Bloodhound: Choosing the best materials for the job

You can imagine the phone call, can't you? Project leader Richard Noble, enthusiastic and nonchalant as ever, asking about the materials for the wheels of Bloodhound, the car that aims to break the 1000mph barrier.

It's not exactly your normal everyday request. This, however, was the situation aluminium stockist Metalweb has found itself in since it got involved on the project around 18 months ago.

"It started out with our customer Castle Precision being approach by Bloodhound to develop the car and in particular the wheel package," says Colin Ord, national business development manager at Metalweb. "As a strategic supplier to Castles we looked at supplying the actual materials for the wheels."

The Bloodhound project is well known in the engineering fraternity and has been a leading light to showcase UK innovation from the technology right through to the way it has been financed and put together. With test runs due to take place later this year and a record attempt scheduled for next year, it is almost time for the engineers behind it to show their 'metal' to the world.

After spending some time with engineers from Castle and Bloodhound, Ord and his team at Metalweb explained the different alloys that were available. Both Bloodhound and the team at Castle were adamant that aluminium was the material for the job.

After several attempts of looking at the different alloys included aluminium 5083 - well known for exceptional performance in extreme environments - and aluminium alloy 6082, a medium strength alloy with excellent corrosion resistance, the engineers from Bloodhound still needed more.

"So we went to the 7000 series," says Ord. "The decision is ultimately down to Bloodhound as they have done all the analysis. The difference between the 6000 series and the 7000 series material is firstly the 6000 is effectively a silicon based alloy and the 7000 is a zinc based alloy. Also the tensile strength characteristics of the 7000 are much higher at about 530MPa as opposed to 320MPa on the 6082. Over the loads that we are talking about, obviously it has a much better chance of surviving."

Aluminium 7075 is a high strength aerospace material that was first produced by the Japanese in 1936. It uses zinc as its primary alloying element, has good fatigue strength and average machinability. The 7000 series of alloys such as 7075 are often used in transport applications, including marine, automotive and aviation, due to its high strength-to-density ratio.

"We have supplied Bloodhound two full sets of material to do what we call the road wheels," says Ord. "These are the wheels that will have pneumatic tyres on them for testing the car up to about 380mph on a UK runway later this year. "

The main event
For the main wheels that will do the actual run itself, the wheels are thought to be forged from a derivative of a 7000 alloy. Due to the stresses involved in the application, a standard off the shelf alloy is unlikely to be used. The special aerospace grade 7085 aluminium alloy, which was developed especially for the Joint Strike Fighter program, is most likely to be the material of choice by Bloodhound engineers.

"For the landspeed record in South Africa Bloodhound will use forged wheels," says Ord. "These won't have any tyres, they will be all aluminium and have a special draft angle on the edge of the wheels so they dig in to the actual mud bed itself, but not too deeply, to give it the right amount of purchase throughout its attempt."

The other all metallic wheels that might spring to mind is that of a train, but these bear little similarity. The road wheels, interestingly were designed around some pneumatic tyres originally from an old Lightning jet, which have since become available for the team to use. With some analysis it was found that these wheels were perfect for the speeds that they want to achieve on test runs later this year.

The main wheels that will be used for the record attempt in South Africa are around 1m in diameter, but are thinner than the road wheels for the obvious reason that there is nothing else on them. They are pure forged wheels that are highly machined and polished.

"They have to be specially scanned to give it them perfect and optimum balance," says Ord. "You can imagine when these things are going at 1000mph the amount of pressure coming off them is incredible. The machinery they have got up at Castles is second to none. They have gone through a very good and thorough process to achieve the finished part."

Justin Cunningham

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