Electric Jet Engine?

[Fireheart318]

It'll be a small parts mod with only four parts, all of which will be electric jet engines based on thermal expansion. The specific engines will be a 1.25m variant, radial 2.50m variant, a 0.625m variant, and a standard radial variant. As for the real world physics, it'll work like a hair dryer mixed with a ramjet. Can I have some audio and tuning help?

Edited July 19, 2016 by Fireheart318

[Van Disaster]

What sort of thrust levels are you looking at? and precisely what tuning help do you need?

[passinglurker]

As for real world physics do you have any examples of this being real and practical in real life?

[Van Disaster]

Throwing some numbers around,

* Sea level figures:
* CFM56 apparently burns around 0.9kg/s at 100% ( I grabbed the first model I could find, so I'm just going to assume that's in the same ballpark for all versions ) - CFM56 is a typical mid sized turbofan
* Rated thrust for that one is 92kN, for reference
* Specific energy for Kerosene is 46 MJ/kg
* So, it's using 41.4MJ/s at full thrust at sea level, which is also conveniently also 41.4Mwatts.

Assuming my muddled brain hasn't misplaced something there, how efficient are these electroturbines?
 

[Streetwind]

It's of course possible to make such parts in KSP with whatever stats the maker wants, but I'd cast some doubt on the feasibility of the physics behind this idea. For a thermal jet to produce useful thrust, you need extreme temperatures, and extreme temperatures need extreme amounts of electricty. In fact, using electricity to create heat is among the least efficient uses of electricity known to man.

Consider hair dryer. Compared to a jet engine, it moves no appreciable amount of air, and it heats that air to at best a couple hundred degrees Celsius, Do do this, it can consume as much as 2 kW of power. Then, how many hairdryers do you need to propel an aircraft? Well, a hairdryer is not able to lift its own weight. Typical hairdryers weigh around a kilogram at most, so the "thrust" produced would be less than 10 Newton. Let's just blindly guess and give it 5 N of thrust. Meanwhile, our favorite jet engines in KSP produce in the neighbourhood of 150 kN worth of thrust. That adds up to 30,000 hairdryers running together.

Those 30,000 hairdryers would each consume 2 kW worth of power, You are looking at 60 megawatts of electric power input to replicate the thrust of a Whiplash in this first-order approximation.

Of course, thermal jets operate at several thousand degrees Celsius, not just several hundreds like hairdryers. This obviously increases power consumption but also increases thrust, and therefore reduces the number of hairdryers required. I am honestly not sure which of the two scales better. Either the final figure will be somewhat lower than 60 MW, or somewhat higher. But regardless: any power consumption figure for electric aircraft engines that is measured in two-digit megawatts is infeasible for actual usage - because you'd have to carry a power plant inside your plane to provide it.

[Fireheart318]

5 hours ago, passinglurker said:

As for real world physics do you have any examples of this being real and practical in real life?

I don't have any examples but it is possible. Normal jets work by heating outside air using fuel and shooting the now pressurized air out the back. This will skip fuel and just use electric coils similar to those in a toaster or electric heater. It may sound weak, but you can melt metal with electricity

2 hours ago, Streetwind said:

It's of course possible to make such parts in KSP with whatever stats the maker wants, but I'd cast some doubt on the feasibility of the physics behind this idea. For a thermal jet to produce useful thrust, you need extreme temperatures, and extreme temperatures need extreme amounts of electricty. In fact, using electricity to create heat is among the least efficient uses of electricity known to man.

Consider hair dryer. Compared to a jet engine, it moves no appreciable amount of air, and it heats that air to at best a couple hundred degrees Celsius, Do do this, it can consume as much as 2 kW of power. Then, how many hairdryers do you need to propel an aircraft? Well, a hairdryer is not able to lift its own weight. Typical hairdryers weigh around a kilogram at most, so the "thrust" produced would be less than 10 Newton. Let's just blindly guess and give it 5 N of thrust. Meanwhile, our favorite jet engines in KSP produce in the neighbourhood of 150 kN worth of thrust. That adds up to 30,000 hairdryers running together.

Those 30,000 hairdryers would each consume 2 kW worth of power, You are looking at 60 megawatts of electric power input to replicate the thrust of a Whiplash in this first-order approximation.

Of course, thermal jets operate at several thousand degrees Celsius, not just several hundreds like hairdryers. This obviously increases power consumption but also increases thrust, and therefore reduces the number of hairdryers required. I am honestly not sure which of the two scales better. Either the final figure will be somewhat lower than 60 MW, or somewhat higher. But regardless: any power consumption figure for electric aircraft engines that is measured in two-digit megawatts is infeasible for actual usage - because you'd have to carry a power plant inside your plane to provide it.

Wow! I did not see that coming! Maybe an air-speed generator could work? Get the plane up to decent speeds with rover wheels or a combustion engine and slowly throttle up the electrojet? Of course, there's always the possibility of using the Interstellar mod as a base because of the beamed power, but I really don't want to do that

6 hours ago, Van Disaster said:

What sort of thrust levels are you looking at? and precisely what tuning help do you need?

I'd say somewhere between "Wheesley" and "Panther" levels. I could use some help figuring out how much electric charge and intake air to use, ISP, atmosphere curves, and probably gimbal

[Red Iron Crown]

2 hours ago, Streetwind said:

In fact, using electricity to create heat is among the least efficient uses of electricity known to man.

Every joule of energy input ends up as the desired output. It's 100% efficient!  

[Fireheart318]

2 minutes ago, Red Iron Crown said:

Every joule of energy input ends up as the desired output. It's 100% efficient!  

And the sound would be generated by the air rushing out of the back of the engine!  What exactly is that part called in jets?

[norup]

If you want to implement something that is reasonably feasible, you might want to consider Electric Ducted Fans. Quite popular for R/C model aircraft, and also used in experimental full scale aircraft.

https://en.wikipedia.org/wiki/Airbus_E-Fan

 

[Fireheart318]

4 minutes ago, norup said:

If you want to implement something that is reasonably feasible, you might want to consider Electric Ducted Fans. Quite popular for R/C model aircraft, and also used in experimental full scale aircraft.

https://en.wikipedia.org/wiki/Airbus_E-Fan

 

How feasible is a high-altitude variant of this? I don't care if I have to bring along some oxidizer to function at that height. How much energy would it need to function up there?

[norup]

11 minutes ago, Fireheart318 said:

How feasible is a high-altitude variant of this? I don't care if I have to bring along some oxidizer to function at that height. How much energy would it need to function up there?

Realistically, not feasible, I would think. An EDF would work best for subsonic speeds at low and medium altitudes, similar to a propeller or high-bypass ratio jet engine. It would be difficult to extend to other ranges.

[p1t1o]

Did a search through archive.org, this was probably the most relevant hit, describes something akin to an air-augmented ion drive. Dont know anything about the author, though his credentials certainly sound legit.

https://archive.org/details/ElectricHypersonicaircraft

 

*edit*

https://archive.org/details/NASA_NTRS_Archive_19930086366

Weirdly, the third type described (helium compressor cycle) looks schematically like a direct reversal of a SABRE-cycle engine.

 

Edited July 19, 2016 by p1t1o

[Van Disaster]

2 hours ago, Fireheart318 said:

I don't have any examples but it is possible. Normal jets work by heating outside air using fuel and shooting the now pressurized air out the back. This will skip fuel and just use electric coils similar to those in a toaster or electric heater. It may sound weak, but you can melt metal with electricity

Wow! I did not see that coming! Maybe an air-speed generator could work? Get the plane up to decent speeds with rover wheels or a combustion engine and slowly throttle up the electrojet? Of course, there's always the possibility of using the Interstellar mod as a base because of the beamed power, but I really don't want to do that.

Yes, and you need a small power station to do it the CFM56 figures I gave are for something Wheesley-ish, and that - assuming for a second that your electric heater is as efficient as the jet combustion chamber - requires 41Megawatts of power. Power stations which feed national power grids are in the order of 2000-4000 Mw, just for reference. The average wind turbine from a wind farm - call it 30m blade length - will generate something in the order of 1.5Mw.

You have a bit of a fallacy here of using a wind generator to power your electric jet - that's generally called "a perpetual motion device" Also you'd need 26 wind turbines, which might be a tad heavy.

For everything bar electric usage just take existing figures from Wheesley/Panther. The conversion from watts  -> ecu is often taken at 1:1, so you need 41 million electric units per second at full thrust for your Wheesley. Seen another estimate at 33:1, so that would be only 1.24 million EC/s.

Ducted fans on the other hand are driven by electric motors, so rather less hungry.

Edited July 19, 2016 by Van Disaster

[Red Iron Crown]

4 minutes ago, Van Disaster said:

Yes, and you need a small power station to do it the CFM56 figures I gave are for something Wheesley-ish, and that - assuming for a second that your electric heater is as efficient as the jet combustion chamber - requires 41Megawatts of power. Power stations which feed national power grids are in the order of 2000-4000 Mw, just for reference. The average wind turbine from a wind farm - call it 30m blade length - will generate something in the order of 1.5Mw.

That sidesteps the whole question of, "Why make electricity in the first place?" Any powerplant capable of generating the kind of power required for electrothermal propulsion is going to be a thermal generator itself, so why not skip the middleman and heat the air directly? Then you get something like a nuclear thermal jet which was a proposed real thing, and are available in mods like Porkjet's Atomic Age.

[Streetwind]

2 hours ago, Red Iron Crown said:

Every joule of energy input ends up as the desired output. It's 100% efficient!  

Touché! I know you know what I mean though.