Question about fixed geometry intakes on supersonic jetfighter.

[aerofan]

Hope there are some aerodynamists or engineers out there who can answer this. As far as I know from materials that I've read, the fixed geometry 'D' type intakes can produce a perfect gas stream upto the mach 2.35 for a turbine engine to still operate effectively. My question is about the blended wing types, as in the Hawker Hunter, F-101 Voodoo, Skyray, etc. What is the highest mach number attainable for a perfect gas stream on these intakes?

[KJ_Lesnick]

How do you define a perfect gas stream?  Stable, or 100% inlet-efficiency?

In regards to blended intakes, at least pertaining to the Skyray and Voodoo, I don't think there actually is any major difference over a non blended design as the airplane at supersonic speeds (with it's intakes ahead of the wing, or wing-root) will not have the airflow into it affected in anyway by the airflow pattern over the wing. 

In regards to the Hawker Hunter, it's got a blunt lip, which although swept looks like it would, at very low supersonic speed, form a shockwave on the root (which is also the fuselage side) which would keep the wave off the rest of the intake, but at mach numbers above that you'd probably get a strong shockwave which would just knock the speed right down to subsonic (normal shockwaves are very energy wasteful).  However to my knowledge the Hunter is only marginally supersonic (though I could be wrong) so I'm not sure how big a deal that is. 


Kendra Lesnick

[aerofan]

How do you define a perfect gas stream?  Stable, or 100% inlet-efficiency?

In regards to blended intakes, at least pertaining to the Skyray and Voodoo, I don't think there actually is any major difference over a non blended design as the airplane at supersonic speeds (with it's intakes ahead of the wing, or wing-root) will not have the airflow into it affected in anyway by the airflow pattern over the wing. 

In regards to the Hawker Hunter, it's got a blunt lip, which although swept looks like it would, at very low supersonic speed, form a shockwave on the root (which is also the fuselage side) which would keep the wave off the rest of the intake, but at mach numbers above that you'd probably get a strong shockwave which would just knock the speed right down to subsonic (normal shockwaves are very energy wasteful).  However to my knowledge the Hunter is only marginally supersonic (though I could be wrong) so I'm not sure how big a deal that is. 


Kendra Lesnick

I would say stable so that the gas turbine engine will still operate properly. The only other blended wing design aircraft that I know of that has a maxium mach 2.0+ number is the F-105 Thunderchief. It quite interesting about the shockwaves as I believe that the air that enters the compressor of the turbine must be reduce to subsonic or else  the engine will stall. Thanks Kendra for the reply.

[Hobbes]

Mach 2.35 with fixed-geometry intakes? I thought it was around Mach 1.8. I don't have the reference to hand, but IIRC this was a factor in deciding the Hornet would have fixed-geometry intakes: it was felt the weight penalty was to great wrt the additional top speed.

[Weaver]

Later Drakens and F-16s can do Mach 2 on fixed intakes. Although the Drakens superfically look "blended", in fact they're more like individual pitot intakes (like two F-100s, if you se what I mean).