In point of fact, the preparation of the Scouts – which had to be equipped quite comprehensively for flight research – took longer than anticipated and there was increased pressure to obtain experience in this type of technology. Of the two British aircraft, XP189 was completed first, at the former Fairey factory at Hayes.
However, in the late summer of 1970, prior to the delivery to RAE of XP191, and under a bilateral agreement, NASA offered the loan, to RAE Aero Flight, of one of their semi-rigid research aircraft – the Lockheed XH51-N. This aircraft had completed a programme of flight research at Langley Air Force Base in Virginia.
Toward the end of that year, XH51 was shipped to RAE Bedford and began a programme of trials which included comparison flying with the Westland owned semi rigid Scout helicopter, XP189 – the only British aircraft having similar rotor technology at the time. The two helicopters are seen together here, flying over the airfield at Bedford during comparison handling trials.