Yesterday, a team of British engineers unveiled Bloodhound SSC: the world's most powerful car, intended to reach speeds of over 1600km/h. Standing beside what looks like a rocket-on-wheels, it's obvious what a marvel of engineering it is. We spoke to the team's Lead Mechanical Engineer to find out how the vehicle was built.
Measuring 13.5m in length and weighing 7.5 tonnes, the car's dual rocket and jet engines will produce the equivalent of 135,000bhp of thrust -- making it the most powerful land vehicle ever built. While its predecessor, Thrust SSC, hit just 1227km/h the team behind Bloodhound intend to push it beyond 1600km/h.
As you can imagine, that kind of target created some major design considerations. Fortunately, a team of Formula 1 and aerospace experts were assembled to design the vehicle from scratch, and along the way they have sought help from the British Army's Royal Electrical and Mechanical Engineers as well as the RAF's 71 Squadron.
In central London, I met Bloodhound's Engineering Lead for Mechanical Design, Mark Elvin, to discuss the technology that's been poured into the car. He certainly knows his stuff: He's worked at Westland Helicopters and Williams F1 as a design engineer before joining the Bloodhound team.
I ask him what the biggest design challenge was, and the answer's not quite what I expect. "The wheels were quite difficult," he says. "They spin at 10,500rpm, which means that the radial G on the rim is 50,000 times the force of gravity. So a one kilo weight put on the rim weighs 50,000kg -- 50 tonnes -- at maximum running speed."
To build something strong enough to withstand those forces, the team has forged the wheels from a long, thin cylinder of aluminium which is squashed flat into a pancake. "That crystallizes the grain structure in a really fantastic way," explains Elvin. "We then machine it and balance the wheel, by removing microns of material. Then they're shot peened to increase the fatigue life."
Fortunately, they have also been thoroughly tested. "Rolls Royce spun one up to 10,000rpm for us and we used a laser to measure their expansion and compare it to out stress analysis." The good news: the wheel survived, and its expansion, of around 0.2mm, matches the team's calculations perfectly.
Rear view of Bloodhound SSC, showing the jet and rocket engines as well as the metal wheels.
In fact when the car attempts to reach 1600km/h in the Hakskeen Pan desert of South Africa next year, its wheels will look unlike those of most cars -- because they won't have any rubber on the outside. They're just bare metal. Close up, the wheels have a 90-degree V-shape to their profile. "It's like a boat," explains Elvin. "It works on the principle that at about 400mph (640km/h) the car will rise up out of the desert floor, like a speedboat. They will be skimming across the surface of the desert, with a patch just 3mm in width in contact with ground."
You might expect a vehicle with such little footprint to squirm at speed -- but you'd be wrong. "The fin at the back is huge, and that's what defines its stability," explains Elvin.
Go With the flow
If you throw a dart towards a board the wrong way round -- so the point faces backward and the flights are moving forwards -- it flips round in mid-air. That's because what's known as the centre of pressure lies in front of the center of gravity. Throw it the right way round, though, and its sails forward with grace. That's because of the large flights at the back that provide stability, and you can think of Bloodhound's huge tail fin performing much the same task. "If it were small, the car would have been unstable," explains Elvin, comparing to "So we've ended up with something very large indeed."
Elvin points out that it's about the same size as the tail fins fitted to the back of a Hawk advanced trainer aircraft. Problem is, those planes travel at around 1126km/h at 30,000 feet; Bloodhound, by comparison, will be travelling at 1600km/h at ground level. "We're trying to push that fin through treacle by comparison, because the air down here is so much thicker," explains Elvin. As a result, the team admit that it's over-engineered, but the entire assembly still weights less than 100kg.
The fin isn't the only aerodynamic challenge the team has faced. When they evaluated their first design, they discovered that the vehicle generated in the region of seven tonnes of lift. Given the car weighs just 7.5 tonnes, that could have been enough to cause it to take off. With a redesigned nose section -- crafted from carbon fibre, naturally -- that's flatter, they have been able to reduce that to just 1 ton of lift, which is spread evenly along the length of the car at all speeds.
A 3D-printed model of the airflow around Bloodhound SSC, used to predict lift and drag forces.
Not everything stays consistent with speed, though. Above 640km/h, the wheels -- which are the only means of steering the car -- begin to lift off the ground slightly and lose grip. That may sound disastrous, but at that point they begin to act like front-mounted air rudders, according to Elvin. "There's 10 degrees of movement in the wheels, lock-to-lock," he explains. "It won't be very sensitive, but he'll have steering feel. Will he need it? We don't think so. We think the car's going to be very stable and should track straight."
Mirror, Signal, Break the Sound Barrier
Inside the cockpit, the driver, Andy Green, will be surrounded by a suite of digital instruments, save for two dials provided by Rolex which will help him know what the car's doing in the event of a system failure. Once he's strapped in, he'll be pushed along by two major sources of thrust: a Rolls Royce EJ200 jet engine, like those used in the Typhoon fighter jet, as well as a Nammo hybrid rocket engine. There's also a supercharged Jaguar V8 engine aboard, which is used to pump the oxidizer required for the rocket to burn.
The engines -- particularly the jet engine -- don't like breathing the supersonic air that will be passing by the car when it breaks the speed of sound, so the team has designed the leading edge of cockpit to generate a huge shockwave, which will slow the air down to sub-sonic speeds. That helps the engine to work, but all the energy has to go somewhere and, sadly for Green, it turns up as noise. "There will be sound deadening around the cockpit, and he'll be wearing noise-cancelling headphones," explains Elvin. "But it's going to be loud. Very loud."
Each run will start off slowly: Even with full power on the jet engine, the acceleration of the car to 240km/h is actually slower than a normal family car, because of its weight. When it reaches 640km/h the rocket will begin to burn, providing consistent 2G of acceleration to take the vehicle to 1600km/h -- hopefully in just 55 seconds. At top speed, it will be covering a kilometre in just 2.23 seconds.
At which point, it's time to stop -- and quickly, because the track in the desert is just 19.3km long.
"Braking is very difficult," admits Elvin. The vehicle has been designed to slow from 1600km/h to standstill in 65 second, a process which creates forces of 3G in the cockpit. "If you drive a family car into a wall at 48km/h, that's what 3G feels like," he explains. "It's what most people call a crash."
Green will experience that force for the duration of the deceleration, meaning that he endures a typical car crash for over a minute. Green's an experienced acrobatic pilot, though, so he won't be using a G-suit during the runs.
In terms of how it slows down, the first 320km/h is scrubbed off using drag alone: when the engines are turned off, the car will experience 3G of wind resistance. When the speed drops below 1286km/h, two air brakes -- one on each side -- will pop out of the car, angled at about 60 degrees. They will provide the bulk of the deceleration for the vehicle, and only when the speed dips below 400km/h will the wheel brakes be applied -- any sooner, and they could burst into flames. If for some reason any of these braking systems fail, there are also two parachutes on board, either one of which could slow the car to a stop safely.
Just in case things don't go to plan, though, Green will be wrapped in a carbon fibre monocoque which the team thinks is "probably the strongest safety-cell ever fitted to a racing car." Elsewhere, the body work is actually all fairly traditional -- at least in design terms, if not material choice.
"The upper chassis looks like someone passed a bandsaw horizontally through a Douglas DC-3," says Elvin. "But instead of using aluminium, we've used titanium. We've taken traditional construction methods and made them work for us." It's beautiful, traditional engineering, with a very modern twist.
The housing for the Rolls Royce EJ200 jet engine uses traditional manufacturing techniques -- but exotic materials like titanium.
The car's panels of pre-stressed titanium are also covered in sensors -- 500 in total -- including pressure and strain gauges across the entire surface. The first enable the team to measure the air-flow around the car during the runs, while the latter will allow them to check that none of the components is being subjected to more force than it should be. Also dotted about its body are 12 cameras, including two in the cockpit, which enable the team to keep a watchful eye on Andy Green, the driver. All the data will be beamed back to the team via mobile data, with three temporary phone masts set up at the record-attempt site. "We get better 4G reception in the middle of the desert than we do in central London!" quips Elvin.
In fact, reliably keeping track of all that data is, perhaps, the most important part of the entire process. When the time comes to attempt the record-breaking speed runs, the team will carefully increase the speed, making sure that all of the measurements tally with their calculations.
"We start running at low speeds, increasing in 80km/h increments, and at each stage we analyse the data from the car, cross reference it with all our modelling, then increase the speed by another 80km/h and do the same thing," explains Elvin. "At every stage, we check every sensor to make sure it matches what we're expecting to see. It's simple: If we can't ensure it's safe, we come home."