Automotive

Designing supersonic wheels for the Bloodhound Supersonic Car

Designing supersonic wheels fo...
The wheels of the Bloodhound SSC generate 50,000 g's, meaning a lot of technology is required to ensure they are up to the task
The wheels of the Bloodhound SSC generate 50,000 g's, meaning a lot of technology is required to ensure they are up to the task
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Wheel blanks being heated before forging
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Wheel blanks being heated before forging
Forging produces a more compact, void-free aluminum structure for the wheels
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Forging produces a more compact, void-free aluminum structure for the wheels
The wheel discs were forged in hot and cold hydraulic presses
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The wheel discs were forged in hot and cold hydraulic presses
One of the wheel blanks being forged
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One of the wheel blanks being forged
A ballistic panel in place
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A ballistic panel in place
Sabot fired at the ballistic panels
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Sabot fired at the ballistic panels
Cross section of a ballistic panel
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Cross section of a ballistic panel
A ballistic panel being tested for impact resistance
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A ballistic panel being tested for impact resistance
Forging the Bloodhound's wheel discs
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Forging the Bloodhound's wheel discs
Inspecting a wheel of the Bloodhound
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Inspecting a wheel of the Bloodhound
Steps in machining the Bloodhound's wheel disks
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Steps in machining the Bloodhound's wheel disks
The wheels of the Bloodhound SSC generate 50,000 g's, meaning a lot of technology is required to ensure they are up to the task
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The wheels of the Bloodhound SSC generate 50,000 g's, meaning a lot of technology is required to ensure they are up to the task
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If the Bloodhound Supersonic Car (SSC) team makes good in its attempt to break the land speed record, the car will be traveling at 1,000 mph (1,609 km/h). At such speeds, the wheels will be spinning so fast that hitting even the smallest pebble could be catastrophic. To protect both the car and the driver, the designers of Bloodhound have had to come up with some high-tech answers to building the wheels and protecting against their failure.

Blasting across salt flats at beyond the speed of sound takes more than engines punching out insane amounts of power. It also requires wheels that can withstand stress than make an F1 race car look like a kiddie wagon. Built by a consortium of companies, the wheels of the Bloodhound have to support 7.5 tonnes (8.2 tons) just standing still, so its no wonder that each 90 cm (35.4 in) wheel disk weighs 91 kg (200 lb).

But it's when Bloodhound makes its run that the problems really begin. At top speed, the wheels will be turning at 10,200 rpm – and even this is an approximation because the Bloodhound is expected to outpace the wheels, so it isn't certain how fast the wheel will actually be turning at top speed. When going flat out, the wheels generate 50,000 radial g at the rim, which means that a 1 kg (2.2 lb) bag of sugar set on the rim would weigh 50 tonnes (55 tons) or as much as a juggernaut lorry.

Inspecting a wheel of the Bloodhound
Inspecting a wheel of the Bloodhound

To handle that sort of stress, the wheel discs are made of a special aluminum alloy created for cutting-edge aerospace applications called 7037, which includes traces of zinc, copper, and manganese. This is forged into a "cheese" in a 3,600 tonne (4,000 ton) hot press and a 20,000 tonne (22,000 ton) cold press with a high degree of precision to make sure that each wheel is perfectly balanced.

According to Bloodhound SSC, the purpose of all this heating and squashing is to press the crystalline structure of the aluminum to remove any voids and form a stronger, more compact matrix that has a radial pattern like the spokes of a wheel.

However, such strengthening, followed by precision machining by the Castle company and testing by Rolls Royce, has its limits and should the ground crew overlook a single stone or the car kick one up from beneath the desert floor, the results could be catastrophic. A foreign object hitting the wheel could cause to lose its balance, which would quickly damage bearings and increase the wobble until the wheel tore itself apart in a manner normally only seen in an exploding jet turbine.

The wheel discs were forged in hot and cold hydraulic presses
The wheel discs were forged in hot and cold hydraulic presses

Another danger is that the front wheel could fire a pebble at the rear wheel or into the body of the car at supersonic speeds. This could be extremely dangerous for the driver Andy Green despite the carbon composite cockpit. To protect against this, Morgan Advanced Materials is developing lightweight composite ballistic panels to guard the cockpit and other vital areas.

These panels are slightly curved to fit the cockpit and other points, but this has the additional advantage of providing a surface for flying objects to strike at an angle rather than dead on. The panels are made out of millions of woven glass fibers that act as energy absorbers. They work not by stopping the projectile, but by dissipating the energy. According to Morgan, as the projectile hits, it tears the fibers. Each tear takes energy and as the projectile rips through the laminated mats, it loses a lot of energy and minimizing damage.

A ballistic panel being tested for impact resistance
A ballistic panel being tested for impact resistance

Morgan has been subjecting the glass fiber mats to tests involving a gun designed to produce the force of a cricket ball traveling at 2,000 mph (3,218 km/h). The company fired metal sabots that simulate the largest piece that could come off the wheels prior to a total failure, and results so far have been positive. The test panels look as though they've been attacked by a buzz saw, but they manage to adequately decelerate the projectile.

If all goes according to schedule, the Bloodhound will make its attempted record run next year in South Africa using its triple power plant of a hybrid rocket motor, F1 racing engine, and the jet engine from a Typhoon fighter.

The video below shows the composite ballistic panels being tested.

Source: Bloodhound SSC

Shooting BLOODHOUND SSC - Ballistic tests on cockpit protection panels

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3 comments
Ikeleaka Kaluva
Maybe they should consider layering about 6 inches of large gaged rock salt on the ground to run over
PaulYak
Following on from comment above, to use large rock salt to make perfect track way, use a second coating of finer rock salt slight damped, to fill most gaps. Use a highway machines to tamp/roll the surface till correct strength. I don't mean wet it, just very fine mists, then tamp/roll again, allow to dry (test then redo till happy). This might work to try and ensure a uniform, solid surface.
Such huge forces involved, I doff my cap to these guys, especially the pilot. Gods speed to you all.
Nelson Hyde Chick
Going supersonic in a car, what a waste of resources, and just to fulfill some rich guys' vanity.