Lost Classics - Bristol Brabazon
In the dark days of World War 2, a British Cabinet committee met under chairmanship of Lord Brabazon of Tara. They were to explore and advise upon what Britain's post-war airliner needs would be, a task which at first sight may appear to have been rather optimistic.
However, a 1942 Anglo-American agreement divided the load of military aircraft construction between Britain and the US. It left Britain unable to develop transport aircraft, which was part of the package assigned to America. So, in something like self-interest, the committee planned for a time when Britain might recover lost ground.
The 1943 committee reccommended upon a number of aircraft categories, one of which was, for the time, a challenge. This was for an aircraft able to fly from London to New York non-stop and with regularity. Britain could claim some sophistication in its development of piston engines, whereas the turbine engine was still an unknown and risky piece of machinery. This aircraft, it was assumed, would be piston-powered.
Bristol Aeroplane Company had already done a design study in 1937 for a long-range strategic bomber, so when invitations were extended in 1942 for studies related to a heavy bomber, they were at an advantage. This led to a design with a range of 5,000 miles, 225 foot wing span, and eight buried engines driving four pusher propellers. It had a thin fuselage and butterfly tail. The Air Staff decided to stay with the Lancaster bomber, so nothing came of the Bristol design.
When the Brabazon Committee's intercontinental airliner was proposed, however, the work already done by Bristol late in WW2 on their heavy bomber design led to them being given an order for two prototypes, to be followed by a possible ten production aircraft.
After considering a variety of capacity and design criteria, in November 1944 the concept solidified around a 177 ft. fuselage with 230 ft wingspan (35 ft. more than a Boeing 747), powered by eight Bristol Centaurus 18-cylinder radial engines nested in pairs in the wing. These drove eight paired counter-rotating propellors on four forward-facing nacelles.
The Brabazon project team were among the best and brightest of their time, and they developed what was probably the first instance of an aircraft designed with an optimal structure. Structural components, including the skin, were designed to meet load requirements whilst having only minimal weight. Skin panels were machined to closer tolerances than ever, and to non-standard gauges. Weight savings through innovation and sophistication could be measured in tons.
The large span and mounting of the engines close inboard, together with structural weight economies, demanded some new measure to prevent bending of wing surfaces in turbulence. A system of gust alleviation was developed for the Brabazon, using servos triggered from a probe in the aircraft's nose. Hydraulic power units were also designed to operate the giant control surfaces.
The Brabazon was the first aircraft with 100% powered flying controls, the first with electric engine controls, the first with high-pressure hydraulics, and the first with AC electrics.
Construction commenced on the Brabazon in October 1945, in a specially-built 8-acre assembly building adjoining a new, strengthened 8,000 ft. runway. This last structure was built in the face of an out-of-date Civil Airworthiness Requirement, which insisted upon the use of runways no longer than 2,000 feet, forcing a landing speed of around 60 mph. This in turn demanded a low wing loading, and thus an increased wing area. Long, narrow wings are more efficient, having lower drag, but long, strong wings were demanding on the techniques of the time, and tended to be heavy.
The solution for Brabazon was to bury the engines in the wings, near the props. This in itself reduced drag on the engines. It made the wings substantially thicker, but it also enabled the wings to be made lighter and stronger.
The aircraft rolled out for engine runs in December 1948. On 4th September, 1949, chief test pilot "Bill" Pegg took the Brabazon up for her first flight. Most of the work force and thousands of other spectators cheered as the aircraft climbed majestically, flew around, and landed.
The aircraft was free of any major problems, especially considering the many groundbreaking technological applications in the design. Everyone who flew in it was impressed by its quietness and smoothness and its spacious interior.
Back in 1946, it had already been decided that a Brabazon Mk.II would be built with four Bristol Coupled Proteus turboprops, driving an eight-bladed contra-prop. These would save an estimated five tons in weight and boost the top speed to 330 mph at 35,000 ft. It would also impose greater airframe stresses which would have to be addressed.
Four days after her first flight, the Brabazon prototype, G-APGW, appeared at the Farnborough Air Show. During June 1950 she visited London's Heathrow Airport, making a number of successful takeoffs and landings, and was demonstrated at the 1951 Paris Air Show. By now about £3.4m had been spent on development. However, half of that went into infrastructures, including massive hangars and the long runway, both of which remained in use for decades.
The Brabazon was to fail for reasons of economics. She was conceived following an era when passenger flying in England and Europe was the domain of civil servants in transit, business executives and the well-off. The airliner was viewed in the same light as the ocean liner. BOAC considered passengers would find a long non-stop flight almost intolerable and should therefore be provided with 200 cu. feet for comfort, and 270 cu. ft. for luxury. This equates with about three times the interior size of a modern family car, per airline passenger.
The 1944 version of the proposed airliner gave it a 25 ft. diameter fuselage (about 5 ft. greater than a Boeing 747) with upper and lower decks. This enclosed sleeping berths for 80 passengers, a dining room, promenade and bar; or day seats for 150 people. The Committee recommended a narrower fuselage designed for 50 passengers. BOAC agreed, but preferred a design for only 25 passengers.
BOAC were assumed to be a major buyer for the new Brabazon design. An agreement with the airline eventually led to an interior layout housing a forward saloon with six compartments, each for six passengers, and another one for just three; a midships section at higher level above the wing with 38 seats arranged around tables in groups of four, plus a pantry and galley; and a rear saloon with 23 seats in an aft-facing cinema, plus cocktail bar and lounge. The Brabazon was be one of the first airliners to be pressurised and air conditioned. It was also be a very big, heavy aircraft - weighing nearly 300,000 lb - for only 100 passengers.
BOAC, despite its preferences being regarded as weighty matters, never showed any real interest in buying the Brabazon, although BEA (British European Airways) considered hiring the Mk.I. A number of problems, such as fatigue cracks appearing in propellor mountings, prevented full airworthiness certification.
These design problems might have been resolved; but the development of turboprops and jet engines for airliners changed the conditions which existed during the Brabazon's gestation. Passengers could travel faster, above the bad weather, and large areas dedicated to the comfort of an uneconomically small passenger load were no longer required.
Passengers would not spend 12 hours in a Brabazon when they could reach their destination in a smaller, faster aircraft in seven. By 1952, the economic validity of the Brabazon project was shaky. In March the British government announced that work on the second prototype had been postponed. In October 1953, after less than 400 hours flying time, the first prototype was broken up, along with the uncompleted second Brabazon prototype. At least until in 1996, the tensile test rig for the Brabazon was still in occasional use in the National Engineering Laboratory, East Kilbride, Scotland.
(Thanks to Stewart Russell, Bishopbriggs, Scotland, for
advising of survival of the tensile test rig for the Brabazon)
|Bristol Brabazon data:
Eight Bristol Centaurus
18-cylinder radial piston engines,
each of 2,650 hp (1976 kW) driving
16 ft (4.88 m) contra-props
Four Bristol Coupled Proteus
turboprops, each of 7,000 hp
(5210 kW) driving eight-bladed contraprops.
NORMAL CRUISING SPEED
(Proposed turboprop Mk.II):
250 mph (402 km/h) at 25,000 ft
330 mph (531 km/h) at 35,000 ft
230 ft 0 in (70.1 m)
177 ft.0 in. (53.95 m.)
FUSELAGE MAX. EXTERNAL DIAM.:
Width 16 ft 9 in (5.1 m)