There's no maximum...they'll all work.
I thought the inlet would become so inefficient that it would be useless after awhile (in terms of thrust being so low and drag becoming so high)
You'll just have really horrible pressure losses (which can be overcome with excess thrust). For really high Mach numbers you'll have a heating problem with a really inefficient inlet, but I suppose you could build a carbon-carbon inlet if you really wanted to.
The pressure losses are a result of the shock-wave formation I would assume? Wouldn't the airflow become more turbulent the more powerful the shockwaves as well?
[quote]Typical is a whole 'nother matter. I would expect nobody uses 1 shock wave on current designs anymore...old MIG's probably did, with the round flat inlets, so that's probably good up into the Mach 1.5 region.
I would have figured you could have made it to 2... didn't the F-16 use a pitot-type inlet?
Things like the F-14 and Foxbat could go Mach 2-2.5 with multi-shock inlets (I think they were 4).
I don't know what the number of shockwaves in the MiG-25's inlets are, but 4-shocks sounds about correct for the F-14.
Regarding high-performance inlets, many high-performance inlet-designs often use porous ramps and surfaces and such to remove turbulent airflow. That I assume would improve performance over the typical figures for a multi-shock inlet (ie. the theoretical maximum efficiency for a 4-shock duct with porous ramps would be more efficient than the theoretical maximum for a 4-shock duct without porous ramps)
Offhand I can't think of any that use 8, although the SR-71 might have.
Okay, could you give me a guess as to what mach number you could get to with a 90-percent efficiency assuming the inlet uses substantial amount of porous-surface?
BTW: I don't know how many shocks the A-12/YF-12/SR-71/M-21 use either -- the aircraft I'm asking questions about is not the Blackbird.