Does anyone know why subsonic jet engine intakes are almost always round when looking at them from the front, while supersonic jets are kind of square?  Do supersonic aircraft still ram all the head on airflow into the intake or does that square shape have some sort of baffle in there to limit airflow once the aircraft is sonic?  Just wondering if I need to re-design my Valkyret. 

Harold

The only other item to consider is that high Mach aircraft tend to have some sort of boundary layer splitter, or suction device (like the plate found in front of the intake of an F-18A/C). This helps direct airflow into the engine while slowing it down to subsonic speed, so that the engine doesn't surge. Moving shock cones, like on the SR-71, likewise have the same effect. Aircraft with square inlets (F-14, F-15) have interior moving ramps in their intakes. So, anything goes, as long as there's some means to slow the air entering the engine.

Ok then.  Guess I’m barking up the wrong tree.
So how does this go… A supersonic aircraft has oncoming relative wind that is also supersonic, but the air is then slowed to subsonic before it reaches the compressor stage of the engine???  Then the air is mixed with full in the combustion chamber.  Then accelerated through the turbine stage, but it has to be leaving the jet pipe at supersonic speeds in order to have a jet reaction driving an aircraft to supersonic speeds.
So what is that “Surge” that CAFedm is talking about?  I’ve never had to worry about Surge on the F-28 or the CRJ 200 and CRJ 705 (the only jets I’ve flown).  They never talked about Surge in the ground schools.

Harold

Maybe some of these applications could help Harold?

http://www.fsworld.co.za/index_files/aeronautics.htm