For unpowered steady gliding flight of an aircraft in still air, the minimum glide angle $\gamma_{min}$ (steepness of descent) depends strictly on:

(A) The maximum lift-to-drag ratio $(L/D)_{max}$ exclusively, and is independent of aircraft weight

(B) Aircraft wing loading $W/S$ only

(C) Aircraft weight directly, such that a heavier aircraft always glides at a steeper glide angle

(D) Ambient air density $\rho$ exclusively

Answer Key:

A

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Equilibrium Equations along and perpendicular to flight path:** * $L = W \cos\gamma$, $D = W \sin\gamma$. 2. **Stage 2: Glide Angle Formulation:** * Dividing drag by lift: $\frac{D}{L} = \frac{W \sin\gamma}{W \cos\gamma} = \tan\gamma$. * Therefore $\tan\gamma = \frac{1}{L/D}$. 3. **Stage 3: Minimum Glide Angle:** $\tan\gamma_{min} = \frac{1}{(L/D)_{max}}$. 4. **Stage 4: Weight Invariance:** Weight $W$ determines the airspeed along the glide path ($V_{glide} \propto \sqrt{W}$), but NOT the glide angle $\gamma$ or the maximum horizontal distance covered. 5. **Stage 5: Official Reference:** John D. Anderson Jr., *Introduction to Flight*, Section 6.11.

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