CL and the Stall

CL and the Stall

You will recall from our earlier lesson on the lift formula & the coefficient of lift (CL) that the CL will increase as angle of attack increases, up to the point of the Maximum Coefficient of Lift (CLMAX). The CLMAX occurs at the critical angle of attack – beyond this point the CL (and the total lift created) sharply decreases because the wing has stalled.

Extending the flaps or slats changes the shape of the aerofoil and so the coefficient of lift is changed. The diagrams below show how the CL graph changes when flaps or slats are extended.

Flaps and the Stall

Extending flaps causes:

An increase in the maximum coefficient of lift (CLMAX)
A decrease in the critical angle of attack

This means that when the flaps are extended the wing will create more lift at any given angle of attack, but the stall will occur at a lower angle of attack.

Slats and the Stall

Extending slats causes:

An increase in the maximum coefficient of lift (CLMAX)
An increase in the critical angle of attack

This means that when the slats are extended the wing will continue to create more lift as angle of attack increases, up to a higher CLMAX and higher critical angle of attack.

Trailing edge flaps, when extended, will give a reduced stalling angle of attack

A slat will delay the stall to a higher angle of attack