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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."
hey asshole, that's power, not energy...
And 4.6kW isn't that much power anyway. About 60HP.
I've seen resistor boxes used for testing EVSEs that take 6.6kW and of course don't fail.
http://lkml.org/lkml/2005/8/20/95
If I had to guess, it isn't that steel is stronger in this case, but better at heat conduction/dissipation.
4.6 kilowatts of energy
Kilowatts is a unit of power, not energy. Sheesh.
I think aerodynamic drag, even without a parachute, will help out a lot with the stopping.
Um, duh? Materials science 101, chubs. But I guess when you have people talking about space elevators in all seriousness, you can't expect too much realism...
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!
Second, minute, hour, century??
I've got lightbulbs absorbing more than 4,6kW...
4.6kW, eh? That's 6.2 horsepower. I'm gonna go out on a limb and say that number is wrong by several orders of magnitude. 4.6MW is more likely.
I am a geek attorney, but not your geek attorney unless you've already retained me. This is not legal advice.
Why don't they just invest in strong ropes, good bolts and a parachute, like literally every other rocket car?
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.
pish, the obvious design is to dump the energy into the oscillation overthruster. That way you don't have sudden deceleration when you collide with the mountain.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
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
Why aren't they using analog flaps to gradually increase drag? At 1000mph you will decelerate pretty quickly by just not applying thrust. Other aircraft can slow down pretty well using them and they don't have the friction of maintaining contact with the ground to help. Bonus for using the same flaps to increase downforce as they open so the mechanical brakes will work better or just deploy a dragster chute once you get below the operating envelope.
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.
Why not a small, strong parachute to start the slowing followed by progressively larger parachutes? If we are considering only brake shoes or pads then I would think ceramic with some embedded metal pieces might be the way to go. If pre-warmed the ceramic should hold together nicely.
Superconducting Super Collider ?
Traditionally, parachutes (strictly, drogue chutes) are used from these speeds. Other drag increasers (flaps) would also work. So would shutting off the motive force!
If you insist upon friction brakes, then you know you'll have a problem with heat removal. For that, water is best. Either pumped supply or static fill, just let the steam blow out of hub-wards pressure valves at 15-100 psig on hollow rotors..
"managed to absorb 4.6 kilowatts of energy"......per what? The number is meaningless without a unit of time.
http://www.acronymfinder.com/S...
Couldn't they mention what they are talking about in the first sentence or two of the summary?
http://www.geoffreylandis.com
If you watch the video on one of the pages linked in the post, they say explicitly that they use drag from airbrakes to slow from 1000mph, and that the steel brakes will only be used to slow from 160mph to a stop near the recovery team. They're just using the steel brakes because they'll (presumably) tolerate being spun at 10000rpm, whereas the carbon brakes disintegrated. Also, the brakes don't need much stopping power because the contact patches of the wheels is tiny on the desert floor; you can add huge brakes, but they'll just lock the wheels up and you'll lose control.
I'm guessing the sequence will be airbrakes at 1000mph --> parachute at 300-350mph (this is what was used on the last record car) --> wheel brakes for final stopping.
A better way to make the comparison would be to say, "steel is a better material choice in this application".
at the end of the run, or if in trouble, simply take off, and recover by parachute.
It's right in the article - the brakes are for below 160mph, before that it'll be air brakes and parachutes.
I don't read AC A human right
They could make the car into a plane. Want to stop? Just flip the wings to the flying position and take off. You lose lots of kinetic energy as you ascend; when the speed is reasonable, you glide back down to earth.
Though... I guess the engineering challenges in making a plane that suddenly takes off at 1600km/h are quite substantial.
Right, that's the first thing I thought of. This is an incredibly stupid way to stop a high speed vehicle. They're going to have to replace those things every run.
Not that big of an issue for a 'car' that's essentially a rocket engine designed to break the land speed record.
Hopefully they have a backup chute in case these silly brakes fail.
Actually, that's being deployed before the brakes. The article mentions air brakes and parachutes. Presumably the stop sequence will be air brakes first, then parachute, then wheel brakes that they're searching for a suitable solution for now, which per the article only start when it's slowed to 160mph.
I don't read AC A human right
I may be feeling a bit of childhood nostalgia, but this car reminds me of the SSP Ram Jet toy.
I think the commentator needs to brush up on his math(s) and physics, the plot shows a disc speed of 1841 Rpm and a torque or 1372 N.m this equals 264 Kw.
Pkw = n(rpm) x t(n.m) / 9550
Energy dissapated is measured in Joules @ 264Kw this is 264Kj per second
Claiming that aluminum is not brittle because it's used on airplanes is silly.
It would be, but this statement is attacking a strawman, since none of us claimed it. For that matter, I suggest rereading my post for any mention of Aluminum. You won't find any. I addressed Carbon Fiber. SuperBannana covered Aluminum, but your post agrees with him - summarized as various materials can be engineered to perform various roles, empasizing or minimizing various characteristics within limits.
As for Aluminum flexing too, I agree, I see it frequently. The difference is one of magnitude. Aluminum wings will fail at far lower stress levels and certainly less bend than CF wings. You also have the problem that Aluminum is known to fatigue far quicker even with less flex than steel, much less CF.
Steel is mostly good because it's cheap and has one of the more forgiving failure modes when overstressed.
The aluminum used on airplanes isn't different; it's a grade of aluminum suitable for planes, with some of aluminum's weaknesses more pronounced and some less.
Contradicting yourself here. Airplane aluminum IS different than what you'll find in something like a Soda Can. The alloy will be different, as well as treatment and forming techniques.
I don't read AC A human right
Why not solid-fuel retrorockets?
4.6kW, eh? That's 6.2 horsepower. I'm gonna go out on a limb and say that number is wrong by several orders of magnitude. 4.6MW is more likely.
And, as others have noted, kW is a unit of power anyway, and so is fairly meaningless for a braking system, which is taking huge amounts of kinetic energy and trying to convert them to something else (eg heat) without that something else causing some sort of spectacular show.
But maybe it's just the journalist's error - 4.6 *kWh* would be a reasonable number; eg the equivalent of slowing down a 1000 kg vehicle from 400 mph to 0. Or, in their example, the 160 mph bus must weigh about 6500 kg. Not coincidentally, Wikipedia lists the curb weight of the Bloodhound SSC as 6,422 kg.
(Of course, whether the road is wet or dry has nothing to do with the amount of energy dissipated in stopping the bus. They might as well have said "It's like stopping a bus from 160 mph on a Tuesday.")
I am a geek attorney, but not your geek attorney unless you've already retained me. This is not legal advice.
Sir, you will be hearing from my attorney shortly on the basis that you have provided me with illegal advice. I will be seeking PUN-ative damages.
Braking is the generation and dissipation of heat. If the rotors are getting to hot, why not dump metered gas (nitrogen?) to maintain the proper temperature? This is not for repeated use, generally in a two way speed run system the brakes are used twice. Once in each direction. The dispensing system does not have to be that large or heavy. This system would activate when the parameters that the engineers set are met otherwise the brakes work without chilling.
Passionately Indifferent
An _engineer_ would design a brake disc (or whatever) to a spec. Some rotational speed, some diameter and some tensile strength for the material.
If you built and tested it and it failed to deliver you should be asking loud questions as to why.
You don't just hope something will work and test it.
That approach is for amateurs who don't know what they are doing.
If this is really what happened then it doesn't bode well.
Maybe time for some maraging steel.
Never mind that the Watt is not a unit of energy...
Please, someone, bring back a public education system rather than subsidized daycare.
kW is the correct unit for power (energy per unit of time), and also for braking. The goal of braking is to quickly turn a lot of kinetic energy into heat, so brake performance is measured in Joules per second aka Watts. That said, 4.6 kW is a bit low for a system, but may be reasonable per disk - you'd just need a bunch.
That was not the sound of a land-speed record vehicle flying over your head.
While most of the retardation will be done by air brakes and parachutes, a set of car-like disc brakes still have to haul it down from 160 mph to a standstill on the slippery earth of South Africa's Kaksken Pan. At that speed, the car's steel wheels will still be spinning at 10,000 rpm.
If at 160 mph the wheels are spinning at 10,000 rpm, then it means that the wheel are about 14 cm in diameter, which, looking at the Bloodhound SSC side on (http://www.car-addicts.com/wp-content/gallery/bloodhound_ssc/Bloodhound_SSC_01.jpg) means that the car's body is about 30cm tall. Truly a marvel of miniaturization, including the driver! In related news, motoring journalists still suck at delivering factual information to the public.
4.6 kW is a bit low for a system
I nominate this for "understatement of the year".
A 4.6 kW braking system would be good for a *bicycle*, which could then stop in about half a second at full braking. As I noted in the GP, the total energy of their vehicle at 160 mph is 4.6 kWh, so it would take an HOUR to stop it at a rate of 4.6 kW. Even if you had 8 discs, it would still take you 7.5 minutes to stop. You'd go well over 10 miles in that time.