Step-by-Step Solution & Explanation
### **Detailed Step-by-Step Solution (GATE AE 2024 Q.27)**
**1. Primary Functions of Aircraft Rudder**:
- **Adverse Yaw Compensation**: When ailerons deflect to initiate a roll, the downgoing aileron creates greater induced drag than the upgoing aileron, producing adverse yaw. The rudder is deflected to counter this yaw. $\implies$ Option (A) is TRUE.
- **One-Engine-Inoperative (OEI) Trim**: In a multi-engine aircraft, asymmetric thrust from an engine failure produces a large yawing moment toward the dead engine. The rudder is used to trim out this yaw. $\implies$ Option (B) is TRUE.
- **Crosswind Landing**: During crosswind approach and touchdown, rudder deflection aligns the aircraft centerline with the runway centerline (decrab or sideslip technique). $\implies$ Option (C) is TRUE.
- **Longitudinal Stability**: Longitudinal stability is governed strictly by the horizontal tail and elevator/c.g. location, not the rudder (which controls directional/yaw stability). $\implies$ Option (D) is FALSE.
**2. Conclusion**:
Options **A, B, and C** are correct.
**3. Official Master Key**:
- **Official Answer Key**: **A, B, C**
- **Exam Takeaway**: The rudder provides yaw control: countering adverse yaw, compensating for engine-out asymmetric thrust, and trimming sideslip in crosswind landings.