Andy Pye discovers that cooling a 135,000bhp, 1000mph car poses critical challenges for safety and performance that the Bloodhound team is looking to solve.
As the build of Bloodhound SSC gains momentum and a planned UK test in Newquay is just months away, engineers are increasingly looking at the detail design challenges to help them push the car to 1000mph and above. These include the issues of cooling the tightly-packaged Rocket engine, together with ensuring the volatile HTP (High Test Peroxide) doesn’t decompose before it reaches the rocket chamber and – in effect – become a bomb.
The team will trial the car in South Africa, providing a real test of the thermal protection. “We plan to thermocouple the car and see where the heat issues are,” suggests Parraman. “It’s a one-off and we are pushing the boundaries so we don’t know all the answers. Once we do, we’ll go to Hakseen Pan in South Africa knowing we are fully prepared to deal with the heat.”
“We’ve got approximately 1000 litres of HTP that has the equivalent explosive force of one stick of dynamite per litre if it reaches 40C and starts to decompose,” says Tony Parraman of the sponsorship liaison team. “Packaging dictates that our supercharged Jaguar engine that we use to pump 900 litres in just 20s, is sat next to the tank. So preventing heat transfer is on our essential list!”
As a prime source of heat in proximity to the tank, the Bloodhound SSC team specified Zircotec’s ThermoHold ceramic coating for the Jaguar exhaust. Plasma-sprayed itself at twice the speed of sound, the coating can reduce surface temperatures by at least 30%, ensuring that, even as heat builds up during the two runs needed for the record to be validated, the tank remains stable.
Unlike previous record challenging cars, a large proportion of the Bloodhound front structure is composite. Chosen for its excellent strength/weight ratio, the drawback of composites re their poor resistance to temperature compared to metals. “Zircotec heat resistant coating again have been supplied to F1 teams for years,” says Parraman. “They are used to prevent the delamination of carbon fibre in high temperature environments, enabling the material to be used above its traditional melting point,”
Zircotec ThermoHold for Composites is a zirconia-based coating that is applied at temperatures exceeding 10,000C but in such a way that the substrate is unaffected. “Zircotec’s patented technology allows the use of lightweight materials in places where they are exposed to significant heat. We only use the coating where it is needed, saving weight where we can,” adds Parraman. “We have used it on the composite upper chassis hoop, offering lightweight resistance that lowers surface temperatures by 100C.”
In addition, the Zircoflex hybrid aluminium/ceramic heatshield, just 0.3mm thick, is being applied around any areas of the vehicle where heat is expected and needs to be resisted. “With ZircoFlex, we can bend and mould it to shape, it is lightweight and with self-adhesive backing, good for up to 500C,” Parraman explains. We can use it in lots of areas. For example, after a two minute run, the internal temperature of the jet or rocket might be 3000C but the externals are 200C. We can manage that heat with ZircoFlex protecting wiring looms and composite panels.”
With ambient temperatures of 40C expected in the South African desert, Zircotec is being relied upon to keep temperatures down during the critical time slot of one hour between the two runs. “We’ve got 60 minutes to turn the car around,” says Parraman. “We want to prevent heat soak during this time. It will help us work faster without the risk of getting burned. And if we do need to change the rocket, it should speed up changeover time.”