large market. Not as long as jet planes aren't paying for their climate externalities.
>We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?
Because those have the same maintenance requirements and use the same fuel as jets, which are just as efficient and faster.
I don't think we'll do many transatlantic electric passenger flights until the climate externalities are priced-in for the cost of air travel or until lithium-air or similar. But now we've moved the goal posts to long-haul and transoceanic flight. Electric flight is clearly possible and for domestic flights it'll likely be cost-competitive even without fully accounting for climate externalities, particularly for these 9 passenger FAR-23 electric aircraft competing with fuel-guzzling and maintenance-heavy 40 year old fleets.
That is basically a negligible amount of power
It's not negligible for its weight. You can always scale up an electric motor. The largest machines in the world (such as bucket wheel excavators) are driven by electric motors. Additionally, electric motors are much simpler to cluster into a distributed propulsion configuration than jet turbines are. That's why NASA's building the X-57 electric aircraft.
yep, BUT cube-square law applies
i think battery swapping is much more realistic for planes than for cars and that would allow to use non-rechargeable or factory rechargeable batteries like the metal-air ones (my favorite is Al-air) which is order of magnitude better than rechargeable Li-ion, and that really gets us close to the gas/jet capabilities given the low thermodynamic efficiency (or extremely high price and complexity) of the combustion based engines.
>In short we need much better batteries and much lighter motors. This is not going to happen anytime soon.
this is exactly what is happening right now in front of our eyes :)
could work with either propulsion method of the plane being lifted.
The main thing you're missing is that modern jet planes have absolutely ridiculous range, and a huge number of flights use only a fraction of that range. Electric planes don't need to match modern jet planes to be viable. They just have to compete on cost at a range that covers a significant amount of routes. And electric planes have a potential for huge cost advantages.
A related aspect is that electric planes are much more quiet. Being cheaper to operate and more quiet means you can fly smaller planes from smaller local airports to other small airports. You can create an entirely new market.
Electric planes are not going to take over transatlantic flights any time soon. But they don't have to in order to have a huge impact.
I do agree that carbon neutral fuels are important for long-haul flights for the coming decades. With batteries for land transport and short-range ships/ferries and planes and hydrogen for heavy trucks and ships, we might be able to sustainably make enough carbon-neutral fuels for long-haul planes.
You do know plane routes have diversions and holding pattern minimum times set by the FAA?
I'm not so sure! Have you ever heard the sound of twin-turbo regional airplanes in small airports? That sound is not from the turboprop engine, but from the propeller itself. Electric planes do have propellers and propellers are usually very loud. Actually much louder than turbofans!
Making propellers quieter has been an active field of research in fluid dynamics for decades but it's a very hard problem.
E.g. the Eviation Alice carries ~8000 pounds of battery and provides its nine passengers a range of 650 miles. That's undeniably a lot of battery and the energy density is indeed not great. However, it doesn't prevent it from flying. Transporting 9 people over that kind of distance for the price of charging that battery is a very disruptive cost improvement over the state of the art that involves burning hundreds of dollars worth of fuel.
It's the cost of fuel that's going to kill jet and piston engines. It doesn't matter how energy efficient they are when the cost difference with battery electric in the first generation is already two orders of magnitude. And while we have pretty much peaked in terms of fuel cost efficiency (order of magnitude improvements seem unlikely), that is definitely not the case for battery electrical. Cheaper and lighter batteries are basically happening. 2-3x seems to be likely within a decade or so. More may come after that. Electricity prices are also not a constant and seem to be dropping rapidly. So, if it's economical now, it's going to be far more economical in a few more decades. I think another two orders of magnitude cost improvements are likely.
For the same reason, hybrid planes are not likely to be more than a stop gap solution. They'd still be burning a lot of fuel which would raise the cost relative to small battery powered planes. I do believe that they will have an important role for longer distances; for the simple reason they'd definitely provide better energy efficiency. Ultimately, synthetic fuels generated using dirt cheap electricity may help bring prices down here but this will take a while and is not likely to be a very efficient way of using electricity (compared to storing it in a battery and using it directly).
As soon as battery powered planes are range competitive, which for short haul is happening right now, orders of magnitude cost improvement means game over for traditional planes.
Here's some back of the envelope math for you for the Eviation Alice vs the A319. You can buy a state of the art A319 for about 110M $. That same amount of money buys you about 30 Eviations (at the announced price of 3M $). You only need about 18 to match the number of passengers of an A319 (160 passengers). The A319 is very popular on short haul flights that are well within the range of an Eviation Alice. The difference is that one burns thousands of dollars worth of fuel and the other has an operational cost measured in the lower tens of dollars. There are of course many other advantages replacing big A319s with small battery powered planes. E.g. they make less noise and they can fly to much smaller airfields. The point here is that we don't need an electrical version of the A319. Big planes are only interesting because of the fuel economy. Small electrical planes don't have that problem.
The biggest bottleneck is actually not going to be batteries, engine efficiency, maintenance, or electricity cost but pilot wages and production volume of these new planes: we'll need a lot of them and with the cost of electricity already being low, pilot cost is going to be the dominant thing. As cost drops, ranges improve, and production volumes go up, the business case for operating an A319 will rapidly disappear. The Eviation arguably already challenges that. Autonomous flight, which is another thing Eviation is working on, will accelerate this. IMHO most A319s shipping today will be retired years or decades before their normal projected end of life because of their operational cost vs the cost of products like this.
This is why Eviation has a full order portfolio. They'll be selling these things as fast as they can build them. Others will follow. This is only the first generation of their product. I expect great things from them and their competitors in the years to come.
here he gets a battery powered drone with solar to gain altitude and charge the batteries during clear skies: https://www.youtube.com/watch?v=xS2iCj-HSqY
here he shows off a new feature in arduinopilot, autonomous thermaling: https://www.youtube.com/watch?v=NwAX3cPvMqw
also, check out the "Sunseeker Duo" https://www.solar-flight.com/sunseeker-duo/ https://www.youtube.com/watch?v=2zvwqJpyahs
its only a matter of time before someone combines them
If that number was 100km with high reliability, it would almost qualify as a new type of aircraft. You could do cross-country flights that you'd never attempt in an unpowered glider, e.g. above big stretches of high, mountainous terrain. The Norwegian Hardanger plateau comes to mind as an example. Un-landable terrain, 1 km above sea level with a small window for unpowered navigation, national park and absolutely beautiful.
They have high launch energy followed by zero propulsion very high-efficiency gliding afterwards.
Covering the large wing area could with solar cells and allow for range extension or possibly even continuous flight.
Solar panels are mostly structural, but the cells themselves are basically a thin foil.
Most likely a first viable step would be to get electrical tow plane first.
* http://front-electric-sustainer.com
All this electric vehicle technology works really well for electric glider winches. You can get a whole lot of peak power off of a battery so you don't need a huge electric power feed.
I have no idea, hence asking and wanting to know :-)
https://newatlas.com/nawa-nanotube-ultracapacitor-production...
I hope they get adopted by Formula E. A bank of ultra-capacitors in front of the main battery should make the cars lighter with stronger regenerative braking.
In Eviation's Alice, the failure or shutdown of one of the wingtip's motors would require the shutdown of the other, on account of asymmetric thrust. It can be flown on the rear motor alone, but I do not know how well it would climb in the case of a motor failure on takeoff. Maybe an EE can step in and say whether electric motors can be over-powered for relatively short durations (in this case, a few minutes to return to the airfield) without much increase in the risk of it failing?
BTW, I see that this prototype is a tail-dragger, though rendered images show a tricycle gear.
[1] https://electrek.co/2018/06/04/siemens-electric-plane-protot...
In this state the motor cannot maintain temperature, so going beyond that time window will shorten its lifespan or cause damage if continued.
Hobbyst EVs often take advantage of this by having a small motor and overloading it when accelerating.
Parachutes. They are now a very practical option for GA aircraft. More than a few cessnas have been saved. The concept of "off-field forced landing" should too be going away.
https://brsaerospace.com/cessna-faqs/
" Q. How many aircraft saves are credited to a BRS Whole Aircraft Rescue Parachute System? A. As of August 2017, 376."
Call me a skeptic until they provide hard numbers and details of what planes make it back into the sky v's scrapped, and those planes have a year or two of a service history showing they make it back into a reasonable service lifestyle, I'd be shocked to hear this is great at saving planes. I find a lot of the old 172's i fly have plenty of bumps and scratches, but wouldn't be super excited to trust the frame of a plane that went through an experience like this.
I like it from a safety perspective, but in my mind, the reward you get out of a system like this should be your life...I have zero expectations the plane will ever fly again.
A 172 or similar that has been retrofitted with a BRS? Yeah, not so much.
This is a 9-passenger airplane, maybe too large for current recovery parachutes? (though I imagine that will change.)
[1] https://www.cirruspilots.org/copa/safety_programs/b/pull_ear...
Actually, this has me thinking: not all low-altitude situations are the same - an airplane with a downwards trajectory, such as one in a spiral dive, will need more height to save than one that is in a glide, such as after a power failure. This is why even a zero-zero ejector seat will not always save you, if you are descending rapidly at low altitude.
Even so, replacing a motor, if that is all it takes, is going to be cheaper than repairing or replacing an airframe that has undergone a parachute recovery.
(Action starts at about 02:05)
I guess it depends on one's definition of low altitude. Rocket-deployed parachutes open very fast.
Overpowering the motor during the entire take-off would bring a high risk of having it fail too. But overpowering it to overcome the most common obstacles is perfectly viable in an emergency.
Anyway, about fires, they are a reasonably easy problem to deal with. Fires on liquid are much more dangerous than fires on solid, and batteries have a lower tendency of exploding and creating fumes than the gasoline that propels smaller planes. I imagine the largest problem of a fire would be on losing power. You can mitigate this by creating many independent battery banks, but this adds weight.
This seems like such a tremendous difference that the market would be in an arms race to make it a reality. Especially considering electric motors have fewer moving parts and so require less maintenance. Oh and it would be so quiet.
“Even assuming huge advances in battery technology, with batteries that are 30 times more efficient and "energy-dense" than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload, says Airbus's chief technology officer Grazia Vittadini.”
I'm sure everyone would like to switch for environmental reasons but that sounds like a really big gap to fill.
would it? I was under the impression that proppelers were much louder!
what is the biggest source of noise in an aircraft/type?
> The XF-84H was almost certainly the loudest aircraft ever built, earning the nickname "Thunderscreech" as well as the "Mighty Ear Banger". On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away. Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down.
[0] https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscree...
Fewer moving parts doesn't mean reliable and not subject to catastrophic unforeseen failures. If it hasn't been out for five years you're a test pilot.
> Even assuming huge advances in battery technology, with batteries that are 30 times more efficient and "energy-dense" than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload, says Airbus's chief technology officer Grazia Vittadini.
> "Unless there is some radical, yet-to-be invented paradigm shift in energy storage, we are going to rely on hydrocarbon fuels for the foreseeable future," says Paul Eremenko, United Technologies chief technology officer.
> The big problem with this is that 80% of the aviation industry's emissions come from passenger flights longer than 1,500km - a distance no electric airliner could yet fly.
The market would be in an arms race if energy density was sufficient for long haul flights. Electric flight is awesome but until energy storage/density gets closer to hydrocarbons, conventional planes aren't going anywhere for the majority of travelers and cargo.
Batteries however, weigh the same amount regardless of charge level.
I wonder if this affects the calculations in an appreciable way.
I'm not sure of that quote either -- a lithium ion battery is currently about 1MJ/kg and 1MJ/litre. Jet fuel is 43MJ/kg and 35MJ per litre (values from from wikipedia)
So a battery that's 30 times more energy dense will be in the region of jet fuel, and thus would presumably be able to fly an A320 for its current range with its current payload.
To do current payloads at 1/4 range (what you'd need for those flights under 1500km) at A320 payloads, you'd need batteries to presumably be in the 5-10 times as dense level, and that's the range that lithium-air batteries would sit.
I somehow always thought that more weight of an aircraft lessened its range almost only because it needs much more power to take off and gain a cruising altitude.
So, to land at take-off weight, you’ll have to significantly strengthen the landing gear.
That already is 2.5 to 5% of the Maximum takeoff weight and 20% of the airframe direct maintenance cost (https://en.wikipedia.org/wiki/Landing_gear#Aircraft_landing_...)
So even if all those flights were switched to magic zero emission electricity, the aggregate improvement over the whole industry would barely beat the relative improvement between a 737 NG and a MAX. (yes, this is an apples to orchards comparison)
Grounded from carrying passengers, but not grounded entirely from flying, and certainly emitting in any case. The two on the map now are out of Boeing Field.
Jet fuel is really about 12-15 MJ/kg when you take thermodynamic losses into account. So you;d need a battery 10 times as dense. Which likely isn't happening any time soon, but still.
I think with full electric aircraft it's not a case of 'won't work' but how big of a niche they can carve out. Probably the sector they'd compete in are general aviation and puddle jumpers.
Think of what it could do in other areas as well too though. Imagine a flight from the SF waterfront to Tahoe via seaplane in 45 minutes (instead of 4+ hours) with no TSA screening, or potentially even SF to LA in 90 minutes.
Several weeks before the Harbour Air / MagniX announcement I ran through an exercise to determine the range/payload of an electric Cessna 208 (Caravan) for a typical flight profile here in the bay area: the daily FedEx flight from Oakland International to some nearby city, such as Petaluma. This involves a 5min climb from take-off to 2000ft, some period of cruise flight (ultimately determined by range), and a 7min decent to land.
This calculation assumes that the C208 swaps the swaps its turbine (PT6A-114A) for the Magni500, saving 85lbs. It also accounts for the substantial increase in conversion efficiency between the MagniX and PT6 (roughly 0.94 from 0.32). Not accounted for are any differences in aircraft systems (de-ice, prop pitch, electric instruments, plumbing, etc).
The results are not surprising given what others have noted about the enormous difference between the specific energy densities of Jet A and LIB. At the specific energy density of today's production batteries, 250 w-hr/kg, the electric C208 could carry one 175lb pilot approximately 100mi in 39min. Due to FAA VFR regulations, this would in reality limit the flight to 9min (FAA requires daytime reserve of 30min), with the subsequent loss in range.
Let's consider the putative solid state battery at 500 w-hr/kg. Now a 60min flight time (really 30min plus 30min reserve) will allow 1080lb payload. Fantastic! That's a pilot plus 4-5 passengers. The catch, of course, is that the timeline for road worthy SS batteries is 5-10 years. How long for before an air worthy battery is available?
With this information parsing the press statements is a little easier. Will the Harbour Air / MagniX Beaver carry 6 passengers over a 30min flight? No. It may demonstrate electric flight of a utility category air frame with the pilot as the "soul" payload. After that both companies will likely be in the same position as the rest of us -- waiting on better battery technology.
It would make about as much noise as it makes now. Nearly all the noise of a commercial aircraft is caused by the air being pushed to propel it, not by the engine internals.
(You can reduce noise and increase efficiency by pushing more air at a smaller speed. You do that by having more engines or larger ones. I would expect electrical planes to have more engines, but that's a small secondary effect.)
REDMOND, WA and VANCOUVER, B.C. – March 26, 2019 – magniX, the company powering the electric aviation revolution, and Harbour Air, North America’s largest seaplane airline, today announced a partnership to transform Harbour Air seaplanes into an all-electric commercial fleet powered by the magni500, a 750 horsepower (HP) all-electric motor. https://news.ycombinator.com/item?id=19539796
Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout
Given that your flight didn't get the "rubber jungle" of deployed masks, the cabin pressure probably never dropped precipitously low, but rather started to oscillate as the safety valve dumped and closed, but never dumped enough to deploy the masks and the crew declared and descended in order to sort things out.
A small number aircraft (non-airliners) are lost each year due to pressurization issues. It's a serious business, even in the high 20s and 30s (of 1000' MSL).
Single pilots are required to continuously wear O2 mask at/above FL350 (35000') and one pilot of a two pilot crew must continuously wear O2 over FL410. Between FL350 and FL410, two pilot crews may rely on quick-donning masks. This is believed to be a commonly violated regulation (in that air crews regularly do not wear the required mask when things are operating smoothly).
I believe that is an understatement. I've heard it described as the most commonly violated rule in aviation. There are a number of youtube pilots who commonly violate this rule seemingly without too much worry.
It shows that the most impressive electric aircraft specs are for the pressurized Eviation Alice (1000km, minus margin for contingency, and 250 knots cruise). If you stay low enough to not require pressurization, then you have to compromise the lift to drag in order to have a decent cruise speed or you have to tolerate a really low cruise speed.
Altitude is essential. Bite the bullet and build a pressurized cabin so we can get on with replacing fossil fuel aviation with full electric. https://www.eviation.co/alice/
Doesn't have to be above the Armstrong Limit, but it sure does help to be above 10,000 feet.
Eventually we'll have supersonic electric aircraft. To have sufficient efficiency, they'll need to be at or above the Armstrong Limit, like Concorde. (And perhaps higher, like the 96,000 feet record holder for horizontal powered flight, NASA's Helios... which just happens to be electrically powered. https://en.wikipedia.org/wiki/Helios_Prototype .)
EDIT: High altitude enables you to use an extremely efficient airframe with sailplane-like lift to drag but STILL achieve high cruise speeds. For instance, the Perlan II glider actually has no engine and is able to soar higher than any towplane, above 76,000 ft where it flies at about 250 knots (actual airspeed). Without any engine at all. https://www.youtube.com/watch?v=NnpE5xS1g80
And here's a solar electric aircraft aiming for similar goals: https://www.solarstratos.com/en/challenge/
If you go above 60k, and the plane experiences a rapid loss of cabin pressure, you have 60 seconds to restore cabin pressure before the passengers start dying. So the failsafe system will have to be massive. That increase in weight and complexity isn't worth the efficiency gains.
You mention Concorde, and indeed it had a very substantial failsafe system even though it only touched the lower end of the limit. Concorde had really small windows, so even with two windows gone it took some time to equalize pressure. The pilots had positive pressure oxygen masks, and the plane had the ability to drop altitude immensely fast in an emergency.
Electric aviation has many merits, but being a lightweight source of plentiful oomph is not currently among them.
Such forceful claims should not be made anonymously. I'm with you on the claim itself but feel that if you want to make that statement and stand by it that you should do so with your name and 'engineering reputation' attached to the claim itself.
From the exaggerated numbers for aviation fuel cost to the ridiculously low cost of electricity all the quoted numbers are obvious lies.
Not to mention that a back-of-the envelope calculation shows that the aircraft would never be able to take off due to the weight of batteries required for a 650 mile range.
You would be absolutely right in staking your engineering reputation on calling bullshit and I would happily join you.
The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.
Otherwise you'll have a really giant bag of gaseous hydrogen which does help your bouyancy, but then you've made an airship instead of a plane and a spark accidentally turns it into the Hindenburg.
Compressed at 690 bar (about 680 atmospheres) it goes all the way up to 5 MJ/L, only 7x as much volume of fuel required compared to jet fuel. But the tanks to pressurize something that much are presumably very heavy and not a reasonable solution in an airplane.
Liquifying it gets that up to 10 MJ/liter and I don't think you need as much pressure to store that (as long as you keep it very very cold).
Per weight instead of volume you beat jet fuel (by 3-4x), so that aspect is a win. Having enough volume to store it and keeping the storage equipment light are the challenges.
It can be burned in a gas turbine, but for now the NOx emissions are pretty horrible.
Pressure vessels though, you're better off making them round.
Either way, the Soviets tried gaseous fuels in the 80s - See Tu-155. They ran on liquid H2, CNG.
If I recall, the weight increase didn't make it practical. On the other hand it was a turbine powered plane. It might work out with fuel cells (although you'd need a big and heavy compressor to run it)
Until recently, making hydrogen by electrolysis was not a benefit, environmentally, as a lot of the electricity would have come from fossil fuels. I think decomposition of methane is an option that would allow the carbon to be sequestered.
What problem are we solving by moving to hydrogen?
This charge seems to indicate liquid hydrogen would require something like three times the volume as jet fuel / kerosene/ diesel.
https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/En...
- It'll be a long time before fuel cells are cost competitive with gas or electric cars, but for planes the cost of fuel and operation is much more significant than with a car, so the upfront cost for building the plane seems less significant in comparison
- Refueling infrastructure is much easier to implement at a (relatively) small number of airports than it is to build many small consumer refueling stations everywhere
- Space is more important than weight in a car, but the opposite may be true for a plane
- Crash safety is a much bigger problem for cars than planes - plane crashes are rare, and if a plane crashes there's a good chance everyone dies anyway, but if you're designing a car you're going to have to be really careful to make sure every other fender bender doesn't result in a hydrogen explosion
Of course there's the issue that most hydrogen today is created from fossil fuels, but perhaps there are ways to generate it sustainably and still remain competitive with the cost of jet fuel?
Electric cars can be a very competitive alternative to gasoline cars, but electric batteries are not yet energy-dense enough to make long-distance air travel viable, so it feels like hydrogen planes might be the least bad solution if we want to get off of fossil fuels.
That's actually not the case. Overall your odds of surviving an accident in a plane are something like 95%. Still above 50% for "serious" incidents. Sure, if the plane drills the ground everyone is going to die, but planes crash somewhat regularly with most/all surviving.
Most rockets use hydrocarbons for this very reason.
Shape will be more interesting - storing the fuel within the wings is not a very bright idea in this case.
This one is a non-problem. I don't think there is any civilian airport with enough fuel storage for two weeks.
(But the tank weight, well that is a problem.)
The ones that aren't supplied by pipelines have trains or fleets of trucks supplying them. Those would see a gain on using water, electricity and some mildly expensive machinery.
Of all the very relevant problems of using hydrogen on planes, long term storage is not one of them.
But don't forget that the stated purpose of funded research is often a lie[0] and this is not necessarily viable outside the lab.
[0] You get other benefits from the research including subsidizing your national industry, training your workforce, doing research you're interested in with a more politically palpable purpose.
Safety is critical on aircraft. Hydrogen is difficult to contain, and has very low viscosity due to its small molecules. It burns with an almost invisible yet very hot ultraviolet flame. It easily mixes with air to form an explosive mixture and has a very low minimum ignition energy (about a tenth of gasoline).
Combustion of hydrogen in a heat engine for propulsion would be very inefficient compared to a battery electric. Fuel cells are in between, at about 40-60% efficiency, but have a substantial weight cost.
~methanol Renewable CO2 recycling and synthetic fuel production in a marine environment https://www.pnas.org/content/early/2019/05/28/1902335116
PS: *small in capacity. I do know that for example Solar Impulse is the biggest aircraft by wingspan.
There are a few things to be weary of; Mostly that thrust is loud and dangerous to air crews. Weight shifts.
Individually driven wheels offer some precision without significant forward thrust.
Wheel propulsion on the other hand can impart momentum at very high efficiency, as well as regeneratively brake.
This can be extremely relevant for shorter flights: "[taxiing] aircraft fuel burn which is estimated to be as high as 27% of total fuel burn for a 90-minute flight where waiting in queue adds to the time on the ground" [2]
[0] https://www.airliners.net/forum/viewtopic.php?t=747735
[1] https://www.aviationtoday.com/2019/05/01/electric-taxiing-sy...
Electric drive wheels don't eliminate that unless you don't start the engines until near the hold short line (in which case, you don't have air conditioning or electric power, meaning you end up running the APU [itself a small jet engine] to provide that power).
If it was a large amount of battery, it would be cool if the batteries were in a small autonomous vehicle that disconnected from the plane when it was time to spin up the main engines and returned on its own to be recharged. Seems like a solvable problem.
A 787 may be ideal for an electric conversion (since it's already a no-bleed airplane). Even then, you probably might as well run the APU for electrics on the ground, since you're going to be carrying around that amount of weight anyway.
You can also turn the turbine off before landing.
The whole point of electrifying flight is that it makes small aircraft economical for airlines. The future of inter-city transport will be light aircraft with less than 20 passengers flying out of of small regional airports. Driving to LAX and waiting in security to get on a huge jet and fly for 90 minutes to SF sucks, but so does the drive. We're stuck with two terrible options there. Driving to a tiny airfield and hopping directly onto an electric plane that costs the price of a bus ticket will change everything about the way people live. They will never replace turbine engines for long haul routes, but the vast majority of commuter flights will be completely electric within 30 years.
Electrified aviation will be more than 10x cheaper vs turbine based. Practically the entire cost of aviation is in the engine, with its' associated fuel logistics, maintenance requirements, and pilot training.
Maybe we need federal legislation to make it less of a hassle to build a new rail line but we should focus on actually solving the problem. I don't see how thousands of 20-person electric airplanes is a scalable solution.
Does weight make a significant difference once the aircraft is at cruising altitude?
Nowadays they just do a better job of loading only the fuel necessary, and circle pointlessly to burn excess fuel before landing. It's still an issue, they just don't dump the fuel on the neighborhood below like they used to.
See: Santa Monica, CA
Burning human fat stores seems a mite dystopian. ;)
Edit: Human at rest. I imagine Ryanair might be keen on pedals for everyone, but I can't see that being popular with the holidaymakers.
Seems a trained person can do 150-250w
https://www.fai.org/news/thirty-years-longest-human-powered-...
Also driving in winter blows.