Here,
v1 = 70 ms-1
v2 = 63ms-1
ρ = 1.3 kg m-3
and A = 2.5 m2
Now, using Bernoulli's theorem (for constant height)
p1 + 1/2 ρv12 = P2 + 1/2 ρv22
⇒ P2 - P1 = 1/2 ρ(v12 = v22)
= 1/2 x 1.3 x |(70)2 - (63)2|
= 605.15 Nm-2
Lift on the wings is,
F = (P2 - P2) x A = 605.15 x 2.5
= 1.51 x 103 N