Designing a car to go 1,000 mph is a constant lesson in compromise.
When it comes to world land-speed records, few people are as experienced and successful as Richard Noble, a Scotsman who has been directly involved in two record-breaking cars, Thrust2 (633 mph) and Thrust SSC (763 mph or Mach 1.02, the current record). So it should come as no surprise that he’s right in the middle of a project to develop a new land-speed record-setting car, the Bloodhound. And he hopes the Bloodhound will make a quantum leap over the current record, taking it to over 1,000 mph.
What’s new in this attempt is the purpose of the project. It seems Noble is concerned about the lack of interest in science and technology among youth in the U.K. and the world. He hopes this engineering effort will excite and inspire them to get involved in math and science, and perhaps kickstart a new generation of engineers and scientists.
The rules set by FIA (Fédération Internationale de l’Automobile) regarding speed records for cars mandate a “car” must have four wheels, be controlled by an onboard driver, and can be steered. This leaves Noble and his team plenty of room to negotiate the various challenges building a 1,000-mph car presents. Still there’s no guarantee the team will succeed.
It’s been quite some time since a piston-powered car held a world land-speed record. Jet engines took over in the mid-1960s with Craig Breedlove’s Spirit of America. Eventually rocket motors made their appearance in the 1970s with Gary Gabelich’s Blue Flame. The Bloodhound will use one of each, along with a piston-powered engine, but it will not be used to power the wheels, at least not directly.
On a high-speed run, Bloodhound’s jet engine alone will get the car up to about 300 mph. The engine, the EF200, was designed and built for the Typhoon Eurofighter. It is relatively compact but still cranks out 20,000 lb of thrust. Best of all, the engine has been exhaustively tested and is readily available. Once the car gets to 300 mph, the rocket kicks in to take it up to 1,0000 mph.
One challenge, however, is to design a duct that will take in enough air and deliver it smoothly and uniformly to the jet. The Bloodhound team studied twin or bifurcated intakes, but they discovered such ducts tended to deliver highly turbulent air to the engine, which can cause engine surges and loss of performance. They quickly switched to a single inlet positioned above the cockpit. CFD simulations indicated that the nose and cockpit canopy, two abrupt transitions for airflow, could play an important role. So they reshaped the canopy and nose so that at supersonic speeds, they would send airflow through two shock zones, decelerating and becoming more uniform prior to be going into the duct. This should give the jet engine maximum performance.
The rocket motor, a custom design from the Bloodhound team, will likely be the largest and most powerful hybrid rocket of its kind. It will supply up to 25,000 lb of thrust, without the drag generated by an intake such as that needed for the car’s jet engine. But the jet, which supplies about 20,000 lb of thrust, can be throttled, unlike the rocket engine which is either burning and supplying thrust or not burning at all. This lets the driver control the car’s speed, which will be more critical during incremental test runs than in the final, go-for-it-all run.
The rocket’s liquid oxidizer is HTP (high-test peroxide, an 85 to 98% solution of hydrogen peroxide). An MCT V-12 racing engine from Menard Competition Technologies Ltd. will power the pump that sends a ton of HTP through a catalyst pack with the resulting decomposition products (O2 and steam) feeding into the rocket motor at 1,200 psi — all in 22 sec. The 800-hp engine will also power a generator and hydraulic pump to provide the car with electricity and hydraulic power, as well as start the jet engine. The solid rocket fuel is 400 lb of synthetic rubber (hydroxl-terminated polybutadiene) shaped to fit into the combustion chamber. The chamber should be about 14-ft long and 0.5 ft in diameter, which lets it hold enough fuel for a 20-sec firing. A starshaped tunnel runs the length of the fuel, right through the center, to let oxidizer and fuel burn thoroughly and completely.
One safety feature of hybrid rockets is that if their supply of oxidizer is shut off, the motor shuts down. There’s never a need to jettison a burning rocket motor if there’s trouble. And there’s no risk of an explosion as there is in bipropellant rockets with horizontal combustion chambers.
Keeping the Bloodhound under control and safe are probably the two greatest engineering challenges, especially considering the wide range of speeds it will be traveling. At the low end, the wheels rely on friction for control. But as speeds build, aerodynamics play the larger role in keeping the vehicle under control. The wheels for example, will need to cope with stresses corresponding to a radial acceleration of 50,000 gs. They must also support the vehicle despite impacts with stones and debris at over 1,000 mph.
A problem Noble discovered on his previous supersonic car is that shock waves from the front wheels “fluidized” the ground, making it nearly impossible for the rear wheels to function properly. So the team is making extensive use of CFD to design the underside of the car to minimize changes to the ground.
The team also chose to tuck the front wheels under the body to reduce friction and drag but also to keep the wheels out of the wind where they could act more like sails or air brakes than wheels at supersonic speeds. The rear wheels also get enclosed, but in space-age-looking wheel covers. And inside all four wheel wells, the 35.8-in., 300-lb titanium wheels waste energy swirling air around as they turn at up to 10,000 rpm. To keep airflow smooth, designers will carefully ventilate the wheel bays so that airflow is more laminar.
The driver will be able to change the steering angle by 5° with his steering wheel, which has a 30:1 turning ratio. They chose that ratio for a number of reasons. First, the car does not have to be maneuverable. There shouldn’t be any tight corners on the course. And secondly, increasing maneuverability would mean a wider front chassis to mount the steering suspension as well as a wider body to keep the wheels enclosed.