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In helicopter aerodynamics, the Lock number is the ratio of aerodynamic forces, which act to lift the rotor blades, to inertial forces, which act to maintain the blades in the plane of rotation. [1] It is named after C. N. H. Lock , a British aerodynamicist who studied autogyros in the 1920s.
Today, on most modern aircraft the swashplate is above the transmission and the pushrods are visible outside the fuselage, but a few early designs, notably light helicopters built by Enstrom Helicopter, placed it underneath the transmission and enclosed the rotating pushrods inside the mainshaft. This reduces rotor hub drag since there are no ...
Helicopters with fly-by-wire systems allow a cyclic-style controller to be mounted to the side of the pilot seat. The cyclic is used to control the main rotor in order to change the helicopter's direction of movement. In a hover, the cyclic controls the movement of the helicopter forward, back, and laterally.
rotor speed (helicopters) Np and Nr are typically shown on the same gauge with two needles, both expressed in percent, so that the pilot can tell if the power turbine is driving the rotor or if it is freewheeling.
The U.S. Department of Transportation has published a “Basic Helicopter Handbook”. One of the chapters in it is titled, “Some Hazards of Helicopter Flight'. Ten hazards have been listed to indicate what a typical single rotor helicopter has to deal with. The coaxial rotor design either reduces or completely eliminates many of these hazards.
Military helicopters play an integral part in the sea, land and air operations of modern militaries. Generally manufacturers will develop airframes in different weight/size classes which can be adapted to different roles through the installation of mission specific equipment.
In the mid-1960s, the helicopter was test flown by a number of government and military agencies, and also the military. The stability offered by the rigid rotor control system made the helicopter easy to fly, [ 2 ] and the lessons learned from the CL-475 rigid rotor were later used to develop the Lockheed XH-51 and AH-56 Cheyenne .
In the case of fighters, this was a concern, especially at landing, but in the case of helicopters, this is less of an issue because the rotor tips do not slow significantly, even during landing. Such swept-tips can be seen a number of helicopter types from the 1970s and 80s, notably the UH-60 Blackhawk and the AH-64 Apache.