1. Lift Reduction: To slow down, helicopter pilots reduce the lift generated by the rotor blades. This can be done by decreasing the collective pitch angle of the blades, which reduces the amount of air pushing down on the helicopter. As the lift decreases, the helicopter starts to descend and slows down.
2. Anti-Torque Rotor: To counteract the rotational force generated by the main rotor, helicopters have a smaller anti-torque rotor (tail rotor) at the rear. Adjusting the pitch angle of the tail rotor blades can provide additional slowing power by increasing drag and counteracting the main rotor's thrust.
3. Autorotation: In case of engine failure, helicopters can enter a state called autorotation. During autorotation, the main rotor continues to spin freely without power from the engine. The helicopter descends in a controlled manner, and the forward air movement keeps the rotor spinning. By carefully managing the descent rate and adjusting the collective pitch, the pilot can control the helicopter's speed and eventually land safely.
4. Directional Control: Helicopters use their flight control systems, including cyclic and collective controls, to precisely direct the airflow over the rotor blades and change the direction of thrust. This allows the helicopter to slow down, hover, and maneuver at low speeds.
5. Ground Effect: When close to the ground, the air under the helicopter is compressed and creates an area of higher pressure. This phenomenon, known as the ground effect, can act as a natural decelerating force due to increased drag and reduced lift. Pilots can use the ground effect to slow down the helicopter during landing.
In summary, helicopters use various techniques involving lift reduction, anti-torque rotor control, autorotation, and precise flight control to manage speed and come to a stop. These methods allow helicopters to perform controlled descents, hover, and land safely without the use of traditional brakes found on ground vehicles.
