Introduction to Helicopters

             A helicopter can be defined as any flying machine using rotating wings (i.e., rotors) to provide lift, propulsion, and control forces that enable the aircraft to hover relative to the ground without forward flight speed to generate these forces. The thrust on the rotors is generated by the aerodynamic lift forces created on the spinning blades. To turn the rotor, power from an engine must be transmitted to the rotor shaft. It is the relatively low-amount of power required to lift the machine compared to other vertical take off and landing (VTOL) aircraft that makes the helicopter unique. Efficient hovering flight with low power requirements comes about by accelerating a large mass of air at a relatively low velocity: hence we have the large diameter rotors that are one obvious characteristic of helicopters. In addition, the helicopter must be able to fly forward, climb, cruise at speed, and then descend and come back into a hover for landing. This demanding flight capability comes at a price, including mechanical and aerodynamic complexity and higher power requirements than for a fixed-wing aircraft of the same gross weight. All of these factors influence the design, acquisition, and operational costs of the helicopter
       Besides generating all of the vertical lift, the rotor is also the primary source of control and propulsion for the helicopter, where as these functions arc separated on a fixed-wing aircraft. For forward flight, the rotor disk plane must be tilted so that the rotor thrust vector is inclined forward to provide a propulsive component to overcome rotor and airframe drag. The orientation of the rotor disk to the flow also provides the forces and moments to control the attitude and position of the aircraft .The pilot controls the magnitude and direction of the rotor thrust vector by changing the blade pitch angles (using collective and cyclic pitch inputs), which changes the blade lift and the distribution of thrust over the rotor disk. By incorporating articulation into the rotor design through the use of mechanical flapping and lead/lag hinges that are situated near the root of each blade, the rotor disk can be tilted in any direction in response to these blade pitch inputs. As the helicopter begins to move into forward flight, the blades on the side of the rotor disk that advance into the relative wind will experience a higher dynamic pressure and lilt than the blades on the retreating side of the disk, and so asymmetric aerodynamic forces and moments will be produced on the rotor. Articulation helps allow the blades to naturally flap and lag so as to help balance out these asymmetric aerodynamic effects. However, the mechanical complexity of the rotor hub required allowing for articulation and pitch control leads to high design and maintenance costs. With the inherently asymmetric flow environment and the flapping and pitching blades, the aerodynamics of the rotor become relatively complicated and lead to unsteady forces. These forces are transmitted from the rotor to the airframe and can be a source of vibrations, resulting in not only crew and passenger discomfort, but also considerably reduced airframe component lives and higher maintenance costs. However, with a thorough knowledge of the aerodynamics and careful design, all these adverse factors can be minimized or overcome to produce a highly reliable and versatile aircraft.

Helicopters come in many sizes and shapes, but most share the same major components. This component include a cabin where the payload and crew are carried; an airframe, which houses the various components, or where components are attached; a power plant or transmission, which, among other engine; and things, takes the power from the engine and transmits it to the main rotor, which provides the aerodynamic forces that make the helicopter fly. Then, to keep the helicopter from turning due to torque, there must be some type of ant torque system. Finally there is the landing gear, which could be skids, wheels, skis, or floats. 

The major components of a helicopter are the Cabin, airframe, landing gear, power plant, transmission, main Rotor system and tail rotor system.