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The Brakes That Stop a 1,000 MPH Bloodhound SSC
cartechboy writes: "The problem: How do you stop the 1,000 mph Bloodhound SSC? The solution: Apparently you use steel rotors from AP Racing, which managed to absorb 4.6 kilowatts of energy on a test stand without failing although the Bloodhound team hasn't spun them up to the full 10,000 rpm just yet. During testing, a set of carbon rotors from a jet fighter shattered under the stress during a half-speed, 5,000-rpm test, thus the team switched to steel rotors. It's like stopping a bus from 160 mph on a wet road. That's how the engineers behind the Bloodhound SSC—the British land-speed record car designed to break the 1,000-mph barrier—described the task of stopping their creation once it's finished breaking the sound barrier. We'll have to wait to see if the steel rotors can handle the full 10,000 rpm run, but until then, it looks like steel is stronger than carbon when it comes to some instances."
I think people forget that "stronger" is meaningless. In the case of steel vs carbon, carbon is going to be stronger for a given weight, but that just makes the word "stronger" even more meaningless.
Steel usually wins out against most materials when it comes to survival. Steel bends, and bends back. Just about everything else loses by being brittle. Aluminum is the best example, being about three times lighter, but incredibly brittle. Carbon is also very brittle, just at the microscopic level. It'll fray, and slowly degrade until it comes a part -- like most fabrics.
Steel deforms, and then melts back together and deforms again. In order for friction to destroy steel, it needs to actually wear it away one particle at a time. Being so much heavier/denser, there are that many more particles to wear away. That's the win.
Why are people surprised when mass wins in a mass-bound effort? The challenge here is to get a heavy car to go really fast, and to then slow it down. That's always been a mass vs mass game. More mass always wins.
My question remains: if the carbon solution were as heavy as the steel solution, would it survive? But we all know that you can't cram that much carbon fibre into the same style of braking system.
Friction brake, electromechanical brake, eddy current brake, drogue parachute, inclined plane, arrester bed, rubber bands, brick/stone wall, etc. You'd think engineers would have been able to think of these things...
If they use a really long bungee cord not only could they use it to brake the vehicle at the end of one run, but use it for initial acceleration on the return run too!
My favorite thing about the Bloodhound SSC is that it uses a 4.2L V12 engine producing 750bhp...to run its fuel pump.
Why not just skip the brakes, save the money, and eject the driver/pilot and let the sucker crash and burn? Could be an awesomely popular YouTube video.
IMHO these are not cars and the records are fairly meaningless. It is a low flying aircraft being precisely controlled to keep the landing gear down on the runway. Don't believe me - watch what happens if the design is wrong. it will definitely be flying and not in a good way.
Very high-end landspeed cars usually use eddy current brakes and only have friction brakes for coming to a complete stop.
More "mundane" (like up to 700kph) landspeed cars use conventional friction brakes - after parachutes have done most of the work of course.
"When information is power, privacy is freedom" - Jah-Wren Ryel
Steel bends, and bends back. Aluminum is the best example, being about three times lighter, but incredibly brittle. Carbon is also very brittle, just at the microscopic level. It'll fray, and slowly degrade until it comes a part -- like most fabrics.
I'm sorry, but you know not what you speak. Aluminum is used on millions of planes for, what, almost a century? There are very malleable forms of steel (like the springs in your car) and very brittle forms of steel (like some kitchen knives.) Go and look at the carbon fiber wings on thousands upon thousands of aircraft.
Go look at the carbon fiber rear seat/chain stays and front forks on millions of bicycles.
People commonly attribute specific qualities to broad material categories like "steel" or "aluminum" like you just did, which is completely ignorant of the fact that all these materials can be engineered for different properties.
Carbon fiber is the most engineer-able material available, just about. Choosing a fighter jet part was pretty stupid, given it was engineered for weight, very occasional use, and lots of airflow, etc. They could almost certainly have a proper ceramic rotor designed for them, but it's probably too expensive or they got sponsorship with AP (given the article etc. this seems likely.)
Please help metamoderate.
You don't want downforce on a landspeed car, adding downforce is almost like dragging the brakes as far as they're concerned. Also air brakes make the vehicle they're attached to squirm around a little - not a problem on a fighter jet or a supercar, but a big problem on a vehicle travelling at speeds you don't want to be on the ground for and that can't turn worth a damn at any speed.
I'm sure it already uses a parachute. Usually these kinds of cars use eddy current brakes to slow to the point that the chutes can be opened, then after the parachutes have done most of their work they use conventional friction brakes to come to a complete stop.
"When information is power, privacy is freedom" - Jah-Wren Ryel
As others have said, Bloodhound already uses airbrakes for higher speeds. The disk brakes are used when the airbrakes become ineffective at lower speeds.
NASCAR is 200 mph, not 300 (and 1/4 the weight). And NASCAR brakes don't have to survive rotating at 1600 km/h. At that speed, the centrifugal force is more than most materials can handle. Bloodhound's wheels are some of the biggest engineering challenges in the project, they have to withstand something like 50,000 G. The brakes are a bit easier because they're smaller, but still a major problem.
Hold on for a metre while I think about this... Yes, lazy reporters who get their units wrong should be sprayed with five square metres of water and then shocked with a 20-coulomb current. Maybe then they'll spend the small extra mass needed to do proper research...
Excuse me AC, but would your name happen to be Wile E Coyote?
Acttually I went to the article, the summary is pretty misleading. The carbon brakes have to rotate with the wheels. At 1000mph they are turning 10,000 rpm and failed under the stresses, When it's time to stop the car airbrakes are deployed which slow the car to 160mph when conventional disk brakes are employed. The carbon brakes would certainly be more effective from 160mph to 0mph, but can't withstand 10,000rpm.