Question

A subsonic aircraft has unswept wing which has maximum lift coefficient of 1.4. Now, consider wing is provided sweep of 25° at quarter chord point. Now, determine the change in maximum lift coefficient due to the provision of sweep.

(a) Maximum Lift coefficient will be reduced by 0.2580 amount

(b) Increment by 1.245

(c) Decreases by 0.0476 amount

(d) Maximum lift coefficient will increase by 56%

I had been asked this question in class test.

The doubt is from Aerodynamics topic in section Aerodynamics of Aircraft Design

Answer 1

Right answer is (a) Maximum Lift coefficient will be reduced by 0.2580 amount

Easy explanation: Given, unswept maximum lift coefficient CL1 = 1.4

Now, sweep of 25° is provided at quarter chord point. Hence sweep angle at quarter chord s = 25°

Maximum lift coefficient CL2 = CL1*0.9*cos (a)

= 1.4*0.9*cos (25°) = 1.1419.

Now, change in maximum lift coefficient = CL2 – CL1 = 1.1419 – 1.4 = -0.2580.

Hence, by implementing the sweep of 25° maximum lift coefficient is reduced by 0.2508 unit.