Bloodhound is going to the desert this year!
02 Aug 2019
Bloodhound have announced that they will be taking part in the 'High-Speed Testing' on the dry lakebed track at Hakskeenpan. Please read below for further details:
'The accommodation is booked, deposits have been paid, and we're arranging charter flights and sea freight space as I write.
Bloodhound will touch down in South Africa in the middle of October for 3-4 weeks of 'High Speed Testing' on the dry lakebed track at Hakskeenpan. This High-Speed Testing is a key part of getting ready for an attempt at a new 800+ mph Land Speed Record next year. We're going to take our slow-speed runway Car, which we tested at 200 mph back in 2017, and turn it into a high-speed racing car.
To do this, we're fitting the high-speed metal wheels, brake parachutes, pressure sensors, wheel fairings, and so on, ready for speeds well in excess of 500 mph. If things go really well for us out in South Africa, we might even finish up at a speed starting with a "6", but anything over 500 will allow us to test the aerodynamics, wheels, chutes, etc., so we won't be pushing too hard just yet. We'll save that for next year.
The first thing to test is the high-speed desert wheels. Each wheel weighs 95 kg and is forged from solid aluminium, without any tyre on it. At 1,000 mph, the wheels experience 50,000 times the force of gravity trying to tear the wheel rim apart, so it has to be solid metal, nothing else will cope with the extreme loads. So far, so well understood. Now we get to the bit that we don't know - how will these wheels behave on the desert surface?
Metal rims running on the hard mud surface of Haskeenpan will have very little grip due to friction. Normal road cars rely on tyre grip for their stability and safety, and tyre companies spend a huge amount on developing the right rubber compounds for maximum grip. None of that helps us, as 50,000 G would destroy any rubber tyre, so we are working with the unusual (and poorly understood) dynamics of solid metal wheels.
We have given the metal wheels some lateral grip on the desert surface by making them a shallow 'V' profile. As the Car runs along the track, the wheels cut ruts in the mud surface, providing the sideways grip that we need. Unfortunately, the faster we go, the shallower the ruts become - at slow speeds (200 mph), they will be 10-15 mm deep, but at supersonic speeds the wheels will be making tracks less than 5 mm deep, which will provide almost no sideways grip.
There is some good news at supersonic speeds, as the aerodynamic grip will be huge, so that Car will get pretty much all of its directional stability from the supersonic airflow. This should also give the Car some very lively steering at high speeds, with the front wheels acting like rudders in the supersonic airflow, producing very rapid steering responses.
Now for the bad news. As the Car accelerates, the mechanical wheel grip goes down quite quickly, but the aerodynamic forces (which depend on the square of the speed) build up much more slowly. This means that at 'medium' speeds (somewhere between 300 and 500 mph), there is very little surface grip from the wheels and there is very little aerodynamic response.'
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