Aircraft

Wright proposes a 100-seat electric airliner powered by aluminum

Wright proposes a 100-seat ele...
The Wright Spirit will be an electric 100-seat regional airliner. Slated to enter service in 2026, it'll either run on green hydrogen, or potentially an aluminum fuel cell
The Wright Spirit will be an electric 100-seat regional airliner. Slated to enter service in 2026, it'll either run on green hydrogen, or potentially an aluminum fuel cell
View 4 Images
The Wright Spirit will be an electric 100-seat regional airliner. Slated to enter service in 2026, it'll either run on green hydrogen, or potentially an aluminum fuel cell
1/4
The Wright Spirit will be an electric 100-seat regional airliner. Slated to enter service in 2026, it'll either run on green hydrogen, or potentially an aluminum fuel cell
Weight and volume comparisons for idealized aluminum, liquid H2 and lithium-ion energy storage
2/4
Weight and volume comparisons for idealized aluminum, liquid H2 and lithium-ion energy storage
First-pass cost estimates would appear to put aluminum on par with jet fuel, and substantially cheaper than hydrogen
3/4
First-pass cost estimates would appear to put aluminum on par with jet fuel, and substantially cheaper than hydrogen
The Wright Spirit could serve plenty of popular short-haul flight routes even if powered by aluminum
4/4
The Wright Spirit could serve plenty of popular short-haul flight routes even if powered by aluminum
View gallery - 4 images

US-based Wright Electric has announced a 100-seat electric short-hop aircraft slated to go into service by 2026. It'll either be powered by hydrogen, or it'll use recyclable metal in what the company calls an "aluminum fuel cell."

Wright is working on a number of large electric aircraft projects, including an even bigger 186-seater it's developing in conjunction with European airline EasyJet and BAE Systems. This would be a "low-emissions" electric, presumably using a fossil-fueled range extender to top up its batteries and extend its flight range to around 1,290 km (800 miles). The partnership is pitching it as a "path" towards clean aviation, a kind of Prius of the skies, that will prove the electric powertrain while waiting for energy storage to come up to scratch.

Wright's latest project, however, will be totally zero-emissions, and will use high-density energy storage to tackle flights up to an hour in duration – that's enough for the ~1,000-km (620-mile) hop between Sydney and Melbourne, or London-Geneva, or Tokyo-Osaka, or LA-San Francisco.

Essentially, once in production, the Wright Spirit, based on the BAE 146, will be a simple 100-seat electric option that carriers can use on a wide variety of very popular flight routes.

The Wright Spirit could serve plenty of popular short-haul flight routes even if powered by aluminum
The Wright Spirit could serve plenty of popular short-haul flight routes even if powered by aluminum

Wright is concentrating mainly on its specialities: the megawatt-scale motors and inverters needed to pull a big ol' Bessie like this through the air. Indeed, the company appears not to have settled on an energy storage solution at this stage, and is evaluating the pros and cons of both a hydrogen fuel cell system, like what we're seeing from a number of different companies now, and an "aluminum fuel cell" system that's really got us fascinated.

Why not run straight at hydrogen like most of the other decent-sized clean airliner programs are doing? One motivating factor is volume. Liquid hydrogen is an excellent lightweight energy storage medium by weight – heck, its specific energy of 33,313.9 Wh/kg is nearly three times that of jet fuel (~12,000 Wh/kg). But volumetrically, it's terrible. At just 2,358.6 Wh/liter, a given amount of energy in the form of liquid hydrogen will take up nearly four times the space of the same energy in jet fuel (~9,000 Wh/l).

Volume is a big deal for commercial aircraft operators; most of these early projects will be retrofits to airframes that weren't designed to carry the extra volume of hydrogen. Every seat that needs to be turfed out of the cabin to make way for fuel is a direct punch in the bottom line. And that's what makes aluminum so interesting.

Weight and volume comparisons for idealized aluminum, liquid H2 and lithium-ion energy storage
Weight and volume comparisons for idealized aluminum, liquid H2 and lithium-ion energy storage

Aluminum doesn't carry as much energy by weight as jet fuel or liquid hydrogen; at a specific energy of 8,611.1 Wh/kg, though, it's about 33 times better than today's leading lithium-ion batteries. And it knocks it out of the park on volume, packing in 23,277.9 Wh/l. That'll be music to the ears of airline companies.

How does it work? Well, effectively it's an aluminum-air battery. The aluminum acts as an anode, opposed by a carbon cathode with catalysts behind a porous polymer separator. Between the two is an electrolyte, typically a basic liquid. The aluminum reacts with atmospheric oxygen at the cathode, forming hydrated aluminum oxide and releasing energy.

The cathode and electrolyte do increase the weight of the overall system somewhat, limiting aluminum's specific energy ceiling to 60-70 percent of what a hydrogen system might achieve. But Wright reasons that "since half of the single aisle market is flights shorter than 800 miles (1,287 km), the range penalty might not be as consequential as it might initially seem."

Wright calls it a fuel cell, rather than an aluminum-air battery, to save on confusion. It can't be recharged like a battery; instead it'll need to be refueled more like a fuel cell, with the added task of taking the aluminum oxide sludge off for recycling at a smelting plant.

Wright says this won't be much harder than dealing with liquid hydrogen tanks, which it says will also need to be sent off to an external facility for refilling. But while the hydrogen infrastructure all needs to be built out, there are aluminum smelters all over the place already that can turn the aluminum oxide back into fresh metal ready to be loaded back into a canister and stuck in a plane, or used for other purposes.

Logistically, it'd be easy; canisters can be carted around in standard trucks and loaded onto the plane much like cargo. In pellet form, the metal can be sent down pipes if need be.

Challenges remain. Thin, cold, low-oxygen air at cruise altitudes mean that aluminum-fueled aircraft would need to run compressors and heat exchangers that threaten to blow out the weight budget. Entire aluminum cells need to be developed further from their current state to realize useful specific energy figures, and today's aluminum-air batteries are typically designed for low C-rates of discharge, as opposed to the demands of running aircraft engines. To get higher reaction rates, you'd need to expose more aluminum, potentially by using powders or pellets instead of plates. So there's a way to go.

Perhaps the most interesting kicker here is the bottom line. Running a rough, "first pass" simulation of an airline's operating costs, Wright projects that where hydrogen fuel cells are likely to raise costs by around 25 percent, and biofuels are likely to add around 32 percent, the aluminum system would actually be a hair cheaper than today's jet fuel operations.

First-pass cost estimates would appear to put aluminum on par with jet fuel, and substantially cheaper than hydrogen
First-pass cost estimates would appear to put aluminum on par with jet fuel, and substantially cheaper than hydrogen

Between the cost advantages and the fact that these planes could potentially run more seats than a hydrogen plane in a retrofit scenario, aluminum-air could potentially put forward a compelling case for shorter range commercial flights.

But for this kind of system to become a green option, carriers will need to source their aluminum from green smelters, using clean energy, clean heat and carbon-neutral smelting anodes. Mind you, these technologies are under development, and hydrogen has its own challenges in getting to zero-emissions.

Wright is agnostic at this point, summing up the hydrogen vs aluminum debate like so:

"Hydrogen fuel cell: longer range, smaller payload, harder operations, higher cost.
Aluminum fuel cell: shorter range, larger payload, easier operations, lower cost."

If the technology makes the necessary strides, it could end up being a matter of horses for courses. But it's certainly good to see that hydrogen might not be the sole viable way to decarbonize commercial air travel – even if it still looks like the only realistic path to clean long-haul flights.

Source: Wright Electric

View gallery - 4 images
18 comments
18 comments
mark34
I wonder if their efficiency calculations considered the difference in the weight of the aircraft as fuel is 'used up' and exhausted out of the engines as opposed to carrying the weight of the spent aluminum fuel residue?
FB36
So all aircraft/airports in the world need to switch to hydrogen or just this aircraft/company?
Let alone from where the hydrogen will come from, hydrogen is extremely dangerous because it is explosive!
Are we really thinking that there will be never mishandling/accidents to trigger massive explosions?

How about we just start producing biodiesel/biofuel at large scale (from all possible waste/biomass/trash/sewage) so that not just all existing aircraft but also all existing heavy trucks, trains, ships etc also can easily become carbon-neutral?
paul314
@mark34 It's even a little worse than that: aluminum oxide will be heavier than the original aluminum. Aircraft typically are designed to take off weighing rather more than when they land, so this may mean either significant structural reinforcement or limiting takeoff weight to maximum landing weight minus gain.
John Thompson
Great concept! Can you consider a hybrid? Jet engines for take off, and electric for all else?
James Reynolds
Why is it that any time they talk about using Hydrogen for fuel they talk about Hydrogen Fuel cells? Hydrogen is the cleanest burning fuel anywhere, its waste products are heat and water, thats it. It is also 100% efficient. Convert Jet engines to burn hydrogen, problem solved, and simply as its just a minor change in the fuel system.
TechGazer
Sorry James, but hydrogen is not clean burning unless you burn it with pure oxygen. Otherwise you get nitrogen oxides. It may be 100% efficient at producing heat, but so are other fuels. It's converting the heat to mechanical or electrical energy where the efficiency is much less.

To FB36, hydrogen is not explosive. Hydrogen and other fuels are explosive when mixed with air in the proper proportions. Hydrogen is safer in some ways than other fuels, since it rises. The Hindenburg didn't explode, it just burned, and there were survivors, so it's really a poor example for hydrogen being dangerous. Just don't coat your hydrogen containers with the equivalent of rocket fuel.
Matt Wilson
Anybody who believes This (Stuff ) is an improvement over existing combustion engines ,Needs to take some elementary Physics courses .over complicated , overweight ,Expensive,maintenance nightmares .
DaveWesely
Aluminum-air could be a game changer, not just for aviation but also other transportation needs. In terms of shipping, the increased volumetric energy density could be used to advantage as ballast. In terms of cars, it would not be advantageous due to weight, complexity, and infrastructure compared to LI-ion. Long haul semi trailers would be a good fit.
Re-smelting the aluminum could also be a good use for energy during excess supply/low demand periods with renewable energy, as opposed to just throwing it away.
@Reynolds It's an issue of efficiency. A PEM fuel cell is about +45% efficient while burning fuel is less than 33% (max theoretical efficiency). When you spend so much to store hydrogen, it doesn't make much sense to waste it.
@FB We already have biofuel produced at large scale. It's called ethanol and 30% of our corn crop is used to produce it. If producing biofuel from waste was economically feasible, we would already do it for ethanol.
paleochocolate
Parking is expensive. How long to recharge?
paleochocolate
@FB36 You need more enery in producing biofuel than there is energy in biofuel itself. It's a scam.

Biofuel is not a solution.
Load More