Brakes and wheels for ThrustSSC have been provided by Dunlop Aviation. Carbon brakes are used as the material is ideally suited to the requirements of ThrustSSC. There are two types of wheel - conventional tyred wheels for low speed runs up to about 250 mph and solid aluminium discs approximately 100mm thick designed to withstand the stresses involved in making the record attempt.
ThrustSSC weights nearly 10 tonnes and the braking system has to meet a number of unusual requirements. These include holding the car against the thrust of two Rolls Royce Spey jet engines during power build up and the ability to stop the 10 tonnes car from speeds as high as 170 mph but, if the parachutes fail, they may be called upon to provide retardation from higher speeds.
The carbon used is developed from that manufactured by Dunlop Aviation for use in its brakes fitted to many of the world's leading civil aircraft. Designed by Glynne Bowsher, Chief Mechanical Engineer ThrustSSC, the brakes are similar to car disc brakes but with a carbon disc of 400mm diameter by 24mm thick. The pads are also carbon and arranged as two sets of horizontally opposed callipers.
As demanding as the actual braking is, it is during high speed runs that the brakes experience their most difficult operating conditions. This is because of the bursting stresses created as the rotor is driven round with the wheel. To spread the load more evenly throughout the disc 16 drive fingers are used with 'keyhole' shaped drive slots to avoid stress raisers, as pioneered in Thrust2.
For similar reasons rubber tyres would disintegrate well below the target speed of 850 mph so tyreless solid aluminium wheels are fitted. These are machined from forgings, supplied by a sister BTR company H.D.A. Forgings, and weigh more than 110 kg. They are of two sizes both almost 1000 mm diameter. For low speed tests up to 250 mph conventional wheels and tyres are used.
Tests have been carried out at 9,500 rev/min - equivalent to a vehicle speed of 1,000 mph. This is well above the ultimate target speed of 850 mph set by the ThrustSSC team.
Vehicle Braking is most effective on the front wheels and this is especially true in ThrustSSC as approximately two thirds of its weight is on the front wheels. This means that more braking effort can be applied without locking up the wheels.
To make the most of this ability and for other reasons it was decided to steer from the rear wheels. This also has the safety advantage that it reduces the gyroscope effect of steering adjustments on the car's stability. Removal of the steering from the front means that the body form can be more streamlined and allows the use of wider wheels. There are six brakes in all, two on each of the front wheels and one on each rear wheel.
Dunlop Aviation, a member of the Specialist Engineering group of BTR plc., is a world leader in aircraft wheels/brakes and brake management systems, electronic, hydraulic and pneumatic equipment. Other aerospace products include aircraft ice protection and composite structures.
For more information please contact Mrs D Plunkett:
Tel: +44 (0)1203 668743 Fax: +44 (0)1203 662294
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