Re: Skylon SSTO



Wayne Throop wrote:

If you had a way to extract the thermal energy, and still maintain the
linear velocity out the tube, that might work out. But an MHD generator
doesn't seem to be such a way, and your hypothesis was that the exhaust
velocity was lower. If it's lower, it has less momentum, and thus less
momentum is imparted to the vehicle.


No, momentum inside the engine is unchanged- the stuff only contracts once it's left the engine proper and is behind it.



Did I misunderstand, and you're saying the velocity out the tube is unchanged?


Hang on, I'm working on it. :-)
This is fun, but kind of involved ounce you get going on the concept.
I think you get a net loss in velocity of the gas in the exhaust stream behind the exhaust nozzle (though not much) by turbulence effects within the exiting gas stream.
But again, the point is to get a net asset asset in regards to engine function at the _front_ of the exhaust stream, in that it reduces pressure on the back of the engine, and allows it to eat more air at the front.
Since intake temperature is one of the limiting factors of how fast a turbine-driven engine can work (get it too high, and the blades on your compressor melt - which was why the Soviets used alcohol injection in the MiG-25's intake trunks.) a plasma airspike equipped intake spike might be able to solve some problems in this regard, by reducing shockwave heating at the front end.
I'm still trying to figure out if you use a plasma airspike ahead of the intake spike to ionize the intake air to a particular positive or negative charge, and then let it flow into the engine in that form...till it's converted into charged plasma itself in the combustor, maintains it ionization that it got on the way in, then reacts with the rear coil and reaches the exit electron gun at the base of the exit nozzle to neutralize its charge before it leaves the aircraft.
Nice thing about all this is how you can bootstrap it.
Electrical power to drive the whole engine and its various plasma generation systems and electron guns can come from it itself as it operates.
You pull this stunt off right, and you can get a turbine engine running at around Mach 6 without overheating.
The other big problem with operating a turbine engine at those speeds is "supersonic compressor blade stall" when the supersonic intake air is still supersonic as it hits the compressor blades and causes the airflow around them to break down; which is why all the intake ramps, shock cones, bleed vents, and what-not are used to convert low-density supersonic intake airflow into high-density subsonic airflow before it reaches the engine's leading compressor stage.
There may be a way around this also.
We've known how to make propellor blades capable of operating at supersonic rotational speeds since the 1950's (we stuck one on the front of a YF-88 Voodoo), and computer designed variants of them were used in the externally bladed turbofan engines that were a brief vogue in the 1980s. They were noisy as hell, and besides passenger discomfort in commercial use, there were concerns about the constant impingement of the supersonic shockwaves on the aircraft's airframe causing metal fatigue (which is why the were generally mounted back at the tail in the promulgated aircraft designs, with their blades at their rear end.)
Would it then be impossible to design turbine compressor intake blades optimized not for subsonic laminar flow, but for supersonic shockwave impingement airflow to deliver air to a compressor?
This could be only a detached first stage of a compressor; at low speeds the supersonic first stage compressor would feather itself and act as a stator, only spinning up as higher velocities were reached - its ability to compress the intake air assuring that the stages behind it would be able to ingest air in a subsonic form, due to its influence and higher pressures reached thereby?

Pat

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