Architecture: Foster and his flying machine

No prizes for guessing who won the Stirling Prize for architecture announced last night at the Royal Institute of British Architects: Sir Norman Foster, for the pounds 8.2m American Air Museum at Duxford.

Ladbroke's favourite to win at 5:2 was Sir Colin St John Wilson, the architect of the British Library which cost pounds 511m and took 14 years to reach a point where it was ready to open its doors. Wilson was bitterly disappointed by the news, especially after the RIBA, in a surprise move last week, reinstated his British Library on the shortlist after the panel had thrown it out.

But the jury knew "almost at first glance" that the Duxford Air Museum, opened by the Queen last year, was likely to be the winner. Running a close second was the Rick Mather three-quarters-of-a-million-pound glass house in Hampstead.

Anyone - and there have been more than 450,000 visitors to the museum since it opened - standing under the big bellied planes suspended from Foster's precast concrete roof at Duxford knows this is the best building to be built in Britain last year. And in Tyneside on Monday, the launch of the plans for a new music centre by Foster Associates added to the feeling that Norman Foster has stopped building walls. Roofs that soar and plunge, swoop and back flip envelop an exhilarating space within. They also bathe cavernous spaces in natural light, which is one of Foster's preoccupations.

The Stirling Prize awarded in honour of James Stirling is, for architects, the equivalent of the Booker Prize. For months the jury tour the buildings that make up the categories in the Royal Institute of British Architects breakdown: best housing, commercial building, sport and leisure, conservations, education and health. Foster had two buildings shortlisted - the vast Commerzbank HQ, a hanging gardens of Babylon under glass in Frankfurt, and the American Air Museum at Duxford in Cambridge.

Just how much the judges liked the Duxford museum is clear from their citation: "a great big, clear span hangar of a building, beautifully integrated into its flat landscape... dramatic, awe-inspiring, an object of beauty displaying a collection of war planes dispassionately, simple yet replete with imagery, from ancient earthworks to the cockpit of a modern jet fighter."

But perhaps it is not so dispassionate because Norman Foster's great passion in life is flying. A commuter by helicopter all over Europe, he pilots himself. When he was younger - he's 65 - he used to relax by hurling himself into competitive aerobatics at intermediate level. He knows the name of every single plane in the Duxford museum and has even gone hang gliding over Arizona in one of the glider planes that hangs there. Set in cement and framed in glass, his love of flight is romantically, and passionately, grounded here. That's what makes the building a palpable experience.

On arrival, you walk straight into the nose of the B-52 bomber that determined the museum's dimensions. Inside, an encircling ramp allows walking or wheelchair access and a narrow strip of window also encircles the building. The silvery grey cement ramps are angled to bounce back as much natural light as possible.

The American Air Museum is both the simplest and the most complicated of Foster's buildings. Simple because it is wide enough to take the B- 52 bomber with its wing span of 63 metres and - at four storeys high - has enough space for another 20 planes. Complicated because its geometry is based upon a geometric shape called the torus and it is elliptical in plan. The torus is like a doughnut with a bite taken out of it, dunked into a grassy knoll.

The front facade - the "bite" - is a gigantic glass-fronted arch 90 metres high, overlooking the operational runway where enthusiasts still coax Airfix model lookalikes into the sky. Chris Wise, a structural engineer from Ove Arup, made the precast concrete roof strong enough to suspend aeroplanes from it. Another plus is that the precast concrete cuts humidity, important when preserving aluminium planes.

How to marshal all that weight in such an elegant form is the real genius of Foster. At Hong Kong airport the roof sinuously wraps itself in great leviathan curves over vast halls. Foster's latest project, the new Music Centre at Gateshead, was unveiled this week in a bid for lottery funding. The scale model features another big sheltering sky roof, even more challenging because it will have to be acoustically sound. Never mind the failure of Siemens and Fujitsu that have caused redundancies in the region. Gateshead Council wants concert halls for brass bands, folk music, Northumbrian pipers and the Northern Sinfonia orchestra, with rehearsal rooms, a music school and a base for a resident music organisation "all under one roof".

And what a roof it is, too, containing three big geometric volumes, shaped to echo the Tyne Bridge and come to rest gently in scale with the adjacent St Mary's Church. It looks as though a Zeppelin has landed at Tyneside. The main hall would seat 1,600 to 1,800 in a rectangular platform, the best configuration at that size to cut reverberation and produce perfect acoustics without amplification. For "music you can play in a power cut" is how Peter Stark project manager at Gateshead describes it. Sandwiched between this and the second 10-sided hall, smaller and more flexible in space, would be the rehearsal hall and the music school which will bring the building to life by day.

It seems a bit mean-spirited to mention a dispute over acoustics, but scholars in the new Foster Law Library at Cambridge University can hear a can of Coca-Cola clunk down into the drinks machine five floors down. Spencer de Grey from Foster Associates is stung by this:

"Everyone now forgets that every spoken word can be heard without amplification in the Cambridge lecture room with 350 seats, also by Foster. Besides, the issue is resolved now with a discreet separation of the reading area with glass screens from the rest of the building."

The Arts Council gave Gateshead Council pounds 1m to develop the Music Centre with the architects. "We have it in writing that if our application meets the criteria, funds will be available," Peter Stark, the project manager, says. The council needs pounds 60m and they intend to apply for pounds 45m from the Lottery. Councillor George Gill, the chairman of the Music Centre steering group, is matter-of-fact: "Gateshead forge ahead because when we say we will deliver, that is what we do."

"We've had the biggest regional arts funding from the Lottery in the country, with over pounds 90m," Andrew Dixon, head of Northern Arts at the Gateshead Council admits. "It was the Angel of the North that started it. Now it's a tourist attraction. On one day it appeared on the Eurovision Song Contest, Top of the Pops and Desert Island Discs."

Would James Stirling have approved of this year's prizewinner? "Yes" is probably the answer. In 1986 he shared a major exhibition at the Royal Academy with Foster and Richard Rogers; as a group the three big names in contemporary British architecture. Stirling, the senior in age and stature at the time, was given central place.

Mark Girouard, biographer of "Big Jim", reveals that in 1991 when Stirling was asked to nominate three post-war buildings in London that will stand the test of time, he named Foster's Sackler galleries at the Royal Academy and Richard Rogers' Lloyd's Building.

He sent Foster a hero-gram in June 1991: "I was at the Sackler last night and this is just a note to say how elegant and good I think your galleries are, and a very clever solution." Which is about as effusive as Stirling ever got.