As I understand it, turbojet thrust decreases both with altitude due to rarefied air reducing massflow, and airspeed due to a smaller speed increase between intake and exhaust relative to the airframe. However aircraft designed for sustained supercruise such as Concorde or Blackbird had intakes that used various amounts of ram-effect pressure recovery, so I was wondering how much that would offset the effects of being fast and high i.e. what was Concorde's mach 2 max thrust compared compared to sea level dry thrust, and/or the Blackbird's mach 3.2 turboramjet thrust compared to take-off wet thrust?


For Concorde, takeoff thrust:weight was 1:0.373. At cruise, the Concorde had a lift:drag ratio of 7:1. At cruise, thrust = drag. So cruise thrust is 1/7 = 0.1429

So, cruise:ASL is 0.14(rounded down for climb fuel burn):0.373 = around 1:3.8

For the SR-71, takeoff thrust:weight is 0.44:1. Using the Kuchemann supersonic L/D formula, we get

4(Mach(=3)+3)/Mach(=3) =1:8

Now this looks too high. And running this formula for Concorde gave 10:1. So, having no better option (yet), I simply took 1:6 as the value. This would give us a cruise thrust:weight of around 1/6:1 = 0.167:1

0.167/0.44 = around 1:3.8 (again?)

The figures for the SR-71 may well be wrong.


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