When an aircraft is flying, let V1 be the speed of air just below the wings and V2 be the speed of air just above the wing. Then

Applying Bernoulli's equation between points 1 and 2, we can write, p1+12ρv12=p2+12ρv22⇒ p1−p2=12ρv22−v12If A be the area of each wing, then total lift on the wings, L=2A×p1−p2=Aρv22−v12Air craft can fly only when L>0 i.e. V2>V1