BLOODHOUND SSC
W
hat are the main challenges aerodynamically
in creating a successful 1000 mph car?
The first one is drag. Obviously to accelerate the car to these sort of speeds you to have to look at the air resistance acting upon it. When you go supersonic, the drag on the car increases significantly. So one of the questions we had to ask was: what kind of drag would a car like this experience at Mach 1.3-1.4, which is about 1000 mph, depending on the temperature. We realized quite early on that you could design a car to do the job, do 1000 mph. The second question was: how on earth do you keep it on the ground? One’s natural instinct is that something travelling at this sort of speed should be flying, not travelling on the ground. When you’re travelling at these sort of speeds, it’s true that you can be generating massive vertical forces but you can direct those vertical forces in whatever direction you want but how finely can you control those vertical forces? You could generate an awful lot of downforce (at those speeds) and you could easily turn it into the world’s fastest plough if you got it wrong. Also, in the other direction, if the lift changed at some point in the run you could change it into an aircraft. We refer to Bloodhound as being “Mach number insensitive”. It’s impossible to design a car that has the same aerodynamic characteristics at all Mach numbers but we’ve tried to design a car that has the minimum variation in vertical forces throughout its Mach number regime. How have you addressed these challenges in your work plan? If you look at the car you’ll see it’s quite long and slender. The sharper the nose, the more slender the car, the lower the drag. It’s long (just over 14 metres long), we’ve tried to minimize the cross-sectional area of the car. And things like the wheels which are outside the car have elaborate wheel fairing on them to minimize the shock waves they’re going to cause. The really sticky one is the management of the vertical forces and, in particular, those wide-spaced rear wheels to give roll stability and the shock waves they generate. There’s a bow shock off those wheels that fans out and intersects with the back end of the car; in effect, the back end is sitting on an air cushion that’s trying to lift it up. 2009 | WIND TUNNEL INTERNATIONAL
“There’s a bow shock off those wheels that fans out and intersects with the back end of the car; in effect, the back end is sitting on an air cushion that’s trying to lift it up.”
We’ve just finished an awful lot of work — including the orientation of the suspension struts, the fairing around the wheels — on getting those bow shocks are as weak as possible: unfortunately, you can never completely get rid of them. Another sensitive area where we’ve spent a huge amount of effort is on the canopy over Andy Green, the driver. It might look like a fairly standard cockpit shape but that angle is at exactly the angle we want so that it doesn’t adversely affect other parts of the vehicle, like the inlet to the jet engine. What unique or innovative solutions have been implemented in the vehicle to address aerodynamic concerns? One of the main keys to our success will be that we’re using a combination of thrust generation. We have the combination of a device — a rocket — that gives you a massive amount of thrust for a small size and weight but is basically on or off, with a jet engine, which gives 23