HELICOPTER By Vinod Kumar K

Working Principle Helicopter What is a Helicopter?  A helicopter is an aircraft that lifted and driven by one or more rotors (propeller) large horizontal. Working Principle Helicopter Helicopters can fly because of lift generated by air flow generated by the blades of its rotor blades. Propeller was a stream of air flow from top to bottom. Air flow is so heavy so it can lift objects weighing dozens of tons. His theory is simple but practically complex.

Special Capabilities of Helicopters A helicopter can fly backwards. The entire aircraft can rotate in the air. A helicopter can hover motionless in the air.

Exploded View

Basic Parts of a Helicopter Fuselage -- The main body of the helicopter is known as the fuselage. A frameless plastic canopy surrounds the pilot and connects in the rear to a flush-riveted aluminium frame.

Basic Parts of a Helicopter Main rotor blade -- The main rotor blade performs the same function as an airplane's wings, providing lift as the blades rotate -- lift being one of the critical aerodynamic forces that keeps aircraft aloft. Stabilizer -- The stabilizer bar sits above and across the main rotor blade. Its weight and rotation dampen unwanted vibrations in the main rotor, helping to stabilize the craft in all flight conditions. Rotor mast -- Also known as the rotor shaft, the mast connects the transmission to the rotor assembly. The mast rotates the upper swash plate and the blades.

Basic Parts of a Helicopter Transmission -- a helicopter's transmission transmits power from the engine to the main and tail rotors. The transmission's main gearbox steps down the speed of the main rotor so it doesn't rotate as rapidly as the engine shaft. A second gearbox does the same for the tail rotor, it is much smaller, can rotate faster than the main rotor. Engine -- The engine generates power for the aircraft. Early helicopters relied on reciprocating gasoline engines, but modern helicopters use gas turbine engines

Basic Parts of a Helicopter Tail boom -- The tail boom extends out from the rear of the fuselage and holds the tail rotor assemblies. Anti-torque tail rotor -- Without a tail rotor, the main rotor of a helicopter simply spins the fuselage in the opposite direction. In twin-rotor helicopters, the torque produced by the rotation of the front rotor is offset by the torque produced by a counter rotating rear rotor. Landing skids -- Some helicopters have wheels, but most have skids, which are hollow tubes with no wheels or brakes.

The Rotor Assembly It provides the lift that allows the helicopter to fly, as well as the control that allows the helicopter to move laterally, make turns and change altitude. The pilot communicates these adjustments through a device known as the swash plate assembly.

Swash Plate assembly The swash plate assembly consists of two parts -- the upper and lower swash plates. The upper swash plate connects to the rotor mast, through special linkages. The engine turns the rotor shaft, it also turns the upper swash plate and the rotor blade system. Control rods from the upper swash plate have a connection point on the blades, making it possible to transfer movements of the upper swash plate to the blades through blade grips, which connect the blades to hub. The hub mounts to the mast via the Jesus nut, so named because its failure is said to bring a pilot face-to-face with Jesus.

Working the Controls Collective-pitch lever -- The collective-pitch lever is responsible for up-and-down movements. The collective control changes the angle of attack on both blades simultaneously.

Working the Controls A helicopter pilot controls the pitch, or angle, of the rotor blades with two inputs: Cyclic & Collective pitch levers. Cyclic-pitch lever -- The cyclic, or "stick," comes out of the floor of the cockpit and sits between the pilot's legs, enabling a person to tilt the craft to either side or forward and backward.

Working the Controls Foot pedals -- A pair of foot pedals controls the tail rotor. Working the pedals affects which way the helicopter points, so pushing the right pedal deflects the tail of the helicopter to the left and the nose to the right; the left pedal turns the nose to the left .

How Helicopters Fly A rotary motion is the easiest way to keep a wing continuously moving with the help of engine. If you give the main rotor wings a slight angle of attack on the shaft and spin the shaft, the wings start to develop lift. The moment helicopter leaves the ground, it starts spin in an opposite direction to the main rotor. The tail rotor produces thrust in a sideways direction, this critical part counteracts the engine's desire to spin the body.

How Helicopters Fly The collective control changes the angle of attack on both blades simultaneously: The cyclic control tilts the swash plate assembly so that the angle of attack on one side of the helicopter is greater than it is on the other

Controlling Vibrations Helicopter fuselage vibration is generated by the main rotor and the rotor blades during blade-pass. Aerodynamic loads, acting on the blades, transmit vibrations to the main rotor hub. Controlling vibration at its source - the blades and fuselage - will prevent it from creating structure pulsations, thus protecting occupants, the helicopter structure, and equipment. Technologies for helicopter vibration control: Passive control system Active control system

Passive control system Only systems have been effectively used to control vibration for decades. New and emerging rotorcraft designs that expand the performance envelope demand a new approach as passive technologies begin to display dis-advantages that outweigh their many benefits. Eg, passive technologies are designed to operate in a very narrow range of flight conditions. Passive systems do not successfully control vibration in aircraft with variable rotor speeds.

Active Vibration Control System •    Reduced Weight – Eliminates heavy, passive-vibration absorbers, •    Improved Performance – Enables expanded flight envelope within aircraft design limits and extended range, •    Improved Comfort – Reduces occupant vibration levels in the cockpit and cabin, and •    Reduced Direct Maintenance Cost – Lowered aircraft vibration levels result in less vibration-induced fatigue of structures and equipment. AVCS advances by a company name LORD Corporation, a supplier of vibration, noise and motion control solutions.

Cargo Helicopters Tandem rotor helicopters have two large horizontal rotor assemblies mounted one in front of the other and use counter-rotating rotors, with each cancelling out the other's torque. Therefore all of the power from the engines can be used for lift.

Controls of Cargo Helicopters Tandem rotor designs achieve yaw by applying opposite left and right cyclic to each rotor, effectively pulling both ends of the helicopter in opposite directions. To achieve pitch, opposite collective is applied to each rotor; decreasing the lift produced at one end, while increasing lift at the opposite end, effectively tilting the helicopter forward or back. Advantages are a larger centre-of-gravity range, good longitudinal stability, able to hold more weight with shorter blades. Disadvantages are a complex transmission, and need for two large rotors.

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