I Place This Up There With Soviet Super-Chopper Claims

Skylon is claiming that it will have its liquid air engine ready for test in 3-4 years.

Considering the fact that it's really being run on a shoe string, I simply do not find this a credible timeline.

Additionally (top video) it's reentry profile appears to be problematic to me. The knife edge canard appears to be in a weak shock on reentry, which means that the surface temperature would much higher than in something like a space capsule, or the relatively blunt edged shuttle wing leading edges, where much of the heating occurs in a strong shock that is some distance from in front of any structures, but I am not an aerodynamicist.

If you look at the bottom video, from a couple of years ago, where Richard Varvill, Technical Director of Reaction Engines Limited talks about a 12+ year development cycle with a demonstration of the heat exchangers in 3 years, that sounds rather more realistic.

The bottom vid is also a nice primer on the basic operation of the Sabre engine.

My earlier post on the vehicle and engine.