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A multirotor or multicopter is a 
In order to allow more power and stability at reduced weight, 
Also possible is the addition of horizontal propellers These types of rotorcraft (which have just 4 vertical propellers) are called quadplanes.It can also be possible by adding additional nonhorizontal wings, which are called lifting-wing multicopters.
A multirotor or multicopter is a rotorcraft
A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapt ...
with more than two lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobile ...
-generating rotor
ROTOR was an elaborate air defence radar system built by the British Government in the early 1950s to counter possible attack by Soviet bombers. To get it operational as quickly as possible, it was initially made up primarily of WWII-era syst ...
s. An advantage of multirotor aircraft is the simpler rotor mechanics required for flight control. Unlike single- and double-rotor helicopter
A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...
s which use complex variable pitch rotors whose pitch varies as the blade rotates for flight stability and control, multirotors often use fixed- pitch blades; control of vehicle motion is achieved by varying the relative speed of each rotor to change the thrust and torque produced by each.
Due to their ease of both construction and control, multirotor aircraft are frequently used in radio control aircraft and unmanned aerial vehicle (UAV) (drone) projects in which the names tricopter, quadcopter
A quadcopter, also called quadrocopter, or quadrotor is a type of helicopter or multicopter that has four rotors.
Although quadrotor helicopters and convertiplanes have long been flown experimentally, the configuration remained a curiosity ...
, hexacopter and octocopter are frequently used to refer to 3-, 4-, 6- and 8-rotor rotorcraft, respectively. There is also the X8 (also called ''octo-quad'') configuration that is similar to the quadracopter design, except that it has eight rotors; the lower of which have a reversed rotation direction.
In order to allow more power and stability at reduced weight, coaxial rotor
A coaxial-rotor aircraft is an aircraft whose rotors are mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions ( contra-rotating).
This rotor configuration is a feature of helicopt ...
s can be employed, in which each arm has two motors, running in opposite directions which cancels out rotational torque (one facing up and one facing down).
Also possible is the addition of horizontal propellers These types of rotorcraft (which have just 4 vertical propellers) are called quadplanes.It can also be possible by adding additional nonhorizontal wings, which are called lifting-wing multicopters.
Rotor configurations
*Coaxial rotors
A coaxial-rotor aircraft is an aircraft whose helicopter rotor, rotors are mounted one above the other on Concentric objects, concentric shafts, with the same axis of rotation, but turning in opposite directions (contra-rotating).
This rotor co ...
* Cyclorotor
* Intermeshing rotors
* Tail rotor
The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. ...
* Tandem rotors
A tandem-rotor aircraft is an aircraft with two large helicopter rotor assemblies mounted one in front of the other in the horizontal plane. This configuration is mainly used for large cargo helicopters. Such aircraft are often informally referr ...
* Transverse rotors
A transverse-rotor aircraft is an aircraft with two large Horizontal plane, horizontal helicopter rotor, rotor assemblies mounted side by side.
Single-rotor helicopters (unicopters) need an additional tail rotor or NOTAR, tail exhaust to neut ...
Examples
* de Bothezat helicopter - an American four-rotor helicopter that first flew on December 18, 1922. * Cierva Air Horse - a British three-rotor "heavy lift" helicopter first flying in 1948. Three rotors were used to give a large lift without compromising rotor strength. * Volocopter designs - a series of German prototype electric multicopters with 18 rotors, the first electric multicopter in the world to achieve crewed flight. The large number of low-cost motors make it economical, quiet and provide redundancy with ability to maintain control with up to four failed motors.
References
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