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Most helicopter rotors spin at constant speed. However slowing the rotor in some situations can bring benefits. As forward speed increases, the advancing rotor tip speed soon approaches the speed of sound. To reduce the problem, the speed of rotation may be slowed, allowing the helicopter to fly faster.
[12] [37] At mu=1, V is equal to u and the tip airspeed is twice the aircraft speed. At the same position on the opposite side (retreating blade), the tip airspeed is the aircraft speed minus relative blade tip speed, or V t =V-u. At mu=1, the tip airspeed is zero. [30] [38] At a mu between 0.7 and 1.0, most of the retreating side has reverse ...
Blade pitch control is a feature of nearly all large modern horizontal-axis wind turbines.It is used to adjust the rotation speed and the generated power. While operating, a wind turbine's control system adjusts the blade pitch to keep the rotor speed within operating limits as the wind speed changes.
The speed of the blade-tip at point A in the diagram relative to the air is the sum of the blade-tip speed and the helicopter forward-flight speed: rω+v. But the speed of the blade-tip at point B, relative to the air, is the difference of its rotational speed and the forward-flight speed: rω-v. Since the lift generated by an aerofoil ...
A tip jet is a jet nozzle at the tip of some helicopter rotor blades, ... [25] [26] On 5 January 1959, the Rotodyne set a world speed record in the convertiplane ...
In 1986, a Lynx specially modified registered G-LYNX set an absolute speed record for helicopters over a 15 and 25 km course by reaching 400.87 km/h (249.09 mph). [2] Following the successful technology demonstration, the BERP III blade went into production. BERP IV uses: a new aerofoil, revised blade tip shape, and increased blade twist.
The advance ratio is a useful non-dimensional quantity in helicopter and propeller theory, since propellers and rotors will experience the same angle of attack on every blade airfoil section at the same advance ratio regardless of actual forward speed. It is the inverse of the tip speed ratio used for wind turbines.
Disk area can be found by using the span of one rotor blade as the radius of a circle and then determining the area the blades encompass during a complete rotation. When a helicopter is being maneuvered, its disk loading changes. The higher the loading, the more power needed to maintain rotor speed. [3]