The appropriately named sprinter, Usain Bolt, holds the human land speed record for bolting from zero to 100 metres in an incredible 9.58 seconds. It takes single-minded resolve, extreme determination and great discipline to develop such physical kinetic power, and Bolt continues to astonish at every athletics meet anywhere in the world.
As a magazine dedicated to motorcars and motoring, our admiration of “superhuman” ability is skewed towards the combination of man and machine, or more specifically, car and driver.
The street-legal Bugatti Veyron Super Sport has a top speed of 430km/h. It’s powered by a mighty 8-litre 12-cylinder engine that produces a whopping 1200bhp. So, the mad men who want to claim the land speed record have to look beyond road-car motors, and the answer lies in jet engines.
One of them is Andy Green, a Royal Air Force fighter pilot. His Thrust SSC has already exceeded the speed of sound – 1224km/h, or just over 340 metres per second. Such velocity at ground level is unknown territory.
Green’s “rocket car” has no mechanical transmission to drive the wheels, because thrust from the jet engines provides the driving force. Twin turbofans, with a staggering 110,000bhp between them, sit on either side of the narrow and sharp “cockpit”. The engines are manufactured by Rolls-Royce PLC, which currently builds Trent engines in Seletar for the Airbus A380. The Thrust uses a much older engine model – designated the RB168, it was previously used on the F4 Phantom fighter-bomber. Despite their basic design that dates back to the 1950s, the RB168s are reliable, safe, and sufficient for a land speed record car.
The making of a modern land speed record-breaking car is a hugely complex science. Essentially, you need to build an aircraft that rides on wheels and does not lift off. To this end, the peculiar aerodynamic and mechanical requirements are neither like a car’s nor an aeroplane’s.
Optimum stability is perhaps more critical than outright thrust. Fortunately, LSR cars need only run in a straight line, so their bodywork is designed to maintain an arrow-straight path. While minimum drag is desirable, the stability requirements (mostly to prevent lift) significantly reduce the aerodynamic efficiency. A teardrop shape, for instance, will not work because of the risk that it might lift off at high speed. The Thrust needs to stick to the ground resolutely, and while it would probably hit even higher speeds if it could “take off” just a little, any record thus achieved would be null and void.
A land speed record requires the vehicle to ride on the road, on wheels which are in contact with the ground at all times. The Thrust has four wheels (to qualify for the LSR attempt) of 864mm diameter. Rolling on ultra-low-resistance bearings, the wheels are made from forged aluminium alloy type L77, a lightweight high-strength material. Rated for 8400rpm (1360km/h), these large rotors experience so much centrifugal force at those speeds that any other material would start to splinter at the circumference, where the maximum force is generated. Therefore, something like rubber is definitely not an option.
Andy Green, driving the Thrust SSC, clocked a speed of 1227.986km/h, becoming the fastest man in a car and the first to break the 1224km/h sound barrier on the ground. For the next phase of the land speed record, using the Bloodhound SSC (pictured), ever more powerful jet engines will feature, but the wheels are a potential problem, unless some genius develops a composite low-mass wheel that can spin safely at 12,000rpm!
