Re: Skylon SSTO



Ian Woollard wrote:


I think they're easier than you would expect, but they're a very new type of engine; and they're closed cycle which is never entirely fun to R&D. To put this into perspective the SR-71's engines were thought to be capable of Mach 4.5,

In the pilot's manual they state that the engines are going to start melting at around Mach 3.4 due to the heat of the air coming into the intake.

but this engine is only aiming for another Mach but the precooler takes out most of the nasties from travelling at high speed- the engine sees almost identical conditions from Mach 0 all the way up to Mach 5.5. In other words, it works the same on the bench as it does in the sky...

Run one up on the bench, and let's see what it does.
If it was that amazing of an idea, someone in Europe or here would have bought the patent rights to it, and put it into production due to its revolutionary nature, either openly or in the black world.
But even the HOTAL engine is pretty well known now due to the fact it didn't do what was advertised, and Sabre is in the unclassified world.
I assume the reason for that is that major aerospace firms have had their boffins look at it, and they have reported that it's not going to do what's claimed for it.
I've seen something a lot like this before...an aviation company comes up with revolutionary new concept that proves unfeasible when you try to build it: http://www.laesieworks.com/ifo/lib/AVRO-pict/silverbug00.gif
More recently we have the VentureStar fiasco.


Another problem is the vehicle's shape; whereas the long and skinny aspect works fine from a low-drag point of view, it also means the front LH2 tank has a lot of surface area for its capacity.

I don't think that this is a problem, the tanks are vaguely similar dimensions to the Space Shuttle Main Tank, but with thicker insulation.

Anyway in terms of drag the important thing isn't the cross-sectional area, it's the ballistic coefficient, which is largely independent of diameter, but is critically dependent on length. That's why the Skylon tank/vehicle is pretty long (~80m). The minimum diameter is then determined by bending moments to avoid buckling.

They ran into the long and skinny tank problem with the Lockheed CL-400 "Suntan" LH-2 powered reconnaissance jet.
Due to the low density of LH2 you end up with something huge to get enough storage space for it once you head into the high fineness ratio type design. Some of the final CL-400 designs ended up being nearly 300 feet long.
Until they get a Sabre running on a bench, I'm going to treat this whole project with a great deal of skepticism.
I also have grave doubts about that incredibly lightweight ceramic TPS the vehicle is supposed to use.
The whole thing smells way too blue sky.


Pat
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