Thrust SSC

Chapter 2 - Proving The Case
The Research Programme, England and Wales, 1992-1994

It must be stated at the start of any account like this that Ron Ayers did not believe at the outset of his research that setting a Supersonic World Land Speed Record was possible. He simply agreed to look into it with Richard Noble on the understanding that if he were to find it could not be done safely, the project would end there. Many at the time agreed with the aerodynamicist - believing that the shockwaves under the car would lift it into the air and send it to its destruction.

Ayers faced a fundamental problem: he had a good idea of what a supersonic car should look like - twin engines to get the weight up front, with a long thin fuselage behind to provide dart-like aerodynamic stability, and the driver at the centre of gravity - but he still needed to prove that stability. When researching such a design one usually relies on two sources of information: past experience and experimental data. By its very nature as a World First there was no data available on supersonic land vehicles, although data from Thrust2 did give some idea of what was happening to the airflow around that car at Mach 0.9. Experimental data would usually be acquired in a wind tunnel, and although supersonic wind tunnels as well as wind tunnels with rolling roads do exist, the two features are never found together.

A new means of experimentally investigating the tentative design needed to be found and the suggestion was raised of using the application 'Flite' on a Cray 92 supercomputer at the University of Swansea. Normally applied to the study of aircraft, the software was unproven in a ground-level analysis, but the figures produced by the lengthy calculations were extremely promising. As Chief Aerodynamicist on the project that developed the Bloodhound missile, Ayers was unused to the use of prediction software, and was uneasy about some of the assumptions he had made. To be able to say that the design was safe, he needed to cross-check the simulations with real experiments.

Thus a new form of supersonic aerodynamic testing was born - the use of a rocket sled. At Pendine Sands in South Wales, coincidentally itself a past LSR site, is a rocket-sled track used to drive missile heads at speeds of up to Mach 3.2 to test their powers of penetration. Using surplus motors from air-to-ground strafing rockets, the research team made 13 supersonic runs with a 1:25.4th scale model of the car bristling with high-speed sensors to measure the pressures around the vehicle. With each run the model was lowered closer to the 'road' until finally it was leaving witness marks in the wooden surface. The runs passed without major incident - provided one excludes a supersonic bird strike from consideration.

The next stage in the process was to marry-up the two sets of figures - those from the simulations, and those from the rocket tests. To Ron Ayers's eternal surprise they matched right across an enormous range of cases - the shape of the new car had been born! Despite his cautious air and meticulous attention to details, there were still some who doubted the result was genuine, and one sponsor engaged specialists to make an independent check of the numbers. They too were astounded by the closeness of the two sets of data, and clearance was given to proceed. Noble named it ThrustSSC - for SuperSonic Car.

With the car's shape represented by a massive spreadsheet of coordinates, the task of marrying that to a mechanical design fell to a member of the old Thrust2 Team. Glynne Bowsher had designed the brakes of that car, as well as undertaking stress analysis of the solid aluminium wheels - without hesitation Richard Noble called on Glynne's expertise again: this time to produce the entire mechanical design of the new vehicle.

The decision to employ a spaceframe with easily removed skins rather than a more technically advanced monocoque was an simple one - access for maintenance would be crucial, as would be the ease of changing the massive Rolls-Royce Spey engines chosen to power the car. One particularly difficult question raised its head, however - there was very limited room available around the engines' intakes to incorporate the front wheels, let alone allow room for steering movements. In addition, with 60% of the vehicle's weight on those wheels, their sheer size would give rise to enormous gyroscopic forces when the driver turned the steering wheel at the maximum design speed of 850mph - forces large enough to risk overturning the car.

Bowsher had a novel solution to the dilemma - there was plenty of room around the rear wheels: why not steer using those? Naturally the idea met with a mixture of acclaim and derision with frequent references to fork-lifts, dumper-trucks and supermarket trolleys, so to test the idea his brother-in-law's old Mini was converted to rear-wheel steering with a scaled-down version of the jet-car's geometry. Those who drove it discovered that it could be driven to an accuracy of 1 inch at 100mph, and although it was unsuited for shopping or for use on busy city roads, the expanses of the Black Rock Desert would pose no problems for a rear-steered record-breaker.

Further research investigated the effect of the reheated exhausts on the adjacent rear bodywork, the suitability of active noise reduction in the cockpit, and the aerodynamic considerations necessary to keep the car on the ground at all times. It was the need to adjust the angle of attack of the car to the oncoming airflow that led to the decision to utilise an active rear suspension - a decision which led to systems expert Jeremy Bliss joining the project team. Utilising computers to monitor sensors and adjust hydraulic rams attached to the rear wheels, the system would enable the ride height of the back of ThrustSSC to be adjusted by up to two inches (5cm) to keep downforce constant regardless of Mach number.

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