An automobile designed with a target speed of 500mph in mind
Donald Campbell’s pursuit of speed records is the stuff of legend, and the vehicle that embodies his attempts on land is the Bluebird CN7. In the planning stages since 1956 – at which point Campbell was chasing records exclusively on the water – the CN7 was almost ready for action by the time it featured in the May 1960 issue of The Engineer.
The land speed record (LSR) stood at 394mph, set by John Cobb in the Railton Mobil Special. Campbell, in collaboration with his engineering partners Norris Brothers, planned to obliterate that number, and Bluebird was designed with a target of 500mph in mind. To achieve this, the CN7 would incorporate a host of groundbreaking technology.
The four-wheel-drive monocoque Bluebird was the first LSR contender to be powered by a gas turbine engine, a Bristol-Siddeley ‘Proteus’ 705 with an output of 4,250bhp. According to this magazine, “the use of a ‘Proteus’ dictated other important characteristics of the design; since it has, in effect, a ring of air intakes around the centre section, a plenum chamber installation was virtually mandatory, so that the steel-tube-frame construction of the Norris-designed ‘Bluebird’ hydroplane was forsaken for an ‘egg-box’ design.”
The ‘egg-box’ construction was apparently selected in order to sustain the pressure differential of around 3lb per square inch expected in the engine bay. To accommodate this, the team used an aluminium alloy, the stiffness of which “was obtained by using ‘sandwich panels’ with stabilising cores of ‘Aeroweb’ honeycomb”.
Sandwiched honeycomb structures are common today in the aerospace industry, but their use for lightweighting in a motor vehicle was, at the time, revolutionary. According to our predecessors, the primary driver of the lightweighting was the split-rim design wheels and – more specifically – 52in diameter tyres, which were manufactured by Dunlop.
“During the design of the car it proved that the one component whose capability limited the performance and dictated alterations to the design was the tyre. Weight saving and even drag reduction are prosecuted solely to lighten the duty of the tyres.”
Tyre performance at speeds in excess of 420mph was so vital that Dunlop built an entirely new test rig on which to trial Bluebird’s custom boots. They would see their first action at Goodwood in July 1960 at the vehicle’s public launch, and would propel Campbell and the CN7 to a speed just shy of 400mph at Utah’s Bonneville Salt Flat two months later.
Shortly after, on 16 September 1960, Campbell suffered a high-speed crash in Bluebird, fracturing his skull. It was 1963 before he was back at the wheel of the CN7 attempting to break the record, this time at the salt flats of Lake Eyre in South Australia. Having not seen rain in 20 years, the dried salt lake witnessed torrential downpours in May, and Campbell had to abandon his efforts. He returned a year later, however, setting an official FIA LSR of 403.10mph on 17 July 1964. But rains that year also prevented Bluebird from reaching its full potential, and Campbell was disappointed not to have posted a speed in excess of 450mph.
His frustration was compounded by American Craig Breedlove having already exceeded Campbell’s speed, although this was not officially recognised by the FIA, as Breedlove’s Spirit of America was not wheel-driven by its jet engine. Bluebird was actually the last wheel-driven vehicle to hold the official record, as the FIA subsequently relaxed its technical rules.
Campbell’s legendary status was cemented later in 1964 when he broke the water speed record (WSR) on the last day of the year, hitting a speed of 276.33mph in the Bluebird K7 hydroplane. He remains the only person to set land and water speed records in the same calendar year. Just over two years later, on 4 January 1967, Campbell was killed attempting to set an eighth WSR. On Coniston Water, in the Lake District, a heavily modified K7 broke up at speeds in excess of 300mph, killing its pilot instantly. Between them, Donald Campbell and his father, Sir Malcolm, set a total of 11 speed records on water and 10 on land.