helicopters: how do they fly? how does it works ?
Helicopters: How Do They Fly? How Does It Works ?
Helicopters fly using the same aerodynamic concepts that airplanes use; they use an airfoil to generate lift. The difference is that helicopters generate vertical thrust while aircraft generate horizontal thrust. When an airplane moves forward, the air flows across the wing and produces downwash which creates lift; the airplane has to gain enough speed for this force to overcome weight. When helicopter blades, or airfoils, begin spinning, it produces downwash which then creates lift. Speed is an important factor in generating enough force to overcome the weight in a helicopter as well. Vertical thrust allows a helicopter to take off vertically and hover.
Most helicopters use gas turbine engines over piston engines (reciprocating engines), but most modern helicopters use turboshaft engines. Turboshaft engines differ from turbojet engines in that they do not utilize exhaust to create thrust. Their main function is to generate shaft power which is used to run the rotor. Shaft power is transferred from the turbine blades. High pressure gas created in the combustion chamber is the force that rotates the turbine blades.
The upper swashplate and the rotor blade system is attached to the rotor shaft, or mast, and they all begin rotating at the same time. A helicopter is controlled by the pilot with a collective, cyclic, two pedals, and the throttle. The collective is used to control the swashplate, which adjusts the blade pitch equally. A swashplate has two plates: one rotates with the rotor and one is fixed. A bearing is between the two plates. The upper plate is connected to the blades with a pitch change arm. The lower plate is connected to hydraulic servos which can raise, lower, or tilt the plate. Once this occurs, the pitch of the blades shift.
The collective control in the cockpit raises and lowers the swashplate and the cyclic control tilts the swashplate. These changes allow the pilot to steer the helicopter. Another rotor is added to a helicopter to counteract torque. This may be a coaxial rotor, which is attached to the same mast as the first rotor, or a tail rotor. The pedals allow the pilot to control the tail rotor. The pedals change the pitch of the tail rotor blades which control the sideways thrust. This allows the pilot to change the direction of the nose of the helicopter. The throttle increases or decreases the engines speed and therefore allows the pilot to control the amount of lift generated. All of these components are used simultaneously to takeoff, hover, change directions, and land.