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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.
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.
As speed increases, blade pitch is increased to keep blade angle of attack constant. A propeller blade's "lift", or its thrust, depends on the angle of attack combined with its speed. Because the velocity of a propeller blade varies from the hub to the tip, it is of twisted form in order for the thrust to remain approximately constant along the ...
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 ...
[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 ...
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 ...
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.
A helicopter rotor blade is an airfoil, which is driven through the air to create lift. The lift generated is proportional to the square of the speed. Because the tips of the rotating blades travel much faster through the air than the parts of the blades near the hub, they generate much more lift.