Reader Question – Can You Explain an Aerodynamic Stall?

A visitor to The FOG HORN read my Air France post and wants to understand what is meant by an aerodynamic stall.

Here we go:

When an aircraft is designed, engineers build it to meet specific requirements. If it’s a military aircraft those requirements may be speed, service ceiling (how high it can go), maneuverability, etc.

In the design and engineering process, the manufacturer documents the aircraft’s performance criteria, for example: maximum payload when fully fuel, runway length requirements for take-off and landings, cruising speed, landing weight, landing airspeed at different weights and runways, aerodynamic stall speed. The pilot knows, that at certain indicated airspeed the wing will no longer generate the lift needed to keep the aircraft in flight. A landing for example is a controlled aerodynamic stall.

When flying, the altitude is controlled by the throttle and the stick or wheel controls the attitude of the aircraft. If you want to increase altitude, you increase throttle. The increased air movement over the wing increases lift and altitude increases. Pulling up on the yoke (the wheel) changes the attitude of the aircraft by raising the nose of the aircraft above the earth’s horizon. Pushing down on the yoke lowers the nose of the aircraft with respect to the earth’s horizon.

When you change the attitude of the aircraft without a corresponding change in the throttle you will impact the indicated airspeed. Pulling up on the yoke causes the nose to rise and airspeed to drop. If airspeed drops sufficiently, the wings stall and loose lift so the aircraft falls.

Generally the greatest risk of an aerodynamic stall is on landing. Your landing gear is down, your flaps are down and your indicated airspeed is low in preparation for landing. If the pilot makes an error and changes the attitude of the aircraft the wings will loose lift and the aircraft will fall. Since you’re at 800 feet, or so depending on the airport, you don’t have sufficient time to recover from the stall. However, when flying at cruising altitude you can recover from a stall by pushing the yoke forward so that airspeed increases and the wings begin to generate lift again.

What I’ve described to you is in general terms; however, every aircraft will differ. That’s the reason that pilots get checked out on a different aircraft.

To recap, an aerodynamic stall occurs when the wings no longer generate lift do to a disruption of airflow over the wing surface. Stalls can occur for a variety of reasons but airspeed and airflow are the key variables.

I hope this helps you and thanks for visiting The FOG HORN. Come back and see us!

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