Question

Which of the following statement(s) is/are true about the ribs of an airplane wing with semi–monocoque construction?

• A. For a rectangular planform wing, the dimensions of the ribs DO NOT depend on their spanwise position in the wing.
• B. Ribs increase the column buckling stress of longitudinal stiffeners connected to them.
• C. Ribs increase plate buckling stress of the skin panels.
• D. Ribs help in maintaining aerodynamic shape of the wing.

Hint:

Ribs act as transverse frames in semi–monocoque wings: they prevent buckling, support skin/stringers, and preserve aerodynamic profile.

Answer 1

The Correct Option is B, C, D

Step 1: Structural role of ribs.
In semi–monocoque construction, the load–carrying structure consists of skin, stringers, spars, and ribs. - Spars carry primary bending. - Stringers carry axial stresses and resist column buckling. - Ribs are transverse frames: they shape the airfoil, support the skin, and tie the stringers/spars.

Step 2: Assess each statement.
(A) Incorrect: Even in a rectangular planform, ribs at root and tip may differ (thickness, cutouts, taper for systems). So rib dimensions do depend on spanwise position.
(B) True: By tying longitudinal stiffeners (stringers), ribs shorten their effective column length, raising their critical buckling stress.
(C) True: Ribs subdivide skin panels into smaller effective spans, thereby raising skin plate buckling stress.
(D) True: Ribs enforce the wing's aerodynamic contour (airfoil shape), preventing distortion under load.

Final Answer:
\[ \boxed{(B),\ (C),\ (D)} \]