QB_AE_STRUC_NEW_030
Section Question Bank
MSQ · 2 Marks
Aerospace Structures • Aeroelasticity - Wing Sweep Effect on Torsional Divergence
Which of the following statements regarding static aeroelastic divergence and dynamic aeroelastic flutter of aircraft wings are **CORRECT**?
(A) Forward wing sweep significantly reduces the torsional divergence speed, making forward-swept wings highly susceptible to static aeroelastic divergence
(B) Aft wing sweep introduces aeroelastic bending-torsion wash-out (wing upward bending reduces local angle of attack), effectively eliminating static torsional divergence
(C) Flexure-torsion flutter is a dynamic aeroelastic instability characterized by self-excited, unstable oscillations coupling wing bending and wing torsion
(D) Locating the wing center of gravity ahead of the elastic axis (shear center) decreases the flutter speed
Answer Key:
Verified in official key
Step-by-Step Verified Solution
### 1. Strategy & Theoretical Principles 1. **Forward Sweep & Divergence:** - On a forward-swept wing, upward bending deformation twists the wing leading edge upward (wash-in), increasing the aerodynamic angle of attack. - This positive aeroelastic feedback severely reduces the divergence speed $q_D$, making forward-swept wings vulnerable to divergence (requiring aeroelastic tailoring with composite plies). 2. **Aft Sweep & Wash-out:** - On an aft-swept wing, upward bending deflects the wing tip downward relative to the oncoming stream (wash-out), reducing the local angle of attack. - This negative feedback completely cures static torsional divergence. 3. **Flutter Mechanics:** - Classical flutter is a dynamic two-degree-of-freedom instability where aerodynamic forces extract energy from the airstream through phase differences between plunge (bending) and pitch (torsion). - Moving the wing center of gravity **forward** of the elastic axis acts as mass balance, coupling bending into stabilizing nose-down pitch inertia, which *increases* (improves) the flutter speed. ### 2. Statement Evaluation - **Statements A, B, C:** **CORRECT.** - **Statement D:** **INCORRECT.** Moving CG forward *increases* (delays) flutter speed; mass-balancing a control surface or wing forward prevents flutter. ### 3. Exam Trap & Standard Reference - **Trap Alert:** Forward CG relative to elastic axis *stabilizes* against flutter (higher flutter speed). - **Standard Reference:** Hodges, D.H. & Pierce, G.A., *Introduction to Structural Dynamics and Aeroelasticity*, Cambridge University Press.