Sustained turn rate at 31.5 °/s with flaps on!? - Page 6 - ED Forums
 


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Old 02-19-2020, 11:21 PM   #51
captain_dalan
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Originally Posted by Figaro9 View Post
Accelerated stall lines, or lines of maximum lift, represent the maximum load factor that an airplane can produce based on airspeed. The accelerated stall lines are determined by CLmax AOA. They are the curving lines on the left side of the V-n diagram. If one tries to maintain a constant airspeed and increase lift beyond the accelerated stall lines, the airplane will stall because we have exceeded the stalling angle of attack.

At high load factors, the sudden loss of lift from one wing (whichever stalls first ) creates a much larger rolling moment than with a 1-g stall. The result is a violent departure that resembles a snap roll.
Some aircraft tend to roll rapidly toward the outside of the turn, because the the outside wing stalls before the inside wing.
During a rapid departure from controlled flight, the normal CLmax may be momentarily exceeded and as a result, the aircraft could be overstressed or damaged below the corner speed.
Hold on, i think i now get it, you are quoting the landing approach tables, right? In such a case, have you applied the correct AoA formula for speeds less then mach 0.4? If so, then the 35 units of max AoA listed in those charts (the AoA meter pegs at 30, but the actual plane goes above that, just like the g-meter pegs at 10, but you can pull in excess of 12) should give you somewhere between 29-30 degrees (true) of angle of attack. That is for wing sweep angle of 20 degrees (landing configuration). If you drop the landing gear as well, then you maximum AoA may drop to...... well, i have no idea how much, but it may actually drop bellow 30. Don't quite me on that though.

However, a 280 KIAS at sea level is above mach 0.4 and your wings should be at 22 degrees by default. This should give you a higher maximum AoA. The units formula does actually change based on configuration, and as a result the maximum AoA can get up to 40 degrees (true) for the wing sweep of 68 degrees.
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Old 02-20-2020, 12:46 AM   #52
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Originally Posted by captain_dalan View Post
Hold on, i think i now get it, you are quoting the landing approach tables, right? In such a case, have you applied the correct AoA formula for speeds less then mach 0.4? If so, then the 35 units of max AoA listed in those charts (the AoA meter pegs at 30, but the actual plane goes above that, just like the g-meter pegs at 10, but you can pull in excess of 12) should give you somewhere between 29-30 degrees (true) of angle of attack. That is for wing sweep angle of 20 degrees (landing configuration). If you drop the landing gear as well, then you maximum AoA may drop to...... well, i have no idea how much, but it may actually drop bellow 30. Don't quite me on that though.

However, a 280 KIAS at sea level is above mach 0.4 and your wings should be at 22 degrees by default. This should give you a higher maximum AoA. The units formula does actually change based on configuration, and as a result the maximum AoA can get up to 40 degrees (true) for the wing sweep of 68 degrees.
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Old 02-20-2020, 11:54 PM   #53
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There it is! 24
Good find mate.

Especially useful are the ones for the deployment of the maneuvering flaps. Pity there is no such data on the fully deployed flaps configuration
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Old 02-21-2020, 06:36 AM   #54
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Thanks guys.

First, I did a math. I took the stall speed out of the natops approach speed charts with 43’000lbs. That is 103 kts. Multiplied with square root of 7.7 g and the stall speed at that g-loading and config then is 285 kts. Since gear in that turn is up and engine thrust is pushing at some degree into the turn, stalling speed is probably lower though.

There is an accident report where a F14 in a dogfight departed contolled flight (high g stall) exeeding 25 units aoa..
I checked also with natops and ‚wing rock modell‘ study:
‚In the takeoff and landing configuration, wing rock is also experienced at high AOA during approach to stall, as indicated by the following excerpt from the NATOPS: At 25 units AOA divergent wing rock and yaw excursions define the stall. Sideslip angle may reach 25 degrees, and bank angle 90 degrees within 6 seconds if AOA is not lowered....‘

Flight beyond stall angle is possible for highly powered act. if lift is replaced by engine thrust... But (at high g) that is probably not the place you want to be in a non-fbw departure prone f14.

And finally, according first posts, Mach is 0.39 in that turn, so wings are probably at 20°?
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Old 02-22-2020, 03:03 PM   #55
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Yep, definitely lower. ASL at 54000lbs of weight it's something like 280-285knots for about 6 and a half g (fighter configuration).

As for departures, you don't really need to be at the edge of stall to depart the plane. What you need is a force/momentum coupling in either of the pitch-roll-yaw axis. If the resulting coupling is strong enough to overcome the plane's stability (as you'd expect easier to accomplish when the plane is already unstable at very high angles of attack) the plane will/can depart. That's why it's so important that any excursions at the edge of the envelope are executed without lateral control inputs and 0 sideslip.

As for the OP's case, i did my calcs for 280 knots ASL, or about mach 0.42. The two charts on the automated wing sweep schedule give me a bit conflicting data, as to what angle is that with the wings on auto, but it's most likely between 20 and 21 degree. Anyways, shouldn't be much of a difference there. The required sustained turn should occur at 14-15 degrees (true) of AoA, or according to the conversion formula, 16.2-17.5 units (depending on how much the lift/drag curves change due to change in sweep angle).

Can you try it in the sim?

Last edited by captain_dalan; 02-22-2020 at 04:04 PM.
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