CFI Topics

Wing Loading and Accelerated Stall

Lesson 6

Now consider the accelerated stall when the aircraft is no longer in a 1G state, as in a 60 degree bank (a 2G mode). The wing-loading increases by 1.41 times normal, increasing the stall speed (stall speed equals the square root of the load × normal 1G stall speed, e.g. square root of 2 = 1.41 × Vs1). Most stall spin accidents occur during a landing approach when a turn from base to final goes wide and is “ruddered” around. A stall in a cross-controlled condition can result in a spin close to the ground. The pilot at a slow airspeed might compensate by excessively pushing the rudder and banking in the opposite direction. If the nose is allowed to drift upward, increasing the AOA, that increases the stall speed, which decreases the vertical component of lift and an accident becomes imminent. Circling-to-Land in IFR conditions can create similar problems at low altitudes making recovery difficult if not impossible. Of course if the wing remains unloaded and the aircraft is in a pitch-down attitude and allowed to “sink” (if you have lots of altitude to spare) the margins are not reduced and the stall speed is not increased, therefore an accelerated stall is prevented. Based on the formula above the stall speed to bank angle is 7% at 30 degrees, 19% at 45 degrees and 41% at 60 degrees (A 175% increase in stall speed between 30 to 45 degrees and a 120% between 45 and 60 degrees).  This is why ‘certificated aircraft in normal category’ are limited to a 60-degree bank angle. It is important to maintain gentle bank angles and safe airspeeds at low altitudes.

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