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## The Brakes That Stop a 1,000 MPH Bloodhound SSC262

Posted by Soulskill
from the stop-speed-racer-stop dept.
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."
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## The Brakes That Stop a 1,000 MPH Bloodhound SSC

• #### Killowatts are power, not energy (Score:4, Informative)

on Wednesday May 21, 2014 @01:00PM (#47058155)

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.

• #### Re: (Score:2)

Brakes on ordinary cars are typically several times more powerful than the car's engine, so we're talking about several hundred kW of available braking power for an ordinary saloon. On one hand, Bloodhound is a 6-ton machine going 250 km/h when the brakes are applied which would suggest the figure needs to be higher than that. On the other hand, it'll have far less grip than rubber tires on tarmac can generate so it's not the maximum power dissipation that counts.

• #### Re:Killowatts are power, not energy (Score:5, Funny)

on Wednesday May 21, 2014 @02:53PM (#47059373)

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...

• #### Re: (Score:2)

getting zapped with 20 coulombs kinda makes sense, though.

• #### Re: (Score:2)

Umm... no.

• #### Stronger? (Score:2)

If I had to guess, it isn't that steel is stronger in this case, but better at heat conduction/dissipation.

• #### Re: (Score:2)

If heat is a problem, it seems like regenerative breaking could be a better option.
• #### Re: (Score:2)

If heat is a problem, it seems like regenerative breaking could be a better option.

It's a jet and rocket powered car. How are you going to regenerate those with brakes? How much weight will they add? And finally, have regenerative brakes been built that would even be practical at 10K RPM?

• #### Re: (Score:3)

Possibly he's mistaken regenerative brakes for resistive/rheostatic brakes. On diesel-powered railway locomotives (which are almost always electric motors powered by a diesel generator) there's a bank of resistors. The motors are run as generators, the electricity put through the resistors and lost as heat: http://en.wikipedia.org/wiki/D... [wikipedia.org]

However, this vehicle doesn't have electric motors, so it's not applicable.

• #### Re:Stronger? (Score:4, Insightful)

on Wednesday May 21, 2014 @03:48PM (#47060049)
Putting magnets into the wheels and slowing the wheels through inductive forces would solve the rotor issue (though introduce its own). I think that was the core of the suggestion.
• #### Re: (Score:2)

I assure you that dumping waste energy as heat as in classical braking systems will be far more effective and robust than any "regenerative" system. If you are having heat dissipation problems you will likewise have overload problems anywhere else you try to direct that energy- along with heat dissipation problems. Although most likely your regenerative system would just be destroyed by the forces involved.

• #### Steel is stronger than carbon in many instances (Score:5, Interesting)

on Wednesday May 21, 2014 @01:06PM (#47058207)

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.

• #### you know not what you speak of (Score:5, Insightful)

on Wednesday May 21, 2014 @01:44PM (#47058599)

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.)

• #### Re: (Score:2)

Airplanes need to use very special flexible joints because Aluminum is so brittle. Aluminum becomes very weak very fast when it flexes to the point of being deformed. Steel, not so much, unless you put a ton of carbon in it.

He was correct when it comes to the general properties of steel, but not all cases.
• #### Re: (Score:2)

You can use brittle materials on airplanes. Some airplanes are carbon fiber framed.

• #### Re: (Score:2)

Have you seen the video of the stress test for the carbon fiber wings? They might be very brittle - they shatter amazingly when they finally break, but they're also very flexible, taking an amazing(for me at least) amount of force and distance of flex before finally snapping.

In this case though they're looking at resistance to heat/friction, so the types of damage resistance necessary is different.

• #### Re: (Score:2)

Aluminum will flex, too, if it's long or thin. A material's profile has a lot of impact on how it behaves.

Aluminum has severe cycling issues. When steel flexes, nothing happens; when aluminum flexes, it weakens. You can flex steel until deformation and weaken it, or you can flex it within deformation limits infinitely; aluminum flexed at all will weaken, and eventually crack.

Claiming that aluminum is not brittle because it's used on airplanes is silly. The aluminum used on airplanes isn't different;

• #### Re: (Score:2)

I find it interesting to note that all of your examples are of structural, non-frictional components, which doesn't really apply here. I'd have argued that while most metals are readily engineered for differing properties, 90% of those efforts fail miserably in frictional, high-heat, high-wear applications, where the base material undergoes chemically-significant physical forces -- like friction.

In any event, my comments were not intended to describe all steel and all carbon. Instead they were meant to d

• #### Re: (Score:2)

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.

Or, you know, heat it up so much that it starts to melt. That's a real possibility for this application. A previous poster suggested rheostatic brakes (basically regenerative braking, where the electricity is dumped into a big resistor instead of being stored for later use). It would add weight and complexity, but if regular brake disks can't dissipate the energy fast enough, then something like that might be necessary.

• #### Re: (Score:2)

That's always been a mass vs mass game. More mass always wins.

• #### Re: (Score:2)

I think you'd have a hard time keeping the lead there. Lead's pretty soft and melts easily, if I remember correctly. So it'd probably fall off faster than it would do anything else.

• #### Re: (Score:2)

The issue isn't how it works under load. The issue is that the wheels turn so fast that the wheels at top speed is a materials problem. Slowing is easy. Surviving top speed is harder.
• #### The solution (Score:5, Funny)

on Wednesday May 21, 2014 @01:07PM (#47058223) Homepage

The problem: How do you stop the 1,000 mph Bloodhound SSC?

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!

• #### Re:The solution (Score:5, Funny)

on Wednesday May 21, 2014 @01:17PM (#47058349)

They tested the brick wall stopping method. It did not end well.

• #### Re: (Score:3)

But it stopped. And depending on the thickness of the wall and size of the subsequent debris field, it probably stopped it the quickest compared to other methods. Subsequent runs became much more difficult though.

• #### Re:The solution (Score:5, Funny)

on Wednesday May 21, 2014 @02:14PM (#47058963)

But it stopped. And depending on the thickness of the wall and size of the subsequent debris field, it probably stopped it the quickest compared to other methods. Subsequent runs became much more difficult though.

Yes, the problem was cost. Using the brick wall meant that all parts of the car, including the driver, were single use only. They at least need the car to be reusable. Driver optionally so.

• #### Re: (Score:3)

Nonsense. Two screws, a bolt, and an eyeball were successfully recovered for reuse.

• #### Re: (Score:2)

I heard that they were actually mortarfied with the results...

• #### Re: (Score:2)

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.

Many moons ago I worked for a bicycle company building bikes for the Olympics down-hill racing team that year. (yes, I've had every weird job you can think f if you follow my posts at all.) Those breaks and wheels had to be replaced after 2 runs, and cost \$800 per set.

I suspect whats happening here is some sort of endorsement. Their putting their

• #### Re: (Score:2)

Those breaks and wheels had to be replaced after 2 runs

Perhaps if you used brakes instead of breaks they'd last longer. Just a thought...

• #### Brakes (Score:2)

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.

• #### Re: (Score:2)

It seems to be propelled by a rocket engine. Why not just apply thrust in the opposite direction?
• #### Journalism students attempting technical reporting (Score:3)

on Wednesday May 21, 2014 @01:14PM (#47058309)
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.
• #### Re: (Score:3)

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 coincidental

• #### Why no parachute? (Score:2)

Why don't they just invest in strong ropes, good bolts and a parachute, like literally every other rocket car?

• #### It's a monster (Score:5, Interesting)

on Wednesday May 21, 2014 @01:17PM (#47058351) Homepage

My favorite thing about the Bloodhound SSC is that it uses a 4.2L V12 engine producing 750bhp...to run its fuel pump.

• #### Re: (Score:3)

Slight correction - it's a 2.4L [bloodhoundssc.com] engine...to run the fuel pump.

• #### Re: (Score:2)

Also it's a V8 not V12.

• #### Re: (Score:2)

Doh. I got the details from a 2009 article. They apparently changed it.

• #### Re:It's a monster (Score:4, Funny)

on Wednesday May 21, 2014 @01:39PM (#47058547) Journal

Hey! You should label posts like that NSFW. I just creamed my pants at an inopportune time.

• #### Re: (Score:2)

My favorite thing about the Bloodhound SSC is that it uses a 4.2L V12 engine producing 750bhp...to run its fuel pump.

Even with the subsequent corrections, that actually is very cool.

• #### Who needs brakes? (Score:5, Funny)

<mark.a.craig@gmai[ ]om ['l.c' in gap]> on Wednesday May 21, 2014 @01:18PM (#47058363)

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.

• #### Re: (Score:3)

Because then they wouldn't have a shiny vehicle to send on world tour as a money making exhibit

• #### Re: (Score:2)

As many hits as that YouTube video would get, I don't think it will pay for the replacement.
• #### Re: (Score:3)

Because the land speed record [wikipedia.org] requires you to run in both directions in the same vehicle within an hour.

The record is standardized as the speed over a course of fixed length, averaged over two runs (commonly called "passes"). Two runs are required in opposite directions within one hour, and a new record mark must exceed the previous one by at least one percent to be validated.

• #### Re:Who needs brakes? (Score:5, Funny)

on Wednesday May 21, 2014 @02:03PM (#47058853)

I suggest they build wings to that machine. A machine of that size would be easily lifted from the ground at even lower speed than 1000 mp/h. There's less friction higher in the air anyway and they could reach speeds well exceeding 1000 mp/h. The team seems to be stuck with the car paradigm which is already well over 100 years old. I believe that humans will be able to fly with the aid of modern technology. All it needs is a change in thinking, an evolution of mind.

• #### Re: (Score:2)

I might be wrong, but my middle school level of physics leads me to believe that would not solve the problem of the pilot's forward momentum.

• #### not a car (Score:5, Insightful)

on Wednesday May 21, 2014 @01:25PM (#47058421)
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.
• #### Re: (Score:2, Informative)

Right. There are wheel-driven land speed records [wikipedia.org], currently 470.444 MPH with a turboshaft engine, 462 MPH with a piston engine, 307.666 with an electric motor, and 139.843 MPH with a steam turbine.

The 139.843 MPH steam speed record was set in 2009, by a British team [steamcar.co.uk]. This is embarassingly low for a custom-built steam turbine powered land speed record car that looks like an aircraft. They brought the car out to the salt flats at Edwards for this.

• #### Re:not a car (Score:4, Informative)

on Wednesday May 21, 2014 @05:38PM (#47061277)

The 139.843 MPH steam speed record was set in 2009, by a British team [steamcar.co.uk]. This is embarassingly low for a custom-built steam turbine powered land speed record car that looks like an aircraft. They brought the car out to the salt flats at Edwards for this.

Embarrassing to who? The team? Steam engine builders local 402 circa 1897? Humanity? The fact that the Land Speed World Record is what it is for a steam engine means that it might be harder than it looks. Now if society had spent hundreds of \$billions over the past century optimizing the steam engine like they have the ICE, you might have a point. From the site you listed:

"No one is going to suggest that this vehicle represents a major technical breakthrough, a relatively small improvement has been won at a cost of enormous complexity but it is unquestionably a triumph of determination, persistence and absolute refusal to give up in the face of adversity. Does it exemplify the "spirit of adventure"? Unquestionably!"

Good on them. I don't know about you but I don't have any world records to my name. I also never thought I'd get so fired up (no pun intended) defending a steam engine...

• #### Re: (Score:2)

Lots of wheel powered cars can take-off if something upsets them.

• #### Re: (Score:2)

That actually makes me wonder if that would be a more efficient way of making it stop. Instead of trying to brake, deploy some surfaces that give lift and just point straight up, pop some parachutes and deploy some landing bags.

I'm sure trying to make it aerodynamic enough to do that would just be massively complicating the whole design to the point that it is worthless, but it'd be a fun way to stop.

• #### Friction brakes, that's unusual (Score:5, Informative)

<gameboyrmh AT gmail DOT com> on Wednesday May 21, 2014 @01:40PM (#47058551) Journal

Very high-end landspeed cars usually use eddy current brakes [wikipedia.org] 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.

• #### FLAPS! (Score:2)

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.
• #### Re:FLAPS! (Score:5, Informative)

<gameboyrmh AT gmail DOT com> on Wednesday May 21, 2014 @01:46PM (#47058617) Journal

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.

• #### Serial parachutes (Score:2)

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.
• #### parachutes or water-cooled rotors (Score:2)

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..

• #### Time unit (Score:3)

on Wednesday May 21, 2014 @02:03PM (#47058847)

"managed to absorb 4.6 kilowatts of energy"......per what? The number is meaningless without a unit of time.

• #### Re: (Score:2)

The same as is the case with this gem?

It's like stopping a bus from 160 mph on a wet road

which is probably relatively easy if you're given 5 minutes to do it.

• #### SSC? (Score:3)

on Wednesday May 21, 2014 @02:20PM (#47059025) Homepage

http://www.acronymfinder.com/S... [acronymfinder.com]

Couldn't they mention what they are talking about in the first sentence or two of the summary?

• #### Re: (Score:2)

And couldn't you actually post what it stands for instead of linking to some other site?!
• #### steel is stronger than carbon... (Score:2)

A better way to make the comparison would be to say, "steel is a better material choice in this application".
• #### Turn it into a plane! (Score:2)

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.

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