Subtopic: Control Surfaces (Elevator, Aileron, Rudder)
Question Statement:
A pilot was flying a single engine propeller aircraft and maintained steady level flight at trim. Due to torque reaction and slipstream rotation from a clockwise rotating propeller (viewed from the cockpit), the airplane tends to naturally:
Options:
(A) Roll right and yaw right
(B) Roll left and yaw left
(C) Roll right and yaw left
(D) Roll left and yaw right
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Detailed Step-by-Step Solution (GATE AE 2017 Q.39)**
**1. Intuitive Physical Setup & Given Parameters**:
- Propeller rotates clockwise as viewed from the pilot's cockpit.
**2. Step-by-Step Physical Derivation**:
1. **Torque Reaction (Newton's Third Law)**:
- The engine exerts clockwise torque to spin the propeller.
- By reaction, the propeller exerts an equal and opposite counter-clockwise (left-rolling) torque on the aircraft fuselage.
- Therefore, the torque reaction causes the aircraft to **roll left**.
2. **Spiraling Slipstream & Asymmetric Blade Effect (P-Factor)**:
- The propeller wash rotates in a clockwise spiral around the fuselage.
- When this rotating corkscrew airflow reaches the vertical tail (fin), it strikes the left surface of the fin.
- This aerodynamic side-force on the fin pushes the tail to the right, which swings the nose to the **left (yaw left)**.
- Thus, the airplane naturally rolls left and yaws left.
**3. Comprehensive Options & Distractor Analysis**:
- **(A)** (roll right, yaw right): ❌ Incorrect. Opposite to Newton's 3rd law and slipstream physics.
- **(B)** (roll left and yaw left): ✅ **CORRECT**. Directly produced by counter-clockwise reaction torque and left-side fin impingement.
- **(C)** (roll right, yaw left): ❌ Incorrect roll direction.
- **(D)** (roll left, yaw right): ❌ Incorrect yaw direction.
**4. Official Master Key & Exam Takeaway**:
- **Official Answer**: **B**
- **Exam Rule**: For standard clockwise propeller (from cockpit): Left rolling tendency + Left yawing tendency.