Transport Technology – Helicopters
Unlike any other aircraft, helicopters can hover, take off perpendicularly, fly slowly, and fly backward. Due to their flexibility, they have a wide variety of uses.
The versatility of the helicopter is due to the fact that helicopters do not have wings bolted to the aircraft.
Thus, aerodynamics is a less important element of design than in airplanes, and helicopter construction can focus on optimizing load volumes, fixed weight, and stability.
Aerodynamics
Helicopter aerodynamics differ from that of a fixed-wing aircraft. Like an airplane, the helicopter needs to exert lift and thrust to take off, but the mechanics are different. Most helicopters are propelled by turbines that power the shaft on which the rotor blades are fixed.
The blades spin on the top of the helicopter, and air flowing over the blade has a higher speed than air flowing underneath, thereby creating a difference in pressure and causing lift. The tail rotor, spinning sideways, provides thrust to move the helicopter forward, but also provides balance to the rotational force of the main rotor to prevent the fuselage from spinning in the opposite direction.
A freewheel between the turbine and gears also greatly reduces the spinning velocity transfer from the rotor to the turbine. In some cases, two main rotors on top of the craft spin in opposite directions to balance the rotational forces and eliminate any need for a tail rotor.
Control
Helicopters change direction on three axes through rolling (tilting sideways), yawing (turning left or right), and pitching (tilting forward and back). The controls include a collective pitch control lever, a cyclic pitch control lever, and pedals for the tail rotor. In order to control ascent and descent, the pilot uses the collective pitch control lever to change the angle of the rotor blades.
The steeper the angle, the greater the amount of lift. To control pitch, the pilot adjusts the angle of the main rotor blades at different points during the rotation. Pressing the cyclic pitch control lever forward causes the angle of the rear rotor blade to increase, which causes the helicopter to move forward.
To control roll, the pilot steepens the angle of the right or the left rotor blade at the proper point of the rotation. Anti-torque pedals, corresponding to the rudder pedals on a fixed-wing aircraft, control the tail rotor, which manages helicopter movement along its normal axis (yaw).
In the case of helicopters with two main rotors and no tail rotor, yaw control is possible through a cyclical blade adjustment of both the rotors.
SWASH PLATES
The central elements of steering control in helicopters are swashplates. Attached to the cyclic and collective control levers, they translate the pilot’s steering commands into movement by controlling the main rotor blades.
Two swashplates are located in the rotor shaft under the rotor head, and each has a different function: the upper swashplate rotates with the rotor, and the lower swashplate is tilted left, right, forward, or backward for cyclical blade control. The swash-plates shift upward or down-ward along the rotor axis for collective blade control.
The angle of attack is steered by the swashplates, and the control and driving rods.