Over 40 different jet VSTOL concepts flown around the world have taught us one thing:
For it to be successful the design/layout of any jet lift aircraft must keep the hot engine efflux out of the intake
This is not a ‘nice to have’ performance enhancing thing but is as important to STOVL as not having wings that drop off is to ordinary flight.
The X-32 incorporated a dam of cool air exhausting down behind the intake that it was hoped would keep the hot air from moving forward towards the intake. It worked at model scale but not at full scale.
The X-35 deliberately had more flow from the front fan than the rear nozzle which stopped the hot efflux moving forward.
