The Hawker P.1127 and the Hawker Siddeley Kestrel FGA.1 were the development aircraft that led to the Hawker Siddeley Harrier, the first VSTOL jet fighter-bomber.
In 1957, the Bristol Engine Company informed Sydney Camm of Hawker that they had a project to combine their Olympus and Orpheus jet engines to produce a directable fan jet, an idea brought to them via NATO's Mutual Weapons Development Project (MWDP) Team from the French engineer Michel Wilbault. Hawker took the planned engine, which became known as the Pegasus, as a basis for a plane that could meet the current NATO specification for a Light Tactical Support Fighter This was a time of deep UK defence cuts, detailed in the 1957 Defence White Paper; as a result, Hawker's had to seek commercial funding and significant engine development funding came from the USA. Much model testing was done by NASA at Langley Field for the project. Hawker test pilot Hugh Merewether went to the US at NASA's request to fly the Bell X-14. In March 1959, the company's board of directors (now Hawker Siddeley) decided to fund two P.1127 prototypes. Then the UK Ministry of Supply contracted for two P.1127 prototypes in late 1959.
The first prototype P.1127, serial XP831 was delivered in July 1960 for static engine testing, and in October the Pegasus flight engine was made available. The first tethered flight took place the same month and free flight hover achieved on 19 November, after which the first publicity photos were released. The second prototype made its first take off conventionally on 7 July 1961. The two aircraft proceeded to "close the gap" between vertical take off and flight, achieved by 8 September.
Four more prototypes were ordered. Throughout this period improved Pegasus engines were being developed, with the Pegasus 3 being capable of 15,000 lbf (67 kN) of thrust. Apart from this, the first four aircraft were quite similar, but the fifth, XP980 introduced the taller fin and tailplane anhedral seen on the Harrier. The fourth machine was used, in part to give the Hawker production test pilots P.1127 familiarisation. The first carrier vertical landing was performed by the first prototype on HMS Ark Royal in 1963. The last P.1127, XP984, introduced the swept wing. It was eventually fitted with the 15,000 lbf (66.7 kN) Pegasus 5 and functioned as the prototype Kestrel.
The first three P.1127s were lost, the second and third during development. The first prototype crashed at the Paris Air Show in 1963. All the pilots involved survived.
Hawker Siddeley XV-6A Kestrel in USAF livery
Nine evaluation aircraft were ordered as the Kestrel FGA.1, an improved version of the P.1127, the first flying on 7 March 1964. The Kestrel had fully swept wings and a larger tail than the early P.1127s, and the fuselage was modified to take the larger 15,000 lbf (85 kN) Pegasus 5 engine as in the P.1127/Kestrel prototype XP984.
Due to interest from the US and Germany, the Tri-partite Evaluation Squadron (TES) was formed on 15 October 1964 at RAF West Raynham, staffed by military test pilots from Britain, the US and West Germany. During testing one aircraft was lost; and evaluations finalised in November 1965.
Six of the eight surviving evaluation aircraft (the three allocated to US plus those allocated to Germany) were transferred to the USA for evaluation by the Army, Air Force, and Navy (but not the US Marine Corp) as the XV-6A Kestrel. After Tri-Service evaluation they were passed to the USAF for further evaluation at Edwards Air Force Base, except for two that were assigned to NASA.
One of the two remaining British based Kestrels was attached to the Blind Landing Experimental Unit (BLEU) at RAE Bedford and the other, XS693, went to Blackburn's for modification to take the uprated Pegasus 6 engine. In addition to some strengthening, there were alterations to the air intake, which had throughout the P.1127 and Kestrel series featured an inflatable lip to smooth the intake airflow when the aircraft was almost stationary. There were concerns about the Service life of these devices, so they were replaced with conventional suction relief doors. This aircraft became the prototype for pre-production Harriers.
NATO requirement NBMR-3 specified for a VTOL aircraft, but one that was expected to have the performance of an aircraft like the F-4 Phantom along with the VTOL capability. Hawker drafted the P.1150, a supersonic P.1127 and the P.1154 which would meet NBMR-3. The latter was a winner of the NATO competition and development continued until cancelled at the point of prototype construction in 1965. The RAF then began looking at a simple upgrade of the Kestrel as the P.1127 (RAF).
In late 1965, six pre-production P.1127 (RAF) aircraft were ordered by the RAF (actually the remaining number from Kestrel order). The first pre-production aircraft flew on 31 August 1966. The aircraft was named Harrier in 1967.
- Crew: 1
- Length: 42 ft 6 in (12.95 m)
- Wingspan: 22 ft 11 in (6.99 m)
- Height: 10 ft 9 in (3.28 m)
- Empty weight: approximately 9,800 lb (4,445 kg)
- Loaded weight: for VTO 14,500 lb (6,580 kg)
- Max takeoff weight: for STO, approximately 17,000 lb (7,700 kg)
- Powerplant: 1× Bristol Siddeley Pegasus 5 vectored-thrust turbofan, 15,000 lbf (67 kN)
- Maximum speed: 710 mph, Mach 0.92 (1,142 km/h) at sea level
- Service ceiling: (service) approximately 55,000 ft (1,675 m)
- Rate of climb: approximately 30,000 ft/min (150 m/s)
- Thrust/weight: 1.04