What is meant by shock stall?

A shock stall is a stall created when the airflow over an aircraft’s wings is disturbed by shock waves formed when flying at or above the aircraft’s drag divergence Mach number.

What is the result of a shock induced separation?

Shock-induced flow separation is the flow mechanism usually responsible for what the structural dynamicist terms “buffet.” The shock-induced flow separation affects the aeroelastic response via two different mechanisms: 1) The flow separation generates fluctuating pressures, i.e., a forcing function that is independent …

What is used to prevent a shock induced stall?

The use of thin supercritical wing sections and swept-back wings are among the more common effective methods of postponing the shock stall to higher speeds. Also called a buffet boundary.

What is shock stall Mach tuck?

Mach tuck is a nose down pitch tendency due to a change in the position of the centre of pressure resulting from a rearward movement of the shock wave which occurs as an aircraft in transonic flight accelerates beyond its limiting mach number (MMO).

What causes drag divergence?

A: Drag divergence occurs when the drag on an airfoil starts to increase faster as the Mach number increases. Drag is the force of flight that acts against motion. Mach number measures speed in terms of the speed of sound.

What is shock induced boundary layer separation?

The incident shock forms sharp adverse pressure gradients in the boundary layer, which causes the separation of the boundary layer. The separation bubble induces a separation shock. Due to the constant pressure in the separation bubble, the incident shock reflects on the bubble and forms expansion waves.

What causes airplane stall?

Stall occurs when a plane is under too great an angle of attack (the angle of attack is the angle between the plane and the direction of flight). Due to the stall the wing produces less lift and more drag; the increased drag causes the speed to decrease further so that the wing produces even less lift.

What are the factors that affect aircraft stalls?

Factors such as total weight, load factor, power, and center of gravity location affect stall speed—sometimes significantly. Stall speed increases as weight increases, since wings need to fly at a higher angle of attack to generate enough lift for a given airspeed.

Why does stall speed increase with altitude?

As air density decreases with increasing altitude, more lift must be generated by an aerofoil to sustain flight and so the true air speed at which an aerofoil will stall will increase.

Why do shock waves cause drag?

The higher pressure behind the shock wave and lower pressure behind the expansion wave result in a single force that pushes the wing up and back. The upward part of this force is lift; the backward part of this force is drag.

What is the difference between supersonic separation of flow and stall?

When the velocity of the airflow locally exceeds speed of sound above the wing a shock wave forms and the flow detaches beyond this shock wave. Similarly to stall, the supersonic separation of flow removes the component of lift produced by decrease of pressure on the upper surface of the wing and so the effects are similar.

What causes an aircraft to stall?

Aircraft stall when the wing cannot produce enough lift to sustain flight. This can happen for two reasons: Flow separation due to high angle of attack. The lift curve slope, which is positive and linear at low angles of attack, becomes negative, such that an increase of the angle of attack results in lower lift.

What is the difference between supersonic stall and Mach tuck?

A difference from normal stall is that after supersonic flow separation the lift remains proportional to angle of attack and so the aircraft continues to behave more or less normally except for the change in trim. Mach tuck may occur as low as Mach 0.7 depending on aircraft design, because the air moves faster over the wing.

What is a high speed stall?

$\\begingroup$ High speed stall is associated with buffeting due to the aforementioned flow separation. Generally the lift is well-maintained even after flow separation. But the buffeting becomes so strong that normal piloting is untenable (deterrent buffet).