Let's pick this up with the completed Key Facts section — Page 206, Lesson 256

Let's pick this up with the completed Key Facts section. I want to walk you through the correct statements, because these are the exact relationships you'll be tested on. First, the super stall. The swept-back wing is the major contributory factor to super stall. And because of that, an aircraft design with super stall tendencies must be fitted with a stick pusher. So remember that pairing: swept wing causes it, stick pusher is the mandatory fix. Now, the factors which can affect VSR — that's the reference stall speed. There are seven of them, and I want you to hold each one. Changes in weight. Manoeuvring the aircraft, which means increasing the load factor. Configuration changes, which alter CLMAX and the pitching moment. Engine thrust and propeller slipstream. Mach number. Wing contamination. And heavy rain. Those are the seven. Next, the load factor. In straight and level flight, the load factor is one. That's your baseline. At a higher weight, the stall speed will be higher. And here's the precise relationship: if the weight is decreased by 50%, the stall speed will decrease by approximately 25%. So a halving of weight gives only a quarter reduction in stall speed — that's the square root relationship at work. Load factor varies with bank angle. And the increase in stall speed in a turn is proportional to the square root of the load factor. So when you bank, you pull more g, and the stall speed climbs with the square root of that g. Now the configuration effects. High lift devices will decrease the stall speed because CLMAX is increased. That's the maximum lift coefficient going up. Forward CG movement will increase stall speed due to the increased tail down load. Lowering the landing gear will increase stall speed due to the increased tail down load as well. And increased engine power will decrease stall speed due to propeller slipstream and/or the upwards inclination of thrust. Then compressibility. The effect of increasing Mach number on stall speed begins at M 0.4. So that's the threshold — Mach 0.4. The effects of compressibility increase stall speed by decreasing CLMAX. Now contamination. The formation of ice on the leading edge of the wing can increase stall speed by 30%. Frost formation on the wing can increase stall speed by 15%. And the rule is absolute: an aircraft must be free of all snow, frost and ice immediately before flight. Airframe contamination increases stall speed by reducing CLMAX, increasing the adverse pressure gradient, and/or reducing the kinetic energy of the boundary layer. So three mechanisms there. Now let's move to the stall recovery procedure. The summary for a single-engine propeller aircraft is due to the rolling and yawing forces generated by the propeller. It is essential to maintain balanced, co-ordinated flight, particularly at low airspeed and high angles of attack. Here's the recovery drill. In whatever configuration, attitude, or power setting a stall warning occurs, the correct pilot action is to decrease the angle of attack below the stall angle to un-stall the wing. Then apply maximum allowable power to minimize altitude loss. And prevent any yaw from developing to minimize the possibility of spinning. The phrase to remember is "keep the ball in the middle." Finally, shock stall. If a large shock wave forms on the wing, due to an inadvertent overspeed, the locally increased adverse pressure gradient will cause the boundary layer to separate immediately behind the shock wave. That separation is called shock stall. So the whole picture: stall speed is driven by weight, load factor, configuration, power, Mach, and contamination — and the recovery is always the same: reduce angle of attack, add power, keep the ball centered.