Friction on non-standard runway surfaces

[Sirius Flying]

Hi everybody,
I am currently looking into literature on rolling and braking friction coefficients (mu braked and unbraked), and there's plenty of stuff available on the net for the usual runway surfaces like concrete, asphalt etc. in dry, wet, snowy etc. conditions. However, I could not find anything freely available dealing with surfaces like gravel, sand, grass and the like. Does anybody here have any info about where to find some aviation-related info in this area?
Thanks,
SF

[GlosMikeP]

Not sure if this will help at all.

http://www.pprune.org/forums/showthread.php?t=239560&highlight=aquaplaning

(Link corrected)

[Shawn Coyle]

I know that Transport Canada and Canada's National Research Council's Institute for Aerospace Research did a lot of work on contaminated runways. Just not sure of where to search for the stuff.

[GlosMikeP]

Safeteetype put the Canadian links on the Aquaplaning thread, the link to which I've corrected in my post above.

[Genghis the Engineer]

I have to apologise for the fact that I don't seem to have kept a note of where these numbers came from (I suspect it was probably from some Transport Canada work), but below for each type of runway surface are (a) type of surface, (b) minimum likely value of braking coefficient, (c) maximum likely value of braking coefficient.

Actually this probably isn't what you want, since it doesn't cover gravel, sand, etc. but it might be of some use.

G


Hard dry runway 0.4 0.4
Damp runway (max. 0.25mm / 0.01” water) 0.347 0.374
Very light snow 0.334 0.347
Wet concrete (up to 0.75mm / 0.03” water) 0.294 0.334
Wet tarmac (ashphalt) (up to 0.75mm / 0.03” water) 0.268 0.347
Gritted compacted snow or ice 0.294 0.321
Compacted snow below -15°C (5°) 0.262 0.268
Heavy rain (0.75-2.5mm / 0.03” – 0.1” water) 0.254 0.268
Snow covered compacted snow below -15°C (5°) 0.241 0.254
Cold ice below -10°C 0.215 0.241
Wet ice above 0°C 0.201 0.215
Hydroplaning on standing water above 2.5mm (0.1”) deep 0.201 0.201

[tribo]

Please be adviced that:

- a friction number is not a property of a surface. It is generated from a pair of surfaces in relative motion.

- a friction number must always be related to the measuring instrument used. (Friction measuring device, aircraft, etc)

- there is a lot of uncertainties related to the generated friction numbers.

- a friction number with multiple decimals (0.261) is not an "accurate" friction number.

- the term "accurate" can not be used together with a friction number as we do not have an universially agreed reference. The correct term is UNCERTAINTY

- the uncertainty involved when it comes to operation of aircrafts is in the order of 0.1

[tribo]

Have a look at the link below and table 9.2.

This might be the kind of stuff you are looking for.

http://www.aviation.org.uk/docs/flighttest.navair.navy.milunrestricted-FTM108/c9.pdf