4 ms·

I'm surprised that no one is discussing electrohydrodynamic engines for this application, for example as used by https://en.wikipedia.org/wiki/MIT_EAD_Airframe_

I'm surprised that no one is discussing electrohydrodynamic engines for this application, for example as used by https://en.wikipedia.org/wiki/MIT_EAD_Airframe_Version_2 https://en.wikipedia.org/wiki/MIT_EAD_Airframe_Version_2. These don't have the same limitations as rotors do with vectoring relative to high speed gas flow. Most of the ones which have been built are small, but that is not an intrinsic limitation; mainly its the battery weight that is the limiting factor. Of course, the whole idea of electric field is depending on the battery breakthrough, but assuming you have that and want to go supersonic, I'd figure you would go EHD.

pluto9 6y ago
For reasons I can't entirely recall, there are pretty serious limitations on the thrust these can generate. I believe it has something to do with the air becoming "saturated" with ions. The limit on the density of charged particles limits how much mass you have to push on. The aircraft in your link has a top speed of 17km/h. Heating the air with microwaves or an electric arc could work, since it would just be replacing burning fuel with another heat source. It would still require moving parts though (unless it's only used as a ramjet), since a jet engine has to compress the air before heating it.
- handol 6y ago
  >It would still require moving parts though (unless it's only used as a ramjet), since a jet engine has to compress the air before heating it. You could use a tesla valve for an electric pulse jet, that would make for no moving parts.
  - pluto9 6y ago
    I hadn't considered that, that's a good idea.
  - mrfusion 6y ago
    Why do you need a tesla valve? Has anyone tried this?
    - pluto9 6y ago
      You need something to make sure the hot air only comes out one end of the engine, otherwise you get net zero thrust. In a normal jet the compressor takes care of this.
    - handol 6y ago
      You don't strictly need one. There are designs that rely on exhaust pulse resonance for pressure. There are designs that use various kinds of mechanical valves. It looks like (propane fuel) tesla valve pulse jets have been built, but I'm not seeing anything flight capable. https://www.youtube.com/watch?v=JYZhZ_qNKfE https://www.youtube.com/watch?v=JYZhZ_qNKfE

pluto9 6y ago

For reasons I can't entirely recall, there are pretty serious limitations on the thrust these can generate. I believe it has something to do with the air becoming "saturated" with ions. The limit on the density of charged particles limits how much mass you have to push on. The aircraft in your link has a top speed of 17km/h. Heating the air with microwaves or an electric arc could work, since it would just be replacing burning fuel with another heat source. It would still require moving parts though (unless it's only used as a ramjet), since a jet engine has to compress the air before heating it.

handol 6y ago
>It would still require moving parts though (unless it's only used as a ramjet), since a jet engine has to compress the air before heating it. You could use a tesla valve for an electric pulse jet, that would make for no moving parts.
- pluto9 6y ago
  I hadn't considered that, that's a good idea.
- mrfusion 6y ago
  Why do you need a tesla valve? Has anyone tried this?
  - pluto9 6y ago
    You need something to make sure the hot air only comes out one end of the engine, otherwise you get net zero thrust. In a normal jet the compressor takes care of this.
  - handol 6y ago
    You don't strictly need one. There are designs that rely on exhaust pulse resonance for pressure. There are designs that use various kinds of mechanical valves. It looks like (propane fuel) tesla valve pulse jets have been built, but I'm not seeing anything flight capable. https://www.youtube.com/watch?v=JYZhZ_qNKfE https://www.youtube.com/watch?v=JYZhZ_qNKfE