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?
$\begingroup$
$\endgroup$
-
$\begingroup$ Related: In what way are the Concorde's engines considered efficient? $\endgroup$ – mins Jan 14 '17 at 12:42
-
$\begingroup$ Thanks for the link that's a pretty interesting read, but I was asking about thrust not efficiency. $\endgroup$ – Talisker Jan 17 '17 at 21:34
$\begingroup$
$\endgroup$
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.
