The four-year mile
Meet the land speed record's answer to the BRM V16. With the might of British industry behind it Donald Cambelesjet-powered bluebird broke the record by just 9mph after four years of effort but it had the potential to go a lot faster, writes Keith Howard
Plot a graph of land speed record marks against the dates they were set and the upward trend holds consistent until August 1939, when John Cobb raced across Bonneville's salt at 369.70mph. There is then, predictably enough, a pause during WWII, after which Cobb continues where he left off, recording 394.196mph at Bonneville in September 1947.
If you were a sober statistician, let alone a betting man, you'd have laid money on 400mph being cracked within a few years and the record being stretched beyond 450mph by 1960. But something odd happens. A glass ceiling is reached and Cobb's mark proves difficult to beat. Mickey Thompson achieves it one-way, and therefore unofficially so far as the FIA is concerned, in September 1960. Bob and Bill Summers eventually raise the official wheel-driven record to 409.277mph in November 1965, where it remains pegged until Don Vesco's recent campaign in Turbinator and his two-way average of 458.440mph for the flying mile, set last October.
Between Thompson and the Summers brothers came Donald Campbell, the only man ever to set world speed records on land and water within one year. In Bluebird CN7 he was the first to crack 400mph for the mile in a wheeldriven car, a two-way 403.135mph set on Australia's remote Lake Eyre in July 1964. And yet Bluebird, and Campbell, are often recalled as failures.
When Bluebird crashed on its first outing at Bonneville in September 1960, rolling across the salt from around 350mph, people questioned whether Campbell had the skill to get the job done. When a further attempt failed, because of bad weather at Lake Eyre in 1963, those same voices asked whether, after the Bonneville accident, Campbell had the guts. Both Sir Alfred Owen, whose company had built Bluebird, and Stirling Moss publicly expressed their doubts as to Campbell's ability an unwise criticism, you might think, to level at a man who had already recorded a one-way average speed of 286.78mph on water (Coniston, September 1956).
Any doubts about Campbell's courage or ability were swept away, to all reasonable observers, when he eventually grasped the record in what were again atrocious conditions in 1964. But for the Bluebird project as a whole there was no reprieve. It had taken almost nine years, and pots of money, to design and build the car and then rebuild it after the accident just to better Cobb's 17-year-old record by a paltry 9mph. When the Summers, whose operation ran on a shoestring by comparison, displaced Campbell less than 16 months later with little apparent effort, the naysayers had their final piece of ammunition. In their eyes, Bluebird was an ill-conceived, over-engineered and vastly expensive folly, a cipher for Britain's lingering imperial notions in a post-colonial world. Writing in Cam in 1981 about the Chrysler Hemi, the engine which powered the Summers' Goldenrod, Leonard Setright distilled this view into two succinct words by describing Bluebird as 'absurdly elaborate'.
But did the car deserve such criticism? Or, had they been blessed with amiddung amount of good fortune, might Campbell and Bluebird have punched a hole in that glass ceiling so large that even with the jet cars reaching to 500mph and beyond the world would have whistled over its newspaper headlines and the Summers brothers stayed at home?
Ken Norris, chief designer of CN7 (Campbell-Norris project number 7), became involved in record-breaking by accident. During WWII, he worked for Armstrong-Whitworth in Coventry, where he began as an apprentice and worked his way up to head of the testing department. He then read for a degree in aeronautical engineering at Imperial College in London. When his professor there learnt of Norris's intention to start his own business upon graduation together with his brothers Lewis (a marine engineer) and Eric (an accountant) he offered Ken his first commission 'doing some stress work'. It turned out that the job was for Frank Harming-Lee and the 'stress work' was on White Hawk, his world water speed record contender.
White Hawk completed, Ken joined Lewis in designing the jet-powered Bluebird K7 for Donald Campbell's new attempt on the water speed record. Lewis had already worked with Campbell converting Bluebird K4 which Campbell had had to buy from his late father's estate from jet power back to propeller drive because, as Campbell had discovered when he ran it in 1947, K4 was prone to unanticipated gyroscopic effects as the Goblin II engine spooled up or down. The redesigned K4 then tore itself apart on Windermere as a result of propshaft whirl, at which point work began designing a jet-powered successor free of K4's misdemeanours. Campbell took the world water speed record aboard K7 in November 1955. It was in the immediate aftermath of that campaign that Ken Norris mischievously offered a toast to the land speed record, to which Campbell replied, `Well, just think about it' — which is precisely what Lewis and Ken did, individually, while working on other commissions. Then they compared notes, agreed the key features of the design — gas turbine engine, four-wheel drive, streamlined bodywork — and set about assembling the key components.
It was clear from the outset that the project would require considerable support from British industry. Before the design process could begin they had first to persuade the Ministry of Supply to donate two gas turbine engines of suitable power. Bristol Siddeley's Proteus — the engine that powered the Bristol Britannia 'whispering giant' turbo-prop airliner — was selected for the task, but after toying with numerous different arrangements for taking drive to both axles from one end of the engine, the brothers concluded that all the options added too much weight and complexity. The design of the car would be much more elegant if drive were available at both ends of the engine, necessitating only a final drive and halfshafts for each axle. So they went cap in hand to Bristol's Sir Stanley Hooker — famous as the designer of the Pegasus engine used in the Harrier — and asked him to spend what would be a considerable amount of the company's time and money modifying the Proteus to provide an output shaft at either end. Hooker absorbed this considerable at request, turned to his colleagues and said, `I think we can oblige, can't we'?
The next important steps were to enlist Dunlop to design the tyres and to use the Imperial College wind tunnel to determine a shape for the car that was not only low-drag but also neutral in lift (in as much as this could be deter mined reliably in a fixed-floor facility). The end result was a shape and major dimensions remarkably similar to those of Reid Railton's design for Cobb, but Ken Norris is adamant no copying was involved. Norris Brothers Ltd always did its own thinking on any project before checking the prior art, he says, so the similarity was a case of convergent evolution. Norris Brothers were influenced by Railton in one respect, though, in the decision not to equip Bluebird with a rear fin to stabilise it in yawed airflows. Railton was opposed to the use of fins, Ken Norris trusted to his judgement — and came to rue that trust when Bluebird crashed at Bonneville.
Dunlop's decision to supply tyres of 52 inches overall diameter came as an unwelcome shock, but tall, streamlined wheel covers were added to accommodate them without too much impact on the aerodynamics. Despite — or perhaps because of— these unexpected excrescences, Bluebird CN7 remains to my eye the most beautiful LSR car ever created, a much more evocative shape than the 'power pencil' Goldenrod. But therein lay one of its purported weaknesses. Whereas Goldenrod had a quoted frontal area of 9sq ft and drag coefficient of 0.117 to give a CdA of 1.05sq ft, Bluebird had a much larger frontal area (26sq ft) and a drag coefficient of 0.16, giving it a CdA of 4.16sq ft — getting on for four times greater.
Much has been made of this aerodynamic disadvantage, but it wasn't so severe as might be supposed. To push Bluebird through the air at 450mph, its original target, would necessitate a power of around 2583hp — considerably more than Goldenrod's 652hp at the same speed but substantially offset by Bluebird's power advantage, on paper, of around 1700hp, which can only have been increased in practice by greater losses in Goldenrod's transmission.
Traction was not a limiting factor either, since to provide the 2154lb of tractive force required, assuming an all-up weight for Bluebird of 9500lb, the friction coefficient between tyre and salt would — need to be 0.23 — a fraction of the 0.5-0.6 available on a good salt surface, although this reduces with speed.
The other great restraining hand on an LSR car is tyre drag, and in this respect Bluebird was almost certainly superior to Goldenrod, as Ron Ayers — Thrust SS C's aerodynamicist — has explained in these pages (October 2001, page 54). Quantifying tyre drag on salt has never been a simple matter, not least because the compression of the surface depends on its condition, which varies from season to season and year to year. But George Eyston's aerodynamicist Jean Andreau had developed an equation to allow its estimation which, in addition to showing that tyre drag is much more highly speed-dependent on salt than on a hard surface like asphalt, established the crucial importance of tyre pressure. According to Andreau's formula, tyre drag at 300mph could be reduced by three-quarters by doubling inflation pressure from 60 to 120psi. For this reason, Cobb's tyres had run at a high 120psi; CN7's were enigmatically specified as operating at 'greater than 100psi', but in truth ran substantially higher. During the Goodwood shakedown in July 1961, Dunlop technicians were spotted setting the pressures to 130psi. For the record attempts, Ken Norris recalls, 160psi was used. So, despite the fact that tyre drag didn't feature in his calculations for Bluebird because of the difficulty in quantifying it, he could be confident that CN7 had unprecedentedly low rolling resistance, a factor that will have helped nullify, at the very least, its higher aerodynamic drag.
In fact, Bluebird had all the essential ingredients necessary not just to break Cobb's record but to smash it. Railton's and Norris's designs had similar aerodynamic drag, but CN7 packed 60 per cent more power in addition to its lower rolling resistance, which may have been further assisted by Bluebird having the same tracks front and rear; its rear tyres could run in the indentations made by the fronts, whereas the Railton car's narrower rear track made this impossible.
Although the initial target was 450mph, CN7 was designed, with a change of gearing, to achieve 500mph. The crash, and then two years of rotten surface conditions, prevented it achieving anything like those speeds, but its capability was plain to anyone paying sufficiently close attention to its runs.
Immediately before the Bonneville accident even on a surface that was acknowledged to be at less than its best Campbell was well ahead of a target schedule that would have seen him enter the measured mile at about 405mph and complete it at 420mph. According to its telemetry, the car was already doing 365mph when it crashed, less than 1.8 miles into its run and with 3.3 miles still to go to the first timing position. Ken Norris conservatively reduced the estimated crash speed to 325mph, but even then the car would have been 35mph (12 per cent) ahead of schedule. The inference is obvious: had the fateful side wind not intervened, Bluebird would comfortably have exceeded Cobb's mark in one direction, at any rate on only its sixth run on the salt.
Criticisms that CN7 was too complex have to be viewed in the light of its considerable ambition. Ken Norris refers to it, with obvious pride, as 'a year 2000 car'. Norris Brothers spent 36,000 man-hours designing it and produced a total of 800 manufacturing drawings (for which they were paid 1,16,000). It included technical novelties such as honeycomb sandwich structural panels, a telemetry system to monitor key operating parameters (which proved to be an abject failure in the difficult radio reception conditions presented by the salt flats) and even a head-up display of vehicle speed developed by Smiths Industries. Campbell didn't like the HUD because of its green digits, but whether his notorious superstitiousness deemed the colour unlucky or he simply couldn't read it against the glare of the salt is uncertain.
In its essentials, CN7 was actually remarkably simple more so than Goldenrod in some key respects, most notably its drivetrain. Whereas the Summers' car had to grapple with synchronising four piston engines and their transmissions, CN7's gas turbine with a driveshaft at both ends required no complex transmission arrangement and no gearchange -just a fixed-ratio final drive at either axle line to gear-down the shaft speed and redirect the torque to the wheels.
Any suggestion that the complex structure of CN7 was overly elaborate is refuted by Donald Campbell surviving the accident with only minor injuries something it is difficult to imagine Cobb having done had he rolled the Raihon Mobil Special at the same speed and the discovery, when the car was returned to Motor Panels' Experimental Department in October 1961, that about 75 per cent of it was salvageable for the rebuild. A tail fin was added and various other refinements incorporated, but the reconstituted CN7/62 was little different overall to the unfortunate CN7/60.
Once the record had finally been broken in Australia, Campbell returned his attention to the water speed record. But CN7 had one last outing before being retired, when Campbell agreed to perform a demo for charity in August 1966, on the long runway of RAF Debden, near Saffron Walden in Essex. Campbell was ill at the time, so a driver unfamiliar with the car drove it in his stead. Unused to the delayed power delivery of a gas turbine, he overshot the end of the runway, crossed a public road just in front of a bus and crashed in the field beyond, causing an estimated 1,50,000 of damage.
Still with its twisted bodyshell, CN7 lines up today alongside other stalwarts of British LSR history in the National Motor Museum at Beaulieu.
My own two-word epitaph to it certainly would not read 'absurdly elaborate' but 'potential unrealised'. It could and should have elevated the wheel-driven land speed record to a remote new plane.