When the wing root enters the stall before the wing tip, the pilot is able to utilize the
aileron to control the aircraft, since the fair low at the outboard section has not yet been
stalled. This provision improves the safety of the aircraft on the advent of wing stall.
The significance of the elliptical lift distribution has been described in Section 0.0. The
major drawback in twist is the loss of lift, since the twist is usually negative. As the angle
of attack of a wing section is decreased, the lift coefficient will be decreased too. The
criterion and the limit for the wing twist are that the twist angle must not be so high that
it results in a negative lift in the outer wing portions. Since any section has a zero-lift
angle of attack (αo), the criterion is formulated as follows: