What is Stall and how is it dangerous?
When we hear the term “Stall”, the first thing which comes into our mind is “ to stop / delay something “. But, when it comes to aerodynamics, it’s not just the literal meaning that we need to be concerned about. The concept of “Stall” and it’s recovery is important to understand theoretically and practically for the safety of the aircraft.
What is Stall?
A stall is an aerodynamic condition which occurs when smooth airflow over the airplane’s wings is disrupted, resulting in loss of lift and increase in drag which causes loss of height and control of the aircraft.
Three main reasons for Stall
- A stall is caused by airflow separation
- Separation of the airflow occurs when there is insufficient kinetic energy to produce lift
- Adverse pressure gradient
A stall occurs when the angle of attack of an aerofoil exceeds the value at which it creates maximum lift. Beyond this angle of attack, the aircraft would stop producing lift since the airflow around the aerofoil starts to become turbulent and separate. The angle of attack at which this occurs is known as the “ STALLING ANGLE”.
This value varies and depends upon the cross section of the aerofoil.
What are the various indications of Stall?
- One of the first indications of stall is a nose down pitch due to loss of lift, which can be readily arrested.
- Flight controls start to become unresponsive.
- Stall warning comes 5kts OR 5% above the stall speed, giving an advance indication to recover the aircraft in the form of aural and visual warning in the cockpit.
- A stall warning device known as a “stick shaker“ is also installed. This device is designed to rapidly and noisily vibrate the control yoke (the “stick”) of an aircraft, warning the flight crew that an imminent aerodynamic stall has been detected.
How to recover from Stall?
- To recover from stall the angle of attack must be reduced
- Maximum power must be applied to minimise the height loss
- Rudders or ailerons can be used to prevent wing drop and keep wing level
Want to know more about the factors affecting Stall? Stay tuned with Tech Talks every Tuesday to find out more!
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