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How about 50 (solid fuel) chemical charges with 100mS burn time each? They fire sequentially while the EBA is active. Might be getting a bit expensive though.

It also might be possible to control the pumping of liquid fuel, but I'm guessing we wouldn't want to carry liquid rocket fuel.

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Paul Smith
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I can't see that, or at least I think 2g is too low a number. If we came up with (say) a 10g system, then we might well choose to deploy the airbags, and the bonus is we avoided the collision. Probably it's better to have 10g managed than 'n'g unmanaged.

Anyway, if we manage to achieve a reliable 2g in theory, I think we'll be applying for patents.

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Paul Smith
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I don't agree with the 'front of the car' part. We could have our forward facing jet near the rear of the car.

The thrust from a rocket engine results from the pressure difference between the forwards and rearwards faces in the combustion chamber. Our diffuser would have to be designed for low back pressure, but with low back pressure I'm sure we could do a lot of diffusion without making our rocket motor ineffective.



But that's a better idea.

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Paul Smith
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But...

I've noticed on snow that sometimes a great deal of wheelspin increases traction, this chart may help to explain why that works:



Notice the yellow snow curve. The more slip the better the coefficient of friction.

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Paul Smith
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Instead of a rocket how about a fast release of very compressed air? It would be easy to refill and wouldn't pose such a risk of burning. In fact in summer it would be like free air conditioning to anyone stepping out in front of a car equipped with it Only those bothered about their hair getting blown around would be upset...Instead of thinking how to stop the car faster why not think about how to get the obstruction out of the way? This air blast could easily knock a ped a few feet and allow just that little bit longer to stop If you kept the air releasing then you'd never actually hit them, unless you blew them into the other lane and they were mown over by a vehicle coming the other way

Yes. Someone else mentioned scuba tanks.

Next step would be to look at the pressures and volumes required. If we could maintain 100psi pressure differential in a chamber with a 10 square inch nozzle we'd have 1,000lbs of thrust.

Standard braking in the dry provides a thrust equivalent of the weight of the vehicle. So with a small car weighing 1200 Kg, we'd need some 3,000 lbs of thrust to double the braking effort. But we're now braking at 40mph per second so we only need three seconds to stop from even 120mph.



I don't think it's a good idea to blow pedestrians out of the way. A goodly percentage of pedestrian fatalities result from the secondary impact with the road (or worse, a curbstone).

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Paul Smith
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The front tyres squeegee a track for the back tyres to run in. If only we could reverse the weight transfer effect and do most of our braking with the back...

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Paul Smith
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this is because snow is a deformable surface you actually get a better braking effect from letting it pack up infront of the tyre (same with deep gravel & some mud/grass)... not really your normal driving scenario.

although if we can drop enough snow in front of the wheels

re: cool jets.. rocket packs use peroxide fuel for the very reason it provides a relatively cool jet. would be cautious about putting them in the C pillar as you immediately remove weight from the front (steered) axle.

as for improvng wet road braking..... the various airless wheel (in particular the michelin tweel i was reading an articale on the other week) concepts allow vertical drainage (i.e. through the tread).. which should be a major advantage. plus they look pretty damn cool..



i think ive read all the variations that have been suggested... anyone want to summarise?

Agreed, but I think there must also be another effect.

I can tell you for sure that I've managed to drive up snowy hills in an old BMW 3 series by keeping a great deal of wheelspin, and a fair bit of opposite lock. These hills couldn't be climbed with the normal gentlest approach. It's possible that it's something to do with the (non LSD) diff. Or something to do with melting the snow, but I know it isn't to do with digging down to the tarmac.

I suspect that part of the rise in the yellow curve is due to 'something other' than the build up of material in front of the wheels.

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Paul Smith
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I think that's a very shrewd guess!


Don't eat yellow snow!


We need to do some calcs, but that's an awful lot of compressed air. Having said that, with something akin to a couple of SCUBA tanks mounted over the rear axle, and a small engine-driven compressor to charge them you could store a fair bit of air. Thinking about it empirically, I've once seen a compressed air welding bottle that fell off the lorry and knocked the valve clean off, turning it into a jet. Let's just say that there was no shortage of thrust!!!


...which is of course just what our "C pillar 45 degree retro jet system" tm would do.


I wouldn't. Adding downforce to the rear doesn't reduce front axle load, in fact it increases it. If we put 10 tons on the rear axle then apply the rear brakes up to the new limit of adhesion the torque reaction acting around the rear axle would load the front wheels right up again.

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I sort of know the effect you mean, but I think it's more about momentum than traction, or to put it another way I don't think the spinning wheel is actually improving it's grip.

I've been in similar situations where the text book approach of trying to prevent wheelspin didn't work, but tackling the hill "all guns blazing" did. I think the problem with the first approach is simply that in certain conditions backing off for grip just doesn't take advantage of the occasional bits of traction that do come your way as the texture of the surface varies, whereas with the wheels spinning a bit more you get an odd bit of impetus here and there whenever a bit of grip comes your way and then your momentum carries you to the next bit of traction etc. But I'd still maintain that even in these conditions you'll still get further by changing up a gear, backing off the throttle and reducing the torque to the wheels.

I suppose that in soft snow there must be an "impulse" effect if your driven wheels are consistently flinging snow rearwards. I wonder how much drive this gives? I've often wondered about rally cars using this as an assistance to cornering on gravel. When you see a high powered 4WD car in a heavily oversteering powerslide the mass of gravel the tyres are flinging outwards is quite considerable - I'd guess at 50lbs or more in a single corner at times. How much does this add to the mechanical grip?

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that statement in isolation clearly isn't right! but granted adding the assumption you are braking restores it somewhat.

in fact i'm wondering if the only effect of the thrusters was to counteract normal weight transfer forwards whether that would be a sufficient improvement for now.

and if we're countering weight transfer, how about movable ballast, pumping a load of water between fore/aft tanks to maintain and/or improve balance under braking.

About 5 or 6 years ago we had a week of heavy snow. And we have hills! The heaviest snowfall was very rapid and took place when I was 100 miles from home. Over the week I did a lot of driving. I started off believing that no wheelspin would provide the best traction. But the gentle approach failed again and again. Sometimes I started with good momentum but gradually lost speed on a hill until I came to a stop.

Bottom line: I'm 100% positive that 'all guns blazing' with up to 40 degrees of sideways was delivering very significantly more traction for hill climbing in that car. In fact there wasn't a single hill I didn't get up using that method. There were little FWD cars with 70% of the weight over the driving wheels failing to climb hills, but my 'all guns blazing' approach delivered again and again and again.

Now we just need to figure out why...

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Paul Smith
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wouldn't work for the same reason that abs hasn't reduced crashes - other than not knowing how to use it properly, people think "well I've got abs so I can drive 2" from the car in front and it will save me".

That could possibly be true, but as it happens I don't think it is.

ABS increases confidence, but fails to reduce stopping distances. That's a recipe for bad.

But if we have rockets going off that's going to be scary and not tend to increase confidence. Meanwhile we're hoping to improve braking quite a bit...

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Paul Smith
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For the want of any better knowledge shall we go with the "reaction" theory? Ie that flinging a few pounds of snow backwards provides an equal and opposite reaction etc. etc. and that getting the car a touch sideways ensures that the rear wheels are being fed with a better supply of snow to chuck?


As an aside, the "FWD has more traction" thing shows itself up as a fallacy the very instant any rearward weight transfer occurs, either (a) when trying to apply a lot of power or (b) when trying to climb a hill. FWD has considerable packaging benefits, lighter weight and often better PMI, but the notion that it gives better traction is nonsense, at least not in the circumstances where you need it most, ie climbing a snowy hill. I did a snowy, icy road rally in a Mk1 Escort last year, and the only real obstacle to climbing the hills was the stranded FWD cars!

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One adverse effect we would need to take into effect is that if emergency braking fired off a loud rocket / blast of compressed air (parachute, skid plate, anchor, skyhook etc) then this would have obvious appeal to the blue neon light brigade and we could expect a sudden surge in last minute braking for the traffic lights outside the town hall.

Perhaps this could be countered by inbuilding a warning siren that goes off as part of the deploment, making a sound like "W-A-N-K-E-R!".

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Here's another one - vacuum downforce.

I remember a sudden change in F1 rules in (perhaps about) 1980 after the teams discovered a way to create vacuum downforce under the car, and cornering speeds shot up.

I guess the big problems are

1) we'd have to deploy skirts (or something) to keep the vacuum under the vehicle

2) we'd have to pump out (or use up?) air

3) it might take too long to create the vacuum and it simply isn't there in useful quantities until the opportunity to brake is past.

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Paul Smith
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And another one...

Magnets!

Scalextric do this (cheating if you ask me...)

Obviously we'd need steel in the road somewhere and a dirty great big (electro?) magnet under the vehicle, but it could be done, and could work very well in locations of random clusters of accidents...

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
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Oh yes, I can see it now.

Man applies brake, giant electromagnet energises, is followed by loud "Clang!" as he is attracted to the nearest speed camera!

Another partial success...

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