CompositesWorld
Issue link: https://cw.epubxp.com/i/532917
JULY 2015 46 CompositesWorld FOCUS ON DESIGN Composite air brakes: Stopping the world's fastest car CFRP sandwich structures are a key element of deceleration in the Bloodhound SSC rocket-powered racer's two-run attempt at resetting the land speed record. » A tiny French Jeantaud Duc electric vehicle set the frst wheeled- vehicle land speed record of 63 kmh, in 1898. One hundred years later, Richard Noble drove the Trust SSC jet-powered vehicle to the frst supersonic and still unbroken record of 1,227.985 kmh, in Black Rock Desert, in the US state of Nevada. Now, Noble and a team of engineers aim to smash his own record in pursuit of a much more ambitious goal: 1610 kmh, the mythic land speed record milestone of 1,000 mph. Te attempt will be made in 2016 at Hakskeen Pan, South Africa, in a third-generation supersonic jet-/rocket-powered vehicle, dubbed the Bloodhound SSC. "Tis project represents most aspects of what would be seen in a major aerospace program," says Tim Edwards, the engineer who oversaw a team within Atkins' (Bristol, UK) aerospace business di- vision, which was responsible for structural analysis of the vehicle's composite elements as consultants to the Bloodhound engineering team. "We were engaged by Bloodhound because of our experience in the analysis of laminated composite structures — especially for aerospace applications." Edwards' team also helped interpret loads from the whole-vehicle fnite element model and select analysis methods for specifc components. Although the car's sole purpose is to achieve extreme speed, sig- nifcant constraints dictated its design. Lightweight carbon compos- ites could be used to create the slender yet highly curved aerody- namic forward body shell and engine intake, but heavier aluminum/ titanium construction was required rearward to withstand the el- evated rocket exhaust temperatures. Because the 7.5-MT, 13.5m- long car will be shipped to South Africa for the record run, the ve- hicle had to include a mid-length joint to permit disassembly for easier handling. Most important, rules require that two runs must be made in opposing directions (recorded speed is the average of the two) within one hour, so the car must be stopped, refueled and turned around very quickly. "Acceleration, deceleration and refuel- ing time are critical, and no time can be wasted in slowing down," Edwards points out, "So, in addition to powerful propulsion, brak- ing is a key element." SLOWING A ROCKET Braking won't be easy: Powered by the same type Rolls-Royce EJ200 jet engine used in the EuroFighter Typhoon aircraf and fve rocket engines from Nammo (a Jaguar 550-hp V8 engine will be used just to pump liquid rocket fuel!), the Bloodhound will cover the 1.6 km-long record segment in a mere 3.6 seconds. To stop it within the confnes of the 19.3-km lake bed test track, Bloodhound's engineers will rely on huge aerodynamic drag to slow the car to about 1,300 kmh. Ten, two slaved, ram-actuated airbrakes, one on each side of the car, will open outward like doors from the craf's body. Similar to aircraf speed brakes, they are designed to slow the car to 300 kmh, when wheel brakes will engage. Edwards explains that the positions of the airbrakes, their actuator arms and door hinges were dictated by the available space inside the vehicle (see drawing, p. 47), the lack of which meant that each door could be no larger in area than 0.6m 2 and no more than 50 mm thick. "We were tasked to consider a door machined from a single piece of aluminum vs. a composite door," says Edwards. Perforations in the doors will break up the airfow, but ensure that oscillatory loading on the rear suspension assembly, located immediately behind the airbrakes, will be minimized. "To avoid any possibility of the natural frequency of the doors coinciding with the frequency of vortex shedding efects from the car's body," he adds, "any material had to exhibit a minimum frst natural frequency of at least 45 Hz." Further, the design must withstand aerodynamic loading when deployed at speed, without excessive defection or By Sara Black / Technical Editor The contender This jet- and rocket-powered supersonic car is the third-generation version of Richard Noble's original recordbreaking Thrust2 land speed racer. The Bloodhound SSC, driven by Andy Green, is designed to exceed 1,000 mph, or 1,610 kmh. Composites are used extensively not only on the car's body but also on its air brakes, which will help slow and control the vehicle after each of its two required runs at the new record. Source (all photos)| Bloodhound