How Helicopters Works

The principles of aerodynamics that effect an airplane, a bird, a rocket or a missile are the same that effect a helicopter. Everything that flies encounters the same basic rules of lift, drag and gravity.

Helicopter AerodynamicsIn order to fly, a helicopter uses different methods than any other aircraft. Its rotors—its “wings” rotate in order to produce lift. In a hover, it is this rotation that is the sole producer of lift. In forward flight, however, the “rotating disk” creating by the rotating individual blades produces additional lift.

The pilot controls the main rotor system by two controls, the cyclic and the collective. The cyclic is the control directly in front of the pilot, which he uses to the aircraft left or right, to bank left or right, and to make the helicopter go forward or aft, It also is used to make the aircraft stop or to stay in one place in the air, or over a particular spot on the ground. The cyclic control performs functions similar to what ailerons and elevators perform on an airplane.

Bell Helicopter CollectiveThe collective is found at the pilot’s left. The pilot raises or lowers this control to make the aircraft climb or descend, or to go faster or slower. Located on the collective is a motorcycle-style throttle, which is usually controlled by a fuel control. If not, when the pilot raises the collective to achieve more aerodynamic power, he or she would have to simultaneously “roll in throttle” by twisting the throttle one way as he or she raises the collective and “roll out throttle” as he or she lowers the collective. Otherwise, the rotor systems and the engine would underspeed with the raising of the collective and overspeed with the lowering of the collective. The collective can be thought of as a power control.

The tail rotor at the rear of the aircraft enables the pilot to control the direction of the nose of the aircraft, left or right. In some helicopters, this rotor has been replaced by a “fan,” and in other aircraft by highly pressurized air flow. The function of this tail rotor is important at all times, but it is most important in slow flight and hover operations. The pilot controls the tail rotor by use of foot pedals. The tail rotor performs the same function in a helicopter that the rudder performs in an aircraft.

Helicopter LiftInterestingly, the main rotor blades are constantly changing their angle of attack, or “pitch,” as they rotate. The input of both the cyclic and collective controls is “blended together” at the main rotor, which allows the main rotor blades not only to produce lift and speed but to also produce directional flight and to hover.

Some helicopters still have piston engines as their source of power, but most have turbine engines. All helicopters have a device, called a transmission, or “main gear box,” which changes the engine power into blade power. If the helicopter has two engines, the power coming out of both engines will be combined in a device called the combiner gear box before reaching the main transmission.

The main drive shaft, either coming directly from the single engine or from the combiner gear box in a multi-engine configuration, sends the power of the engine(s) to the main transmission. From there power is carried to the main rotor blades though the main rotor shaft, or the mast, and to the tail rotor through the tail rotor drive shaft. On aircraft with two main rotor systems, there are two main transmissions.

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