Questions on High Speed Stall

[Dani]

Iceman, that's exactly what's the definition of high speed stall: flow separation because of mach shock waves.

Studi is basically right. Dear old D.P. "Deep" Davies ("handling the big jets") would have answered: Stall speed is always at the same EAS if you disregard some compressibility effects for high mach numbers.

Dani

[ICEMAN757200]

Thatīs what I know as Shock Stall, We use to think in airspeed terms when we speak about stalls but stalls are related to AOA.An airfoil can stall at any speed but the Critical AOA will be always the same for a given airfoil Lim V tends to + infinite in L = (1/2) d v2 s CL then L increases to infinite.

[ICEMAN757200]

The higher the altitude the lower the EAS at wich Mcrit is reached so the answer for Q1 is High Altitude.An increase in aircraft weight(or load factor) will result in a decrease in Mcrit thus the answer for Q2 is the same, high altitude ,but Mcrit will be reached at the lowest altitude than for any other gross weight lower than max .

[chornedsnorkack]

Originally Posted by ICEMAN757200

The critical angle of attack is the angle of attack on the lift coefficient versus angle-of-attack curve at which the maximum lift coefficient occurs, and it defines the boundary between the wing's linear and nonlinear regimes. Flow separation begins to occur at this point, decreasing lift, increasing drag, and changing the wing's pitching moment.

However, while one can expect that flow separation would increase drag and decrease lift, this does not mean maximum lift coefficient! The lift coefficient comes from many parts of airfoil - including the high-pressure area under the wing - so increase of lift there might more than compensate loss of lift due to flow separation...

[ICEMAN757200]

At a constant AOA , the increase of CL as speed increases from about M 0.4 into the low end of the transonic region gives a steeper lift ccurve slope, i.e. the change of CL per degree of AOA will increase.However, because of early separation resulting from the formation of shockwave,CLmax and the stalling angle will be reduced.