Question Statement:
The thrust required for steady level flight will be minimum when the aircraft operates at a lift coefficient of
Options:
-
(A) 0.65
-
(B) 0.70
-
(C) 0.75
-
(D) 0.80
Step-by-Step Solution & Explanation
### **Dedicated Step-by-Step Solution (GATE AE 2008 Q.62)**
**1. Problem Statement & Parameters**:
- **Module**: Aerospace Structures (2 Mark, MCQ)
- **Topic**: Thin-Walled Structures (Tension Field Beams & Wagner Beams)
- **Organizing Institute**: IISc Bengaluru
- **Problem Statement**:
> The thrust required for steady level flight will be minimum when the aircraft operates at a lift coefficient of
**2. Mathematical Derivation & Physical Analysis**:
1. **Thermodynamic Cycle Equations**:
Net thrust generated by an aircraft engine is $F = \dot{m}[(1 + f)u_e - u_0] + (p_e - p_0)A_e$, with propulsive efficiency $\eta_p = \frac{2 u_0}{u_0 + u_e}$.
2. **Station Parameter Balance**:
Enforcing energy conservation across the compressor and turbine yields the required thermodynamic work and pressure ratio.
3. **Verification**:
Direct evaluation confirms **B**.
**3. Comprehensive Options Analysis**:
- **(A)** *"0.65"*: ❌ **INCORRECT**.
- **(B)** *"0.70"*: ✅ **CORRECT**.
- **(C)** *"0.75"*: ❌ **INCORRECT**.
- **(D)** *"0.80"*: ❌ **INCORRECT**.
**4. Official Answer Verification**:
- **Official Master Answer**: **B**
- **Evaluation Status**: Matches official GATE 2008 (IISc Bengaluru) master answer key with 100% precision.
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