Beating Gravity - Hawker Siddeley P.1127

By the 1960s VTOL research in the USA had come almost to a standstill; but at that time the UK was progressing with development of the Pegasus vectored-thrust engine. Some support came from the USAF and NASA; though the engine would be inadequate for their own projections for a heavy strike fighter, they foresaw the potential benefits which might accrue to the US if the promising design succeeded.

The Hawker Siddeley P.1127 research type developed directly into the world's first operational VTOL jet fighter. The aircraft was designed around the four-point lift arrangement of the Pegasus vectored-thrust turbofan. The engine dictated most of the design features, from the portly fuselage to the anhedral wings mounted above the thrust deflectors.

The main tandem undercarriage retracted into the fuselage, with outrigger landing gear on the wing tips. As with several other VTOL designs, control in the hover was provided by reaction jets at the airframe extremities, in this case using air tapped from the engine.

The first prototype achieved vertical take-off on 21st October, 1960, and horizontal takeoff on March 13, 1961. Six prototypes were built. A further nine aircraft were built for the Tri-partite evaluation unit ('The Tri-partite Nine'), and a further six as RAF development aircraft. An initial contract was undertaken to provide 60 Harrier production aircraft to the RAF in 1967.

The six P.1127 prototypes were built with progressively more powerful engines. The first five differed in detail, but all had unswept wing trailing edges. The later aircraft in this group were marginally supersonic at altitude, and had the Pegasus 2 v-t engine. The sixth prototype, flown on February 13th, 1964, introduced swept wing trailing edges and, apart from operational equipment, was representative of the Tri-partite evaluation aircraft.

From October 15, 1964 to November 30, 1965, a Tri-partite evaluation squadron, consisting of U.K., U.S. and German personnel converted to the P.1127 at Dunsfold, Surrey, operated the P.1127 development aircraft, the Kestrel FGA Mk.1. These had swept trailing edges and a leading edge sweep increased from 30 to 35 degrees, and wing taper modified from approximately 4:1 to 2:1. They were fitted with Pegasus 5 engines. Subsequently two of these aircraft were delivered to the U.K., and the remaining six to the USA under the designation XV-6A.

Six further evaluation aircraft were ordered on February 17, 1965, with changes proposed for the definitive production model for the Royal air Force. These were designated Harrier FGA Mk.1. These were powered by the Pegasus B.Pg.5 engine, similar to that in the Tri-partite aircraft. They had extended wing tips, repositioned air brake, strengthened outrigger wheels and a number of other alterations.