Invention
Friday 5th January
Bristol Airport invents new ‘negative friction’ material.
“I’ve landed in wet weather, put the brakes on and come to the bit that is being re-surfaced, and just skated across it - we actually speeded up. When it is wet, you have no grip.”
Now, either Bristol Airport is built on a steep hill (unlikely), or someone is exaggerating. See the story here.
I am happy to have my opinion on this story swayed. 
There is a slope at the airport, but nothing much..
http://www.abpic.co.uk/photo/1012839/
Peter Olding
5 Jan 07 at 2:32 pm
It’s dangerous enough to stop flights today. Presumably the ’speeding-up’ effect is due to the change of degree of friction from one surface to another. When you’ve been decelerating at a regular rate and suddenly decelerate less due to a less ‘grippy’ surface, you will apparently speed up.
JG
5 Jan 07 at 2:44 pm
If the engines are not fully backed off and the reverse thrust panels are shut, then they could be putting out enough power to counter act the effect of the air brakes and speed the aircraft back up? I’ll stop here
DoGGa
5 Jan 07 at 2:46 pm
I agree with JG that it will _feel_ like you’re speeding up, but not _actually_ speeding up.
I don’t fully understand DoGGa comment, not knowing how hairyplanes land - but I’d suggest it’s very silly if, while they’re trying to stop the plane, they’re applying forward thrust with the engines.
stu
5 Jan 07 at 2:50 pm
They might have slowed enough to reach the point where they start ‘driving’ it again, to get to the taxiway.
JG
5 Jan 07 at 3:20 pm
Besides, if you’re decelerating less than before, technically you *have* increased speed.
JG
5 Jan 07 at 3:22 pm
“Besides, if you’re decelerating less than before, technically you *have* increased speed.”
Ouch.
Get in your car and drive at 50mph. Push hard on the brakes until you’re at 40mph. Now let off the braking a little. After a short time are you more likely to be at 35mph or 45mph?
stu
5 Jan 07 at 3:24 pm
I agree with the taxiing point. But then they should have said “we couldn’t taxi due to the slippy surface”. Their statement implies they touched down and were braking and suddenly the runway catapulted them forwards towards certain death at the perimeter fence.
stu
5 Jan 07 at 3:29 pm
Or maybe the jet engines strapped to each wing had some influence
sweavo
5 Jan 07 at 5:19 pm
45 or more, stu, since if you are doing 50 you’re likely on a dual carriageway, and after slamming on the brakes there will be a big truck bearing down on you at a closing speed of about 25-30 mph, necessitating an urgent and rapid depression of the accelerator.
sweavo
5 Jan 07 at 5:22 pm
oh dear. *triple checks he is on caffeine-free*
sweavo
5 Jan 07 at 5:24 pm
Ok. So do we reckon the jets continue pushing forwards while the air brakes (and wheel brakes?) try to resist?
Possible.
stu
5 Jan 07 at 5:24 pm
I think they would keep the engines ready for an immediate re-takeoff in case of problems on the runway like giant lobsters or sudden slippiness.
However, I’m not so sure after trying to recall what happens from memory. It goes something like:
1) bump
2) bump as the last set of wheels hits the tarmac
3) immediate helluva racket from the engines and feeling of slowage
4) squeaky brake stuff
so I think the engines are usually pointing backwards (or they have engaged reverse gear or however they do it) during landing.
sweavo
5 Jan 07 at 5:40 pm
I was thinking more along the lines of a graph. Look, I’ve drawn one here … the plane’s landed and this line at 45° downwards shows the rate of deceleration. At a certain point on that line (let’s put it here and mark it X) the surface changes to one with less friction and so the rate of deceleration is slowed and the line levels off somewhat. So at any point further along the bottom axis (time) the plane is now going *faster* than it would have been if the surface hadn’t changed.
If you’re walking along and you step on something slippery, doesn’t that foot move more quickly than it did before, and you fall over?
JG
5 Jan 07 at 6:17 pm
Faster _than it would have been_… yes, absolutely. The foot argument doesn’t work because that has the weight of the body pushing down on it to make it slip faster.
stu
5 Jan 07 at 7:10 pm
And plane wheels have the weight of the plane pushing down …
JG
5 Jan 07 at 7:17 pm
Your foot is part of a system. When you slip on ice, the _system_ doesn’t suddenly accelerate, part of it (the foot) accelerates sideways as another part (the body) drops downwards.
The plane is a system. If the weight of the plane causes the wheel to accelerate, you’ll soon find the stick that the wheel is on will snap.
Or in other words…
Yeah. Ok.
stu
5 Jan 07 at 7:24 pm
Brizzle Airport is closed this weekend for resurfacing. Read from that what you will.
lordhutton
5 Jan 07 at 8:12 pm
I agree with Stu. It’s nonsense.
Rich
5 Jan 07 at 8:22 pm
mountains are very slippery yet planes stop very quickly when they land on them.
perhaps they should resurface bristol airport with a mountain.
henry
6 Jan 07 at 11:02 am
Haha!
stu
6 Jan 07 at 1:54 pm
I put forward that conjecture that the phenomenon was caused by mischievous relativitists, changing the rate of spin of the planet to effect a corresponding acceleration of the plane with respect to the runway.
Of course, this hypothesis could be easily disproved if it were found that Bristol airports runway does not run East/West. They’d never get away with spinning the Earth in any other plane.
I open the floor to other examples of their work.
Simon's Tall
6 Jan 07 at 8:05 pm
I reckon it was pygmies.
Omally
12 Feb 07 at 1:28 pm