Aeroelastic classical flutter of an aircraft wing is best described as:

(A) A dynamic aeroelastic instability involving coupled bending and torsional oscillations with energy extraction from the airstream

(B) A static divergence occurring when aerodynamic pitching moment exceeds torsional restoring stiffness

(C) A high-frequency resonance caused strictly by jet engine acoustic vibrations

(D) A control surface reversal where ailerons produce rolling moments in the opposite direction

Answer Key:

A

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Definition:** Classical flutter is a self-excited dynamic aeroelastic phenomenon. 2. **Stage 2: Mechanism:** Phasing between bending deflection and torsional twist causes the wing to absorb net positive energy from the freestream flow over an oscillatory cycle. 3. **Stage 3: Distractor Elimination:** Option B describes static divergence; Option D describes control reversal; Option C describes acoustic fatigue. 4. **Stage 4: Selection:** Option A is correct.

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