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for a small anti-submarine warfare helicopter, the Flettner Fl 282 Kolibri. During the Cold War the American Kaman Aircraft company produced the HH-43 Huskie, for USAF firefighting purposes. The latest Kaman K-MAX model is a dedicated sky crane design used for construction work. 

## Tail Rotor 

The tail rotor is a smaller rotor mounted vertically or near- vertically on the tail of a traditional single-rotor helicopter. The tail rotor either pushes or pulls against the tail to counter the torque. The tail rotor drive system consists of a drive shaft 

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powered from the main transmission and a gearbox mounted at the end of the tail boom. [Figure 1-9]  The drive shaft may consist of one long shaft or a series of shorter shafts connected at both ends with flexible couplings. The flexible couplings allow the drive shaft to flex with the tail boom. 

The gearbox at the end of the tail boom provides an angled drive for the tail rotor and may also include gearing to adjust the output to the optimum rotational speed typically measured in revolutions per minute (rpm) for the tail rotor. On some larger helicopters, intermediate gearboxes are used to angle the tail rotor drive shaft from along the tail boom or tailcone to the top of the tail rotor pylon, which also serves as a vertical stabilizing airfoil to alleviate the power requirement for the tail rotor in forward flight. The pylon (or vertical fin) may also provide limited antitorque within certain airspeed ranges if the tail rotor or the tail rotor flight controls fail. 

## Controlling Flight 

A helicopter has four primary flight controls: 

• Cyclic 

• Collective 

• Antitorque pedals 

• Throttle 

## Cyclic 

The cyclic control is usually located between the pilot’s legs and is commonly called the “cyclic stick” or simply “cyclic.” On most helicopters, the cyclic is similar to a joystick; however, Robinson helicopters have unique T-bar cyclic control systems. A few helicopters have cyclic controls that descend into the cockpit from overhead while others use side cyclic controls. 

The control is called the cyclic because it can vary the pitch of the rotor blades throughout each revolution of the main rotor system (i.e., through each cycle of rotation) to develop unequal lift (thrust). The result is to tilt the rotor disk in a particular direction, resulting in the helicopter moving in that direction. If the pilot pushes the cyclic forward, the rotor disk tilts forward, and the rotor produces a thrust in the forward direction. If the pilot pushes the cyclic to the side, the rotor disk tilts to that side and produces thrust in that direction, causing the helicopter to hover sideways. [Figure 1-10] 

## Collective 

The collective pitch control, or collective, is located on the left side of the pilot’s seat with a pilot-selected variable friction control to prevent inadvertent movement. The collective changes the pitch angle of all the main rotor blades 

