Rolls-Royce calls off bets on electric planes, says low-carbon fuel is future | Hacker News Reader

Rolls-Royce calls off bets on electric planes, says low-carbon fuel is future

electrek.co

145 pointsburkaman246 comments

It's a crowded market and they are targeting planes that can replace jets for medium and longer distance. Which at least short term won't be electric. That would require breakthroughs in fuel cells that I think they are starting to conclude are a combination of expensive and impractical. And there's the whole notion that green hydrogen is more of a promise than a reality right now.

Battery electric makes a lot of sense for smaller planes and distances. But that's a very dynamic market with a lot of players and not a lot of clear added value for Rolls-Royce. Also, it's very different from their current market which is basically focused on jet engines for big planes. That stuff is just way out of their comfort zone.

IMHO, the commuter plane market will change quite dramatically in the next decade. Basically battery electric is not a drop in replacement for those planes. But instead that market will start shifting to much simpler and smaller planes that are dirt cheap to manufacture and operate. Basically the main cost is the battery and the maintenance. Add autonomous flight or at least vastly simpler operations to the mix and pilot cost goes down as well.

That enables flying with much more but smaller planes. Which in turn enables flying to and from much smaller airfields closer to where people want to go. With vtol, potentially even inside cities. Long term commuter jets (with fuel cells or sustainable fuel) won't be able to compete on cost for short hops.

I think you are too optimistic. While we can do everything you state, I don't think there is enough demand. Most people don't want to be a pilot these days, the exceptions are not enough to support all the R&D needed to get there. Likewise, the other niches where people use airplanes for short flights are not large enough to support the R&D needed to get there. So small flights will be stuck with 1960s airplanes they keep rebuilding, with a few small manufactures doing small refinements on designs that are decades old, as a major redesign is just too expensive. Once in a while some rich person will finance a new airplane, but it will always be a money losing investment and so only flying enthusiasts will spend that money.

> I think you are too optimistic. While we can do everything you state, I don't think there is enough demand. Most people don't want to be a pilot these days, the exceptions are not enough to support all the R&D needed to get there.

IIRC, there isn't even enough demand there to switch away from leaded fuel.

It's not that there's not a demand for unleaded avgas, I'd say most GA pilots are ambivalent to leaded vs. unleaded fuel; they just want whatever makes the prop spin.

The issues with the unleaded avgas rollout are purely bureaucratic. The FAA has been dragging its feet for literally decades to get it done. Even when we have fuels like G100UL approved which is a drop-in replacement for ~80% of the GA fleet, it still takes forever to get across the finish line.

Indeed. G100UL is drop in for the entire piston GA fleet, though, not 80percent.

> the entire piston GA fleet

All the spark-ignited piston fleet, but not the diesel piston fleet (which cannot use G100UL [nor is it needed for them as diesel is already unleaded]).

Aren’t they using Jet-A anyway?

In practice: yes; kerosene (Jet-A) and auto diesel are very close compositions, with the former flowing better at low temperatures (as might be found high in the atmosphere). Jet-A comes out of convenient pumps already located on airports.

They’re part of the piston GA fleet for which that fuel is not approved (and neither safe nor needed).

Why would there be a demand for solving someone else’s problem, when you can just say ‘it’s aviation, change is too hard’ and people will eat it up anyway.

Agreed, GP is way too optimistic. Airplane manufacturing peaked in the late 1970s with over 18,000 planes manufactured a year. These days the numbers are under 3,000 planes a year!

Switching to a new power source isn't going to change the fundamental economics of airplane manufacturing. There just isn't enough demand to reach any kind of scale and it's not the gas prices - manufacturing collapsed to its lowest point in the early 1990s before gas prices went out of control.

Autonomous flight would be the game changer. The problem with small planes is that you're splitting the pilot & FO salaries across fewer people. If you're not doing that then 20 person flights become a lot more economical.

Planes could be flown autonomously, as they have all of the systems to fly and land automatically.

The problem is mostly about what to do if for some reason the autoland system can't work, if there are sensors that are malfunctioning, conditions aren't nominal and some non standard corrections need to be done, etc.

> people don't want to be a pilot these days, the exceptions are not enough to support all the R&D needed to get there

There is a massive market for short-hop flights. They're just difficult to do at a good price, at scale, with human pilots.

Autonomous short-hop air travel, especially when demand is periodic or occasional, ably complements or even beats rail and autonomous cars in many real-world scenarios.

Fuel weight for liquid fuel at start of flight: 10x Fuel weight for liquid fuel at end of flight: 3x

Fuel weight for battery at start of flight: 100x Fuel weight for battery at end of flight: 100x

Batteries are not a great idea for a planes primary energy source. Liquid fueled planes get lighter and more efficient as they fly, a battery plane starts with a much larger and heavier fuel load and carries it the whole trip. Not only that, battery costs a lot more than fuel tanks.

>Liquid fueled planes get lighter and more efficient as they fly, a battery plane starts with a much larger and heavier fuel load and carries it the whole trip

I saw a concept once that had the plane drop the big battery after takeoff (maybe after reaching cruising altitude too) and let the battery fly back to the airport autonomously. Then it doesn't have to carry that dead weight for the entire trip.

But, just like the promise of extended range batteries you could tow behind your EV for long trips, it's probably not real-world feasible.

> I saw a concept once that had the plane drop the big battery after takeoff (maybe after reaching cruising altitude too) and let the battery fly back to the airport autonomously. Then it doesn't have to carry that dead weight for the entire trip.

This sounds unrealistic. What if the plane needs "big energy" in the sky for emergency failure? Isn't the standard in aviation failure to the level of the 3rd degree or something (1 signal has 2 backups for 3 total or something)

I agree it's unrealistic, but not because the plane might need "big energy" later -- I don't see how dropping the battery is any different than burning the fuel?

If the plane burns 25% of its fuel on takeoff and climb, then that fuel is gone.

If the plane drops 25% of its battery capacity (which is now depleted) after takeoff and climb, that battery capacity was already depleted, it's just acting as dead weight.

The difference is that when you burn fuel, you burn fuel, and the mass exits the aircraft through the engine.

When you discharge an electric cell, you're still carrying that electric cell with you.

I suspect you're trying to express this and are fingering some other element of this concept as unrealistic, but that's not how your comment reads.

I literally said that the depleted battery would be physically detached, I don't see how there is any other interpretation?

It's unrealistic because of all of the details in making a an autonomously flying battery pack that can detach from an aircraft in flight and do it with the kind of safety a civilian passenger aircraft demands.

Apart from the detaching and flying a battery part, you've also got to seamlessly switch power source in midflight

Otherwise you've depleted 25% of all your batteries and jettisoned a single battery pack, which (like the others) is 75% full. (That might of been a source of confusion).

This is a problem we solved decades ago. At this point it's such a trivial problem that it's totally irrelevant and not even worth discussion.

The difficult part isn't designing a means of switching from one battery pack to another, it's convincing regulators that took decades to be convinced by things like two engines being enough redundancy that a mid-flight power source change is a good idea

Bureaucracy is not the problem being posed here. It was a question of technical possibility.

When I said it's trivial, I meant trivial. You can simply just discharge one pack preferentially over another. It's something that would be inherent to the power management circuit.

Whatever you're imagining, this is not that. There is no giant lever to changeover the packs. The circuit is never broken and power is never interrupted. It really, truly is as simple as drawing power from one battery and not the other.

Given the ridiculous power requirements involved, 'simple' is perhaps a bit generous. But the complexity is in physically handling that amount of current, not in switching it. Again, these are solved problems with standard solutions. This is stuff we've been doing industrially for years.

That seems like the easiest part, flip the relays to disconnect the battery pack, evaluate remaining capacity and if the detachable pack is discharged by the expected amount and the onboard packs are full, then go ahead and jettison.

You have to do that realibly, millions of times without failure, safely and without loosing redundancy. Flipping a relay is easy, doing in flight with one of most safety critical systems not so much.

Man, I just hope all those aerospace companies YC is funding have founders with a much better understanding of these things...

>Flipping a relay is easy, doing in flight with one of most safety critical systems not so much

This system assumes an aircraft that is already battery powered and requires routinely detaching a very heavy piece of equipment in flight without causing undue risk to the aircraft and then autonomously flying that heavy battery pack over populated areas in airspace shared with other aircraft. The power control system for detaching battery pack is the least complicated part of this system.

Power decoupling is the only part that actually deserves any discussion at all, everything else is beyound rediculously laughable.

So it sounds like you're agreeing with me -- the power management piece of this system is pretty much the only part that we understand how to do?

That's clearer.

> What if the plane needs "big energy" in the sky for emergency failure?

Electric and existing planes can already tap into another energy source for this - potential energy. Most planes have decent glide ratios and can safely travel over long distances for an emergency landing from cruising altitude, as long as the pilot can maintain control authority.

In a world where loss of forward travel means an uncontrolled dive, having energy on tap is life. Unfortunately, scenarios like a slow base to final or a go around in a crosswind don't afford the ability to just trade altitude for airspeed. High density altitude + downdrafts or mountain rotors are another situation where I don't want to be underpowered.

The only thing that will be transformative for aviation will be a dramatic improvement in energy density or engine efficiency, be that battery electric or otherwise.

I believe dropping and catching new battery pack in the air is the way to go as well! Electric motors are smaller and can enable stationary flight. So stopping to change your pack is maybe a solution.

Something like a carrier launch catapult, I think, would make more sense to be honest

Does the rollout from 0 - 200mph takeoff speed really use the bulk of the takeoff energy? I figured most of the energy went to climbing 6 miles in altitude.

I believe you're correct in this.

An aircraft carrier's catapult isn't about getting an aircraft to altitude, but about getting it to flight speed, on the attenuated runway of a carrier deck.

(Landing and arrestor cables are the equivalent problem in reverse.)

That said, a divide-and-conquer approach to reducing overall aircraft energy use might go some way to making electrically-powered flight ... at least more feasible, for larger payloads / passenger capacities, and distances, than is now conceived.

This includes ground taxiing (jet engines are quite inefficient at low speeds) via tugs, some form of take-off assist, jettisonable battery packs (after take-off and climb phases), general lightweighting of the airframe itself (already a major area of both research and accomplishment for electric aircraft), and automation and removing requirements for onboard pilots and flight attendants (the more paying bodies the more effective the business proposition).

There's possibly some room for optimisation of engine and airframe efficiencies, routing, and traffic control, and possibly some gains by hybrid designs (fuel + battery with electric drives, say).

As a whole though I suspect electric aircraft have been oversold, and that aviation as a whole will see reduced availability and usage in future.

Probably not, but takeoff is at when engines are at its most inefficient

And at a proper airfield it wouldn't need to use nearly as much g-force, since you can accelerate at a slower rate when you have a runway.

They could use steam powered catapults like on carriers.

I hear mass catapulting passengers into the air is a thing now.

At least in theory the battery could be used to recover some of the energy on descent (similar to regenerative braking, but with the spinning propeller instead of wheels). No idea if that’s at all efficient or if anyone experimented with this though.

The main drawback to that suggestion is that aircraft really don't need more charge as they descend.

The high-energy flight segments are take-off and climb. If you're charging batteries on descent ... the only gain is that the next take-off/climb phase can use that recovered energy.

But from a mass and capacity standpoint, which seem to be the real challenges for electric flight, you're gaining very little. The ability to get rid of the battery you've spent on take-off/climb would be far more useful.

Or solar

I agree, we should limit flight to exclusively across large oceans. And replace flights over land with more practical low carbon options like high speed trains.

Simply not realistic for major routes in the US for the foreseeable future. Los Angeles and New York are 2500+ miles apart across over 10 states that would need to properly coordinate and invest to make this a reality.

Or high-speed cars. I hate trains.

I'm just imagining the carnage from everyone barreling down the highway at 200 km/h (125 mph)...

https://alt.pavethe.earth/

> Today roads are narrow, you have to turn, and most governments frown at ground travel over Mach2. With endless blacktop in every direction, there will be no restriction to your movement, and rocket powered hypercars will whiz in all directions. We will be able to amuse ourselves with endless driving at incredible speeds while drinking beer and eating wonderfully juicy burgers.

The cars are the problem, not the solution.

What is a train? A collection of cars.

Lower pilot costs are unlikely any time soon. The FAA might eventually allow single pilot operation for some cargo flights, but it's just not going to happen for passenger airliners larger than an air taxi. The routine flying operations can be automated to an extent, but nothing on the horizon will allow for automated failure management. Two experienced pilots are the bare minimum to handle the workload of major in-flight emergencies.

Where do you think the term autopilot came from? ;)

Smaller planes means more crowded airspace. I bet the permits will be the biggest obstacle. How would you price these? It would be hilarious if small planes took over instead of high speed rail. I could see cheaper helicopters being popular.

Airspace is used very inefficiently right now. With today's tech it's ridiculous we're still using primarily human vision for collision avoidance in most conditions, and in instrument conditions, spacing is typically 3nm.

If you mostly have maneuverable VTOLs or even with more automated systems on traditional planes, you could safely bring down that spacing considerably. Imagine if we required cars on the highway to keep even a 1 mile spacing/following distance and then complained about highway congestion.

Perhaps the distance requirements reflect airplane wakes, rather than collision avoidance [0]. Analagously, I don't like to follow cars closely on wet roads, given the plume of side spray [1].

[0] https://www.faa.gov/air_traffic/publications/atpubs/aim_html... subsection 7-4-9, titled Air Traffic Wake Turbulence Separations

[1] https://www.youtube.com/watch?v=C-1-btUcMiA 20 seconds long

Wake turbulence is mostly a concern for small planes following large planes. In the right conditions (pilots visually maintaining separation), planes do get quite close and at many airports like SFO, it's the only way to accommodate all the scheduled flights: https://www.youtube.com/watch?v=NLCcxCdrL5w

> spacing is typically 3nm

For anyone else not that familiar with aviation and very confused, this means three nautical miles—about 3½ regular miles, not that it's smaller than a transistor fin.

> Imagine if we required cars on the highway to keep even a 1 mile spacing

Distance doesn't matter, what matters is time.

Planes traveling at say 500 knots obviously need more safety margin distance than cars traveling an order of magnitude slower.

I mean learning to fly a plane is about the price of a car and the rental price is ~200/hr. You can use it really for recreational purposes only because it can only transit between certain places & it seats 2 people. That really puts it into the expensive hobby category.

If you had autopilot remove the need to learn to fly the thing and provide for increased density of air space + figure out how to let aviation vehicles takeoff and land more flexibly, it would become the commute option of choice for more people (it would still be quite pricy due to fuel costs but you’d see way more of them)

Oh, wouldn't it be hi· lar· i· ous to see 250 gCO2eq/km/person domestic flights overtake 4 gCO2eq/km/person rail... and the numbers for helicopters are even worse!

https://ourworldindata.org/travel-carbon-footprint

I'm wondering if helicopter pads make a big difference or if they're taking off from the ground. Sky bridges, underground walkways, or trams could be used in highly congested areas, but the US lacks long term planning, and can't into 3D space.

I really wonder if a mixed approach isn't best. Make the planes like trains, where the propellors would be electric motors, while there's a generator in the fuselage running on AVFUEL it was already going to burn in a jet engine. Reduced complexity, centralized weight, possibly modular system where bigger loads can be possible with a generator swap for more output and propellor swap for more bite.

I'm sure some level of batteries would be required for safety if the generator dies mid flight, but a load of emergency batteries is much smaller than a load of main fuel cell batteries.

That type of series hybrid architecture works well in locomotives where weight isn't much of an issue but it's totally unsuitable for aircraft. The necessary generator hardware is too heavy, and it loses a lot of efficiency compared to a direct mechanical connection.

Some sort of parallel hybrid architecture is more likely for short to medium haul airliners. They will use somewhat smaller turbine engines for cruise, augmented by battery powered electric motors for takeoff (or emergencies).

Turboprops that is turbine driven propellers(also turbines produce some trust) are very efficient. Better than generators you could use. And they are also simple for power produced.

Only down side really is that the optimal speed is quite a bit lower than jets.

I feel like if we’re serious about decarbonization it’s likely that the solution involves fewer people flying, particularly on overland routes.

When I worked in London a lot of weekly commuters flew rather than to the train from Scotland, or even Manchester given the absurd peak time train fares even though flying was usually slower on that route.

These commuter trips definitely won’t be replaced with small planes since capacity at London airports is too constrained.

You assume that you would need big airports. The UK is full of smaller airports. And more could be built if there is demand. Noise and pollution are much less of a factor with electrical planes. And with vtols, any open space or roof potentially qualifies as a spot where you can land. Most of the constraints with current aviation don't really apply here.

Lilium is one of the companies that aimed for the "air taxi" market and touted any space or roof. They've since both increased the size of their planes a bit and dropped the idea in favour of flying between dedicated sites and backed away from the "air taxi" vision towards flying between small regional sites.

I think the issue being that even if you get to the noise level needed, convincing regulators about the safety will take a long time.

I think there will be market, and it might also very well make expansion of existing airports less controversial if it is for less noisy tiny electric VTOL planes, but I think at best in the short to medium term they'll also be able to fly to helipads.

Getting additional locations approved will probably happen, but I suspect it will be a very slow, arduous process at first, which will only accelerate once people have both spent significant time near a landing site and not felt inconvenienced enough to oppose one elsewhere and flown in these planes and felt them convenient enough to want them nearby.

The flight is only part of the journey. People mostly want to get to city centres where the offices are. Small airports just don't have the transport links to get into the centre. It's bad enough trying to get to Stansted Airport on its slow train and that has 27M annual passengers.

Nobody is going to be flying to Europe or Australia on a smaller plane.

Maybe SAF provides an answer for these flights, but it would likely be prohibitively expensive.

The solution likely is mandating carbon offset payments for these passengers.

Carbon offset payments kind of smell like a sham to me. I don’t think it really solves much.

> Nobody is going to be flying to Europe or Australia on a smaller plane.

We've already seen a shift to smaller planes. Fleets are replacing 747s with 787s, and the A380 is already out of production.

787 isn't a small plane! 787 is just 11% smaller by wingspan and just 3% smaller range than long-range 747. In large part, 747 and 380 went away because they were fuel-inefficient 4-engine planes, not because airlines wanted to fly tiny planes between LA and NY.

Its definitely smaller in terms of capacity. Different seating configurations aside, notionally the 747 could seat 366 passengers whilst the 787 can seat 242.

Your notional figures are low for both aircraft. You can get 330 passengers in the 787-10 in a reasonably spacious two class configuration, or cram another hundred more in a single class configuration.

Either way the difference in cabin space is essentially irrelevant to arguments about "smaller planes" in the context of suitability for battery power.

We're still talking about widebodies carrying well over 200 passengers which would be entirely unsuitable for battery powered replacements, and the 787 is larger than many of the other widebodies it's replacing.

> 11% smaller by wingspan

Wingspan is not a good measure of "size", that's just an output of engineering decisions on how to get the actual payload into the air.

> 3% smaller range

Range is not a measure of size. Making a smaller plane with similar range is a technological coup and major part of making smaller planes successful.

The heaviest 787's max weight is 250 t, but for 747 that is 442 t. That's a 40% difference!

And self-driving cars should be here by 2015!

Sorry, but the 2010s called, and want their naïve techbro optimism back.

Batteries are heavy. Teslas are very heavy cars. Aircraft are extraordinary light, compared to ground-based vehicles. Even in flight, large aircraft will burn a lot of their fuel during ascent. Electric powered aircraft get to drag around the heavy used batteries until recharge. And then you have to figure out how to refuel. Until a significant change in battery density, electric planes aren't going to be a thing.

Would you class them as very heavy? Trying to find some figures to compare: https://www.quora.com/Is-a-Tesla-heavier-than-an-ICE-car-of-...

Tesla Model S - Curb weight 4,647 lbs Audi A8 - Curb weight 4,751 lbs BMW 7 series - Curb weight 4,244 - 4,848 lbs

Tesla Model 3 - Curb weight 3,627 to 4,072 lbs Audi A4 - Curb weight 3,450 to 3,627 lbs BMW 3 series - 3,582 to 4,010 lbs

Compare a Bolt (~3700 lbs) to a Fit (~2600 lbs).

A luxury car usually weighs more due to higher quality materials, larger displacement, more overall modules and wiring. Tesla is an ecobox made with cheap materials so majority of its weight is the battery.

Sure, when you're comparing them to German tanks, they look pretty normal weight. How about a Kia? The K5 is comparable to a model 3, if not as nice, and it maxes out at 3,534 lbs

>Even in flight, large aircraft will burn a lot of their fuel during ascent.

I've been wondering if this offers any escape. Suppose that you have a power supply from the ground during the initial acceleration, and the final cruising velocity is not much higher. Or just build a huge ramp.

It sounds like a joke at first, but it might not be impossible. You just need some kind of reverse linear induction motor that doesn't require much weight on the plane side. Perhaps the fuselage is the magnet? If the takeoff acceleration is 2g, you need a 1 km ramp. The varying lift of the wings will be an obstacle, though this might be manageable with flaps. Of course, a 2g takeoff would be a dramatic experience for the passengers.

This principle is already in use in "Ski-jump" aircraft carriers[0] like the British and Chinese use, compared to the catapult operated American carriers. The problem is it isn't remotely high enough. It does have an effect on take off distance, so for that short amount would help for fuel efficiency, but then you still have +30,000ft to climb. 737's often cruise at 30-40k feet, as the air is thinner up there so there's less drag and you have better fuel efficiency. Even if you launched airplanes off the tallest structure ever built (Burj Khalifa, 2,700ft), you'd still have the majority of the climb ahead of you. Planes go high.

My non-credible idea would be to just use an Apple-style magsafe charger on the back of the airplane that disconnects midair at 30,000ft and falls on the helpless people below.

[0] https://en.wikipedia.org/wiki/Ski-jump_(aviation)

Yeah, I didn't check to consider that the specific potential energy (10 km times g = 100 kJ/kg) is actually much larger than the specific kinetic energy (200 m/s squared over two = 20 kJ/kg) so my idea of pre-charging the velocity doesn't pencil out.

I do like the magsafe charger idea. However, I anticipate some regulatory issues.

It's not takeoff that consumes a lot of fuel, it's climbing to cruising altitude. You're not going to get much savings with a launch catapult. A catapult really only helps with shortening the runway distances required to take off (e.g. off an aircraft carrier).

You just need a fast enough catapult mounted on a slope. ;-)

An object dropped at 30,000 feet would be traveling at about 3,000 mph when it impacted the earth, ignoring the atmosphere.

Maybe launch at 4,000 mph to overcome drag to throw something into cruising altitude? We'll just wear some noise canceling headphones to block out the OVERSPEED alarms.

I mean, isn't ignoring the atmosphere ignoring like 90% of the domain?

Just for perspective this is about mach 5. But I guess there is no speed of sound if you're ignoring the atmosphere :)

A catapult that launches a commercial aircraft with enough force (over a typical runway length) to get it to cruising altitude with no other power source would also turn all the passengers into raspberry jam.

I wonder how much energy would be stored in that catapult and what would happen if something went slightly wrong. Like it got stuck midway... Will we have a plane left? Or how many pieces?

Brush up on your Jules Verne - clearly the solution is (perhaps not so much) a giant cannon....

So the ramp needs to be about 35,000 feet high?

If you're going to try and get an aircraft to cruising altitude without using its own energy, surely the easiest concept is with a tug aircraft towing to altitude. Hell, there's even fairly speculative concepts like Magpie envisaging a series of tows.

So if I understand correctly you'd like to shoot planes into the sky with a giant railgun?

This is how they launch some jets on aircraft carriers. It sounds ridiculous to apply that to a passenger jet, but not really any more ridiculous than the fact that we routinely fly through the air for thousands of miles in the first place.

I'm no expert, but catapulting a sturdy ~30 ton fighter plane seems like a fundamentally different engineering challenge to catapulting a ~400 ton aluminum can.

The E-2 Hawkeye is one of the largest plane that regularly uses catapult takeoff and it has a wingspan of 92' and weighs about 43,000 lbs.

A220 and 737 both carry roughly 100-150 passengers and have wingspans of 115-120' and the lightest versions weigh around 130,000 lbs.

Seems doable if the jet and catapult system were specifically designed for this purpose. Maybe less plausible for jumbo jets.

Catapults just shorten the runway needed. The plane still needs a ton of fuel to climb to altitude. Plus, I doubt you'd ever get a lot of civilians to fly off a catapult...

The goal is to reduce the onboard fuel needed to achieve flight. I thought that was obvious from the parent comment.

> Plus, I doubt you'd ever get a lot of civilians to fly off a catapult...

I'm sure many short-sighted people said that about passenger air travel in general. Plus, if you actually watch a video of a modern catapult launch, you will see that it would be mostly invisible to passengers.

The amount of fuel needed to become airborne is a fraction of the amount of fuel needed to achieve cruising altitude. So using a catapult would only save a puny amount of fuel, as well as add risk to takeoffs.

Plus, if you actually watch a video of a modern catapult launch, you'd realize that you're speaking out of your ass. Going from 0-170mph (the rotation speed of an A320), in a short amount of space is going to impart huge G forces on both the aircraft as well as the crew and passengers. Catapults also fail, and a "cold cat" on an airline sized plane (without zero/zero ejection seats for everyone) means a mass fatality event.

Man, HN is just full of people suffering from Dunning-Kruger.

When you think about it, that attitude explains a lot of VC funding in certain companies.

I'm not sure why you think this needs to be exactly like an aircraft carrier, it does not. Why in the world would it need a shorter amount of space? An electric aircraft with heavy batteries could be brought up to speed with the same acceleration as current aircraft, and all of that energy used is weight not needed for the remainder of the ascent and flight. I have no idea how much energy could be saved, but it's not nothing.

If that's not good enough for you, here's what fucking Airbus has to say:

"In the report, Airbus explains that the initial power required for a passenger plane to take-off is only needed for a brief part of the total flight. This therefore poses an opportunity for a ground-based device to provide the propulsion needed and free the plane of its additional burden. With this in mind, the engineers at Airbus came up with an idea dubbed "eco-climb" which appears to draw inspiration from the catapult-assisted take-off system utilized on aircraft carriers."

Dunning-Kruger indeed.

Catapults have almost always been used to minimize takeoff space, or eliminate it entirely (drone launches). The tradeoffs in using a catapult are stress on the airframe, heavier planes due to hardening the airframe to mitigate this stress, as well as an uncomfortable experience for the passengers. There's also the risk of cold cats as I mentioned. You seem to be ignoring these issues entirely.

Airbus's "Eco Climb" was greenwashing at its finest, and despite them touting it in 2012, here we are over a decade later without ANYONE doing something this dumb. The comment above misses out on some basic aircraft fundamentals. One, most of the energy used by an aircraft is in flight, not in rolling off a runway. So the amount of energy saved compared to the added complexity makes it a dumb idea.

Sure, you could make the catapult the length of a runway, mitigating the G force etc. Then you have a Rube Goldberg device that needs to accommodate every aircraft that uses the runway. And this device can't interfere with landing or taxiing either. Then you need to get this device adopted by most airports, otherwise you've immediately gimped your airliner when it lands somewhere that lacks this device.

This idea reminds me of crap I used to read in Popular Mechanics and Popular Science (RIP) that had great ideas that were never developed because their underlying assumptions didn't match with the real world.

You might as well off up the idea of using a blimp/dirigible to lift the airliner up to altitude then drop it off...

Oh and I believe referring to the Airbus quote is an appeal to authority? Considering that Airbus design flaws killed a lot of people, maybe reconsider?

Yes, Dunning-Kruger indeed. Or have seen any real world use of said catapult?

Engineers come up with all kinds of ideas all the time. Most don't result in more than some PR piece, like the one you quoted above...

It sounds ridiculous because it is ridiculous.

I think getting the passengers to flap has a similar physics outcome.

Sometimes passengers clap already, we are one letter away from harvesting that energy!

>Until a significant change in battery density, electric planes aren't going to be a thing.

There's a big caveat there though. Current aircraft engines are extremely expensive to operate and maintain, regardless of fuel costs. Even a simple GA piston engine would cost more to operate than a small commercial EV aircraft's motors. Replacing turbines with electric motors will provide cost savings that actually make small commuter flights economical again. Kerosene and jet engines aren't going anywhere for the long haul flights. But the future for electric aviation is in the sub 300 mile regional commuter market, where it's faster than a train and has the simplicity of catching a bus.

See Eviation Alice for an example: https://www.popularmechanics.com/flight/a41453056/eviation-e...

Today's battery tech is just barely good enough at this point to start becoming useful for these kinds of flight profiles.

Sub 300 miles the train should be faster door to door. Trains a better able to get into the middle of a city - airports both take a lot of space and are noisy so they get pushed to the edge of the city. Trains are also better able to integrate with a public transport system so they are easy to get to. Trains don't have the silly security lines (normally - though planes don't need them either). Trains also don't have large economic benefits from every seat full, so they can better handle someone making a last minute decision to go.

Note that I said should above. The reality is North America has terrible train service, and management (congress!) doesn't care: so airplanes end up better despite all reasons they are worse for short trips.

It's hard for me to imagine (in the US) the government allowing an explosion in small commercial flights w/o TSA and all that rigamarole. If you get 10x, 100x the volume today, with a less upper-crust passenger base, the perceived security/terrorism risk probably starts getting talked about.

and there is already a massive shortage of ATC employees right now. At minimum this would need to be addressed and more than double the workforce of ATC. That's without accounting for any additional infra that might be needed to support a 10x or 100x in traffic.

>That's without accounting for any additional infra that might be needed to support a 10x or 100x in traffic.

The TSA requirement is nil for 10 person flights and these would be VFR only anyways. You would avoid a vast majority of the need for added ATC by operating between uncontrolled fields and relying on enhanced automation. The traditional airport model doesn't really apply when flights can be made so casually. Imagine a world where tiny runways that only service EVs are integrated into the city and you can hop between them as easily as catching a bus. Crosscountry travel would be also be possible via smaller hops, and cost less than a direct long haul jet liner ticket.

All of that is enabled by the orders of magnitude reduction in operating costs. EV Alice is claiming $200/hr to operate an aircraft that has the equivalent performance to a $1k+/hr turbine within the range limitation.

> Imagine a world where tiny runways that only service EVs are integrated into the city and you can hop between them as easily as catching a bus.

I mean, that sounds like a massive shift in infrastructure and city planning. I am not sure how efficient and affordable this would need to be to achieve that level of integration into daily society. Currently nothing, in the US at least, is setup to function this way. Whereas rail and roads are already deployed.

And again, this ignores any of the issues brought on by scale. If this is the way we want people traveling at a 10x or 100x rate, the airspace is going to be busier and likely will need some sort of coordination, whether ATC or some other mechanism.

I struggle to conceive of a green future for aviation. I'm not saying we can't have planes, we absolutely should and for many applications they are the only answer: but high speed rail could offer a lot of what airlines currently do at significantly lower cost to both passengers and to the environment, and with less need for such extensive and radical safety features as are required for aircraft.

But just like, reading this comments about everything from batteries to from-ground power sources for ascent to dragging dead batteries after use... like, what if we just flew less? Yes for international travel that needs to happen at speed, a plane is basically the best option. But for... basically everything else, what if we just sacrificed some convenience to not be dumping industrial amounts of waste into the atmosphere?

I'm reminded of how much air quality improved almost worldwide when covid first hit and offices were shut down, offices that, I remind you, continued to function largely just fine after a period of adjustment to remote work. I'm obviously extremely for making all transportation tech more efficient, but an under-discussed element I feel in this is just... doing less shit? Moving fewer people when moving said people isn't really needed? Maybe not growing all the pineapple in one country and shipping it over to a different country to be packaged in plastic and then shipping those all over the world so everyone on the planet has ready access to pineapple, a ton of which is just going to go straight in the garbage because we don't actually need all that damn pineapple?

Where do you confidently take the idea from, that electro motors for electric aircraft are cheaper to maintain than piston engines?

I would've thought that the main challenge is the density of energy storage. It's hard for a battery to beat kerosene.

The article mentions the industry took a hit during Covid. It's interesting to note that a company like Air Lease Corporation (which buys aircraft and leases it to airlines) basically soldiered on unaffected by the pandemic [https://valustox.com/AL - there's a big dip in profit a year ago, but that's due to the Russian war sanctions].

Plus burnt jet fuel weighs nothing, whereas a spent battery weighs the same as a fully charged one.

It seems there needs to be a radical price difference between electrical and chemical energy before the virtues of the rocket equation are overcome for airline travel.

Considering just how cheap renewable energy can be, even poor efficiency might not matter. If you have process that can be scaled by supply of cheap electric power, it could work even if there is inefficiencies in process and in use.

It's not a matter of electricity cost, it's a question of watt hours per Kg. A battery powered plane cannot fly far, no matter how cheap electricity is, because the energy density just isn't there: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

I'm really talking about synthetic fuels made using electric energy.

Traditional fuels would also benefit from the cost savings of cheap renewable energy.

Don't forget watt per volume. H2 has great w/kg but poor w/liter.

It's not generating the energy -- it's storing it. Fossil fuels are massively more energy dense than our current electric batteries.

Fossil fuels are literally dead animals pressurized by Earth... all that energy went into the fuel. Planets work on massively larger scales of energy than human society right now and we're using stored energy created by planets to fly.

The energy is not exactly stored in the fossil fuels directly. Indeed you have to put in extra energy to break those bonds - pulling atoms apart is work. The “stored” energy comes from the fact that long time ago various processes split various compounds into two components, A and B. And putting them back together makes them snap like magnets with enough force to release some extra heat. We call A “fuel” since that’s the part that’s somewhat difficult to come by. We often forget about B altogether as it’s literally all around us. Fossil fuels are fundamentally efficient for flight since the oxygen is something you don’t have to carry around with you (unless of course you’re going to space).

> Fossil fuels are literally dead animals

By mass, fossil fuels are mostly from plants, algae, and bacteria rather than animals.

A spent battery doesn't weight anything if you drop it once it's done; similarly the spent fuel has weight if you have to store the hot gasses after burning.

Turning a fossil fuel based plane carbon free has the same weight problem

Are you seriously suggesting that airplanes could just drop batteries weighing tons while flying across the sky?

Since this is HN, he probably is. And not only that, he is probably going to select this as his hill to die on. Good luck.

Li-Ion batteries at that! Ibdon't see any reason why regulator wouod object to that. Also, those batteries cost close to nothing, so yeah, just use as consumables...

I think the point was that the only reason burned fuel weighs nothing is because we throw out the waste into the atmosphere.

Filled with toxic substances, no less. There’s probably some treaties that would frown upon that.

It'd go over as well as a lead... acid battery

> a spent battery weighs the same as a fully charged one

A Tesla's battery pack weighs ~3.2 nanograms less when it's fully depleted. Think of the weight savings with a bigger battery pack for a plane! /s

> It's interesting to note that a company like Air Lease Corporation basically soldiered on unaffected by the pandemic

Because governments bailed out airlines so that leasing companies wouldn't go default which would then have caused the banks to get into trouble. It's ~180 billion dollars each year just for new airplanes - with ten or fifteen years worth of active contracts, a collapse of the industry would have let the 2008ff crisis look harmless.

[1] https://www.statista.com/topics/3877/aircraft-leasing/

Absolutely wild how much machinery we have flying around

Yeah, and these things cost a ton of money - around 200 million $ for your average Airbus A320. If you now ask yourself, hey how are airlines making money, the answer is: they aren't, the money all comes from frequent flyer programs [1] - it's gotten so ridiculous that the value of many airlines has shrunk to less than their FFP programs are worth and they are loss leaders [2]!

Barely any airline actually has physical or real estate assets any more in their own name. It's all leased, rented or otherwise not on their books anymore, which was contributing to how badly airlines were losing money during COVID.

[1] https://www.theatlantic.com/ideas/archive/2023/09/airlines-b...

[2] https://happyrichadvisor.com/loss-leaders/

No one is paying 200m for an a320

Don't you say!

The article doesn't mention that, but I'm sure that is the root. Electric planes might make sense for short trips - a handful a enthusiasts fly to work every day (they live at/near an airport and work at/near an airport) instead of driving. A handful of rich people will hire an airplane (or helicopter) to get around cities faster. Some cross water transit is served by short haul flights (ferries are cheap, but boats are slow because of physics). However these are tiny niches and don't cover much air travel. In general air travel doesn't make sense unless your trip is 1500km or more, and the weight of batteries needed for those trips just doesn't make them possible.

We know how to make zero carbon jet fuel today using WWII technology (which has been improved on since, and can be improved). The hard part is cost: synthetic fuel generally costs 4 times as much as pumping oil. (synthetic fuels normally use coal or natural gas for the energy but the process would work with renewables). Still this is very promising: we know from experience it scales up to produce very large volumes of great fuel, and there is reason to think we can make it better/cheaper.

Carbon-neutral generation of hydrocarbon fuels from air with solar energy surplus is the future for applications that need energy density.

There will never be a battery that's anywhere close to 13kwh/kg of gasoline or similar fuels. So the 2nd best thing is to generate emission free gasoline and burn it as cleanly as possible.

I think this may be wise given the rapid pace of development that batteries are still undergoing. Pretty hard to create a design around a battery when you dont even know what chemistry you are working with. And there is a bit of a revolution happening with lower carbon fuels, even though it sucks compared to pure electric, and it still has a lot of work to make sense(https://www.youtube.com/watch?v=OpEB6hCpIGM). I was under the impression though that this was a potentially good area for hydrogen fuel? can anyone confirm?

Edit: Here is the video i was looking for https://www.youtube.com/watch?v=OpEB6hCpIGM

Summary: Jet-A/A1 kerosene is the current mass fuel for passenger planes in the United States, and its dirty, but the most economical.

Simple biofuels have all sorts of chemical drawbacks that make them a nonstarter. super processed biofuels however, can match the properties of JetA/A1 very closely, but they are very recently developed. Unfortunately, right now, they cost so much energy to develop that they arent environmentally friendly at all, even disregarding the rainforest destruction it provokes (palm oils).

hydrogen may work some day but production is still too costly and it requires a complete redesign of planes and engines, unlike super processed biofuels. it also requires expensive and sensitive cryogenic storage to make energy density work.

e-fuels, or hydrogen composite fuel (liquid methanol, etc) may solve all of the above problems and grow as a more economical option rapidly, but they will still not match the cost performance of JetA/A1 which means increased costs for travel/shipping are unavoidable.

electric is an option with the most uncertainty, but there are already niche use cases that already make more sense than other options. mostly small craft and short flight distances. but that does take a decent chunk out of our current consumption. if battery chemistry keeps moving forward at a rapid pace, this could legitimately replace a lot of the air travel we do, but until those batteries are already coming out of factories, its difficult to design around.

so here we are.

Your statement sounds like a contradiction.

If the development of batteries is so rapid, Rolls Royce not investing in electric engines and doubling down on fuel-burning engines instead could open them up for a book story worthy "disruption".

By the time batteries/electric plane engines suddenly become good enough, Rolls Royce might face themselves in a "why does nobody want our fuel-burning engines anymore" situation that will require multiple years to catch up to electric engine manufacturers. Multiple years of catching up that Rolls Royce might not have at the time they find themselves in the "nobody wants our engines anymore" situation.

We know the laws of physics behind batteries. The theoretical best possible battery (which assumes things like spherical cows) is still very heavy compared to burning liquid fuels.

Yes battery advancement is happening rapidly, but it can only asymptotically approach the limits which are not very good for the purposes of flight.

I believe there as chemists and physicist better qualified than me to tell you what the limits are.

Rolls Royce is owned by BMW. BMW does strategic investments and R&D for them.

They just look what they need for next few models.

Different Rolls Royce: https://en.wikipedia.org/wiki/Rolls-Royce_Holdings

The Rolls Royce company of discussion is not owned by BMW. The car brand Rolls Royce is owned by BMW.

Moving to battery would increase demand for power, so unless we are charging all these new batteries with low or zero carbon would we not just end up with the same issue?

You're just moving the problem from the vehicles to the power generation

No, even if you're charging your batteries with carbon-emitting power plants, those plants are much more efficient than the engine in a car or plane. Internal combustion engines are very impressive technology, but they are constrained by their form factor, and can't possibly extract as much energy from fuel as a large power plant.

In reality, almost every power grid in the world is already cleaner than an internal combustion engine, and rapidly becoming cleaner as more renewable energy is deployed.

Isn't this a better outcome ? Instead of having millions of mobile sources of emissions , you will have few thousand sources of emissions which could be regulated, monitored and modernized.

79% of new energy capacity added in 2022 was clean energy (solar, wind, storage), so yes we can expect that the increased demand for power will mostly be met with low carbon solutions.

Renewable energy is already cheaper to build than coal or gas plants in many places, and it will just continue to scale as the technology improves.

Last time I checked, solar and wind power were low-carbon.

I don't see the issue unless the fuel-powered cars are able to reduce carbon emissions at a faster pace than the energy grid can, which seems doubtful.

In the US on average an EV gets the equivalent of 91mpg. On the dirtiest local grid (MROE) it gets 42mpg, the cleanest (NYUP) is 247mpg. 42 isn't that great but for most driving habits it will eventually come out ahead in carbon emissions.

That's for cars, a plane's lifetime emissions are way more weighted towards fuel.

> so unless we are charging all these new batteries with low or zero carbon

It's not exactly science fiction.

What are the chances that planes are just not a viable mode of travel in 100 years time? It would be interesting if it only existed for less than 200 years throughout all of human history.

Zero, barring any kind of civilization-ending event. There is no conceivable way we run out of every possible fuel option.

In fact, just last year Airbus completed a flight with their A380 (2nd largest passenger jet in the world) using only biofuels.

We have to have planes - they are the most effective way of waging war.

The US DoD is rolling out big initiatives to address the "post-fuel" era like technologies that convert captured carbon into jet fuel and micro reactors on bases to power these systems. In 10 years or so the same technology will filter down to commercial aviation and everything will be just fine.

Governments doing whatever it takes and spending any amount to make sure they still have flying vehicles is one thing, but being an economically viable civilian mode of transportation is another.

Alaska Airlines is going to start flying on a 50/50 mix of traditional and harvested jet fuel next year. Fully harvested should get certification from engine manufactures in the next few years.

Or... a cleaner/more powerful fuel source comes up (nuclear, fuel cells, other sci fi stuff) and everyone flies their own "Flying Cars"(Tm).

I am actually more optimistic this would happen than people giving up on planes tbh.

What do you propose would replace them?

Trains, mostly.

With existing technology, a truly global rail system is highly tractable, if you're willing to forgo a transatlantic crossing (either EU <-> NA or Africa <-> SA). Other than that, bridges and tunnels already connect three continents: Europe, Asia, and Africa.

The biggest challenges are the Bering Strait, the Darién Gap, and the South-Asia to Australia crossings.

The Bering Strait is shallow (30--50 m) and narrow (85 km) enough that a conventional tunnel similar to the Chunnel should be viable. It's interesting to note that extant sea routes are already quite close to an Alaska-Siberia land crossing, as the Great Circle from the US West Coast runs along the track of the Aleutian Islands. With trains' greater speed, freight transit times might actually benefit.

The Darién Gap is a swamp, jungle, and mountain barrier to a continuous land crossing between North and South America, between Panama and Columbia. Roughly 100km of this is not traversed by any established roadway. Environmental, political, cultural, and economic concerns have barred creation of a vehicle roadway, but at least technologically the region should be amenable to rail.

The ocean between Indonesia and Australia is, as with the Bering Strait, reasonably shallow, though parts of it are exceedingly seismically active. A mix of bridge and tunnel connections is conceivable and there are actually proposals that have been ... floated ... such as here:

"Beijing to Sydney by Train: The Potential Development of a Singapore, Indonesia & Australia Rail Network" (2015)

<https://www.aseanbriefing.com/news/beijing-to-sydney-by-trai...>

That leaves the Atlantic as the largest present transport route without a ready option.

Conditions are too rough for a floating bridge, and the ocean is too deep for a conventional tunnel. The option of a submerged floating tunnel, proposed as part of Norway's E39 highway, might offer an opportunity for a continuous rail link between both North America and Europe, and possibly South America and Africa (say, Recife to Freetown or Monrovia). Both would be extraordinarily ambitious and would strain extant technology, but are at least theoretically possible.

Transit times would depend on rail speed.

At 320 kph, a 3,200 km (200 mph, 2,000 mile) transatlantic crossing would be a 10 hour journey, ideal for a night train. A 480 kph (300 mph) speed, fastest present tracked rail, would drop that to 6h 40m. At 970 kph (600 mph), roughly jet airliner cruise speed, 3h 20m.

Advantages over air travel should be greater energy efficiency, elimination of turbulence and weather considerations, possibly greater per-passenger space and luggage allowances, and far more continuous departures and arrivals. Disadvantages would be lack of view, technical risks (including catastrophic system failure), and likely longer transit time. I suspect that maximum tunnel speeds will tend to reflect present train systems, which range from 160 -- 300 kph (100 -- 185 mph).

Transoceanic rail crossings have some history at least in the proposal stage:

<https://en.wikipedia.org/wiki/Transatlantic_tunnel>

<https://news.ycombinator.com/item?id=33556153>

The thing that existed before planes. Boats and trains.

Before that. Walking.

Those burn the same fuel...

Boats aren't constrained by weight like planes are. You could put any amount of batteries on a boat and get it to float and move on water. They can also be moved by wind. I may be wrong, but I also thought there existed some nuclear powered boats.

Boats are very much so.

The largest container ships consume 250 tons of heavy fuel oil per day, they haul up to 15k containers and are at sea for months.

Filling a ship with enough battery power to replace that isn't remotely feasible. Just charging it at port would be an insane undertaking.

It's a truly crazy amount of energy.

We've had nuclear powered ships for 50+ years (even some civilians ones!). It seems like the problem is making them commercially viable. Maybe they would be if their competitors had to pay for the negative externalities of burning 250 tons of fuel per day?

Boats do, but trains are mostly electric.

Not in the US, their mostly diesel here

This is quite a probable scenario.

or just very limited. like the famous zip disk bell curve.

What is the zip disk bell curve in this context?

Close to 0

I wonder if satellite-based system to use space-based solar power generation and convert to microwaves to beam power to aircraft would work? Store just enough on the plane for take off and emergency landing nearby plus a buffer for in-flight space power. For long flights the plane receives a beam of energy. Everyone would probably die from being cooked but it may work.

Just to put that into perspective: a 747 uses 90 MW peak power during takeoff. And that's the useful power it needs as thrust, so the engines produce quite a bit more than that.

Yeah, microwaves are right out. Lasers, maybe, but lasers that can focus so closely qualify as offensive weapons.

Generally, less-focused lasers, picked up by nighttime solar farms that absorb sunlight directly in the daytime, are a much more likely medium for orbital power than microwaves. Monochromatic light can be converted to electrical power with much higher efficiency than can blackbody solar radiation. Lasers producing no greater intensity than sunlight worry people less than microwave radiation.

What is the surface area of the top of a plane? How much power do you need? How much power per area do you need to deliver and with what efficiency?

https://energycentral.com/c/ec/flying-without-fossil-fuels-n...:

“Mid-flight a Boeing 747 uses around 4 litres of jet fuel per second. Therefore given the energy density of jet fuel, approximately 35 MJ/litre, a Boeing 747 consumes energy at a rate of around 140 MW (million watts).

We can then convert this rate of energy consumption into power density, that is the rate of energy consumption per square metre. Typically this is measured in watts per square metre (W/m2 ). A Boeing 747 is 70 by 65 metres. So the power density over this 70 by 65 metre square is approximately 30,000 W/², and of course the power density over the surface area of the plane will be a few times higher, over 100,000 W/m²”

There may be gains there if electric motors are more efficient than jet engines (are they?), but overall, you’d need a lot more power than solar.

I think that density is attainable, but wouldn’t bet on it being practical except, maybe, for military use, and probably not for planes but for ground use (beaming energy to a base in Iraq may be easier than transporting oil there via trucks driving through a war zone)

For powering planes, I guess you’ll have to give up speed. That drastically decreases power need at level flight (the planes that flew around the world on solar energy were slow for a reason)

You also will have to track the plane withyour energy beam as it moves.

I wasn't planning that far ahead I'll file my patent later. But a quick Google shows:

A320 900 sq m for wings and top of fuselage and elevators. https://aviation.stackexchange.com/questions/54511/what-is-t...

A320 needs 150 G Joule / hour https://www.quora.com/How-many-joules-of-energy-does-it-take... edit: make it 1.5GJ not 150

To make it easy assume 1,000 sq m and 1.5GJ spread over that area 1.5MJ per sq m/hour.

As for power transfer efficiency it may require a few thousand satellites per aircraft if this is any indication. https://www.esa.int/Applications/Technology_Transfer/More_ef...

I've not heard of sustainable aviation fuel. Is it snake oil? Why wouldn't it just be "sustainable fuel" suitable for trains and automobiles?

And if we simply slowed the world down a little bit I wonder if blimps could take over for a majority of ocean-crossing journeys. Not that it will ever happen.

Trains are, by their nature, very suitable for electrification. As with renewable energy the expense is almost all capital, it's cheaper to run electric trains it's just expensive to build electric railway lines they run on.

Planes are not well suited to electrification. Trainers can reasonably be made electric, as might certain commercial purpose aircraft, but if there will be electric New York to LA passenger flights it won't happen any time soon.

Although the fuel in a Cessna would be AvGas which is basically leaded gasoline, essentially anything you'd pay to fly on has turbine engines running on JetA which is basically kerosene instead. Small local planes, especially in Europe might look like just the Cessna only bigger, but the propellers are spun by a jet turbine, they don't have internal combustion engines.

A jet turbine is an internal combustion engine. It isn't a "reciprocating" engine, though.

Well, unless it has an afterburner like Concorde's engines

That's still considered "internal" combustion, as the combustion is occurring within the context of the engine itself.

The traditional contrast to the I.C.E. is the external combustion of a steam engine, where the combustion occurs in a boiler, which then directs steam to the actual reciprocating engine (in a traditional steam engine).

Steam turbines actually could be a case of an external-combustion turbine, as these are powered by steam which is heated externally to the turbine itself (e.g., there is no internal combustion chamber).

Not all steam turbines are combustion engines, however. A nuclear power plant's steam turbines are fed by steam created from nuclear fission rather than chemical combustion. Some solar thermal power systems runs steam turbines based on solar power, and I believe that most geothermal power involves steam and turbines. Functionally, the steam turbine bits of these systems are identical to a coal-fired steam turbine, but the heat cycle differs.

Oops, thanks

It's just the same as the non-fossil versions of diesel like HVO100 and similar. Whether this fuel is "sustainable" or "emission free" of course depends on how you see it. It will depend on what the source of the fats used is, and how those were produced, how much and what energy was used in the processing and so on. But at least it's significantly better than regular fossil fuel.

An interesting thing about this is that there has been quite a lot of infrastructure built to create these fuels for road transport in the last decades. So if road transport is electrified but flight isn't, then all those resources could quite easily be redirected to make aircraft fuel instead. If I recall the interview correctly that I heard regarding the flight mentioned below, I think there are some countries that have enough biofuel production (currently for road transport) already, to replace all the aircraft fuel used domestically.

The first commercial transatlantic flight with this type of fuel was just two days ago:

https://apnews.com/article/transatlantic-flight-sustainable-...

> Is it snake oil?

While renewable, the worlds entire production of snake oil would only make a small dent in the fuel needs of the airline industry.

> I've not heard of sustainable aviation fuel. Is it snake oil? Why wouldn't it just be "sustainable fuel" suitable for trains and automobiles?

Planes don't run on the same fuel as trains and automobiles. The basic idea is pretty simple: it's all hydrocarbons. We traditionally use hydrocarbons grown as plants millions of years ago and stashed in the ground until we dig them up/pump out the ground. We don't put the carbon back in the ground -- it goes into the atmosphere mostly.

"Sustainable" fuels are the same thing except you grow the plants today. Since plants growing today use carbon from the atmosphere, even when the fuel is burned like traditional fuel, you're not adding much net carbon to the atmosphere.

Everything else is mere details, such as: growing plants today is much more costly than digging up plant material from the Cambrian; the fuel has to have the same energy density as traditional fuels; it has to not gunge up the engine; etc.

They are developing these fuels for Formula1 and the like. Probably won't see them in road vehicles due to cost. But never know. It's likely normal fuels in hybrids or pure electric vehicles will be better (cheaper and lower carbon). For trains overhead electrification would be better.

I'm not sure the fuel itself is that low carbon but the cycle of producing it may be. I'm sure a quick search would reveal they produce slightly less CO2 or something in a suitable engine.

Do you mean synthetic fuel? Haven't heard of Formula1 being interested in biofuel.

There's no mention of biofuel in the article. But yes any technology designed to reduce the impact of the fuel production/use cycle. In F1 it's branded as synthetic fuel right? It's like a natural gas derived fuel but could be derived from anything the scientists engineers can make work. Jet fuel is heavier so starting with an oil derived from bio matter might make more sense. Either way something designed with less impact than drilling for fuel.

The fuel mentioned in the article — "sustainable aviation fuels, or SAF" — is biofuel I believe, not synthetic fuel.

oh gotcha. To me it's all in the same. Some engineered alternative that produces less carbon. it's terribly semantic though because every fuel today is engineered to produce less emissions.

Right, agreed - it's an improvement over what we currently use! From what I read E-fuel is very expensive to produce, so I was surprised by the possibility of airplanes switching to it.

Sounds more feasible than electric planes though. That never made viable sense to me. At least they could build a 737 sized alternative fuel plane today.

It's a huge part of the 2026 rule changes.

E-fuel is different from SAF that is described in this article. E-fuel is carbon-neutral and SAF is low-carbon (made from tallow, algae, etc).

It's a hydrocarbon chain produced from corn and waste fats. Fairly similar to bio fuel for cars. Sustainable trains are nuclear powered.

Blimps are either too slow or can't carry enough cargo. Solving the use of heavy tanker fuel is quietly a massive priority, the naive answer is nuclear, the real world answer isn't clear.

The way it's "sustainable" is that it's not a fossil fuel (well, currently it's 50% fossil fuel, they hope it can be 100% fossil fuel free by 2030), so it's just part of the normal carbon cycle like forest fires and breathing.

IMO it's probably just a stand-in until hydrogen really works.

> Is it snake oil?

It's biofuel made from palm oil, algae, tallow, etc.

Hydrogen could be the fuel of the future. Go for the moonshot, a space elevator.

It's snake oil. It's renewable is the same sense that cow farts are renewable : if you dedicated the entire arable surface of the planet you could make fuel with it for 5% of our consumption.

Don't get me started on the oil USED to produce this wonderful green fuel.

Snake oil is at least renewable. Just grow more snakes.

not really "sustainable" but "more sustainable"

It probably will not be sustainable...

But it might be carbon-neutral... Which might not or might be part of sustainability...

Until we can actually find something with an energy/mass ratio as good as chemical fuels, we going to have to continue using those chemical fuels indefinitely.

No matter what the good intentions of the day happen to be.

It isn't just about electric planes: Rolls-Royce were trying to be G.E. and failing.

  slashing divisions such as R2 Factory, an in-house artificial intelligence software unit, and a direct air carbon capture project.
  Rolls-Royce said it would cut 2,500 management and administration jobs. 
 The next head to roll is its electrical business, which develops propulsion systems for flying taxis and other aircraft.

Did Rolls-Royce think they were a VC/incubator for inventions with multi-decade payoffs? Tough market.

Rolls-Royce continue to develop for the nuclear power market - I'm guessing driven by government/military money. Compare to GE Hitachi: https://www.gevernova.com/nuclear

Then again, looking at the General Electric website makes me want to short GE! Read and weep their AI initiative to develop buzzwords: https://www.ge.com/research/initiative/industrial-ai Or the bigger picture:

  Q: What is GE's mission/purpose statement?
  A: GE's newly defined Purpose is “We rise to the challenge of building a world that works.”
  Q: What industries does GE operate in?
  A: GE has long been a leader in Power, Renewable Energy and Aerospace. Today, GE also leads in delivering solutions across Additive Manufacturing, materials science and data analytics.

Financially, a basket of options is worth more than an option on a basket (RR share price). https://medium.com/@kentbeck_7670/decisions-decisions-or-why...

Rolls-Royce blurb:

  Rolls-Royce develops and delivers complex power and propulsion solutions for safety-critical applications in the air, at sea and on land.
  Strategic initiatives: Detailed divisional plans that will focus on opportunities where key drivers give us competitive advantage: widebody aircraft, business aviation, transport & patrol, combat, submarines, governmental and marine.

> Rolls-Royce continue to develop for the nuclear power market - I'm guessing driven by government/military money.

Correct - RR are the manufacturer of the PWR reactors that power the Royal Navy's submarines. They are trying to capitalise on this by branching out in to SMRs.

Is there a primer on what exactly "SAF" or "low-carbon fuel" actually is? It's not "just" hydrogen, or is it?

It just sounds too convenient to be a real thing. "Oh, just use the LOW-carbon fuels. There's your problem!"

Edit: Not disputing the fact that electrical airplanes present a staggering affront to the laws of physics due to weight. Just seems like the "third alternative" here (to status quo or battery) is being taken for granted.

LH2 may, in fact, be low-carbon fuel, depending of course on how it was produced.

An LH2-powered aircraft would use exactly the electric turbines that Rolls-Royce just cancelled work on.

Once LH2-powered aircraft enter any given market, kerosene-powered craft would be wholly unable to compete. But it will take a long time to build up infrastructure for it. Ultimately, international airports will electrolyse their own LH2 using power delivered from regional solar and wind farms, but don't expect to see much of it before 2050.

> Once LH2-powered aircraft enter any given market, kerosene-powered craft would be wholly unable to compete.

Liquid hydrogen has about 1/4 the energy density of kerosene by volume. It's better per kilo which is nice for aircraft but you're still looking at finding lots more space in the structure for fuel or accepting that you can't fly very far. I don't see that being competitive with kerosene.

LH2 would not fit in the wings, but would fit handily in nacelles slung under them. Space aboard aircraft is cheap; it is weight that costs.

It's sort of still being defined. There's a rush to develop a universal SAF, but companies can develop blends of alternative fuel sources and get money back from the US government in the process.

https://afdc.energy.gov/fuels/sustainable_aviation_fuel.html

The future of electric planes is going to be based on drone motor technology at this rate!

Can’t we have high energy density liquid fuels and electric engines?

Sure. Run a genset off the fuel and drive a motor with that. Works fine. Not very sensible in terms of drivetrain mass or efficiency.

You wouldn’t get any of the benefits of hybrid electric cars, you are saying.

I believe genset+motor is the implementation of some hybrid cars, possibly calling it a range extender. Some others have a combustion engine and motors attached to the same gearbox (iirc that's the Prius setup). However I'm not very clear on what non-marketing advantages there are supposed to be to having both petrol and lithium fuels on board.

He's right to gut pointless divisions on fake futures:

  - Carbon capture is nonsense. 
  - So are flying taxis. 
  - So are electric planes.
  - Hydrogen planes is even more of a joke.

All of those things are possible and being actively developed by countless companies and governments. They may not end up being economically feasible on any meaningful scale. That doesn't make them fake or nonsense.

Nah they are all fake. Just because people are 'working on them' doesn't make them viable.

Is shitting on people smarter than you like you entire deal?

Why is hydrogen plane a joke?

I am BuildsJets now, but 20 years ago I was BuildsCryoFuelsystems.

Go look at the cross section of an actual hydrogen-powered aircraft that has flown actual missions under it's own power, such as the Boeing Phantom Eye. The USSR's TU-155 flying testbed aircraft does not count, it did not fly under hydrogen power or fly an actual mission, it just ran an engine in the air.

Observe how much of the airframe's space is used by fuel storage, compared to payload. Now do the same thing for a commercial airliner, and realize that commercial aircraft are just barely profitable with their current payload:fuel weight ratio.

Also, did you know that when you refuel a liquid hydrogen tank, a significant portion of the fuel is vented off to the atmosphere? In the case of the Space Shuttle, LH2 filling losses are around 20% of total fuel load. Then there are boil-off significant losses while the vehicle sits around warming up. So to be most efficient, you would need to either fuel up IMMEDIATELY before loading passengers, or hot-loading propellant with passengers on-board, like SpaceX does, and the FAA prohibits for commercial passenger operation. There are also boil-off losses in the transportation and storage equipment to consider, and boil-off losses everytime you transfer to a different storage or transportation medium.

Just a few months ago, Universal Hydrogen did a 200-mile flight of their Dash-8 which has been converted with one hydrogen engine. I’m not going to make any predictions about the future price of hydrogen vs. other fuels, but it doesn’t seem like there are any insurmountable technical barriers to mid-range hydrogen airliners.

Storage of large quantities of hydrogen is a pain and also heavy (which matters a lot on a plane), so if you really want clean fuel, then synthetic hydrocarbons make more sense on a plane than hydrogen.

Storage of LH2 is not, in fact, heavy. Rockets are even launched carrying it.

Management of bulk LH2 is a chore, but is mature technology. The value proposition of LH2 as aircraft fuel is such that, in any market where LH2 airframes come into service, kerosene craft will be immediately wholly unable to compete.

Ah, I was thinking more about hydrogen fuel cells and gaseous hydrogen (which I've seen discussed for the plane replacements) not cryogenic liquid hydrogen.

Hydrogen has great energy density by mass. But creating a very lightweight container to store either liquid hydrogen or highly pressurized hydrogen is challenging. More feasible than powering planes with lithium batteries, though.

Lightweight containers for LH2 have proven so trivial as to have already been in use for many decades aboard space launch systems, which are even more sensitive to weight than aircraft. Aircraft LH2 tanks would want insulation usually omitted from rockets, but insulation is mature tech.

Weight of LH2 is so enormously less than kerosene that, once LH2 aircraft enter a market, no kerosene airframe could continue competing. Given the low volumetric density, such that LH2 tanks would not fit in the wings, they will probably instead be removable nacelles slung under wings alongside the engines. This has the further advantages of eliminating need for mobile hoses and for complicated onboard plumbing. I doubt anybody would want to fly with inboard hydrogen tankage, anyway.

Probably cargo craft will be first to use LH2, because carriers cannot load on another 40% more passengers just because the fuel weighs so much less.

The fuel is too dangerous to store..

Yet, millions of tons of H2 is produced, stored and transported annually, today.

It needs adequate ventilation to ensure that any leakage doesn't accumulate to exceed a 25% mix with air. That is done where H2 is used now. You are not hearing about hydrogen detonations.

every industry inflection point always has the dinosaurs who go extinct.

Those who don't see the inflection and want to keep their momentum in their set direction will find themselves in bankruptcy.

Unfortunate that rolls royce seems to have decided not to keep up.

There have been a lot of predicted disasters that never happened.

There are fundamental physics in play when I confidentially say that battery airplanes will never be more than a small niche.

>battery airplanes will never be more than a small niche.

I wish I could take that bet. I'd put whatever amount of money down on that.

They say never say never but you are asserting fundamental physics prevents it from happening?

Within 5 years I expect to see my local GA manufacturer start pumping out battery electric planes.

Within 10 years it will be reasonably possible to get yourself on an electric plane. Regional electric planes will start replacing older planes. The like 20-seater type size. I expect the niche stuff like seaplanes probably start getting certified around this spot.

Within 20 years the regional flight will have mostly converted to electric and some of the early adopters will have finished amortizing those planes.

within 30 years the massive airliners will be replaced with 20MW or so battery electrics. I will even go further and say these won't look like traditional planes.

A typical high-end 18650 li-ion cell from 1996 was 1400mAh.

A typical high-end 18650 from 2023 is about 3200mAh.

In other words, it took 27 years for battery tech to achieve a bit over a doubling in energy capacity.

Even if we wait another 20+ years and batteries double again, it will still be an order of magnitude less dense than gas. In a plane, this is absolutely critical.

I want to be flying electric planes, hell I'd settle for just an electric car that got somewhat good range. But battery tech has taken eons to get to where it is. We can only hope to get some quantum leap in storage density or we're going to be flying with dinosaurs for a long time.

> you are asserting fundamental physics prevents it from happening?

The energy density of batteries vs fuels is the current limitation. We don't know if this problem can ever be solved. A business cannot gamble on some magical hopes and dreams.

> within 30 years the massive airliners will be replaced with 20MW or so battery electrics

And how much will those 20MW batteries weigh?

With the current lithium battery technology, you would need a 7,167 metric ton battery to store the same amount of energy as 150 tons of jet fuel, which is typical for a long haul passenger jet.

> The energy density of batteries vs fuels is the current limitation

It's not just that. Fuels mean the aeroplane gets lighter with distance, especially on ascent. Batteries need so much more energy just to carry their own weight the whole way.

Also often forgotten thing is that aircrafts have also designed max landing weight. This isn't hard limit, but limit for normal operations. This is why they go in holding pattern to burn fuel for example if cabin pressure is lost. So not immediate emergency, but something where you want to land sooner than planned.

To put it in perspective, the A380 max landing weight is 391 tonnes, versus the 7000 tonnes of lithium batteries required to power a long haul flight.

> you are asserting fundamental physics prevents it from happening?

Yes. The chemistry of burning fuel vs batteries is very different. Even though engines are much less efficient, that doesn't make up for how much more dense fuel that you burn is. (you could perhaps burn the battery, but that would be a very different thing, and probably too toxic to consider in the real world)

> I expect to see my local GA manufacturer start pumping out battery electric planes.

Since GA airplanes are currently being made at a rate of about 3000/year you could be right and yet not make any dent in total airplanes.

>Within 10 years it will be reasonably possible to get yourself on an electric plane.

Maybe, but those airplanes will have a very limited range. For most aviation uses range is important - by the time you get to the airport, run all the preflight checklists: you could have driven the same distance as the range of an electric plane, and the electric plane hasn't even got off the ground yet! There are short range niches where this is acceptable, and they will switch to electric planes for sure.

> Regional electric planes will start replacing older planes. The like 20-seater type size.

RANGE RANGE RANGE. Most people who get in a 20 seat plane are going far enough that electric can't make the trip. Batteries are too heavy, and this is the physics of the chemistry that innovation cannot work around no matter how much you want to ignore the laws of physics and chemistry.

Try reading the article before commenting

Here's a link from the article

https://www.rolls-royce.com/media/press-releases/2023/13-11-...

The same engines they cancelled would have been used on LH2-fueled aircraft.

Not viable.

"An aviation-size, worldwide hydrogen supply and airliners capable of using it are decades and trillions of dollars away. In terms of a timely green return on investment, the money would be much better spent on SAJF, both for capital investments in capacity and for technologies that improve yields and reduce costs." - Alan H. Epstein (professor at MIT)

https://aviationweek.com/aerospace/program-management/opinio...

AW is right that it will take decades and trillions of dollars, but the rewards are large enough to drive such investment. RR is acknowledging the long-term nature of the market and pivoting to shorter-term profit, probably correctly. You will not fly in LH2 aircraft, but your grandchildren will.

You need to be able to tell the difference between what will happen and what might happen. If you don't remember the losers, you will assume every idea is a winner.

I still wonder if most of the human impact on climate is not the CO2 but the water vapor put out by planes. See the post 911 weather, and more recently around here a lot of people know what "covid sky" means. The sky was very clear and blue during the early shutdowns.

If this hypothesis is correct then low-carbon fuels (say methane) are the wrong answer. Low hydrogen fuel would be better. Bring on the coal fired airplanes!! Sounds so silly, but hey...

Reply on news.ycombinator.com