"One of the YUH-1Bs was used as an aerodynamic test bed as the "Model 533" and modified to a number of configurations as part of a US Army program.
The first series of modifications, flown in 1962, features aerodynamic fairings, a new tail surface to offload the tail rotor, and a tilting rotor mast inside a large fairing structure.
The Model 533 was then fitted with a swept wing, two Continental J69-T-29 turbojets with 770 kilograms (1,700 pounds) thrust each, and a modified rotor blade with swept tips. This compound rotorcraft achieved a speed record of 370 KPH (236 MPH or 200 knots) in level flight on 15 October 1964, and on 6 April 1965 topped that record with a speed of 402 KPH (250 MPH) in level flight.
The Model 533 was finally fitted with two wingtip-mounted Pratt & Whitney JT12A-3 turbojets with 1,500 kilogram (3,300 pounds) thrust each. In this configuration, it achieved speeds of over 480 KPH (300 MPH)."
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