Rotorcraft Operations

Rotorcraft Operations

Overview of the Helicopters

A helicopter rises by the same principle by which an aircraft takes off: The movement of an airfoil or airfoil through the air. The wing of an airplane is an airfoil moving through the air with a forward movement. The blade of helicopter rotor airfoils also moves through the air with a circular motion without requiring any movement or displacement of the aircraft. As the air passes through an airfoil, a pressure differential occurs. The pressure on the upper surface is lower than the pressure at the bottom. This results in the lift force. When the lift is greater than the weight of the helicopter, it starts to fly. The main rotor of a helicopter is controlled by the stick "cyclical" which is usually located between the pilot's legs. By using the cyclic, the pilot can tilt the rotor through 360 degrees, i.e. in the direction person want to fly the helicopter. Tilting the main rotor, part of the lift force of the rotor disc becomes feed force (traction), which allows the helicopter to move in the desired direction.

As the rotor disk is more inclined, and power is increased, the displacement also increases and the helicopter is moving faster in that direction. Moving slowly cycling back, the velocity decreases, and if a person focuses to balance the pilot can plan on a particular point. Moving further back on the cyclic, the helicopter flies backward. Helicopter movements also involve other controls. The "collective", located to the left of the pilot, collectively increasing or decreasing the angle of the main rotor blades. Collective movement upward or downward also increases or decreases the power of the engine. The tail rotor is used to counteract the force (torque) required to rotate the main rotor and prevent the helicopter to rotate in the opposite direction to the main rotor. To accomplish this, the pilot presses the pedal right or left as the power increases or decreases. In turn, this causes the tail rotor to produce more or less lift according to what is required for directional control. The tail rotor also allows the pilot turned the helicopter while hovering done. Some manufacturers install two main rotors on the helicopter either in tandem or coaxial configuration. Two in helicopter main rotors spin in opposite directions; each counterbalancing the force (torque) required rotating the other. This eliminates the need for a tail rotor. Transnational movements of the helicopter are achieved by coordinated movements of the two rotor systems, through mechanical or hydraulic gear. Another method of directional control without tail rotor is achieved by means of what is known as the Coanda effect. A fan located at the end of the helicopter sends air through the tail section outwardly through slots or vents at the side of the tail. This produces an air stream at a higher speed side of the tail. This method gives excellent steering control without taking moving parts outside the helicopter.

Safety of Helicopters

The helicopters have evolved rapidly since ...