The Vickers-Armstrongs Valiant was a British four-jet bomber, once part of the Royal Air Force's V bomber nuclear force in the 1950s and 1960s. The Valiant was originally developed for use as high-level strategic bomber, but its role, like other V bombers, was changed to low-level attacks.
Low-level flying brought a number of serious problems as the Valiant's wing spar attachment castings showed premature fatiguing and inter-crystalline corrosion traced to the use of an inappropriate type of aluminium alloy. The Valiant had been the first of the V bombers to become operational, and its role was already shifting to that of a tanker. Rather than repair or rebuild the fleet, the Valiant was grounded and the Handley Page Victor took over the tanker role.
The Valiant was a conservative design, with a shoulder-mounted wing and four Avon RA.3 turbojets, each of 6,500 lbf (29 kN) thrust, two in each wing root. The design gave an overall impression of a plain and clean aircraft with simple aerodynamics. George Edwards described it appropriately as an "unfunny" aircraft. The root chord thickness ratio was 12% and allowed the Avon engines to be within the wing rather than on pods as in the contemporary Boeing B-47. This "buried engine" fit contributed to the aircraft's aerodynamic cleanliness. However, it made engine access for maintenance and repair difficult and increased the risk that the failure of one engine would contribute to the failure of its pair due to flying debris such as turbine blades. It also increased the complexity of the design of the main spar which had to be routed round the engines.
The Valiant wing had a "compound sweep" configuration, devised (and patented) by Vickers aerodynamicist Elfyn Richards. It had a 37° angle of sweepback in the inner third of the wing, reducing to an angle of about 21° at the tips. This was because the thickness/chord ratio could be reduced closer to the tips, balancing this against the sweep reduction in postponement of Mach effects such as buffeting and drag rise. Limiting in-service speed was Mach 0.84 and a typical cruise of Mach 0.75 at heights up to 55,000 ft when light. A "clean" Valiant (one without underwing tanks) could climb straight to 50,000 ft after takeoff unless it had heavy stores in the large bomb bay. The tail surfaces were swept back, and the horizontal tailplane was mounted well up the vertical fin to keep it clear of the engines' exhaust. The wing loading was low by modern standards and the Valiant was fitted with double-slotted flaps for takeoff (20° flap) and landing (40° or full flap, about 60°). The aircraft featured tricycle landing gear, with twin-wheel nosegear and tandem-wheel main gear retracting outward into the wing. Most of the aircraft's systems were electric including flaps and undercarriage.
Initial Valiant production aircraft had four Rolls-Royce Avon 201 turbojet engines, with 9,500 lbf (42 kN) thrust each. Trials were performed with two underwing de Havilland Sprite rocket booster engines; however these were deemed unnecessary due to the availability of more powerful Avon variants, as well as fear of accidents if one booster rocket failed on take-off, resulting in asymmetric thrust. The engine inlets were long rectangular slots in the first prototype, but later Valiants featured oval or "spectacle" shaped inlets to permit greater airflow for more powerful Avon engine variants. The jet exhausts emerged from fairings above the trailing edge of the wings. Water injection was fitted to some Valiants and increased takeoff thrust by about 1,000 lb (450 kg) per engine.
Electrics were based on 112 volt direct current generators for functions requiring large amounts of electrical power and a 28 V DC system provided a controlling voltage for other systems and the actuators that initiated the high-voltage system functions. Backup batteries were a bank of 24 V units and 96 V batteries. 115 V alternating current was provided to systems such as radio and radar that required it. The brakes and steering gear were hydraulic, however pumps were electrically driven. The flight controls consisted of two channels of power control with full manual back-up; flying in manual was allowed but limited.
The Valiant was built around a massive backbone beam that supported the wing spars and the weight of bombs in the long bomb bay. The crew were contained in a pressurized "egg" and consisted of pilot, copilot, two navigators, and an electronics operator. Only the pilot and copilot had ejection seats. The other three crew members had to bail out of the crew door on the port side of the fuselage. The main structural components, spars and beams etc. were built with the zinc/magnesium/copper aluminum alloy designated as DTD683 in the U.K., which was problematic in the production of the Valiant. The aircraft was designed with a 'Safe-Life' strategy. This combination of 'Safe-Life' and DTD683 came to be viewed as a severe mistake. In 1956, a publication within the Journal of the Institute of Metals of a paper that condemned the material DTD683 as being unstable and capable of catastrophic failure while stressing the airframe close to its design limits. The "Safe-Life" design strategy was dismissed by a Lockheed engineer in a talk given to the Royal Aeronautical Society in 1956, because it did not guarantee safety in a catastrophic failure.
The Valiant B.1 could carry a single 10,000 lb (4,500 kg) nuclear weapon or up to 21 1,000 lb (450 kg) conventional bombs in its bomb bay. Large external fuel tanks under each wing with a capacity of 1,650 Imp gal (7,500 L), could be used to extend range.
Of the three prototypes, two were Mark 1s and one was for a developed version, the Valiant B.2, designed for low level attack. As such it had a strengthened airframe to cope with the rougher ride at low level. The B.2 had a lengthened fuselage with a total length of 114 ft (34.8 m), in contrast to a length of 108 ft 3 in (33 m) for the Valiant B.1. The strengthened wing entailed changes to the main landing gear. Each main undercarriage leg had four wheels instead of two and it retracted backwards into fairings to the rear of the wings. Finished in a gloss black night operations paint scheme, it became known as the "Black Bomber". Its performance at low level was superior to that of the B.1, 655 mph (1,054 km/h) at sea level compared to 414 mph (666 km/h).
The Air Ministry ordered 17 B.2s, including two prototypes and 15 operational aircraft, in April 1952. The prototype was completed, and flew for the first time in September 1953. However, although the Valiant B.2's low-level capabilities would later prove to be highly desirable, the B.2 program was cancelled in 1955. The B.2 prototype was used for tests for a few years, then incrementally destroyed by being used as a target for ground gunnery.
