When a helicopter loses engine power, it doesn't simply fall out of the sky. Instead, it enters a state called autorotation mode, which allows it to descend in a controlled manner. This is a critical safety feature inherent in helicopter design.
Understanding Autorotation
Here's a breakdown of what happens during autorotation:
- Loss of Power: When the engine fails, the helicopter's rotor blades are no longer being driven by the engine.
- Airflow Upwards: Instead of the engine driving the rotor, the airflow now travels upwards through the rotor disc, which causes the blades to spin.
- Controlled Descent: This upward airflow is what maintains the rotor's rotation, providing lift and allowing the pilot to control the descent rate and direction.
- Gyroscopic Effect: The blades continue to spin, similar to how a gyroplane operates (also known as an autogyro), providing lift.
Comparison with a Fixed-Wing Aircraft
Unlike a fixed-wing airplane that glides, a helicopter in autorotation uses the spinning rotor as a kind of wing to generate lift, albeit in a downward direction.
Key Aspects of Autorotation
| Aspect | Description |
|---|---|
| Rotor Direction | Rotates from bottom to top with upward airflow through the disc |
| Lift Source | Airflow moving upward through the rotor disk instead of downward airflow from the engine |
| Control | The pilot maintains control by adjusting the collective and cyclic controls |
| Landing | The final stage of the autorotation involves flaring to cushion the landing |
Practical Steps in Autorotation
- Immediate Response: The pilot immediately lowers the collective pitch and maintains airspeed.
- Maintaining Rotor RPM: The pilot ensures the rotor RPM stays within the optimal range.
- Controlled Descent: The helicopter descends at a controlled rate.
- Flaring: At the end of the descent, the pilot increases the blade pitch (flares) just before landing, using the stored rotational energy of the rotor to slow down the descent and soften the landing.
Examples and Insights
- Training: Pilots receive extensive training in autorotation techniques to handle engine failures effectively.
- Safety Feature: Autorotation is a standard safety mechanism in virtually all helicopters.
- Not a Glide: Helicopters do not glide in the same way a fixed-wing airplane does.
Conclusion
In summary, losing an engine in a helicopter leads to the helicopter entering autorotation mode, which is a controlled descent relying on the upward airflow through the rotor to maintain lift and control until landing.
