... that the people who gave Britain the likes of the
Percival Proctor also made a foray into rotary-wing design!
In 1951 a helicopter division was formed by Hunting Percival and design work commenced on a medium-sized helicopter designated the P74. This machine had a teardrop-shaped fuselage with the two-seat cockpit in the nose and a large cabin running the full length of the fuselage. Beneath the cabin floor was a Napier Oryx gas generator which fed compressed air to the tips of the three rotor blades. The prototype was completed in the spring of 1956, carrying the military serial number XK889. Ground testing commenced but the Oryx engine was insufficiently powerful and the P74 failed to fly. It was planned to fit a more powerful Rolls-Royce RB.108 turbine but the rationalisation of the helicopter industry later that year resulted in the P74 project being cancelled.
The lack of gearbox and simplified coupling of rotor to the aircraft meant that a tilting rotor hub could be used and drag hinges were not needed.The low torque coupling at the mast meant that very little was needed in the form of lateral control. The P74 rotor was expected to be quieter in operation than tip jets following tests with a Derwent engine powered rotor. The stainless-steel rotors were thick in cross section to allow for the necessary ducting to the tips and non-feathering - as a result ailerons were fitted to the blades.
The rotor blades used ailerons on the trailing edges with pitch control achieved by a screw jack. The unusual engine location necessitated exhaust pipes coming through the cabin wall between the rows of seats, creating an unenviable amount of din and heat for the intended passengers.
The Hunting Percival P74 was intended as a demonstrator for a new type of helicopter. It worked on the tip-jet principle, but unlike the Hiller Hornet with its individual ramjets, the P74 had a gas generator under the cabin floor which fed compressed air through triple ducts to the three-bladed rotor, each blade of which had triple ejector ducts.
Months of testing in a static rig showed up many problems with the power system which refused to develop full power and maximum gas flow. Finally these problems were fixed and a first flight attempted. Despite the efforts of two pilots on the very stiff controls, the P74 resolutely refused to fly. One engineer associated with the project says that a consultant designer used the wrong formula for calculating lift. All the figures added up but the P74 went nowhere. Actually it was ordered to be towed across the airfield out of sight, and that is about the last anyone heard of it.
And that .. in the 1960's Westlands were planning a commercial tilt-rotor?
Proposed Westland Tilt-Rotor G-AXXP (1968)