The 1000mph Challengers

Bloodhound isn’t alone in aiming for the 1000mph mark. An Australian effort, headed by perennial land speed record challenger Rosco McGlashan, is also putting together a car which they hope will break the barrier. And in trademark McGlashan style his car sports a very Australian theme, named the Aussie Invader 5R.

Aussie Invader 5R. Image by Mike Annear

The design of Aussie Invader 5R
The first noticeable design feature of the 5R is the rounded pencil-like shape, in comparison to the more squared off shape of Bloodhound SSC. Part of this design is due to aerodynamics, the other is due to ingenuity and resourcefulness. In order to keep costs down the body will be made of a 40-foot long high grade steel pipe provided by an oil drilling supplier and steel company. A raised area on the rear third of the car contains the driver’s cockpit, electrical systems and braking parachutes, while a V-shaped underbody has been designed to deflect shockwaves bouncing off the ground, reducing their buffeting effect and increasing the stability of the car.

Aussie Invader 5R from the front. Image by Mike Annear

One potential drawback of this narrow pencil-like design in the need to set the front wheels very close together. Such an arrangement, while being good for aerodynamics, may make the car quite unstable and difficult to keep in line. Supersonic cars have a tendency to wander, and such a close set track may make Aussie Invader 5R difficult to control.

The body shape and aerodynamics have been designed using CFD by the Fluid Dynamics Research Group at Curtin University, Perth, Western Australia. Using their know how and expertise built from working with the Jordan Formula 1 team, Aussie Invader’s aerodynamicist Dan McKeon has developed a shape which should be very “slippery” and yet provide good stability.

CFD Pressure chart. Image by the Fluid Dynamics Research Group, Curtin University.

This CFD simulation shows where pressure builds up on the car’s body, creating drag and instability. One advantage of the close-set front wheels is the reduced area creating drag at the front, indicated by the red area under the nose. The rear wheels also create a large amount of drag, and create an areas where shockwaves will likely form. These high drag and shockwave forming areas could potentially be lessened by creating streamlined cowlings such as those seen on the rear wheels of Bloodhound. The wide-set rear wheels are important for stability, so narrowing the distance probably wouldn’t be an option.

As mentioned, the V-shaped underbody should aid stability by deflecting shockwaves bouncing off the ground. An important part of designing a car such as 5R is understanding how the shockwaves will form and interact with the car. The image below shows that shockwaves are expected to form from the nose and the rear section of the car, with a small shockwave forming from the start of the driver’s canopy.

Shockwave formation at approximately 900mph. Image by the Fluid Dynamics Research Group, Curtin University.

A considerable amount of work has gone into designing the front nose. 7 options were investigated using CFD to create a shape which lessens shockwave formation, does not create lift, nor downforce which would result in drag. Subtle differences in nosecone shape were found to have profound changes to the airflow around the car, and in some cases critical differences which could upset the stability of the car at supersonic speeds. In one instance, a nose shape which drooped twards the ground and was almost flat underneath was found to create downforce, but also created drag (shape 5 below). These characteristics were due to a slowing of the air speed over top of the nose cone which increased the downward pressure on the car. By reducing the amount of droop the airflow over the top of the nosecone was smoothened, preventing this area of slow air and reducing the amount of downforce and the amount of drag (shape 6). Just by extending the length of this nose the airflow was again smoothened, reducing drag by around 30% without any noticeable loss of downforce (shape 7). From optimising the shape of the nosecone not only did the engineers reduce drag and increase the stability at the nose by smoothening the airflow, this smoother airflow also potentially reduced shockwave formation further down the car.

Nose design evolution. Image by Dan McKeon

Apart from the differences in shape and design, there is a very big difference in the way Aussie Invader 5R and Bloodhound SSC will be powered. Rather than going for the combination jet-rocket design of Bloodhound, the 5R will be powered only by a rocket developed by New Zealand based Rocket Lab.

Cutaway image of Aussie Invader 5R's rocket. Image by Mike Annear

The design of the 5R’s rocket is based on that of the Atlas rocket used by NASA and is expected to produce around 62,000 lbs of thrust, or the equivalent of 200,000bhp. This makes it around 50% more powerful than Bloodhound’s two engines, which together will produce the equivalent of around 135,000bhp.

The design they have developed uses two liquid fuels rather than the liquid and solid fuel combination used by Bloodhound. A similar design had been considered, but owing to cost and restrictions on the import of hydrogen peroxide the plan was dropped and a new design developed. Instead, a liquid fuel (bio kerosene) and a liquid oxidiser (liquid oxygen) are combined in the combustion chamber and ignited to produce thrust. The complication of this design is that the fuel and oxidiser won’t spontaneously combust in the way the solid fuel and oxidiser used by Bloodhound would. Instead, a third liquid, TEA, is also injected into the engine to ignite and maintain ignition of the engine.

The way the fuel is delivered into the jet engine is a particularly clever piece of design. The team have done away with fuel pumps, and instead the liquid fuels are forced into the engine using pressurised helium. In essence, the pressurised helium is fed into the fuel tanks from one end, pushing the fuel out the other. To start this process, valves at the engine end of the fuel tanks are opened, and the fuel is pushed through and into the engine by the pressurised helium. Because the amount the fuel valves are opened can be controlled, the fuel flow rates can also be controlled, allowing the throttling of the engine and control over the amount of thrust being produced.

This design of the engine for 5R is notable for its few moving parts, which they hope will ultimately be more reliable through its simplicity.

Cutaway image of Aussie Invader 5R. Image by Mike Annear

The cutaway picture above shows the packaging of the 5R. From the front, the large tank is the liquid oxygen reservoir, with the pressurised helium tank behind it responsible for forcing the oxidiser into the engine. Behind a bulkhead is the cockpit and safety roll cage for the driver, with the bio-kerosene fuel tank and helium pressure tank behind another bulkhead. The liquid fuel and oxidiser are piped from their tanks into the rocket engine at the rear of the car. Parachutes and electrical systems are contained in the raised section behind the cockpit, above the bio-kerosene tank and rocket engine.

Should all go as planned, the engine should be able to power the car to its maximum velocity in around 20 seconds. Once at 1000mph the driver will then have to throttle back to 75% power, enough to stop acceleration but maintain speed. After leaving the timing area the driver will reduce power in increments until at a safe speed to deploy the air brakes, parachutes and wheel brakes. The reason for reducing power slowly is to avoid the sudden reversing of g-forces which would occur if the power was immediately cut. As discussed in What it takes to go 1000mph Part 2, this sudden reversal of g-force can cause the driver to black out, potentially causing him to lose control of the car.

Rosco McGlashan and his team are currently building the Aussie Invader 5R and hope to be able to have a tilt at the record at about the same time as Bloodhound. With Aussie Invader planning on running at desert locations in the United States or in the north of Western Australia, there may well be a race to reach the mark between the two teams running simultaneously in two locations. While there is no guarantee either team will reach 1000mph, these two engineering adventures will inspire the next generation of engineers, and that should be considered a success in itself.


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