NASA is experimenting with an electric airplane, the X-57 Maxwell. It has several changes that should make it more efficient than just replacing the engines and fuel tanks with electric motors and batteries. They’re taking their time on studying it, making only one change at a time, so it’s going to be a while before they get done.
Assuming these experiments all work out the way they expect and adding in other ways to make airplanes lighter (e.g. carbon fiber fuselage and wings), how good of an electric airliner is likely? That is, how many passengers and what kind of range are we looking at? What speed are they likely to have during routine flight?
Nantucket based Cape Air actually already has electric planes on order, the Eviation Alice. Although that isn’t an airliner along the lines of the 737, it will be an electric plane flying for an actual commercial airline.
Fun Fact: The airline portrayed in the sitcom Wings was loosely based on Cape Air.
What NASA is working on goes beyond the concept plane you linked to. I couldn’t generate any links to the stuff they exhibit to the public but it’s interesting in how diverse the research is.
As to the one you posted that would fall under the commuter airline. Using electric motors allows all kinds of engineering designs beyond what a traditional jet engine can proved. It would be really easy to have a series of engines/props that can tilt to change the air flow characteristics of a wing.
And the current Lithium battery technology probably isn’t going to be the power source. However, they can use a traditional liquid fuel tank as a battery source with liquids that can be charged with electrons. Instead of just adding fuel like a traditional jet they would download the liquid for recharging and upload fresh fuel.
As for making them lighter with carbon fiber and other materials that’s already being done by the airlines. You’ll note that the winglets that were so popular on new aircraft have already been replaced by a tapered wingtip design that does the same thing more efficiently.
Probably the neatest thing I’ve seen was a ducted electric “coreless” engine. instead of putting the motor in the center the motor is in the rim with the traditional blades in the center. I wish I could find a link to it but I don’t know what to call it. They’re definitely working on propulsion for larger aircraft.
Batteries don’t yet have the energy density for long-haul flight. But shorter runs, say <1000 miles, have some potential in the relatively near future.
One advantage electric planes will have is that the engines are not dependent on oxygen. They can fly at an altitude limited by the wings and props/fans, not by the engines. Electric motors can put out maximum power at any altitude. There’s no reason they can’t fly at 70k feet or so.
It’s also easy to get a very high power density out of motors without much additional weight, since it’s really the batteries that are the limiting factor. Hence we may see VTOL or SVTOL flight out of electric planes.
Size is only an issue with regards to recharging the planes. Like other aircraft, they get more efficient the bigger they are. So electrics only get more practical as the size scales up. But they’ll need many megawatts of ground power to recharge in a reasonable time and that will be a challenge. Like cars, the fastest charge time will be somewhere in the 30-60 minute range assuming they aren’t limited by ground power.
Here’s my mini-optimization for electric planes: sodium power conductors. Normally, sodium isn’t thought of as a great conductor, and per cubic centimeter it’s not. But per unit weight it is better than aluminum or copper. And its low melting point can be used as an advantage: pump it through the conductors and motor housing as coolant.
Yes, that’s better than what’s being done so far. Just replacing ICE engines+fuel tanks with electric motors+batteries and no other changes usually only allows about 100 miles range. If we could get a small to medium sized electric airliner with 500 miles range, it’d be a significant step up. A large one would be even better. There’s lots of cities less than that far apart that have heavy air traffic between them. LA-SF and DC-NY-Boston, for examples.
Air taxis seem to be going with that. But to get VTOL, don’t you have to have rotating motor mounts or wings so that the propellors can blow air downward and then blow backward for level cruising? Won’t that add a lot of weight? The range would be longer without it. Also without using up lots of power to do VTOL. It’s not like we don’t have runways for traditional take offs.
The idea of liquid sodium on an airplane does not appeal to me for some reason.
Yep, and I expect routes like these to be the first to be electrified. It’ll need more work than a simple conversion to get there–just as long-range electric cars took more redesign than stuffing a bunch of batteries in the trunk and putting a motor in the engine bay. But there’s no “magic” required here. They’ll need to dedicate a large fraction of the internal volume to batteries and design the plane around that.
Right–I’m not expecting VTOL for the longish range routes. I’m thinking more puddle-jumper routes, like say the turboprops that run all day from Portland to Seattle. Airport fees are a higher relative cost the shorter the route, so there’s an advantage in making use of shorter airstrips.
Like anything else, it’s safe if handled properly. Normal jets fill their wings with highly energetic hydrocarbons. Liquid sodium is pretty benign in comparison.
for that to work financially that have to leverage the savings EV’s should produce against the loss of freight revenue built into long distance flights. I don’t know if electric propulsion is capable of generating the thrust of jet engines so it might involve electric/ICE hybrid motors.
Lightweight jump-start gyroplanes aren’t true VTOL - more like STO-VL. To jump-start, the engine drives rotors to lift the craft a few feet; then power shifts to the (usually pusher) propeller for forward motion and fast ascent. IANAP but vertical landing seems simple and autorotation is reportedly safe. But they’re a bit short on passenger capacity and speed; electro gyroplanes would probably be best-suited as urban aero taxis as well as their surveillance roles.
Oops, missed the edit window. That last part should read,
But they’re a bit short on passenger capacity and speed. Electro-gyroplanes would probably be best-suited as urban aero taxis as well as their surveillance roles.
Long distance, sure. But we’re talking short-medium distance here. I suspect that anything less than a day’s drive in a truck tends to go by truck in the first place.
Thrust is no problem in principle. The lithium-polymer batteries used with RC aircraft have absurd power density, and the cells can lift many times their own weight. However, this comes at the expense of energy density. One approach might be to dedicate some smaller fraction of the total to high-power-density chemistries, and the rest to high-energy-density chemistries. You only need a short burst to take off, and then when cruising you can draw from the energy dense cells.
Or maybe we’ll just see chemistries with the best of both worlds. Cars aren’t really limited by their power density, so there’s not huge a motivation to optimize for that.
Yes, but existing smaller airports are not currently built to handle large volumes of passengers. At least not in the Portland area and for most in the Seattle area, although Boeing Field does handle small volumes of passengers. So there’d be a lot of expenses upgrading those airports. Any savings is going to be rather long term. Diitto if they create new airports for this.
I had in mind the standard HS chem demo where the teacher puts a small bit of sodium in some water. Not really applicable unless the plane crashes, but I’m not the only one who will have that reaction.
What kind of advantages do rim-driven props have? Do they just make it easier to rotate the propellor mount or can they be made lighter and thus extend range?
Answering my own question here. After posting, I realized that rim-driven props have less obstruction of the air flow. Of course, electric motors already have significantly less obstruction than ICE engines. And a disadvantage is additional bearings needed to support the rim-driven prop. Not that we can’t do bearings, but they’re another thing that can go bad.
However, I can see that rim-driven could also be safer. The X-57 will have its main props way out at the end of the wings to reduce vortex drag. But that creates a hazard to ground crew servicing the plane. Enclose them and that hazard is much reduced.
One point to keep in mind is that, while lower vehicle weight would undoubtedly help an electric aircraft, it’d also help an internal-combustion aircraft, and so the internal-combustion aircraft with those same weight reductions would probably still be much more economical. If you’re really serious about carbon footprint, probably the best way to make an airplane is to keep using hydrocarbon fuels, and either manufacture the fuels greenly, or offset the carbon in some other way.
I suspect that hydrocabon-burning aircraft are mainly more efficient because they’re allowed to externalize their environmental costs. At any rate, continuing to use them, even with mitigation of their carbon footprint, still leaves the problem of contrails, which also cause warming of the planet.
NASA is looking at all of air travel. Clearly electric power is only suitable for shorter flights NOW but the goal is for full range flights.
I don’t think it’s a hp power issue. You can only generate so much thrust with propellers. High bypass engines get a lot of their thrust from fan blades but there’s a cutoff point. Jet airliners are 200 mph faster than prop airliners.
It will be interesting to see what the TBO (time before overhaul) is with electric motors along with the energy cost savings.