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I was just wondering that the fighter jets like F-16, F-35 and Rafale when they are doing a steady flight at a certain airspeed, try to rotate 90 degrees and aim to obtain a vertical motion, so does the angle of attack during this maneuver crosses the stall angle on these fighter jets or not?

Since by definition, angle of attack means the angle between the incoming airflow and the aircraft wing chord line, so I don't know if this changes (or goes beyond the stall angle) during this maneuver.

Even if it goes beyond the stall angle, can it still create a problem for the fighter jet (because I heard that the high Thrust/Weight ratio allows the fighter jets to do these unusual and extreme maneuvers without causing it to stall).

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Federico
    Nov 9 '21 at 7:22
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The answer depends on two factors - aircraft speed, and pitch rate. There are virtually infinite combinations of these two variables, but let's consider four for the sake of discussion:

  1. Low speed, slow pitch rate - Done in a controlled manner, a fighter with a better than 1:1 thrust to weight ratio can rotate smoothly to vertical without exceeding stalling AOA, light the burners, and accelerate upwards. The Blue Angels do a quasi-demonstration of this during their airshows.

  2. Low speed, fast pitch rate - This is where stalling AOA can be easily exceeded, and a rather violent departure from controlled flight may result. To be avoided.

  3. High speed, slow pitch rate - An airplane with sufficient kinetic energy can arc gracefully into the vertical in a zoom climb, trading excess airspeed for altitude. Thrust to weight ratio has nothing to do with it since gliders are capable of this. However, the better the thrust weight ratio the longer you can sustain the climb.

  4. High speed, fast pitch rate - This is where in the high speed portion of the performance envelope, (above cornering speed) you would exceed the max G limits of the aircraft before you reach a stalling AOA.

A good fighter pilot understands the energy state of the aircraft as well as the performance envelope, and can manage both to achieve maximum performance. But there isn't a single correct answer to the basic question.

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    $\begingroup$ Sorry that I could only give you one upvote. $\endgroup$ Nov 9 '21 at 6:34
  • $\begingroup$ Great answer. For the 1st and 2nd cases (i.e. low speed), after the aircraft reaches the vertical position, now the speed of motion towards the sky will be different (I guess much more higher) than at what it was turning, right? Since now the thrust has to play an important role in overcoming the weight of aircraft. $\endgroup$ Nov 9 '21 at 7:41
  • $\begingroup$ Moreover, the G limits can also be exceeded for 3rd as well, right? $\endgroup$ Nov 9 '21 at 7:44
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    $\begingroup$ @RameezUlHaq, Thanks, and yes - extreme thrust is required to recover from 1 & 2. Any airplane other than a high performance fighter will mush into a stall. I know these two scenarios are not what you were asking, but I felt it was worth bringing them up to define the corners of the "box". You could exceed G limits in #3 because of the speed, but not if you are careful and pitch slowly. Again, there are infinite combinations of speed, thrust setting, and pitch rate available to a pilot... $\endgroup$ Nov 9 '21 at 15:21
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    $\begingroup$ @RameezUlHaq, yes, if “decreasing AOA” in a climb just means “use less than what will overstress the airframe”. But the way you describe it sounds like you need to be extra cautious. You can fly a fighter very aggressively and not exceed G limits as long as you have some awareness and know what you are doing. $\endgroup$ Nov 10 '21 at 15:37
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An examination of a typical flight envelope may leave one wondering about exceeding G limits, rather than stalling. A zoom climb typically starts by gaining as much kinetic energy as possible (speed) before turning sharply skyward. As excess drag would result in a lower, slower climb, stalls would be strictly avoided.

At high speeds one would pull the stick to climb, experiencing crushing G's long before stall. The pilot's ability to withstand the G's would be the limiting factor in a fighter jet, followed by the G loading limits of the aircraft itself.

Unless trying to complete a loop at a much lower airspeed, high AoA's will likely overstress the pilot/aircraft well before stall.

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  • $\begingroup$ so you are saying the aircraft will not experience stall during this transition? $\endgroup$ Nov 8 '21 at 19:43
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    $\begingroup$ If it is going very fast it will exceed G loads first. $\endgroup$ Nov 8 '21 at 20:10

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