The wheel brakes on BLOODHOUND SSC are the final step in slowing the car to a halt after its record-breaking runs. What makes them unusual is that when the Car is being driven on those record-breaking runs the discs will be made from steel, rather than the usual carbon discs used on cars and planes.
BLOODHOUND’s aerodynamicist and performance expert, Ron Ayers, calculated that when slowing down about 52% of the Car’s energy will be absorbed by aerodynamic drag, 36% will be absorbed by the airbrakes (and/or drag chutes) and 11% will be dissipated by the vehicle’s rolling resistance. Only 1% needs to be absorbed by the Car’s wheel brakes.
Nevertheless, the engineering challenge was to provide wheel brakes that could survive spinning at over 10,000rpm, even though they would only be used from about 200mph downwards. In addition, BLOODHOUND’s wheels will have very little grip on the desert surface, so although the surface will be dry when the Car runs, the wheel brakes will be doing a job that’s more akin to trying to stop a car on a very wet road.
An additional requirement is the need to stop as close as possible to the BLOODHOUND team at the end of the first run for refuelling and replacement of any parts. With such a short time allowed in the world land speed record rules to do both runs, driver Andy Green needs the brakes slow the car down controllably, so that he can turn it around and then stop the car exactly where he wants to stop it – ie right next to the crew – not just bring it to a halt randomly somewhere at the end of the desert track.
The original plan was to use carbon discs from a fighter plane but they fell apart above 5,000rpm. So it was vital to make sure that any alternative would be much, much stronger.
In testing, the steel brake discs reached temperatures of over 850°C and survived the spin tests as well. More importantly, inspection showed that they would be able to survive multiple runs at high speed.
The result is that when BLOODHOUND is being driven at Hakskeenpan it will have steel wheel brakes on the front wheels (with no back wheel brakes).
During the UK runway tests at the Newquay Aero Hub the brakes will have to do most of the work. For these runs, BLOODHOUND will have carbon brakes on all four wheels, with dual circuits, to provide plenty of stopping power plus redundancy.