Hawker P.1127 and Kestrel (1960 - 1966)

Prototype P.1127 XP831 at Dunsfold (Hawker Aircraft)

In the short history of powered flight there are no more than a dozen or so major milestones. One has to be the P.1127 development aircraft leading via the Kestrel to the vertical take off and landing (VTOL) Harrier. There were two schools of thought in relation to VTOL. Rolls Royce, among others, developed high thrust to weight ratio engines for fixed vertical installation for lift with separate engines for horizontal flight. The format was abandoned in the West but employed on the Yak-36, albeit with a main vectored thrust engine.

The P.1127 design began in 1957 of an airframe to be built around the revolutionary BE53 vectored thrust engine. By 1960 the Ministry of Supply issued ER.204D funding two protoypes, the first of which (XP831) flew on 21 October 1960. The installed engine delivered 11,300lb of thrust and weight was reduced to just 10,000lbs for the first tethered 'flight'. The first conventional take-off was on 13 March 1961 and transition from vertical to horizontal flight in September of the same year. The aircraft went supersonic in a dive on 12 December 1961.

By now a second prototype (XP836) had joined the first and in the light of experience numerous design changes were incorporated in subsequent prototypes (XP972, 976, 980, 984). Engines were improved and replaced frequently. In 1959 the BE53 produced only 9,000lbs thrust; as the Pegasus 2 (11,300lbs) it powered the protoype and as the 3 (14,000lbs) it saw the aircraft into transition. The Pegasus 4 (15,500lbs) powered the last prototype. From the outset the P.1127 was intended to act as a prototype for an operational aircraft rather than simply being a research machine. As solutions to problems were identified they were incorporated in airframes. By 1963 there was interest from Germany and the United States in the project and an agreement reached to build nine trials aircraft to examine every aspect of VTOL operations.

Third P.1127 XP972 with the Pegasus 2 engine seen here at Farnborough in 1962

Colour shot of the fourth, Pegasus 3 engined P.1127, XP976 at Biggin Hill, 1965 (Author)

Fine shot of fifth P.1127, XP980, in the hover (Hawker Aircraft)

Kestrel F(GA) Mark 1

The Kestrel was the response to the agreement and in effect the prototype was the last P.1127 development aircraft. It was produced to requirement GOR.345. Compared to the earlier P.1127s it had the Pegasus 5 of 15,500lbs thrust, inflatable intake lips, a swept wing, longer fuselage and a tailplane of increased span. Nine Kestrels were constructed (starting XS688) and the Tripartite Evaluation Squadron was formed at West Raynham in March 1965 within the Central Fighter Establishment. The unit flew the Kestrel intensively for nine months during which 930 sorties covering 600 hours were flown. The type was never more than an interim vehicle and from January 1965, at which time the intended supersonic P.1154 was cancelled, the subsonic fully operational P.1127/Kestrel derivative was ordered. Those trials aircraft transferred to the US were given the designation XV-6A.

First Kestrel XS688 at a high angle of hover and showing the tri-partite markings

Kestrel XS695 with mock-up Sea Harrier nose

Kestrel XS695 at Farnborough in 1964 in 1966 with SNEB rocket pod under wings (Author)

Service Trials Tripartite Trials Squadron; CFE

Specification and production

Mark	Role	Engine	Thrust lbs	Weight lbs	Speed mph	Nos
P.1127	Proto	Pegasus 1	11,300	10,000	-	2*
P.1127	Proto	Pegasus 2	12,500	12,000	-	1+
P.1127	Proto	Pegasus 3	13,500	12,000	700	3~
P.1127	Proto	Pegasus 4	15,500	13,000	700	1#
Kestrel	Trials	Pegasus 4	15,500	15,000	660	9

Notes

* XP831, 836

+ XP972

~ XP831, 976, 980

# XP984

Further reading

Braybrook, R British Aerospace Harrier and Sea Harrier Osprey, London, 1984

Calvert, D J Harrier Ian Allan, London, 1990

Gunston, W Harrier Ian Allan, Shepperton, 1984

Mason, F K Harrier Patrick Stephens, 1986

Mason, F K Hawker P.1127 and Kestrel (Profile 198) Profile Publications, Leatherhead, 1969