Only a handful of men know the secret of what happens to air when it is pushed over and beneath a car exceeding the speed of sound - and those in this elite club are keeping that knowledge very much to themselves.
Richard Noble and Ron Ayers - the masterminds behind the Thrust SSC project to break the Sound Barrier on land - are among those who know, and because they do they are convinced that their record contender will become the first vehicle ever to travel at supersonic speed at ground level.
Aeroplanes have, of course, been travelling at such speed since Chuck Yeager's historic flight in the Bell X-1 research plane on October 14 1947, but planes have air all around them and operate at such a height that they have a valuable safety net should anything go wrong. But what will happen when the shock waves generated by supersonic motion have the ground plane upon which to reflect?
Without question, the Castrol-supported Thrust SSC project is a dramatic engineering programme that is venturing into a region previously only the preserve of the foremost aircraft designers. 'We are,' says prime mover Noble, 'making an enormous leap forward.'
Power alone is a relatively minor part of the record breaking equation. A vehicle must have sufficient, of course, but it must also behave in a manner that allows the pilot to use that power. 'You've got to have a stable car,' Noble stresses time and again. 'Without it, you run the risk of the most appallmg accident. You always have to remember,' he adds with cold-blooded acceptance, 'that we are dealing with enormous forces.'
Aerodynamicist Ayers, once the man behind the Bloodhound missiles, gives a graphic insight into the problems facing motorsport's aspiring Yeagers.
'If the front of the car lifts by as little as one degree - or even half a degree - all the weight will come off the front wheels. The car will then nose up and flip over backwards. The forces acting upon it at maximum speed will be in excess of 40 times the force of gravity.'
No vehicle could possibly survive that.
The problem is two-edged, as Noble illustrates. 'If the nose comes up, you're going flying. But, equally if it goes down, then you're going mining! The car's aerodynamic behaviour has got to be neutral.'
This is why Noble and Ayers began their project by studying the aerodynamic factors. Without knowing precisely what happens when airflow under a vehicle goes supersonic, they could not pursue their dream. Castrol provided the seed capital that they had required for their initial analysis, and in a leap of lateral thinking Noble enlisted the help of the Proof and Experimental Establishment at Pendine. There a scale model of the proposed vehicle was run at speeds of up to 850mph (1368kmh) - Mach 1.1 - on a rocket powered sled.
'These were unique tests,' says Ayers. 'Nobody had ever tried anything like that before.'
By studying frame by frame film footage of the runs, he and Noble were able to prepare an analysis of the airflow at all stages of the speed regime, and to draw up accurate predictions of the car's behaviour. It was a vital step forward. To be absolutely sure of the integrity of their findings, they then enlisted the support of Cray C92 Computers to conduct a separate computational fluid dynamics study of the same factors. Using a Cray C90 computer capable of 16 billion calculations per second, they were able to calculate once again the airflow and forces acting upon Thrust SSC.
Meanwhile, the McLaren team had been doing a similar exercise on the rival Maverick contender, but only Thrust SSC has authenticated such findings by comparing them with the empirical rocket sled testing at Pendine. When Noble and Ayers plotted both sets of figures together - and found to their profound relief that each agreed with the other - they knew they were on the right track.
Recent further testing at Kingston University matched the aerodynamic performance of the car and its two Rolls-Royce Spey 205 turbojet engines for the first time, simulating it with a scale model of SSC powered by two rocket motors. This indicated that at certain speeds the exhaust from the engines would have an adverse effect on the efficiency of the tailplane that is an essential part of Thrust SSC's stabilising system. As a result the tailplane has been brought forward slightly to alleviate the problem.
Otherwise, Thrust SSC's basic shape has changed little since Ayers produced his first model, the twin-engined car breaks new ground and goes against accepted wisdom on what shape very fast cars such as this should take. In the past, supersonic aspirants had opted for a vee-shape for the underside of the chassis, to deflect the shockwaves as smoothly as possible. Ayers, however, dismisses that theory.
'The idea of a vee-shaped fuselage means nothing, because nobody who shaped it that way actually knows what happens with the shockwave. But we do. Through the rocket test I know exactly what happens to the airflow under the car and to the shockwaves. It's like we've tackled the problem head-on, where others have tended to shy away from it and avoided actually investigating it.'
He is adamant that the pencil-slim fuselage with an engine mounted either side at the front is the best concept, and is also convinced that a system of moveable aerodynamic surfaces - which would require a change in the technical regulations - is not necessary to solve the problems SSC faces.
'I have a better way,' he smiles, 'and I can't say what it is because we are effectively inventing something. We now know about the complexities of the airflow under the car, and no-one else in the world knows that. And at this stage of our development programme I'm keeping that to myself!'
Nobody has yet put their knowledge to the final test, but Richard Noble and Ron Ayers are the closest to realising that goal and will move forward with confidence as Thrust SSC makes its first runs in 1996.
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