Page 1 of 2 12 LastLast
Results 1 to 30 of 50

Thread: Supersonic Electric Aircraft

  1. #1
    Join Date
    Feb 2011
    Posts
    466

    Supersonic Electric Aircraft

    Would it ever be possible to have a supersonic aircraft that is electric?

  2. #2
    Join Date
    Jun 2005
    Posts
    12,463
    Quote Originally Posted by cjackson View Post
    Would it ever be possible to have a supersonic aircraft that is electric?
    In level flight or in a dive?
    As above, so below

  3. #3
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    46,499
    Quote Originally Posted by cjackson View Post
    Would it ever be possible to have a supersonic aircraft that is electric?
    "Ever" is a very long time. I can't conceive of it with current technology.

    One problem is that current electric planes are prop planes. As far as I know, no one has come up with a supersonic prop plane. So you'd have to convert your electricity to forward motion some other way.

    Second, I doubt there is any current or near-term electrical storage device that could give you enough power.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  4. #4
    Join Date
    Jun 2007
    Posts
    5,478
    Quote Originally Posted by Swift View Post
    "Ever" is a very long time. I can't conceive of it with current technology.

    One problem is that current electric planes are prop planes. As far as I know, no one has come up with a supersonic prop plane. So you'd have to convert your electricity to forward motion some other way.

    Second, I doubt there is any current or near-term electrical storage device that could give you enough power.
    Lithium-ion batteries should easily give you the power required and electrically driven fans should be able to manage supersonic flight (the compressors and intakes in a jet engine would work the same no matter what power source you have driving them), the difficulty is really the energy density needed to achieve a useful flight time. Something that's depleted its batteries by the time it breaks the sound barrier isn't going to be much use.

  5. #5
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    12,540
    Quote Originally Posted by cjameshuff View Post
    Lithium-ion batteries should easily give you the power required and electrically driven fans should be able to manage supersonic flight (the compressors and intakes in a jet engine would work the same no matter what power source you have driving them), the difficulty is really the energy density needed to achieve a useful flight time. Something that's depleted its batteries by the time it breaks the sound barrier isn't going to be much use.
    Exactly right. I can easily conceive of using electric power to create jet thrust or even heat air. The problem is energy density for storage. I suppose you could cheat a bit by having a gas turbine to generate electricity which is then used to drive the plane, but it's kind of pointless except just to say you've done it. Fuel cells might be a bit more sensible.

    Of course, we've made significant strides in battery technology in the past 50 years. How much more is available is an open question.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  6. #6
    Join Date
    Jun 2005
    Posts
    12,463
    I'm sort of surprised that the answers have been so positive. Nobody has ever crossed the sound barrier with even a turboprop engine, and a battery powered engine will never achieve the weight to power efficiency of a combustion engine, due to the physical limitations of the charge available.
    As above, so below

  7. #7
    Join Date
    Jun 2007
    Posts
    5,478
    Quote Originally Posted by Jens View Post
    I'm sort of surprised that the answers have been so positive. Nobody has ever crossed the sound barrier with even a turboprop engine, and a battery powered engine will never achieve the weight to power efficiency of a combustion engine, due to the physical limitations of the charge available.
    Battery electric systems can easily outperform internal combustion in terms of power density, where they fall short is energy density. And nothing about electric power requires a propeller aircraft. Nothing about the operation of the compressor fans in a jet engine has anything to do with combustion, they will perform just as well if driven electrically instead of by a turbine following a combustor.

  8. #8
    Join Date
    Jun 2005
    Posts
    12,463
    Quote Originally Posted by cjameshuff View Post
    Battery electric systems can easily outperform internal combustion in terms of power density, where they fall short is energy density. And nothing about electric power requires a propeller aircraft. Nothing about the operation of the compressor fans in a jet engine has anything to do with combustion, they will perform just as well if driven electrically instead of by a turbine following a combustor.
    I'm sorry, I guess I don't understand how a turbojet works well enough. Could you explain a little more? You have air entering a compressor that is driven by a turbine run by a battery-powered engine, and then the air goes out the back of the engine? So the thrust is purely generated by the compressor?
    As above, so below

  9. #9
    Join Date
    Jun 2007
    Posts
    5,478
    Quote Originally Posted by Jens View Post
    I'm sorry, I guess I don't understand how a turbojet works well enough. Could you explain a little more? You have air entering a compressor that is driven by a turbine run by a battery-powered engine, and then the air goes out the back of the engine? So the thrust is purely generated by the compressor?
    In a high-bypass turbofan, most of the thrust is done by the first low-pressure stages of the compressor, most of the compressed air being directed around the engine and out through an outer nozzle. Even in a low-bypass turbofan or a turbojet, almost all of the mass flow comes from the air being forced through the engine. Some of the thrust comes from the heating of the air in the combustor and its subsequent expansion at a higher exit velocity than would otherwise be the case, but this isn't required for the engine to produce thrust, and much of the power produced is picked up by the turbine to run the compressor. An all-electric system wouldn't have the heating from fuel combustion, but could have additional compressor stages that add to the thrust instead of the turbine stage.

    It would also be easy to drive the different stages separately at rotation rates optimal for their operating conditions without needing a some kind of geared transmission to convert the mechanical power from the turbine, and the lack of a need for a high temperature combustor and turbine would greatly relax the material requirements. The biggest problem is really just the lack of a power source with both the energy and the power density required. Lithium ion batteries easily have enough power density, but probably wouldn't run the thing for more than a few minutes. Fuel cells have the energy density, but nowhere near the power density required.

  10. #10
    Join Date
    Sep 2017
    Posts
    9
    For rockets, as with jets, mass ejection applies as the mechanism by which propulsion is achieved. If you can throw enough molecules out the back of your 'engine', you can break the speed of sound. If it can be done, someone would have tried - so the easy answer is present day technology wouldn't support this as yet.

  11. #11
    Join Date
    Feb 2014
    Posts
    187
    Quote Originally Posted by Jens View Post
    I'm sort of surprised that the answers have been so positive. Nobody has ever crossed the sound barrier with even a turboprop engine, and a battery powered engine will never achieve the weight to power efficiency of a combustion engine, due to the physical limitations of the charge available.
    A supersonic battery/capacitor powered electric aircraft is likely doable without any major advances in technology, but the combination of high power draw and low energy density means the flight duration would be very short. So, impractical to build.

    Electric systems have higher power to weight ratio than combustion engines if the powered duration is short. For a powered flight duration of tens of seconds, I think capacitors win.

    No one's mentioned microwave power transmission yet. The energy doesn't need to be stored on board an electric aircraft.

    As for how to convert the electric power to momentum, what about a ramjet that uses resistance heaters or arc-lamps as the heating source? Simple and lightweight.

  12. #12
    Join Date
    Jun 2005
    Posts
    12,463
    Quote Originally Posted by VQkr View Post
    As for how to convert the electric power to momentum, what about a ramjet that uses resistance heaters or arc-lamps as the heating source? Simple and lightweight.
    Doesn't that require fuel, though? Or can you build a ramjet without fuel?
    As above, so below

  13. #13
    Join Date
    Feb 2014
    Posts
    187
    Quote Originally Posted by Jens View Post
    Doesn't that require fuel, though? Or can you build a ramjet without fuel?
    What do you mean by "fuel"? A ramjet uses acceleration of atmospheric air to provide momentum (as does a jet engine or a propeller), so it doesn't need to carry reaction mass with it the way a rocket does. It needs energy to accelerate that air. In a chemical ramjet, that energy comes from burning hydrocarbons. In the electric variant, it would come from an electric heater of some sort.

  14. #14
    Join Date
    Jun 2005
    Posts
    12,463
    Quote Originally Posted by VQkr View Post
    What do you mean by "fuel"? A ramjet uses acceleration of atmospheric air to provide momentum (as does a jet engine or a propeller), so it doesn't need to carry reaction mass with it the way a rocket does. It needs energy to accelerate that air. In a chemical ramjet, that energy comes from burning hydrocarbons. In the electric variant, it would come from an electric heater of some sort.
    There's a picture on Wikipedia which shows it burning fuel (https://en.wikipedia.org/wiki/Ramjet..._operation.svg). I see what you're saying though. Will the electric device be able to heat up the air enough to create thrust? I know that air increases in volume when it's heated, but can you really drive an airplane that way?
    As above, so below

  15. #15
    Join Date
    May 2007
    Location
    Earth
    Posts
    9,818
    Quote Originally Posted by Swift View Post
    "Ever" is a very long time. I can't conceive of it with current technology.

    One problem is that current electric planes are prop planes. As far as I know, no one has come up with a supersonic prop plane. So you'd have to convert your electricity to forward motion some other way.

    Second, I doubt there is any current or near-term electrical storage device that could give you enough power.
    No ones built one, but props for supersonic aircraft were worked on in the 1950s. They were judged not worth the bother, but there may have some testing.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  16. #16
    Join Date
    Jun 2007
    Posts
    5,478
    Quote Originally Posted by Jens View Post
    There's a picture on Wikipedia which shows it burning fuel (https://en.wikipedia.org/wiki/Ramjet..._operation.svg). I see what you're saying though. Will the electric device be able to heat up the air enough to create thrust? I know that air increases in volume when it's heated, but can you really drive an airplane that way?
    The only role combustion plays in a conventional jet engine is to heat the air. If you had the power source, you could certainly do so electrically instead.

  17. #17
    Join Date
    Feb 2014
    Posts
    187
    Quote Originally Posted by Jens View Post
    Will the electric device be able to heat up the air enough to create thrust?
    I don't see why not. Electric arc furnaces can be hotter than any chemical flame.

  18. #18
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    46,499
    Quote Originally Posted by cjameshuff View Post
    Lithium ion batteries easily have enough power density, but probably wouldn't run the thing for more than a few minutes. Fuel cells have the energy density, but nowhere near the power density required.
    I guess we get into a debate between "possible" and "practical". An electric supersonic plane that runs for minutes might be possible, but it doesn't seem very practical to me.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  19. #19
    Join Date
    Feb 2014
    Posts
    187
    Quote Originally Posted by Swift View Post
    I guess we get into a debate between "possible" and "practical". An electric supersonic plane that runs for minutes might be possible, but it doesn't seem very practical to me.
    Rather decidedly impractical, yes. Even the microwave power transmission I mentioned above really is attractive for indefinitely long loiters or hovers by heavier-than-air craft, not for going fast. Anything a battery-powered supersonic jet could do with a minute of flight time, a solid- or hybrid-fueled rocket could do better, more simply, and much much cheaper.

  20. #20
    Join Date
    Mar 2014
    Posts
    24
    Wow, searching for the energy requirements and seems a supersonic fighter jet can use upwards of 75MW at peak power.

    A Boeing 747-8 would take around 90MW to take off.
    https://aviation.stackexchange.com/q...747-8-airborne

    Even a 1GW power plant using beamed energy would only be able to power 13 supersonic jets. And that's assuming very little energy loss.

    However, you could use nuclear power to generate the electricity. Maybe a Polonium-210 RTG? Even with an efficiency of 8% it would take close to seven tons of the materials using an RTG, or perhaps a heat engine could be used, to generate 75MWe. Maybe thermophotovoltaics? Not that it would be desirable to convert all the heat to electricity before using it. Just don't crash land anywhere close to where I live, and by close I mean within several thousand kilometers. (That's a lot of Polonium !!!!)

  21. #21
    Join Date
    May 2007
    Location
    Earth
    Posts
    9,818
    The F-22 uses a low-bypass fan; the fan produces net thrust at supersonic speeds and could do so if powered by an electric motor instead of the gas turbine core.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  22. #22
    Join Date
    Feb 2005
    Posts
    10,862
    Now supersonic flight by electric means is probably beyond us--but large nuclear powered craft--that might surprise you.

    I heard it said that nuclear power plants might make a SHIELD Helicarrier a real thing
    https://www.nextbigfuture.com/2013/1...-be-power.html

    Don't go fast--go big.

  23. #23
    Join Date
    May 2007
    Location
    Earth
    Posts
    9,818
    Quote Originally Posted by publiusr View Post
    Now supersonic flight by electric means is probably beyond us--but large nuclear powered craft--that might surprise you.

    I heard it said that nuclear power plants might make a SHIELD Helicarrier a real thing
    https://www.nextbigfuture.com/2013/1...-be-power.html

    Don't go fast--go big.
    One of my college profs worked at CANEL during the US government's program to develop a nuclear-powered aircraft. GE chose an open cycle system, using a moderated, air-cooled reactor (and you thought Chernobyl was bad....) and Pratt & Whitney (CANEL) was developing a reactor using a molten salt-based coolant loop.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  24. #24
    Join Date
    Oct 2006
    Posts
    3,684
    Quote Originally Posted by geoffgallo View Post
    For rockets, as with jets, mass ejection applies as the mechanism by which propulsion is achieved.
    No, the role of the burning of fuel in a standard jet engine is to drive a turbine, which is the power source which drives a fan at the front, which is what propels the plane. (A turbine is like a fan, but functionally backward; instead of using some other power source to move air, it uses moving air to spin the thing and thus draw power.)

    An engine meant for supersonic flight just needs to spin the fan fast enough (which tends to also come with having a smallish fan). So electric supersonic flight would just need an electric motor to spin the fan instead of a turbine; it's fundamentally the same as an electric subsonic "jet", electric propeller plane, or electric helicopter. But nobody's bothered because of the fuel issue; supersonic flight is already seen as enough of a fuel-guzzler even with normal fuel-burning engines.

  25. #25
    Join Date
    Jul 2006
    Posts
    11,467
    Quote Originally Posted by swampyankee View Post
    No ones built one, but props for supersonic aircraft were worked on in the 1950s. They were judged not worth the bother, but there may have some testing.
    Judged not worth the bother because supersonic aircraft require supersonic propellers. Supersonic propellers created sonic booms at the tips equal to the rpms X the numbers of props.

    Super sonic propeller driven aircraft literally beat the ground crew to death over time.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

  26. #26
    Join Date
    Jun 2007
    Posts
    5,478

  27. #27
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    12,540
    Quote Originally Posted by cjameshuff View Post
    You beat me to it.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  28. #28
    Join Date
    May 2007
    Location
    Earth
    Posts
    9,818
    Quote Originally Posted by BigDon View Post
    Judged not worth the bother because supersonic aircraft require supersonic propellers. Supersonic propellers created sonic booms at the tips equal to the rpms X the numbers of props.

    Super sonic propeller driven aircraft literally beat the ground crew to death over time.
    Have you ever heard of the F-84H (video: https://youtu.be/YItexQxJS9U)?

    Deafen, nauseate, and possibly cause incontinence, but no reported deaths

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  29. #29
    Join Date
    Aug 2006
    Posts
    2,692
    Can an electric heater element heat fast-moving air so quickly - causing it to expand so voluminously - as to be comparable to the ignition of jet fuel?

  30. #30
    Join Date
    May 2007
    Location
    Earth
    Posts
    9,818
    Quote Originally Posted by DaveC426913 View Post
    Can an electric heater element heat fast-moving air so quickly - causing it to expand so voluminously - as to be comparable to the ignition of jet fuel?

    The combustors are as small as they are because they're direct contact heat exchangers; electric heating elements can provide comparable heat transfer rates to liquid metal or molten salt heat exchangers. The latter were planned for Pratt & Whitney's turbojets to be used on the (thankfully) cancelled nuclear-powered bomber.
    Last edited by swampyankee; 2017-Oct-07 at 02:07 PM.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •