The Boulton Paul P.111 was an experimental delta winged jet aircraft used for research into the performance of delta wings at high speed.
The P.111 was produced in response to Air Ministry Specification E.27/46, for a dedicated delta wing research aircraft. It had a mid mounted delta wing, with a straight trailing edge and leading edge sloping back at 45 degrees. The vertical tail had a similar shape, and there was no horizontal tail surface. Both the wings and vertical tail had detachable tips, so they could be used with pointed tips or cut-off tips (it thus had three wing spans - 25ft 8in without any tips, 29ft 9in with small tips and 33ft 6in with almost pointed tips). It was powered by the Rolls-Royce Nene turbojet. This wasn't an especially powerful engine, and so the aircraft was limited in size to give it the required performance.
The horizontal oval air intake was in the tip of the nose, the exhaust pipe in the tail. The main wings carried powered ailerons. There was an anti-spin parachute on the starboard side of the rear fuselage.
Work on the P.111 began in 1947. It made its maiden flight on 10 October 1950 at Boscombe Down (Boulton Paul's own airfields still had grass runways). The P.111 was reported to be pleasant to fly, but the controls were over-sensitive at high speeds, and there wasn't enough feedback to the pilot from the controls. After the first 28 hours of flight a new windscreen was installed and the aircraft then appeared at the 1951 Farnborough Air Show. Over the next two years the aircraft crashed three times. The last of those, a forced landing on 29 August 1952, was serious enough to require significant repairs back at Boulton Paul.
At the same time as these repairs the P.11 was given a nose probe and four air brakes around the front of the fuselage, becoming the P.111A. The air brakes were installed in an attempt to reduce the high landing speed of the aircraft. More 'feel' was added to the controls. It was also painted bright yellow, and gained the nickname 'Yellow Peril'. The modified version resumed test flights on 2 July 1953.The modified aircraft flew forty times at Boulton Paul, before it was delivered to the A& AEE and Bedford. It was used in a series of trials that lasted until June 1958. The aircraft was then used as an instructional airframe at Cranwell. During this second period of trials a pilot controlled adjustable 'feel' system was added, to allow the pilot to decide how much feedback he wanted from the controls. The more feedback was provided, the harder the controls got to operate.
The P.111 could reach Mach 0.98 in level flight and go supersonic in a dive.
The P.111A, now painted bright yellow (2016) is part of the collection of the Midland Air Museum at Coventry Airport.
A modified version, the P.120, was produced to test out all moving horizontal tail surfaces, but that aircraft made its maiden flight and was lost in August 1942.
Engine: Rolls-Royce Nene turbojet
Power: 5,100lb thrust
Span: 33ft 6in
Length: 26ft 1in
Height: 12ft 6.5in
Empty weight: 7,517lb
Maximum take-off weight: 9,778lb-10,217lb (with different ballast levels)
Max speed: 564kt at sea level, 554kt at 20,000ft, 550kt at 30,000ft, 540kt (Mach 0.93) at 35,000ft
Climb Rate: 9,400ft/ min