Assuming you didn't have to make it flyable at low speeds for take off and landing how feasible is it to make a small supersonic plane powered by electricity?
The best brushless motors peak power output to weight ratios compares favorably to miniature turbines. But existing electric ducted fan planes usually end up with a top speed of around 700km/h as they can't accelerate air much faster than that.
Assuming you had around 20KW of power to use is there anyway to translate that into thrust capable of supersonic speeds? Would using intake ramps to slow the air to subsonic speeds then compressing it with the fan and sending it through a variable nozzle that decreases in size at higher speeds work?
I have seen people speculate that at higher speeds it might be more effective to switch something similar to an electric ramjet where compressed air is rapidly heated via a plasma arc or other heating element. But there's very little information regarding possible supersonic electric planes in general.
> is it to make a small supersonic plane powered by electricity?
Figure it out yourself.
We are not your wetware CPU's.
Noah Morris
I remember reading about a material that when water droplets move across the flat surface, it will generate electricity. Build the exterior out of this material, and at supersonic speeds it can power itself when passing through clouds.
Zachary Sanchez
thats basically drawing a small current from frictional forces.
supersonic speeds are achievable by combustion because it gives tons of energy in heat and pressure to a gas, how would you do the same with electricity?
I'm not sure if its possible to accelerate air beyond supersonic speeds using a propeller.
Hunter Lee
calculate it yourself. Also, wave drag is a drag.
Grayson Taylor
>supersonic speeds are achievable by combustion because it gives tons of energy in heat and pressure to a gas, how would you do the same with electricity? >I'm not sure if its possible to accelerate air beyond supersonic speeds using a propeller. That's the issue, technically the electric vehicle has more power but energy density is lower so range would be reduced. However it's not difficult to have batteries capable of 500A at 100V for a small drone 1 or 2 meters in size, it won't fly for very long but the power output would be 5x higher or more than hobby jet engines.
But the question is how to efficiently convert electrical energy into thrust at supersonic speeds. The only proposal I have seen is to use conventional ducted fans up to around 500km/h then switch to an electric jet engine, the inlet slows the air to subsonic speeds and compresses, then an axial compressor driven by an electric motor further compresses it 8:1, it's then ejected into a chamber where it accelerates to supersonic speeds being violently heated and pressurized before exiting the small diameter rear nozzle.
But the efficiency of this type of engine I can't find any information on and I'm unsure how much energy is needed to overcome drag on something like this at mach 1+. If it's only 5-10KW it's probably quite feasible , a 20-50KW electric motor operating the compressor is feasible, assuming at least 25% of the energy is converted into thrust.
This engine looks like it mainly uses heat and expansion to generate thrust which makes me think turning the electricity directly into heat may be more effective, but I'm even less sure how that could be done. I was thinking you could expose compressed air to a plasma arc for heating and possibly even accelerate the plasma via a magnetic stage before it exits to the final chamber. I haven't found anything useful on air breathing plasma engines, only very low thrust ones aimed for use in space.
Andrew Taylor
I mean electric heating is generally perfectly efficient, and if the air is compressed that much and slowed to a stop it may be possible to have a grid heat it up.
BUT. inst a jet intake only compressed to improve combustion efficiency? Would the same compression ratios be required with no combustion? Are there any examples of electric heating being used for propulsion?
The calculations to find how much heat is required to get the pressure you want are straight forward, you would basically compress the air into a heater then eject it through basically a rocket nozzle.
I'd like to see the calculation done to see if the idea is at all viable but I'm dealing with exams so I don't really have the time to spare.
Jose Gray
>inst a jet intake only compressed to improve combustion efficiency? Would the same compression ratios be required with no combustion? Are there any examples of electric heating being used for propulsion? Depends on the speed, at low speeds a modern turbofan needs the compressor to enable combustion but it uses that energy to drive the large ducted fan barely any thrust comes out of the turbine itself.
They have the same limitation as a remote control ducted fan plane, the turbofan can only move the air to a certain velocity, you can't spin the fan any faster because the blade tips break the sound barrier, if you add more torque nothing happens because the thrust it produces drops to zero once you're moving faster than it's maximum speed.
Turbojets work the same way as that electric jet engine, the compressor blades do not propel the air to supersonic speeds, the compression and pressure from heat expansion causes the air to reach supersonic speeds as it gets shot out of a small hole. The amount of thrust produced is much lower but the exhaust velocity is much higher. Of course the fuel gets hurled out with the hot air but provided you can efficiently heat the air you can just replace the fuel with more air.
This is how they planned to make those nuclear jet aircraft in the 1960s, the reactor just took over the job of heating the compressed air where it was normally heated via flames in a conventional turbojet.
Adrian Williams
supersonic and small sounds like its never gonna work
Grayson Collins
>Did you just decide to draw and post a picture of your penis?
Ian Sanders
The key term would probably be "electrothermal jet". They're researching the same concept for weapon propellants.
Eh I'm no expert but I assume supersonic speeds at those miniature scales isnt feasible for the same reason hitting big mach numbers with real aircraft isnt feasible without rockets or something.
Owen Kelly
Heat engines are inefficient
Jack Russell
>using intake ramps to slow the air to subsonic speeds holy drag, Batman
Caleb Thomas
You're right I forgot about those nuclear jet ideas. The amount of power still doesn't seem feasible for today's electrical energy density but The concept could work.
The nuclear jets were an interesting concept but they would have basically orbited the earth with nuclear bombs as payloads being a constant reminder of mutually assured destruction.
Blake Wood
He kinda drew some internal shockwaves so I don't think its a picture of his dick
Isaiah Powell
That's how today's jets work user. You slow the intake air to subsonic speeds over a few shockwaves and get huge amounts of pressure to work with in combustion.
The energy/speed you lose slowing it down is basically recovered by the added thrust at higher pressure.
Jaxon Jones
There's two ways you could approach this.
One way to do this is to make your plane break the sound barrier at high altitudes only. Think of the U-2 spy plane. At 60,000ft it flies at around 120 knots. A little faster and it will break the sound barrier. Make the engine with a large fan to move a large amount of mass. You won't have to worry about the fan blades reaching the sound barrier. Then make your plane have a very high lift to weight ratio. With a wing design were the shock wave won't stall the plane and it would be relatively easy to brake the sound barrier. Of course this only works at very high altitudes and it will end up resembling a glider more than a supersonic jet.
If you want to break the sound barrier at sea level or near it, it would be a bit more difficult. You will need to slow the incoming air down to subsonic speeds and then speed it back up to super sonic speeds (you want the exhaust to be at almost the same speeds but a little faster than the wind speed over the plane). You could achieve this using the venturi effect. The bigger problem that I could see is the battery storage. This plane would need to be sleek and that means less room for batteries yet the energy requirements are very high. Combustion engines don't have as much of a problem since chemical energy density btfo battery energy density: ~42 MJ/Kg for jet a and ~1.8 MJ/Kg for Li.
I can see the high altitude version working easily. Due to it's configuration it would allow for more batteries or fly wheels to store energy and since it's flying high above the clouds you could also use solar panels which there will be plenty of room for due it's large wings. The low altitude version seems much more of an engineering challenge.
Ryder Jenkins
>>The amount of power still doesn't seem feasible for today's electrical energy density just use a really long extension cord.
Jackson Powell
They're starting to use tethered camera drones too, microwave radiation aimed to just heat and propel a missile would be pretty cool though.
Do you have any idea how much power it takes to blast through the skies at any mach worth talking about? Just for example, to push a 1000 kg vehicle at mach 2 with L/D=10 (and that's a lot) you'll need 580 kW of power before any losses. Good luck finding a battery that won't drain before you even accelerate to half that speed.
Ian Hughes
an onboard fusion power plant
Jonathan Reed
supersonic turbines exist, but don't ask me any details about it
Michael Ward
How are you going to cool it?
Aiden Hall
emdrive
Brody Gonzalez
>actually taking the joke serious
Gabriel Campbell
>Do you have any idea how much power it takes to blast through the skies at any mach worth talking about? Just for example, to push a 1000 kg vehicle at mach 2 with L/D=10 (and that's a lot) you'll need 580 kW of power before any losses. Good luck finding a battery that won't drain before you even accelerate to half that speed. 1000kg is much too big I'm thinking of something around 2M long with 20kg-40kg weight. 580KW in 1000kg is quite possible, electric motorbikes can manage close to 200KW with 250kg weights.
An all electric version may be able to be built better than the nuclear version as you aren't relying on a turbine shaft to power the compressor, you could have multiple radial compressors feeding into a chamber at the front, cool it so you get even more air density in the the heating chamber. Then question becomes, what is the most effective way to rapidly heat large volumes of compressed air using electricity? Heating elements? Or something like electrical arc or plasma generation via RF?
Henry Davis
good to know, I don't think that's an undergrad topic.
Jace Wright
I think passing the air through a grate before expansion while the air is still low speed would be more straight forward than an arc or plasma, but idk desu senpai
Thomas Bennett
The nuclear ones do this however all they can do is use the 1000C degree heat from the reactor while electrical arcs producing plasma go as high as 20,000C.
Lucas Johnson
the subject was touched very briefly during a gas turbine course
