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Is Elon Musk's supersonic Tesla electric plane idea possible?

Our engineering background is limited. Maybe our readers could tell us if Tesla's founder's idea of a supersonic airliner (that takes off vertically and lands vertically just for added difficulty) is technically possible.

Elon Musk has more ideas about transportation using electricity. In a recent interview, which seemed more like an outlined discussion than a true inquisition, the rock star of automotive manufacturing revealed two more ideas that involve using electricity to move people. The first is not that hard to envision. A pickup truck powered by electricity. We will address that in another story. The second, is a real head scratcher for those with any engineering background. It is a supersonic, vertical take of airplane – powered of course by electricity.

Before we begin, check our yesterday's story if you are not current on Tesla's stock drop, Q3 loss, and fires in 3 Model S cars. The link as the full interview as well as a summary of this week's big Tesla news.

Let’s look at his airplane idea proposed in an interview with the New York Time Deal Book this week. The interview turned towards air travel, which leads us to believe that the questions were submitted in advance. In any case, the interviewer spoke about Musk’s opinion of the 787 battery fires and from there segued into what planes Musk liked and why. It turns out Elon likes the 747 calling it fast and aerodynamically efficient. Saying “I do think there is an interesting opportunity to create a supersonic, electric, vertical take-off and landing jet. I think that would be really great.” Expanding on where this idea came from Musk said “Well the Concord was canceled. I was like, well that’s sad. Now there’s no supersonic transport. And is the future getting worse? It bothers me when the future is getting worse, so that is where the supersonic plane thing came from.”

Having studied mechanical engineering, and taken some limited courses in aerodynamics and thermodynamics at the undergraduate level, this sounds just kooky to me. In order to move an airframe through the air past the sound barrier it needs to create a huge push in the opposite direction via the engines. Using only electricity, rather than expanding gases, it is hard to envision accelerating turbine blades to the point that they are well past supersonic and compressing air in a way it would then be able to move a huge structure. Maybe electricity could somehow be used to convert liquid phase water to the superheated gas phase and thus push the plane past supersonic. Sort of an inverse steam generator. Interestingly, Musk said in the same interview he thinks rockets (as in space travel rockets) would never be electric, and thinks steam power used in the past is quaint. If we have readers who can tell us how an electric plane might work, please weigh in below. Let’s set aside the energy density issue related to the batteries for now.

Musk is currently the big thinker in the room, if you consider the world the room. Had he not already created a new currency, a new type of luxury car, and also a spaceship we would laugh at this idea. However, we are learning to take his ideas more seriously as time goes on. What do you think of a supersonic electric “jet” plane? Lark, or possible workable idea?

Still image courtesy of Youtube.com and AviationExplorer

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Comments

Google "railgun". Electro-magnetic levitated trains enclosed in a vacuum tube could very well pass the speed of sound relative to the outside of the tube. I remember in school learning that there was a time that science believed a man could not survive traveling faster than, I believe, 25 miles per hour.
Those old predictions are great. I get ground-based systems based on electricity, but I'm looking for a good explanation of how you fly a (big) plane from New York to Tokyo using electricity in about 6 hours. Thanks for commenting!
Air is composed of 78% nitrogen, 21% oxygen. Boiling point of liquid nitrogen is -196 C (-320F). Using solar power, do the heavy lifting on the ground to liquify nitrogen from the air. Liquid oxygen boils at -183 C (-297 F). As the air cools, the oxygen may be drained off before the nitrogen liquifies. As it continues to cool, the remainder is almost pure nitrogen liquid. Density of liquid nitrogen is 0.807 g/ml, that of nitrogen gas is approximately 1/750 of that amount. So, an enormous volume of nitrogen gas coil be created from a small amount of nitrogen liquid. No heat would need to be drawn from the batteries because the atmospheric temperature is going to be far higher than the boiling point of liquid nitrogen. Seems like this would be the propellant of choice. Atmospheric pollution equals zero; you simply return the nitrogen back to the atmosphere as you propel the plane using electric turbines. Exactly how this might be done would require engineering. Seems like you might want to draw in warm atmospheric air in using the turbines, and then apply a mist of liquid nitrogen as the gas exits the plane. The expanding nitrogen would create enormous thrust.
That is the coolest thing I read this week.
I absolutely second that.
Battery powered airplanes should work just fine... As soon they invent really, really powerful batteries that weight absolutely nothing. Of course, to allow room for passengers those really, really powerful but weightless batteries would have to be really, really small. I have studied engineering. I did not need to study engineering to "evaluate" this. I think Musk just likes screwing with the press. He should be announcing the opening of his new unicorn ranch any day now. LOL
The electric unicorn ranch? Thanks for injecting some welcome levity.
It's technically possible to run any machine using a combustion engine on an electric motor. There are designs for small planes using electric motors to power props and there have been reports off and on over the years of the Air Force and Navy studying electric turbofans using fuel cells as the power source. The trouble is that, as Amused wrote, batteries start getting heavier than liquid fuel very quickly and the amount of thrust required to lift a large jetliner off the ground is immense. A Top Fuel dragster produces more thrust than a 727 at takeoff, but only has to do it for about a quarter mile whereas the aircraft must do it for hundreds of miles at a time. Therein lies the problem. Technically, anything can be run on electricity, but that doesn't mean it's always real-world feasible to do so.
Good overview. I think too that the drag and therefore the thrust needed at supersonic speeds is not just linearly more than at lower speeds. A jetliner would have to have space for people, so it would be hard to make perfect in terms of aerodynamic efficiency at supersonic speeds. That means the thrust maker (electric motor) has to be pretty amazing, and I am not sure that without expanding hot gases, like from combustion fuels, it would be possible.
I think the aerodynamics have already been taken care of. It's not like passenger planes at supersonic speeds have not already been done. It's more a question of fuel efficiency, storage, and capacity. Musk may be thinking of some things that haven't been tried (publicly) but are likely already in use in some flying machines. There's been a rumor that high-altitude stealth planes are using some kind of ionic field to both mask themselves and lower their air resistance at speed. No idea how that would work, since I'm not a physicist.
The main thrust of any modern turbine comes from the fan moving the air. It's true that, historically, this hasn't been enough to breach the sonic barrier. For decades, military aircraft used afterburners to provide that extra thrust necessary. Afterburners act just like rockets - burning fuel with exhaust gases providing direct thrust. They are, however, fuel intensive. Many supersonic fighters designed in the last decade are actually able to breach the sonic barrier without afterburners. Most notable examples are the F-22 and the F-35. While it's true that these aircraft still use liquid fuels, the thrust does, ultimately, come from the fans and turbine. This provides more than a proof-of-concept for purely fan-powered thrust.
As a Mechanical Engineer with some graduate level study of advanced aerodynamics & propulsion systems under Dr. M.H. Jones, I agree that the industry has stagnated with the loss of the Concord. Supersonic flight takes lots of energy, however such could become much more economical using electricity, and the flight technique of atmospheric skipping as proposed by NASA. If Elon Musk is touting the idea of electric flight, he likely already has some basic patents on how he would accomplish it. An electric propulsion system would likely be powered by a combination of batteries for high energy usage during takeoff and climb out, with fuel cells to provide energy for sustained flight in order to reduce the total weight requirements for sustained propulsion energy storage. It would be quite interesting to be part of his design team for this project.
I like your idea of an 'inverse steam generator'. Congratulations! You have invented the steam engine :D The beauty of using electric motors is that they don't need oxygen to burn anything, so you can fly really high, where the atmosphere is very thin. Thin atmosphere means lower drag, so you can fly faster and/or more efficiently. Those blades would have to be spinning really fast, but I guess that's already the case in jet engines today.
Any design similar to or based on a propeller quickly drops in effectiveness as you approach Mach 1. There are a bunch of electric propulsion ideas that work completely without moving parts and thus work well at supersonic speeds. The most notable ones are probably: 1. arc-jets (You generate lightning inside your propulsion chamber to head up and expand air) 2. magneto-plasma-dynamic thrusters (You once again generate a lightning arc, but then you use a powerful magnetic field to deflect the ions towards the rear to produce thrust) Both of theses are heavily in science fiction territory though since in order to work at acceptable efficiency they require the air to be way more conductive than it normally is. One article I read on the subject proposed using a combination of burning caesium and micro waves in order to ionize the air inside the thruster which might work, but is pretty expensive and energy consuming on it's own...