BAC 221

"Originally built as a Fairey Delta 2 and set a new world air speed record of 1,132mph in March 1956. Rebuilt in 1964 for Concorde research. This was politically motivated, the other FD2 'WG777' remains un-rebuilt and is on display at Cosford. The record holder was picked for a reason."

- Alan Wilson from Weston, Spalding, Lincs, UK

The BAC 221 was a development of the Fairey Delta 2 supersonic research aircraft.

Development
Having performed brilliantly as the FD 2, WG774 re-emerged as the BAC 221, in which form it provided further invaluable research data and flight experience, by making it possible to investigate the control and handling characteristics of a thin delta wing, in support of the Concorde supersonic airliner project. To prepare the Delta 2 for its new role, the Filton division of the British Aircraft Corporation carried out an extensive modification programme on the former World speed record—holder. New ogival delta wings, similar in shape to those designed for Concorde, were fitted, along With revised control surfaces and new air intakes and undercarriage. The nose droop angle was made variable, and an automatic stabilisation system, that could be used to simulate changes in the aircraft's stability characteristics, was fitted. This enabled a variety of aerodynamic and centre-of-gravity configurations to be tested.

Now known as the BAC 221, the rebuilt aircraft ﬂew for the first time in May 1964. Two years later, it was delivered to the Royal Aircraft Establishment at Bedford for ﬂight trials at speeds up to Mach 1.6. The Handley Page HP 115 was used to investigate delta-winged handling at lower speeds. Among the trials carried out were studies of the airﬂow and vortex formation across the wings. Pressure transducers were fitted to record the pressure pattern on ﬁlm, and woolen tufts were also used to allow the airﬂow pattern to be recorded. The ﬂight data was then compared with information gathered in wind-tunnel tests.

Ogival wing planform
The thin delta wing was the principal feature of the design. Referred to as an ogival delta, the wing planform of the BAC 221 was very close to that of Concorde, and was designed by BAC in two halves, attached to either side of the fuselage. The wingroot attachments were similar to those of the FD 2. The sweep was 65° on the straight section of the leading edge, which extended forwards along the side of the fuselage to form chines. An ogival wing was chosen to give the best combination of lift, drag and stability characteristics at high Mach numbers. Press releases of the period referred to the BAC 221 as a ‘slender delta research aircraft’.

Engine mount
Fixed inlets for optimum performance at Mach 1.5-1.75 were chosen for simplicity. Some parts of the control system were based on those of the Hawker R1127. A total redesign of the engine air intakes was necessary, as the 221 required a sharp unbroken leading edge. The exhaust was similar to that of the FD 2 but. with a little modification, it gave increased power.

Equipment
Components from several different aircraft were ‘borrowed’ for the BAG 221. These included the main undercarriage which was based on that of the Lightning Other Lightning parts featured in the nose gear,  Unusually long undercarriage legs were a feature of the 221. Two pairs of doors were required to cover the retracted nose-wheel unit which retained the twin wheels of the FD 2. One of the BAC 221’s hydraulic systems was similar to that of the Bristol 188; the second was similar to that of the P.1127. Continuous voice transmission enabled the chase-plane to hear the 221 pilot. The blue finish was applied to make the woollen tufts connected to the starboard wing stand out better on film, recorded by a 16-mm cine camera housed in a prominent fairing at the leading edge of the ﬁn-tip.

Nose droop
Pilot visibility on landing was improved by the drooping nose. This could be set at a variety of angles, unlike that of the Delta 2. The 221 inherited its drooping nose from the FD 2, although it had a more complex unit than the earlier type. Conditions in the cockpit of the FD 2 had become increasingly cramped as more items of equipment were added. For the 221, new instrumentation was supplied, along with a revised canopy. but the layout remained unchanged.

Post test history
On 9 June 1973, the BAC 221 was retired from test duties, and is now on display at the Fleet Air Arm Museum, Yeovilton, resplendent in its blue colour scheme.