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."

Comments

Killowatts are power, not energy

[YesIAmAScript]

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:Killowatts are power, not energy

[Anonymous Coward]

Power is energy per time. But 6HP is correct.

Re:Killowatts are power, not energy

[Connie_Lingus]

watch TFV...

it clearly states that air brakes will slow the machine from 1000mph to 160mph and the brakes are simply used for fine-tuning the stop location.

Re:Killowatts are power, not energy

[hackertourist]

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.

Re:Killowatts are power, not energy

[dskoll]

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:Killowatts are power, not energy

[AK Marc]

I didn't say they should have done it, but the question was why didn't they? That's not arm-chairing, but trying to learn. Why do you hate learning?

Re:Killowatts are power, not energy

[AK Marc]

I would have considered something in the axle, though no idea what they used for it. To better spread the stresses, longer than minimum axles are generally used, and putting small magnets embedded into them with copper wire around would have minimal effect on rotating mass and be able to provide non-contact stopping power. The other option I though of was putting the same thing in the wheel, but even the smallest weight in the wheel could have large knock-on effects.

Or what about going with friction braking. Have a roller come down on the top of the wheel, and generate resistance. Use the wheel itself as the braking surface. There are 100 ways I can think of for stopping a car without having brake disks. Drum brakes started out by having the calipers work from the outside in, before it was reversed to make the "drum" appearance style widely called drum brakes. Putting them in a drum increased performance, but increased cost and complexity. Going back to the basics and re-inventing automotive brakes could give them something better than adapting current brakes to a special situation. The precursers to drum brakes were lighter and cheaper than their replacement, but were bad for wear and wet weather performance, but something tells me they won't be taking their runs in the rain (but may need to consider the large amount of cast-off of the ground surface that could pollute the braking surface in them.

This article is devoid of scientific and engineering details. It's "ooh look, this car is so fast that it breaks fighter-jet brake rotors before even trying to use them." Yeah, cool. So if it's so hard, why didn't you try other ways? What are the pads, as regular pads will no work at the temperatures given. Also, I noted the rotors were vented, but not slotted or drilled. Is this because survivability is more important than effectiveness?

Re:Killowatts are power, not energy

[michelcolman]

The problem was that, even though they don't use the brakes at high speeds, those break disks are still on the wheels and spinning at whatever speed the wheels are spinning at, for the entire duration of the run. And apparently just that centrifugal force was enough to shatter carbon brakes. Vibrations at 1000 mph over desert ground certainly didn't help either.

Re:Killowatts are power, not energy

[tibit]

Of course if you actually looked at what you propose you'd realize that any inductive system still needs to use bulky rotors. It's the rotor's survivability that is the problem. The fact that it's a friction brake is rather inconsequential here. It's not the braking that is the problem. It's mere survivability of a disc brake at rotational speeds of an enterprise hard drive.

Steel is stronger than carbon in many instances

[holophrastic]

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.

Re:Steel is stronger than carbon in many instances

[holophrastic]

Umm, whatever your industry's definition of "strength", you'll find that it morphs across the three disciplines involved here. You'll also note that your own industry's definition of "strength" doesn't distinguish between various directions. So if I were to say that steel is stronger laterally, vs carbon's strength longitudinally, I'd still be within your industry.

Your industry also flexes in terms of the definition of the term "failure under load". Failure in some instances means breaking under the stress applied, but in others in means breaking as a result of the stress applied. In this case, we're talking about a spinning disk. If the material can withstand the load without the spinning, but then breaks due to the spinning, the term "strength" either does or does not cover the actual environment being discussed.

All of that aside, you'll note that this is not a materials sciences web-site, nor is it a theorhetical sciences journal. It is a site specifically for autistic yaps who make billions of dollars by transforming complicated depths into familiar fundamentals.

So why are you here?

The solution

[cdrudge]

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

[NotDrWho]

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

Re:The solution

[cdrudge]

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

[EvilSS]

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:The solution

[NotDrWho]

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

Journalism students attempting technical reporting

[mpoulton]

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.

It's a monster

[Ralph Wiggam]

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

Re:It's a monster

[njnnja]

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

Re:It's a monster

[KingOfBLASH]

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

Re:Stronger?

[The Grim Reefer]

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?

Who needs brakes?

[macraig]

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:Who needs brakes?

[l0ungeb0y]

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

Re:Who needs brakes?

[jklovanc]

Because the land speed record 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?

[jovius]

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.

not a car

[deadweight]

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:not a car

[CaptainLard]

The 139.843 MPH steam speed record was set in 2009, by a British team. 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...

Red Lectroids drool!

[Thud457]

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.

Friction brakes, that's unusual

[GameboyRMH]

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.

Re: Aerodynamics

[KingOfBLASH]

Actually if your airplane is going 1,000 mph into your descent, you, sir, have a problem.

I don't know the top speed you can land, but I would bet it's not much more than 200mph....

FLAPS!

[TheRealSteveDallas]

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!

[GameboyRMH]

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.

you know not what you speak of

[SuperBanana]

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:Stronger?

[xaxa]

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...

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

Time unit

[g8oz]

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

Re:Stronger?

[The Grim Reefer]

When the brake pedal (or control or whatever) is pushed, redirect the jet / rocket exhaust out the front and accelerate in the opposite direction. It is just force vectors. You might need some ablative shield on the front where the exhaust exits. Sure, there will be some amount of loss as you do this (with a U shaped pipe or whatever) and it will need to handle the heat, but should prove more robust than exploding brakes.

Uh huh. While that sounds great in theory, you need to keep in mind this is a 1000 mph land vehicle. What happens if at full speed the redirected thrust doesn't function quite right? At best the pilot/driver will need to change his/her underwear. Worst case he/she has to be hosed out of what is left of the car as it will become one fast moving uncontrollable centrifuge of death.

Steel rotors may not be elegant, but they are also fairly simple and we've understood the tech for a long time. I think I'd prefer a drag chute and rotors over some vectored thrust contraption. It's not like they are going to be doing continuous laps in this thing. Plus they won't need to entirely redesign the vehicle to accommodate a bunch of duct work and heat shielding.

SSC?

[Geoffrey.landis]

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

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

Re:Stronger?

[NatasRevol]

A freaking lightning bolt coming out of the tail as it slows would be spectacular.

Re: Aerodynamics

[Firethorn]

The SR-71 Blackbird has one of the highest take off and landing speeds going. Around 200 KEAS, or 230mph.

Passenger jets are 120-150 mph.

Unless you're flying high performance military aircraft 'under 200mph' is a good bet.

Re:Stronger?

[AK Marc]

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:4.6 kilowatts of energy

[Zynder]

Great Scott!

Re:Stronger?

[Zynder]

Excuse me AC, but would your name happen to be Wile E Coyote?

Re:Stronger?

[Bartles]

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.

Re:Journalism students attempting technical report

[Macman408]

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.