aquaplaning again

[error_401]

After completing my studies and earning my ATPL (A) frozen I'd like to compile a small thesis about aquaplaning. (yes I know - one more...

The fun part is that within all the available information either you get only simplyfied explanations or the very deep digging stuff like: what happens in the 1/150th of a second a tread block hits the runway surface.

Now I'm looking for information which a pilot is able to understand and can eventually use. More in detail I'd like to compile a written explanation of the hydrodynamics of the formation of aquaplaning.

Concerning the well known formulas for aquaplaning speed I'd now like to learn what is behind the ominous constant before the square root of the tire pressure. These constanst are stated in various discussions in this forum but the circumstances of the involved parameters are never enlightened.

I'd therefore thank you for any ISBN code of literature, links on the web on the subject or indications found in OPS-Manuals.

thanks

error_401

(from my former life as a web-designer)

[Flash2001]

The conventional wisdom that tread design plays little part in aquaplaning speed seems to be changing. The automotive tyre companies seem to have developed deep groove tread designs that increase it. There ought to be some papers in the proceedings of the SAE.

[error_401]

Thank you Flash2001

You are right! Tread is important. I have been in contact with various engineers from tire companies (all for cars and trucks). There tread is used to pump water away. Unfortunately most commercial aircraft do not have treads except for the radial grooves.

I had a look at SAE, not really what I'm looking for and with prohibitive prices for their publications.

So - still looking for some light shed on the hydrodynamics under the tires...

[Flash2001]

Just from pictures, the important thing seems to be a wide, deep groove around the centre of the tread.

On racing motorcycles "Block pattern" tyres used to be used in the rain. These had wide circular and transverse grooves. Examination of the contact patch in detail suggests that this increases the unit pressure on the surface as the material of the tread and casing has a non-zero Youngs modulus. Conventional wisdom at the time placed a lot of importance on the tyre being new and thus having sharp edges on the blocks. Occasionaly the block pattern was cut in conventional tyres the night before the race. Block patterns probably wouldn't work on aircraft, though, as blocks would probably be torn off the casing during the violent spin-up caused by landing.

[mono]

Flash,

Not really a good example the main reason for the block pattern on m/c racing tyres is to allow more movement of the compound to increase the heat generated (more heat - better adhesion to the road/track surface). Transverse or diagonal grooves alone will disperse water away from the contact area.

I personally think that talk of youngs modulus and other deep scientific data is too much and it is simply a matter of when the standing water is deeper than the available tread depth (allowing for compound compression due to material characteristics and tyre pressure) which causes aquaplanning to start.

Only my lay opinion though!

Cheers.

[Flash2001]

But on a wet track the tyre is pretty well cooled...

[OverRun]

error_401

There are some of the historic posts on aquaplaning, with some additional engineering words at:
http://www.geocities.com/profemery/aviation.html

I've picked up a paper (746kB size) with some of the latest thinking - if you send me your e-mail address, and I'll send you (and anyone else) a copy of it - but only in about 10 days from now.

[mono]

Flash,

'But on a wet track the tyre is pretty well cooled...'

Hence the need to get as much heat into the tyre as possible and therefore the block tread pattern. If you ever get the chance to see a race bike on full wets just after it has stopped you will see masses of steam rising of the tyre due to the heat produced evaporating the water.

[Flash2001]

I last raced before either slicks or block patterns were in general use. Condensation rising from tyres wasn't unknown but the tyres certainly weren't very hot. Certainly we knew that tyre pressures should be raised in the rain. I did notice that on tracks that were old EFTS i.e. airports, the very coarse flint surface of the runways gave excellent traction wet or dry. These surfaces also had a wonderful grip on leather when they met. There were many interesting, nay fascinating, moments when one transitioned from the old flint surface to a newly laid asphalt patch in the wet.

I remain unconvinced that temperature raised by hysteresis is the main cause of the superior performance of block patterns. I think that increased unit pressure has more to do with it. I am willing to learn, however. Can you direct me to any scientific or engineering paper on the subject?

[error_401]

thanks for the comments so far

... just - not exactly what i've been looking for. Some more enlighting came yesterday after a visit to our national Goodyear/Dunlop dealer.

Found some interesting grafs and the source of measured skid coeficients on dusty surface after a light rain! Gets down to .3 and explains viscous aquaplaning.

Still working on the hydrodynamics under the footprint. I started looking in places like - ship engineering ...

Aquaplaning by itself suggests some fun ideas. If you could hold your speed up you could land on a lake or so ... but I suspect that a solid layer under the water has something to do with aquaplaning on a runway. And my guess is that passengers would not jump from the door at 150 kt.

Anyone knows about hydrodynamics involved when the footprint of the tire displaces the water?

Thanks for any enlightment


error_401

OverRun

Thanks for the link. Been there seen it.

Interesting site about the problems involved with landing on a wet runway. Once seen from the road engineers side as prof emery seems to be a capacity among the builders.

error_401

[Alex Whittingham]

There's an NPA here about contaminated runway performance that has a list of useful looking references at the end.

[RAT 5]

Just a thought.

All the talk about tread types is perhaps true in the ideal world. You could design the perfect anti-aquaplaning tyre. However, there will still be wear limits, and the bean counters that control most things these days will get their pound of flesh, and more, out of every tyre. The odd bit of canvas showing is not uncommon, especially as there might not be a spare to hand. What effect 3 re-treds will have on the tread pattern and strength would also be a factor.
Sod's law operates in most accidents. The days of a down-pour will coincide with the tyres being at their wear limits. The storm will cause the wind to be from other than the prevailing direction, which means the runway aligment will be wrong and the cross wind testing.
Plant it, was the advice from the old crusties. Avoid it, was another. Easy to say.
Better runway surface design would help. Certainly better surface cleaning. The rubber slick is left too long. There have been various accidents, DC.8 at ATH and L-1011 at LBA spring to mind, where the position of desired max braking turned out to be near to non-existant. The surface was more suitable for Torvil & Dean than Captain Prune.
In the V1 stop case, I believe that on limiting field lengths, if you are departing on a damp runway opposite to the normal landing traffic direction, the braking action towards the end will be way lower than that generaly published.
Like many things it seems an inexact science. I wonder if the data gained from the racing track can really be extrapolated upto the energy levels of 350 tons doing 170mph?

[error_401]

alex

Thanks - some more references. At least the JAA seems to show some interest in the matter too.

RAT5

You are completely right. Many of the factors you point out will be included in my compilation. It is exactly the real world things that i'm trying to adress with that work.

To give an insight in various formulas to pilots but also to give some advice. I'm in contact with various captains from 747, MD11, A310 which will help with their accounts and insights in aquaplaning. I learned that it is ways more common but usually ends in - geeeeee that was close incidents which never show up except in the memories of the two people (or three) in the cockpit that actually saw how close it went.

As for the physics part - I'm getting closer to it and guess what - aquaplaning has to do with lift, lift coeficient of the tire in question and the omnipresent density...

Once finished I'll probably publish the work on the internet.

Thanks for all comments so far

error_401

[lunkenheimer]

Regarding your comment about "you could land on a lake or so" it turns out that bush pilots in Alaska (typically flying Super Cubs) actually use that trick (or at least brag about it).

Balloon-style tundra tires appear to be a prerequisite...the strategy seems to be to 'ski' up to a sandbar or beach.

[dvt]

Here's an good read on the subject....

http://www.flightsafety.org/members/.../fsd_mar93.pdf


You say toe-mah-toe, I say tah-may-toe

You say aquaplaning, I say hydroplaning

You say shed-ule....I say what sh-ule did you go to?