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I was recently comparing two aircraft, and, although I feel stupid asking this question, I wondered why one had a maximum speed of M2.2 compared to M0.94, when both have similar weight, both are supersonic capable and both have similar thrust.

Compare for example the Hawker Hunter F.6 which has:

  • Empty weight 6,406kg
  • Max speed M0.94 (>M1.0 In a dive)
  • Engine thrust 10,145lbf
  • Climbrate 17,200ft/min

And the Mirage F.1:

  • Empty weight 7,050kg
  • Max speed M2.2
  • Engine thrust 13,700lbf (WET)
  • Climbrate 16,400ft/min

As you can see, both have similar rates of climb, similar empty weights, and both are aerodynamically supersonic capable. Only major difference being the the F.1 has ~35% more thrust- yet, with this extra thrust and weight, it is able to go over twice as fast? How does this work?

As I write this the only thing I can think is that wave drag plays a part, and the afterburner is required to give it that extra boost to break through the transonic barrier?

If the above is the case, then does this mean that all aircraft that can supercruise require the use of afterburner to get there, but can then hold it in mil power? And, if so, could this mean theoretically you could use a rocket booster of some form to push the Hunter F.6 through the transonic region and hold a supersonic speed, or, is there a minimum thrust to weight ratio in mil power required to achieve supercruise, or do more special aerodynamics need to be involved to keep wave drag down to make it possible?

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    $\begingroup$ One possible mistake is in treating thrust as one single number. It's not. Max thrust varies a lot with altitude, temperature, and mach number. What you are quoting is just one specific point (maybe takeoff?) If your engine is not specifically designed for supersonic flight, performance can drop a lot as you go up in speed. I was not able to find any performance curves for engines in this specific planes (thus comment not answer), but I'm guessing that if you did, you might find a wide variation in performance vs mach number. $\endgroup$
    – Daniel K
    Jun 29, 2020 at 23:53
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    $\begingroup$ The aircraft were designed for different things. It's like asking why your road car with a 300HP V8 can't go 1-100MPH in under 2 seconds and brake at 5G+ while an F1 car with a 750HP V6 can. Different specs. Different purpose. Different tools. Heck, if you pulled that V6 F1 engine and put it in your road car, you still wouldn't get that kind of performance. (It would be a whole lotta fun, though! :) $\endgroup$
    – FreeMan
    Jun 30, 2020 at 12:42

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and both are aerodynamically supersonic capable

No, not really.

  • The blunt nose and rather thick wing with not all that much sweep of the Hawker Hunter are not suited for supersonic flight.

  • The engine inlets of the Hunter lack the (movable) shock cones like the Mirage, which are needed for flight at higher Mach numbers (either a movable shock cone or a variable inlet vane are needed above around M1.6), and the shape is generally not suited for supersonic flight. Supersonic inlet needs to create an orderly pattern of shock waves inside to maintain smooth air flow and the triangular shape does not look like it would do that.

Also the Hunter engine probably has lower exhaust velocity, which makes it more efficient, but limits the maximum power at which it can still produce thrust.

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    $\begingroup$ Ministry of Supply Memorandum 3420 shows in Fig. 9 the zero-lift drag of the Hunter up to Mach 1.2. While transsonic drag doubles for a good supersonic design, for the Hunter it increases by almost a factor of 5. $\endgroup$
    – Peter Kämpf
    Jun 30, 2020 at 21:12

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