While the idea of the helicopter has existed since 400 BC in China in children’s toys, the first true powered examples were developed in the 1900s throughout Europe. These early aircraft had trouble getting off the ground — literally. In fact, they could only make short tethered flights that lasted a few seconds, as they were unreliable and difficult to control. One issue lay with the main rotor, which, as it spun to generate lift caused the entire fuselage to spin with it.
In 1931, Igor Sikorsky devised a solution. A Russian-born aeronautical engineer working in the United States, Sikorsky’s design was revolutionary. It featured a single main rotor that would provide the primary lift and thrust, and a tail rotor that would spin in opposition of the rotating force generated by the main rotor, thus balancing the helicopter. Alternatives have been developed since then, as seen on the CH-47 Chinook, which has two main rotors that rotate in opposite directions. However, many helicopters still utilize the main rotor/tail rotor design to this day.
Like all self-propelled vehicles, a helicopter needs an engine. Modern examples use gas turbines similar to those found on commercial aircraft. However, all this power is useless without the transmission. Just like in an automobile, the transmission’s gearboxes (one for the main rotor and one for the tail) transmit power from the engine to the main and tail rotors through a complex system of gears. Finally, a stabilizer bar sits atop the main rotor blades, rotating along with the main rotor. The stabilizer’s weight and rotation dampen vibrations in the main rotor, which in turn keeps the helicopter stable and makes it easier to control.
A set of levers and pedals control the helicopter’s movement from within the cockpit. The cyclic-pitch lever, or “stick,” is mounted on the floor and situated between the pilot’s legs. This allows the pilot to tilt the aircraft forward and back and side to side by adjusting the pitch of individual rotor blades. Meanwhile, the collective-pitch lever handles up and down movement by adjusting all rotor blades in unison. The foot pedals control what direction the helicopter’s nose is pointed by adjusting the pitch of the tail rotor’s blades.
When a pilot adjusts the cyclic-pitch lever, the main rotor’s swash plate assembly responds. An upper swash plate is connected to the rotor shaft and spins in sync with the rotor. A lower plate is fixed in position and does not spin, with a set of ball bearings between them. The bearings let the upper plate spin, as the entire assembly tilts and shifts as the pilot adjusts the stick. Control rods run from the upper swash plate to the rotor blades overhead that transfer the pilot’s input, changing the angle of the blades, causing the helicopter to move in the pilot’s intended direction. All of these processes ensure the helicopter’s conflicting forces are balanced and at the pilot’s full control.
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