[topspin]

It's true that a lot of aircraft development has occurred using substitute engines while the final engines where still being developed. The problem for Boom isn't getting airborne. It's convincing one of the few outfits capable of this to put billions of dollars into a clean sheet engine design.

Klimov RD-33's (the Mig-29 engine) are not super-cruise engines and aren't capable of demonstrating the intent of the Boom design. And frankly I think even a retrofit like that is beyond Boom's means.

[trhway]

With correct inlet design those high power military engines I think can be made into super cruise - it is just that the inlet and the compressor will not work for long in that regime due to heat. Again for tests/demo should probably be fine. Not having chops for retrofits like this would definitely be a total disqualifier in that business though.