Buttock-planes are used to _______

A)
evaluate the smoothness of A/C fuselage
B)
evaluate Lift
C)
find lift curve
D)
find lift curve slope

Correct Answer :   evaluate the smoothness of A/C fuselage


Explanation : Buttock planes or butt planes are vertically oriented cuts which can be used to find smoothness of the A/C fuselage. Lift curve slope is found by using lift and AOA. Lift can be estimated by measuring pressure difference between upper and lower surface.