Project H1, as the JCB DIESELMAX programme was initially known, always had one very clear directive: the diesel engine from the company’s backhoe loader was to be the heart of the Bonneville streamliner. The vehicle itself needed sufficient power to reach 350mph, which meant using two modified versions of the engine. It also needed excellent aerodynamics to ensure minimal drag and impeccable stability and total reliability. It had to be capable of making two runs, one in each direction, within an hour of each other, in order to comply with international record breaking rules. That meant it had to be serviced, refuelled and turned round in no more than 45 minutes, in preparation for its return runs.
Lord Bamford announced his plans not just to turn his humble 140bhp engine into a 750bhp racing unit, but to challenge for honours in the land speed record arena.
Its tyres had to withstand loads in excess of 750kgs while travelling at maximum speed and to do so without fear of failure, which could be catastrophic at the speeds envisaged. Perhaps most difficult of all, the complex vehicle had to operate smoothly in an inhospitable environment, 6,000 miles from home, in which the salt upon which it ran could and would get into any part of the car, with the potential to upset its delicate and sophisticated mechanisms. Small wonder, then, that the world gasped when Lord Bamford announced his plans not just to turn his humble 140bhp engine into a 750bhp racing unit, but to challenge for honours in the land speed record arena.
The concept of JCB DIESELMAX called for two specially modified JCB LSR engines to be used to achieve the required horsepower. To keep the profile of the car as aerodynamically efficient, and therefore as narrow, as possible, they were installed in line, one behind the other. The front engine would drive the front wheels, the rear engine the rear wheels, and there would be no mechanical connection between the two. Synchronisation was handled purely electronically. All four wheels were thus driven, maximising grip, traction and stability.
A key part of the concept was to have the front track wider than the rear. This was important for stability, but also to ensure that the rear wheels would not have to run in any tracks that might be made in the salt by the fronts. To keep the car as low as possible, the engines were installed at an angle of 10 degrees from the horizontal, but in turn that made the car slightly wider than conventional Bonneville streamliners.
The strength of the JCB DIESELMAX diesel engine was a key factor in enabling the use of two-stage, six-bar turbocharging with water injection to boost power. Matt Beasley, Project Chief Engineer, opted for a bespoke fuel system utilising Ricardo’s High Speed Diesel Race direct injection combustion technology to deliver fuel to a common rail system generating an injection pressure of around 1,600 bar. The revised induction and fuel systems were complemented by revised pistons and connecting rods. The crankshaft was lightened but otherwise standard. The racing engines weighed only 375kg. Peak power was 750bhp at 3,800rpm and peak torque rose to 1,500Nm.
Generating more than five times the power of the production version and, at 150bhp/litre, were the world’s highest specific power diesel car engines.
In accordance with the default to safety that was inherent in every aspect of the vehicle’s design, Andy Green sat in a bespoke carbon fibre composite monocoque safety cell which incorporated a mandatory SCTA steel tube rollover cage. The 15 litre wedge-shaped fuel cell was located behind his seat. Green himself had significant input into the design and layout of the dashboard and controls. As a trained RAF fighter pilot he had very firm ideas on what he wanted. "I knew where I wanted the key controls and I knew exactly what sort of graphics would work on the various instruments." Wing Commander Andy Green
"It is very important when you are aiming for very high speeds that you have a simple layout. There is no point in over-complicating things."Wing Commander Andy Green
Aerodynamicist Ron Ayers MBE made three basic stipulations: Drag had to be minimal; download had to be controlled; and yaw stability had to be impeccable. Right from the start the project broke new ground. Ayers was the first to use Computational Fluid Dynamics (CFD) – a branch of fluid mechanics – in conjunction with empirical speed tests of a rocket-powered model, in the design of the supersonic ThrustSSC. As of now he relied exclusively on CFD, for the first time in record breaking history. He was concerned that undercar ‘spray drag’ had robbed competitors of speed. Thus the underside of the car was very carefully sculpted so that the airflow there, which accounted for just under half of the total drag, was particularly smooth.
Right from the start the project broke new ground. Ayers was the first to use Computational Fluid Dynamics (CFD).
JCB DIESELMAX’s remarkable performance was testimony to the breakthrough achieved. It was also important that the vehicle did not generate excessive aerodynamic lift at high speed, but equally too much download would increase rolling resistance. Ayers thus aimed for zero lift and zero downforce, seeking to create a neutral shape. The tall rear fin ensured that the back end of the car stayed at the back, controlling yaw like the flights on an arrow. The overall result was an outstandingly beautiful and effective car with a CdA (drag coefficient) less than 0.15, extraordinary even by land speed record standards.
Braking was therefore one of the most critical factors. The design philosophy always defaulted to safety, so it was decided there would be three separate systems comprising dual-circuit friction wheel brakes, driver-activated exhaust braking and parachutes. In conjunction, custom designed brakes using carbon stators clamped by pistons mounted within the upright. The pistons were activated hydraulically in contact with stators, that clamped the rotor, which was keyed into the wheel. This increased the swept area of the brakes and their effectiveness and provided braking capable of stopping the car in an emergency, such as complete failure of the parachutes. The system was validated by performing two full-speed stops within 50 minutes of each other, confirming that the car could stop from 225mph on wheel brakes alone, make a turnaround and do it again, even if the parachutes failed. The exhaust brake was a proprietary US truck system comprising a simple butterfly in the exhaust pipe activated by a pneumatic cylinder. There were two parachutes. These were each 30 square feet, with 60 foot tow lines.
JCB DIESELMAX weighed four times as much and reached speeds twice as fast as a Formula One car.
Initially, three-speed gearboxes were considered, but they were rejected on the grounds of excessive weight, the need for more ratios and general simplification, in favour of six-speed transaxles. These were used in conjunction with stepper boxes designed by JCB Transmissions, between each engine and gearbox. The powertrains and final drive units were rigid in order to help to stiffen the car and react the drive torque through the gearbox casing rather than through the chassis. This made a big difference to the vehicle’s dynamic behaviour.
Andy Green changed gear via a steering wheel-mounted paddle-shift mechanism similar to those used in Formula One cars, while torque tubes and oil-immersed multi-plate clutches transmitted the power to the wheels.
Initially 26.5 inch tyres seemed the best option for a crucial area of the car design, but subsequently 23 inch proprietary Goodyears were selected. They conferred very significant aerodynamic advantages because they enabled the profile of the JCB DIESELMAX to be much smaller. In turn that meant it could go faster because it created less drag. But in order to ensure maximum safety the Goodyears had to be validated. That meant conducting a series of exhaustive tests which included free-spinning them to over 400mph, then running them through four cycles up to 350mph under a 1,700lb load on a special test rig at Wright Patterson Air Force Base in Dayton, Ohio.
A careful handling protocol was developed which entailed mounting the tyre and giving it a 12-hour pressure soak at 70psi.
Only when they reached the point at which the tyres showed only very slight tendency to blister after the fourth run could they be sure that they were safe enough for the intended record speed runs. Even so, a careful handling protocol was developed which entailed mounting the tyre and giving it a 12-hour pressure soak at 70psi. Then it got a 20 minute break-in period at 60mph, after which it was allowed to cool to room temperature and then repressurised. They were then stored at 30psi, horizontally, and kept out of hard direct sunlight.
There had been several vehicles in the past which had not bothered at all with any kind of springing medium, Chief Designer John Piper was adamant from the outset that the JCB DIESELMAX must have a proper suspension system to maximise both elements and to ensure adequate stability at high speed. He specified conventional heavy-duty titanium wishbone suspension front and rear, with coil springs and hydraulic dampers. The wishbones were kept particularly short in order to keep the suspension geometry as perfect as possible and minimise any camber change that might lead to loss of grip or traction. It was also vital to incorporate ride height adjustment.
Grip and traction are key elements in any Bonneville streamliner.
The rake of the car - the difference between front and rear ride height - can exert a critical effect on its overall aerodynamic performance, so it was extremely important that there was a sufficiently wide range of adjustment to enable a number of permutations to be tested. The suspension at each end of the car was mounted on a subframe and each engine pivoted with its subframe when any ride height adjustment was made. In this way the principal system could accommodate a range of tyre sizes, ranging from the original 26.5 inch choice to the option of 23 inch Goodyears on which JCB DIESELMAX eventually ran.