|Quoting Blackbird (Reply 56):|
Actually, I thought planes like the F-22 and YF-23 had no alpha limits (at least the F-23 from what I was told)?
Not quite sure what you mean, but the situation I was describing happens at a (relatively) low alpha. IOW, get your airplane to 500kts indicated, and haul back on the stick, and the wings will come off long before the AoA reaches the typical 14 degree stalling point. Artificial mechanisms preventing excessive G loads excepted, of course.
|Quoting Blackbird (Reply 56):|
Additionally, it's probably possible to have a situation in which you're going so fast (above corner velocity) in which you wouldn't have enough control power to get the alpha high enough to get a stall (up to a point the faster you go the more responsive the plane gets, above a point though the plane becomes less and less responsive as the higher speed makes it harder for the plane to change direction.
That's exactly backwards. Changes in alpha require rotating the aircraft around its CG. That's done with the horizontal stabilizer and elevator. The faster you're going, the more force those can produce, and the more rotation they can create around the CG. It's at low speeds that you can run out of elevator authority (that, for example, is where the forward CG limit comes from - too far forward, and you can no longer hold the nose up at landing speeds).
Changing direction is *not* the same as pitching. The rate at which you can change direction is dependent on how much lift you can produce (which depends on alpha, indicated airspeed and the structural capabilities of the aircraft), and your true velocity. The time needed to turn is linearly dependent on the first, and inversely dependent on the second. In terms of space, it’s related to the square and inverse square of the two parameters.
Pitching requires none of that and can be very, very fast assuming sufficient elevator authority, which is primarily dependent on indicated airspeed. At high speeds some mach effects (like the aft movement of the center of lift and the general blanking of the elevator by the shockwave from the structure in front of it) will reduce the effectiveness of the elevator. Obviously stalling the horizontal stabilizer and elevator will also (drastically) reduce its effectiveness.
At high speeds most aircraft can aerodynamically pitch well into the stall regime in a very, very short time. Likewise into the wings-come-off regime. That's why most aircraft (with conventional control systems) are flown much more gingerly at high speeds. That near full stick deflection that you can (and often do) use at low speeds is fatal at high speeds. That's the structural limit I was mentioning. At low speeds you may not be able to do a 4G
turn period, because your wings will stall. At high speed you might be able to pull 4G
with only a 3 degree alpha (obviously well below the stall). That high speed 4G
turn will require only a very small elevator deflection (although that might** require a substantial amount of force - but not movement - on the stick).
*Assuming acceleration in the plane of the turn - the actual G load will be higher in a typical level turn since you also have to hold the aircraft up.
**Assuming typically balanced flight controls.