Reducing the rotational speed and increasing the angle of attack can therefore give a significant reduction in rotor drag, allowing lower fuel consumption. Technical parameters given for each type listed:   When Juan de la Cierva developed the autogyro through the 1920s and 30s, it was found that the tip speeds of the advancing rotor blade could become excessive. Designers such as he and Harold F. Pitcairn developed the idea of adding a conventional wing to offload the rotor during high-speed flight, allowing it to rotate at slower speeds. The Pitcairn PCA-2 of 1932 had a maximum speed of 20-, "μ" = 0.7, and L/D = 4.8  NACA engineer John Wheatley examined the effect of varying advance ratios up to about 0.7 in a wind tunnel in 1933 and published a landmark study in 1934. Although lift could be predicted with some accuracy, by 1939 the state of the art theory still gave unrealistically low values for rotor drag. Fairey Aviation in the UK developed a series of experimental tip-jet driven gyrodynes in the late 1940s and 1950s. They culminated in the Fairey Rotodyne, a VTOL passenger aircraft with a single main rotor supplemented by wings and twin turboprop engines. In forward flight the power to the rotor was reduced to about 10%. . 0.6. 120 to 140 60% \ 40%. At the same time, the US Air Force was investigating fast VTOL aircraft. McDonnell developed what became the McDonnell XV-1, the first of the V-designated types, which flew in 1955. It was a tip-jet driven gyrodyne, which turned off rotor thrust at high airspeeds and relied on a pusher propeller to maintain forward flight and rotor autorotation. Lift was shared between the rotor and stub wings. It established a rotorcraft speed record of . 0.95. 180-410 (50%). 85% \ 15%. 6.5 (Wind tunnel tests at 180 RPM with no propeller.) The Lockheed AH-56 Cheyenne arose out of Lockheed's ongoing research programme into rigid rotors, which began with the CL-475 in 1959. Stub wings and a thrust turbojet to offload the rotor were first added to an XH-51A and in 1965 this allowed the craft to achieve a world speed record of . The Cheyenne flew just two years later, obtaining its forward thrust from a pusher propeller.