In calculating the lift force,
- AAlways the frontal area is used
- BAlways the planform area is used
- CPlanform area is used if the body is a lifting surfaceCorrect
- DActual surface area of the body is used
Solution
Concept
Reference area for lift
Formula
FL = CL ½ρV²A
Step-by-step solution
1. For lifting surfaces (wings) the planform area is used.
Explanation
Frontal area is for bluff bodies.
Why the other options are wrong
Always-frontal and always-planform are wrong.
Shortcut
Lift: planform.
Correct answer: C) Planform area is used if the body is a lifting surface