In our last article we had discussed about the basic phenomena of stall, the indications and the recovery actions. Please visit the previous article in our Tech Talks section if you want to review the basics of stall.
To expand our knowledge further about stall, let us discuss the factors affecting it.
Factors Affecting Stall:
- Thickness – Chord ratio of the Aerofoil:
- An aerofoil with a small leading edge radius (pointed leading edge) would stall at a smaller angle of attack. In this case, the stall would be more sudden.
- Whereas, for an aerofoil with a large thickness-chord ratio, the aircraft would stall at a higher angle of attack and the stall would be more gentle (since thickness of the aerofoil adds to the camber and helps in the production of adequate lift).
- Shape of the Wing:
- Rectangular Wing: This type of wing tends to stall at the root, making all the flight controls available for a longer period of time , delaying the onset of stall.
- Tapered Wing: All the tapered wings have less surface area towards the tip causing less vortices being formed on the wing tips, therefore the wing tips aren’t able to stay energised for a longer period of time. At last making the aircraft stall at the tips first, which results in loss of flight controls
Hence, to resolve this problem of the tapered wings, some devices are installed on the wings to promote root stall , delaying the onset of stall.
Modifications done to the tapered wing:
- VORTEX GENERATORS: They regenerate the boundary layer by mixing free stream flow into turbulent airflow.
- SLATS AND SLOTS: They allow high pressure air to leak towards low pressure area, thus re- energising the boundary layer.
- STALL STRIP: It is located at the leading edge near the wing root, and prevents separation of airflow at high angles of attack.