A helicopter is an aircraft that moves air over a rotor by spinning blades. Helicopters are used for a wide variety of purposes, such as search and rescue, transporting outsized slung loads, and delivering military artillery pieces. They are also used by police departments to pursue suspects. In the United States, there are hundreds of civilian and law enforcement helicopters in use.
There are four main types of flight controls for a helicopter. These controls are cyclic, collective, swashplate, and mechanical feedback. Each type has its own characteristics, and some helicopters have unique systems. Usually, the controls are mounted between the pilot and his or her legs.
Cyclic control is an input that works by changing the angle of the blades on the rotor. This causes the rotor disk to tilt. Rotor tip vortices then circulate from high pressure air underneath the rotor disk. The angle of the blades also affects the height of the rotor.
The collective control is located on the left side of the pilot’s seat and is responsible for the pitch angle of all the main rotor blades. It is used to adjust the collective lift of all the rotors at the same time. Some helicopters have an internal impeller that prevents the rotor from sputtering and losing lift.
Swashplate is a mechanical feedback system that moves the main rotor blades in either the left or the right direction. It is often mounted with a heat-sensing device for night pursuits. When the swashplate is moved to the left, the main blades can move upward, which generates a more vertical angle of attack. On the other hand, when the swashplate is moved to the right, the main blades can move downward, generating a more horizontal angle of attack.
A helicopter can fly at excessive speeds, which is usually not recommended. Excessive airspeed is associated with a number of problems, including the possibility of blade stalls, rollovers, and high vibration. Additionally, it can cause the rotor to flap too much, which is unsafe.
In addition to the rotor, the aircraft includes a tail rotor that provides horizontal thrust to counter torque from the main rotors. Helicopters are often mounted with lighting for night pursuits.
Vertical flight is the most efficient form of flight, because it removes the need for intervening modes of travel. However, vertical flight also requires a greater degree of control. For example, if a helicopter enters a translational lift state, the lift can be used to increase altitude without increasing power. Similarly, if the aircraft enters a vortex ring state, the lift is unable to be withdrawn, leading to a loss of control.
Helicopters are generally considered to be safe aircraft, and they have been used successfully for a number of missions. During the Korean War, the aircraft could be used to deliver patients to medical facilities in just three hours. Similarly, during the Chernobyl nuclear disaster, hundreds of helicopters took off and made dozens of sorties each day.
