Bloodhound on the land speed record trail

  • 11-Feb-2010 01:06 EST
BLOODHOUND SSC Front Dynamic.jpg
Bloodhound aims to raise the Land Speed Record to 1000 mph from the current 760.343 mph.

One thousand miles per hour is the ambitious target for Project Bloodhound SSC (super sonic car) to set a World Land Speed Record in runs planned for August 2011 at the Hakskeen Pan, in Northern Cape Province, South Africa. The project, launched in October 2008, has now moved forward to the construction phase. Since it was launched, the car has progressed through 10 evolutions, and the team has now adopted the design that it will take to South Africa for the record attempt.

Project director for Bloodhound SSC is Richard Noble, who set the World Land Speed Record at 633.468 mph over a measured mile with his Rolls Royce Avon jet-powered car Thrust in 1983. Noble was subsequently project director for Project Thrust SSC in 1997 when Andy Green broke Noble’s record. Green set two successive records in September and October that year, raising the record first to 714.144 mph and then to 760.343 mph in the Black Rock desert of Nevada. Green subsequently set a land speed record for a diesel-powered vehicle at 328.767 mph with the JCB Dieselmax car at Bonneville Salt Flats in Utah.

Green, a Wing Commander in the U.K. Royal Air Force and former fighter pilot, will drive Bloodhound SSC.

Project Bloodhound has support from a number of sponsors including STP, Lockheed Martin, and IT partner Intel. Noble has also brought together many of the team members that worked on Thrust SSC and the JCB Dieselmax project.

Designing a super sonic car

The second phase sees Project Bloodhound relocate to the city of Bristol in the U.K. from the nearby University of the West of England to the project’s new technical center, where the vehicle will be built. The timeline for the project is to complete the CAD master in 2010, followed by a rollout of the completed vehicle in May 2011. Testing will then begin at Hakskeen Pan in July 2011 with the record attempt slated for August.

The principal redesign work has centered on the positioning of the power sources. Bloodhound SSC is propelled by an EJ200 Eurofighter Typhoon jet engine weighing 1000 kg (2205 lb) and a hybrid prototype rocket motor. In the early design evolutions, a rocket motor weighing 200 kg (440 lb) was positioned above the Eurofighter jet engine. As the design work continued, it became clear that more thrust than was available from the jet engine/rocket motor combination would be required to overcome aerodynamic drag.

To provide the thrust required, a larger hybrid rocket motor, weighing 400 kg (880 lb), was needed. The car initially runs under jet power alone, adding reheat at approximately 80 mph (130 km/h). At around 130 mph (210 km/h), the oxidizing valve for the rocket is opened. At around 320 mph (515 km/h), some 30 s into the run, full thrust from both engines will be applied. In this sequence of events, the simulations showed that with the original configuration of rocket motor above jet engine, the car would pitch violently nose downward as the rocket motor was fired, causing serious instability problems.

Consequently, the final design sees the engine configuration reversed, with the jet engine positioned above the rocket motor. The redesign work involved was made possible when Intel gave the project access to one of the largest computer clusters in the U.K., based in Swindon, close to the project’s Bristol base. Previous CFD work that had taken three to four days using computers at Swansea University now took two hours.

The 400-kg rocket motor will be the largest hybrid rocket ever designed in the U.K. It measures 45 cm (17.7 in) in diameter and 425 cm (13.9 ft) long and is designed to produce 122 kN (27,500 lb) of thrust. Combined with the EJ200 jet engine’s 90 kN (20,000 lb) of thrust, the output from both engines will be 212 kN (47,500 lb) of thrust, which equates to some 135,000 hp (100,710 kW).

The rocket motor will be fueled by hydrogen peroxide. A V12 800-hp (597-kW) gasoline engine on board Bloodhound SSC will act as a fuel pump to supply the rocket motor at the rate it will need. At the beginning of the record attempts, the vehicle will weigh 6.5 t (7.2 ton). At the end of the run around 100 s later, it will weigh 4.8 t (5.3 ton). The rocket burns 1 t (1.1 ton) of hydrogen peroxide in 17 s.

Taking control of the car

The Senior Engineer responsible for control systems is Dr. John Davis. The systems control everything on board from the jet engine, rocket motor, the wings, braking, and air brakes as well as monitoring the overall performance of the car, providing information to the driver in real time and transmitting data to the support crew.

Davis has been supported by The MathWorks, which has supplied some of the software tools used in the design and development of the vehicle.

“The control systems on the car are not actually that complicated, insomuch as the intention is that they will support the car rather than grab hold and control it,” Davis told AEI. “Obviously with the wings on board the car, we can actually lift the car up quite easily and the rocket and the jet could accelerate it at 2.0 g vertically if it got out of hand, so what we’re trying to do is keep it all calm, keep it on the ground, and allow it to run as a car—allow Andy to drive it as a car—so the prime functions are to provide the power for him when he wants it, and in the background keep it under control.

“The idea is to keep the car below the threshold where it can get away from us. So it isn’t a case of sitting on the stability margin and grabbing control, such as a fly-by-wire aircraft, which sits right on the edge, or beyond it,” Davis continued. “The intention here is that we maintain the car in a safe manner, so that the car fundamentally is controlling itself and behaving nicely. It’s a design philosophy of the car that it should be able to run safely and not have to rely on high frequency control just to keep it safe.”

The short wings that Davis referred to are hydraulically controlled to help maintain control of the car. He explained how they will work: “If the wings are too big, obviously they can pull out massive forces, both to stabilize and destabilize. It’s not possible, we don’t believe, to have a car that can run without any wing control. The wings will move according to a fixed profile; they won’t react to events on the car. Movement will be preprogrammed according to the map of the runs.

“With a world record car like this, you don’t suddenly go out and try to go 30% quicker; it will be a few percent per time,” Davis noted. “The idea is to predict forward what you think will happen, control that, monitor it. We have the option on this car, unlike the aircraft, to just stop. We can actually call and abort and stop in a safe manner. So if we have any departures we’re not satisfied with or the control system detects them, it will call a halt to the run.”

Aero experience on their side

Because many of the Thrust SSC team members are involved in Project Bloodhound, they bring valuable expertise with them. “The guys working on Thrust SSC did the hard bit,” reckons Davis. “We hopefully will be able to use their experience. The car has been designed to not have the faults that the last one had that created problems...It should be more a case of making sure that we’ve got the structures and the thrust and everything right rather than fighting some unknown demons that happened with the first aircraft and car going through.”

Chief of aerodynamics is Ron Ayers, who worked on the aerodynamics of Thrust SSC and was the aerodynamicist on the JCB Dieselmax project. He told AEI about the particular aerodynamic issues faced by the project: “We’re pioneering because we are going supersonic on land, so we have supersonic ground effect. We use CFD to compute all the interactions of flow, in particular, underneath the car.”

He highlights airflows beneath the car because, as he explains, the Thrust SSC car encountered a serious problem at 760 mph (1223 km/h). “The shockwaves were biting into the desert and destroying it, so before the wheels even got there, it was turning it into a fluidized bed,” Ayers explained. “So instead of riding on the surface, the wheels were plowing through it and that made the drag very much greater indeed, so the car wouldn’t go any faster than that.

“So to start with I thought that must be the limit because you can’t keep the ground intact. Then I thought about it a bit more, and just as we’re using CFD to design the vehicle, what about using it to design the pressure distribution over the surface of the ground and protect it? The shape that you see is very slender and the pressure gradually increases underneath but never violently changes, so I’m hoping that the ground will still be intact by the time the wheels get there.”

But another problem presents itself, according to Ayers. “The ground effect problem has now got to be solved all the way from M=0 to M=1.4, and that is a lot more difficult than just doing it up to M=1.” (M equals the speed of sound.)

Even the shape of the all-aluminum wheels has been determined by aerodynamic flow. At the speeds that Bloodhound SSC will be traveling, the vehicle will be steered at least as much by aerodynamic flow around the wheels as by steering contact with the ground. The early designs produced sharp cornered wheels.

“As a result,” Ayers told AEI, “the flow either broke one way or the other way, so we had an unsteady flow. By putting a slight radius on the corner of the wheels, we’ve stabilized the flow. When the wheels interact with the desert, they destroy the desert surface, so they are no longer on a solid surface, so we’ve now got wheels acting as rudder in the air and also acting as rudder in a fluid flow underground.”

Engineering Director John Piper outlined some of the other issues the wheels have produced: “We had a steering geometry criteria that we wanted to stick to because the wheels being quite heavy and running quite fast produce huge gyroscopic forces. We need to be under control with absolutely no camber change.

“We realized we could use a virtual steering pickup,” Piper continued. “It’s been done before, but it’s new when you’ve got the forces that we’re talking about. Thirty percent of the aero drag is trying to rip the rear wheels off. Anything we can do to reduce the wheel periphery mass is a good thing.”

The virtual steering pickup means that the wheels can be made from aluminum. Then the team found that the ground pressure conditions at Hakskeen meant that the wheel could be up to around 25% narrower. “It all comes off the rim, where you want to lose weight,” said Piper.

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