[QUOTE=ORAC;11010418]Can’t help thinking Sabre is like fusion - always just a few years away....

Exactly. As noted above, the presumed cost savings from reuse-ability of HOTOL have been largely met by Space-X's approach.
That leaves the technology searching for a mission, but hypersonic fighters are just as operationally dubious as the US Army's pursuit of a 1000 mile range cannon.

https://aviation-xtended.co.uk/ep-171-reaction-engines/

There is a section of the podcast referring to the hypersonic UAV shown in concept photos below - apparently work is underway.


https://i0.wp.com/aviation-xtended.c...24%2C576&ssl=1

It was in 2019 when this thread started...............

Indeed and things have happened - including various commercial applications of the heat exchanger technology, and a "higher speed" test of their precooler for AFRL which handled 10MW of heat transfer proving that it could handle high flow.
If you cannot see the Twitter link (like me!) this is next best:
https://reactionengines.co.uk/fct-testing/

Also tests of the preburner that is the "starter motor" of a SABRE engine which puts heat into the system via their HX3 heat exchanger until the vehicle is moving fast enough that the heat can be supplied by slowing incoming air:

This UAV (announced Jul 2022 IIRC) will presumably let them advance the TRLs of various bits of their technology although it will be a precooler in front of a jet engine rather than an air-breathing rocket. I'm sure they want it to fly but it probably doesn't need to to still help them.

they originally were talking about 2020 for first ground test of the whole engine IIRC

this months "Flight " has an interesting article on the cancelation of the USAF ARRW AGM-183A hypersonic system - "numerous technical challenges"

Well, I think they have chronically too little money but at least they've moved the state of the art ahead some steps and nobody in the future history of the world ever again needs to doubt that those things are possible. That's a solid achievement. There's a report on how they spent some government money which might be interesting even if you only dip into it:

https://www.gov.uk/government/public...on-report-2022

W.R.T. the AGM-183A I can see how all these things are hard and in that case the performance is either OK or not acceptable. With this precooled jet engine there's obviously a similar judgement but one can approach it gradually. I have to speculate but Rolls Royce have at least run a gas turbine on hydrogen recently:

https://www.bbc.co.uk/news/business-63758937

One has to hope that Rolls/REL/BAE can apply what they learned to a smaller engine.

So assuming that they have an engine which they can make run on hydrogen it should fly without any precooling at all and all the precooling will do is to enable it to go faster than it would have otherwise. Mach 5 would be the absolute upper limit but it might not need to approach more than a fraction of that to prove it is working properly and that would be great for REL.

Even testing such an engine on a bench might have value for them - and they have a "bench" in Colorado which might be suitable.

I'm sure that there is a large chance of failure