How the Delta 2 supersonic research aircraft broke the world air speed record beating that held by the F-100 Super Sabre

It was the ease with which the aeroplane passed into the supersonic regime, with none of the violent behaviour experienced by other types in the transonic region, that made obvious that the Delta 2 could easily set a new world air speed record.

The Fairey Delta 2 was a supersonic research aircraft designed to investigate the flight characteristics of a delta planform with 60 degrees of sweep on the wing leading edges when flying at speeds well above Mach 1. The two examples built (serials WG774 and WG777) and flown proved to be invaluable research tools over a long period of time and, in addition, in March 1956 the first Delta 2 broke the world air speed record, beating the 823mph held by Col Horace Hanes in a North American F-100C Super Sabre, in one of the finest achievements in British aviation history.

As told by Tony Buttler in his book Cold War Delta Prototypes, it was the ease with which the aeroplane passed into the supersonic regime, with none of the violent behaviour experienced by other types in the transonic region, that made obvious that the Delta 2 could easily set a new world air speed record. Mach 1.56 was reached in November 1955, and the flight team realised that the record could go beyond 1,000mph. Once the planning for the record attempt was under way, everything was kept as secret as possible to the point where the cover story proved so effective that many engineers were unaware of what was happening until shortly before the attempt began.

Since WG774 was based at Boscombe Down, the decision was made to lay out a flight course across West Sussex between Chichester and the Royal Navy base at Ford – ground observation and recording sites were set up at both locations. The flying height was fixed at 38,000ft because this approximated to the level for optimum performance, and also ensured a good contrail (the latter was essential for ground tracking). For previous record attempts using subsonic (i.e. Mach-limited) aeroplanes, it had been necessary to fly in hot weather conditions to reduce the Mach number appropriate to a given airspeed. For the Delta 2, however, the coldest atmosphere was needed in order to increase the thrust of its engine.

Extensive telephone services were set up by the General Post Office and plugged straight into lines laid down for a now disused airfield. In addition, two complete installations of the most advanced British Army radar were made available. Gloster Meteor NF 11 nightfighters of No. 29 Sqn took off each day to assess the true contrail height, calibrate the radars and check the communication systems, and during the Delta 2’s flights a specially calibrated de Havilland Venom measured the height as WG774 flashed by. The ground radar would vector the two aeroplanes into the best positions, but getting WG774 into the right place and height at the right moment called for meticulous timing and superb piloting skills. By Mar. 7 everything was in place and ready for ‘Exercise Metrical’.

Between Mar. 7 and 10, in superb weather for the time of year, Lt Cdr Peter Twiss (the Delta 2’s lead test pilot for manufacturer’s trials flying) made nine flights, but on each sortie either technical problems with the ground equipment or some other factor prevented a new record from being set. He always took off on a westerly course and followed a route designed to make the best use of the fuel load. A climb was made over the New Forest, and then reheat was lit and the aircraft’s acceleration made continuous from here until the run ended. Reheat was cancelled after the eastward pass and a wide 180-degree turn made over the sea, before Twiss brought WG774 back in to repeat the whole procedure in a westerly direction. A minimum-power let-down ended in a landing at Boscombe Down after approximately 24 minutes flying time (following the record run Twiss landed without enough fuel to make an overshoot and another approach).

At last, a tenth flight, which started at 1121hrs on Mar. 10, 1956, yielded the results that secured the record – speeds of 1,117.6mph and 1,146.9mph on the two runs gave a mean figure of 1,132.1mph. This equated to 983.7 knots Indicated Air Speed (IAS) and a mean Mach number of 1.731 (a maximum of Mach 1.8 was recorded during the flight). Peter Twiss had increased the world air speed record by no less than 37 per cent, WG774 having flown at a speed in excess of Mach 1.6 for 2.8 minutes. The aeroplane was still accelerating at the end of each run.

When the record was announced on Mar. 11 the popular press went crazy. Worldwide, the record produced quite an effect, and in general it was received with great enthusiasm. The Air Ministry’s Stuart Scott-Hall was in the USA when the record flight took place, and he found the Americans gave generous acclaim to the achievement. He thought it true to say, however, that ‘they were quite astonished. For months they had been reading that the British aircraft industry had failed to produce the goods in this direction and in that. They would have had good excuse for thinking that the British were in a bad way. The capture of the record gave the British aircraft industry a tremendous uplift, while Americans concerned with high-speed aircraft development, no matter what type of wing they favoured, swept wing, straight wing, or delta, appeared to be equally surprised at the performance achieved.’

A few days later, when the press arrived at Boscombe Down, WG774 was being serviced and so the second Delta 2, WG777, had its fuselage serial number quickly changed to WG774 in readiness for the cameras. Fairey intended to display the aircraft’s speed capability to the public at the September 1956 SBAC Farnborough Airshow. WG774 and WG777, flown by Gp Capt Gordon Slade Slade and Twiss, would essay a supersonic crossover directly above Farnborough at 38,000ft (visible to the public by their contrails), and in doing so produce level-flight sonic bangs, which at this time had not previously been publicly demonstrated in Britain (these would be audible on the ground some 25 seconds later). During practice for the display, their routine went smoothly, but persistent wet weather prevented the Delta 2s from performing this unique routine during the airshow itself.

On Dec. 12, 1957 the USA reclaimed the record with a speed of 1,207.6mph set by a McDonnell F-101A Voodoo.

Cold War Delta prototypes is published by Osprey Publishing and is available to order here.

Photo credit: Crown Copyright, U.S. Air Force