Racing ahead

The team behind Thrust SSC is back – and aiming to build a car that will break 1,000mph. Lou Reade reports



Bloodhound, the engineering project set up by Richard Noble to develop a 1,000mph car, is working “at the technological limit”, according to a leading member of the team.
Ron Ayers, the chief aerodynamicist – who performed a similar role on the sound barrier-breaking Thrust SSC in 1997 – told Eureka that current technologies are capable of delivering the car, but would be unable to go much faster.
Bloodhound SSC, named after a surface-to-air missile that Ayers help to design back in the 1960s, certainly has its work cut out if it is to succeed. Based on extensive virtual modelling and technical knowledge, the team believes it is feasible to design and build a car that will run at 1,050mph – and smash its previous landspeed record.
The car’s forward thrust is provided by two meaty pieces of kit: an EJ-200 jet engine that was used in the development of fighter aircraft; and a hybrid rocket motor. The jet engine will take the car up to the sound barrier (763mph), while the rocket will propel it beyond 1,000mph.
Ayers was careful not to rule out faster cars in future, stating only that existing technology was likely to limit the speed to around 1,000mph – in the same way that vehicles based on piston engines have reached a maximum of just over 400mph.
“I think it’s the limit that can be achieved with current technology,” Ayers told Eureka at the launch of the Bloodhound SSC car. “We are exploring the area between the sound barrier and the technology barrier.”
As an example, Ayers points to the enormous strain – more than 50,000G – that will be put on the vehicle’s wheels at top speed.
“Structural strength and stiffness must be high enough to withstand these forces,” he said. “There aren’t many materials that can do that.”
It will come as no surprise to learn that the team intends to build the wheels from titanium – which has an enormous strength to weight ratio. Each 900mm diameter wheel is likely to weigh around 140kg, and spin at 10,500rpm in full flight.
“We’ve not yet found anybody to make them for us,” said Ayers.
Wheel design took place very early in the project, independent to the rest of the car. The dimensions were fixed, but the exact design will continue to be adapted: single, double and triple keel designs have all been made, for example.
There is an alternative wheel design, using a composite centre and aluminium rim. Though the design is less robust, it would be lighter, easier to make and have lower radial G forces.
“My motivation is to see if this barrier exists,” said Ayers. “We have found nothing that tells us that 1,000mph is impossible.”

Shock result
Possible it might be, but the hurdles to reaching the goal just keep stacking up. The enormous shock waves produced as the car approaches the speed of sound cause massive changes in the ground – turning it into a fluidised surface.
John Piper, the project’s chief engineer, said: “We have no way of understanding the contact conditions between the wheels and the desert surface. At the start of the run, the wheels are steering by reacting with the ground. As the speed builds to 700mph, they effectively turn into rudders.”
Another key element of the design is the intake duct for the jet engine. Initial designs had a twin-duct configuration, but detailed simulations showed that this made symmetric airflow difficult to achieve. For that reason, the design switched to a single intake, positioned above the cockpit canopy.
The size of the input is usually optimised for a specific speed, but Bloodhound SSC will move at a range of velocities.
“The requirements at low speeds are quite different to those at supersonic speed,” said Piper. “We are running this engine well out of its comfort zone and want to run at full reheat at sea level – which has never been done before.”
The intake will be optimised to allow extra performance at lower speeds – as the car is approaching the speed at which the rocket is switched on. It will lose a little jet thrust at top speeds – but the rocket power should compensate for this.
The shape of the cockpit, which is directly below the intake duct, is part of the intake shock management structure.
“We need to be careful that shock waves do not travel down the canopy and hit the blades,” said Piper.
Much of the ‘proof of concept’ so far is based on computational fluid dynamics (CFD) modelling. This has been carried out at Swansea University using its own Flite3D program – which will be “tuned to meet the specific needs of the project” according to Ben Evans of Swansea’s school of engineering.
“One thing we’re going to do is try to understand how the surface interacts with the airflow,” he said. “This ‘spray drag’ – caused by fluidisation of the surface – is very high, and we’re going to try and incorporate it into our software.”
While CFD modelling will provide an accurate picture of likely behaviour, Evans admits: “We don’t know how the drag will increase with greater speed.”
Testing will come in three phases, with the first car being tested up to 800mph.
“The first year will be to validate the models,” he said. “The car may have to change after we run it and 800mph, if the models have not predicted something.”
And Richard Noble, the project director, says that the project will begin to develop innovations of its own after this stage.
“There won’t be much innovation as we test the car up to 800mph,” he said. “It’s when we test between 800 and 900mph that we’ll get innovative and creative. This will increase as we edge towards 1,000mph and deal with some of the dragons that are out there.”

Look out for:

Winglets
These four small structures ensure that the load is balanced equally across all four wheels, at all speeds.

Fuel pump
Needs to pump 1 tonne of hydrogen peroxide to the rocket catalyst inside 22 seconds, and is powered by an 800bhp V12 engine.

Author
Written by Lou Reade

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