1
$\begingroup$

Is it possible to have a fully electric airliner?

How much room would have to be sacrificed for a power bank in these aircraft to allow similar range to the current models (e.g., A320, 737, etc.)?

Would it shrink the passenger capacity by a lot? Or is the concern mainly having enough power to push such weight?

$\endgroup$
4
  • $\begingroup$ What do you mean by "electric"? If you want to replace jet engines by electric propulsion, you would end up with engines not optimised for the airframe cruise speed design, the need of electrical and hydraulic power generation (usually done by jet engines while in flight), ... $\endgroup$ – Manu H Nov 27 '19 at 7:20
  • $\begingroup$ Related: How many kilowatts to get an electric 747-8 airborne? and How far would an all electric A380 fly? $\endgroup$ – ymb1 Nov 27 '19 at 7:42
  • $\begingroup$ Since this wasn't closed, perhaps we need a respective question for every single aircraft model ever produced. I can write the bot, anyone got the API specs? $\endgroup$ – Therac Nov 28 '19 at 20:38
  • $\begingroup$ @Therac: see update ;) $\endgroup$ – ymb1 Nov 29 '19 at 9:07
6
$\begingroup$

Well, to use the same airframe, you'd basically have to find a way to replace the fuel volume in the wings with battery volume, and batteries are somewhere around 15-20% of the power density of fuel, as the answers in this ASE post lay out pretty well.

So if you had an electric fan that made the required thrust, and somehow figured out how to replace all the fuel tanks with batteries, you'd probably have something, but only with about an hour's endurance, which wouldn't even make up the IFR reserve range requirements most of the time. You would have to replace a lot of pax with batteries to get even a couple hours endurance, which would kind of kill the business case.

So that kind of concept is pretty much a dead end until battery power density starts to approach the level of kerosene, maybe 20 or 30 years from now unless some massive new development comes along.

$\endgroup$
5
  • 1
    $\begingroup$ And don't forget that a battery pack has far more mass per cubic meter than a fuel tank, ESPECIALLY when averaged out over the duration of the flight as the battery remains at the same mass throughout the flight while the fuel tank gets lighter as fuel is used up, making batteries even less efficient. $\endgroup$ – jwenting Nov 27 '19 at 4:20
  • $\begingroup$ One hour with an heavier airplane, not to mention additional weight due to hydraulic power generation (an electric APU?), you hardly have time to get to cruise altitude and speed. $\endgroup$ – Manu H Nov 27 '19 at 7:25
  • $\begingroup$ That just accounts for the cruise power. Another big issue would be the C-rate/power required during takeoff. Large C-rate and high density are inverse to each other, unfortunately. $\endgroup$ – JZYL Nov 27 '19 at 13:24
  • $\begingroup$ An hour? That sounds really optimistic :D $\endgroup$ – Jan Nov 28 '19 at 20:50
  • $\begingroup$ IF. In 20-30 years IF some massive new development comes along, not unless. It will take 10 from development to mass production, and it took 20 from Li-Ion mass production to Tesla cars. Airplanes are a bit more complex and a bit tighter-regulated. $\endgroup$ – Therac Nov 29 '19 at 5:38
3
$\begingroup$

John K.s answer applies to lithium batteries. They're quite convenient in many ways, but they clearly don't work for this application.

Fuel cells on the other hand are more reasonable. A fuel cell produces electricity from fuel, such as hydrogen or ethanol. As such, it doesn't have the weight penalties of batteries. Additionally, this mostly solves the problem mentioned by jwenting. The fuel is still oxidized and therefore the plane loses weight in flight.

$\endgroup$
1
  • $\begingroup$ It also does not have most of the advantages of electric planes though, because it still releases carbon dioxide—hydrogen has a lot of energy for weight, but due to its very little density, too little for volume, so it is not practical and any fuel cell design is stuck with hydrocarbon fuel anyway. At best this can increase the efficiency a bit, not being a thermodynamic cycle. $\endgroup$ – Jan Hudec yesterday
0
$\begingroup$

I know this is an old question but I find this topic interesting and thought I'd contribute.

Why not an electric plane? The YouTube channel Real Engineering answers that question here:

It's over 10 minutes long but they give a good summary of the problem in the first 2 minutes. To cut that down even shorter, it is the energy density of the batteries we have today.

Why not fuel cells instead of batteries? Fuel cells will get hot and need to be cooled. The air needs to come in at a rate sufficient to supply the oxygen required. The exhaust will likewise need a free flow into the air. So, you have a very hot fuel cell, very hot exhaust, a big fan to cool the fuel cell, pump in air, and presumably propel the craft. To assist in the air in and out while stationary a turbine can be placed on the exhaust to drive an inlet fan. Question, what do we need the fuel cell for? Right, to power the big fan at the front. That brings more mass to the plane with a motor and then problems with the fuels that I'll get to later on.

The ability to "cut out the middleman" so to speak was discovered with piston engine development during World War II. All sides of that conflict figured out that as piston engines grew the contribution of the engine exhaust to the thrust grew. With a turbocharger required to get the most performance, especially at greater altitudes, the piston engine in the middle wasn't helping much. By just dumping fuel into a combustion chamber, putting a turbine on the exhaust, and use that to drive a fan to feed the flames of the burning fuel, the exhaust alone could propel an airplane to high speeds and quite efficiently. This efficiency over a propeller improved with greater speeds and altitudes. Later on bypass fans and propellers driven by the turbine were added when speeds remained subsonic.

What's the goal of using an electric airplane? Why bother when jet engines work so well? Oh, right, to lower CO2 emissions. We can use a biofuel for that. But there is a problem with biofuel, as it is currently done this is an energy negative process. We can improve this process but that comes with other problems. Again, Real Engineering explains:

If corn ethanol is out, as is soybean oil, then what about hydrogen fuel? Real Engineering has a video on this too:

While it is focused on cars much of the problems addressed comes in producing and storing the fuel. One problem pointed out is that producing hydrogen is an energy negative process. This is not a deal killer as there is a benefit in being able to turn energy from the wind, sun, nuclear fission, or heat within the planet into a liquid fuel. This means biofuels are not killed by being energy negative either, but by the need for land, fresh water, and labor that would be better spent on crops for food and clothing fiber.

What it comes down to is that the jet engine is just fine, it is the fuel that needs to change. The most likely candidate is synthesized hydrocarbons. These are drop in replacements for existing petroleum fuels and can be produced in a way that is a net carbon neutral. Burning the fuel does release CO2 into the air but we know how to get that carbon back and build more hydrocarbon chains with carbon neutral energy.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.