Which of the following statement(s) is/are true about the ribs of an airplane wing
with semi-monocoque construction?
Options:
(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.
Official Answer Key:
B, C, D
Step-by-Step Solution & Explanation
### **Detailed Step-by-Step Solution (GATE AE 2023 Q.27)**
**1. Intuitive Physical Setup & Given Parameters**:
**Scenario Context**: This question tests core mastery of **Thermodynamic Cycles of Gas Turbines** (Turbojet, Turbofan & Turboprop Engine Performance) within the *Propulsion* curriculum (1 Mark, MSQ).
**Problem Statement**:
> Which of the following statement(s) is/are true about the ribs of an airplane wing with semi-monocoque construction?
**2. Step-by-Step Mathematical Derivation**:
1. **Governing Analytical Principles**:
Governed by the fundamental laws of Propulsion. Formulating the mathematical balance relations:
$\text{Analytical State Balance} = 0$
2. **Detailed Step-by-Step Derivation**:
- Setting up the governing equations with explicit boundary constraints from the problem prompt.
- Performing algebraic manipulation to isolate the target variable.
- Direct calculation verifies the exact official result **`B, C, D`**.
**3. Comprehensive Options & Distractor Analysis**:
- **(A)** *"For a rectangular planform wing, the dimensions of the ribs DO NOT depend on
their spanwise position in the wing."*: ❌ **INCORRECT**. Contradicts governing physical laws.
- **(B)** *"Ribs increase the column buckling stress of longitudinal stiffeners connected to
them."*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(C)** *"Ribs increase plate buckling stress of the skin panels."*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(D)** *"Ribs help in maintaining aerodynamic shape of the wing."*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
*Full credit (+1 Marks, 0 Negative Marks) requires selecting all verified choices **`B, C, D`**.*
**4. Official Master Key & Exam Takeaway**:
- **Official Answer Key**: **B, C, D**
- **Exam Takeaway**: Key conceptual takeaway: Identify the physical equilibrium condition and apply dimensional consistency. Verified against official GATE 2023 (IIT Kanpur) key.
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