Flying colours - design of the American Air Museum in Duxford, England

Architectural Review, The, Feb, 1998 by Penny McGuire

The design of a new museum in East Anglia, sheltering a collection of historical American aircraft, pays powerful tribute to all US airmen, past and present.

Of all proposals to Norman Foster in recent years, the one by the Imperial War Museum to design the American Air Museum in Britain must have caught his imagination with particular force. A pilot himself, his passion for flying and aircraft is well-known.

The American Air Museum is part of the aviation museum, run under the auspices of the Imperial War Museum at Duxford, about eight miles from Cambridge. As part of one of the best collections of historic aircraft in the world, the museum also has what is thought to be the finest collection of American military aircraft outside the USA.

This featureless stretch of land is an emotive place. The airfield has been in existence as an RAF station since 1918, when British pilots training for the Great War were joined by an American squadron. In the Second World War, Duxford was a Battle of Britain fighter station and occupied between 1943 and 1945 by the US Eighth Air Force. Closed down in 1961, it was taken over by the Imperial War Museum and opened to the public about 15 years later.

Today, standing beside the airfield, which is still active, you can watch the more agile of the old planes - Spitfires, Mustangs and Lightnings - climb into the sky. Relics of the Great War are the hangars which, now listed, serve as exhibition halls for the various collections.

The Foster design of a new American hangar took shape over 10 years ago when it became clear that aircraft displayed outside, rotting and corroding in the English climate,(1) had to be sheltered. Recession and lack of funds delayed construction until the arrival of a grant from the Heritage Lottery Fund. It was supplemented by money from fundraising on both sides of the Atlantic - by such glamorous former pilots as Charlton Heston and the late James Stewart - and from Saudi Arabia, grateful for British and US efforts in the Gulf War.

The client wanted a landmark but also a building that would be a neutral backdrop for the planes; and Foster's museum is both an elaboration of the basic hangar and in substance a monumental tribute to the machinery it shelters.

Set at one extremity of the airfield, the building is a huge shell-like structure emerging from a grassy mound (it is not the same, but you cannot help recalling the Sainsbury Centre extension). This toroidally generated shell - like the sliced half of an odd bi-valve - is slashed around the base by a crescent of glass and enclosed where sliced through by a glass wall. Abstract form and the building's tendency to dematerialize (it is sheathed in a silvery membrane that at times disappears into the skies), dissipate size and make accord with the ephemeral nature of the wide Cambridgeshire landscape.

Inherent in the design of the structure is a nice opposition, for if aircraft design is to do with detailing, the architects of this starkly dynamic shed have eliminated it, leaving the thrust of the structure to speak for itself. At its greatest, the free-spanning arch of the roof measures 90m across and 18m in height, and elliptical on plan, the building is 100m long. Its design was driven mainly by the need to house the sinister B-52 Stratofortress, the long-range bomber famously used in Vietnam and the Gulf with a wingspan of 61m and a tailfin 16m high; but also by the desire to suspend some of the smaller aircraft, weighing up to 10 tonnes, from the roof. The building had also to be economic to build, run and maintain, for the only source of Duxford's income is admission charges. While heating costs were felt to be prohibitive, humidity control was considered essential. As much daylight as possible was to be admitted to reduce lighting bills.

Comparative analyses showed that a concrete building could keep the temperature above dew-point, so that condensation did not occur and dehumidifying plant could be kept to a minimum; and in effect, the Foster and Arup engineers have devised a structure that is self-regulating - within limits. Thermal mass helps delay the change in temperatures, ironing out peaks and troughs and taking 2 to 3 degrees Celsius off external extremes.(2) Daylight flooding through the glass facade is augmented by light bounced through the inclined glass crescent off surfaces at the rear of the hall.

The roof is composed of two shells, each built up from precast concrete panels and fitted together like a Roman vault. Because a torus is defined by only two constant radii, using toroidal geometry simplified and cheapened construction. There are only five panel types for the entire roof. Those of the lower shell are T-shaped in cross section, the stems of the Ts separating the shells and forming the ribs to which the upper panels are fixed. The roof was erected, much as Roman vaults were, by means of false towers; and when completed, sockets of the lower panel were cleaned out and converted into suspension points, each having a capacity of 12 tonnes. At the front of the building the structure behaves mainly as an arch, and at the back, where it is very flat, as a beam. Membrane action of the shells permits load sharing in two directions under the weight of the suspended aircraft.