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You've probably been told to be careful when using ailerons in an imminent stall - they can cause a wing to drop instead of rise. But why does that happen?
It comes down to each wing's angle of attack - lowering an aileron to raise the wing can actually push the wingtip over the critical angle of attack, stalling the wing and causing it to drop abruptly.
When engineers developed your aircraft, they designed the wing to stall at the root first (closest to the fuselage). As the stall deepens, it moves out towards the wingtips.
So, as your aircraft begins to stall, the entire wing is not stalled - only the root is. However, the rest of the wing is very close to the critical angle of attack and is about to stall.
If a wing starts to drop and you lower the aileron on that wing to raise it, you increase the wing's angle of attack. You can quickly push the wing over the critical angle of attack - stalling and dropping the wing.
So, what should you do when a wing drops during a stall? First - keep the aircraft coordinated. If a wing starts to drop, you're probably uncoordinated - centering the ball with rudder will help stabilize the airplane.
Second - start your stall recovery. Lowering the nose and adding power restores airflow over the wing and reduces the angle of attack. You'll break the stall and the wing will start flying again - which means your ailerons become effective.
You may notice that your ailerons are more effective during a power-off stall than during a power-on stall. Remember, stalls start at the root - so your ailerons still have some effect at early stages of a stall.
However, in a power-on stall, the propellor is pushing some air over the root, delaying its stall. In a power-on stall, the wing may stall all at once, or the stall will move very quickly from the root to the wingtip. In this case, your wingtips are very close to the critical angle of attack as the root starts to stall - so any downward aileron deflection can push them over the critical angle of attack and into a stall.
Next time you're practicing stalls, keep a close eye on your coordination. By keeping the ball centered, you'll only need small aileron corrections and you'll prevent your aileron from stalling your wingtip.
Aleks is a Boldmethod co-founder and technical director. He's worked in safety and operations in the airline industry, and was a flight instructor and course manager for the University of North Dakota. You can reach him at firstname.lastname@example.org.