Founder
23rd Oct 2006, 07:33
What SG (Specific Gravity) of the Runway contaminant do you use to calculate aquaplaning (hydroplaning) speed?
What I'm thinking of here is what SG do you calculate if you have slush, standing water or patches of water..?
Kind Regards
Tim
safetypee
23rd Oct 2006, 08:40
A range of values is given in para 5.0 (Contaminant Properties to be Considered) in EASA NPA 14/2004 Operation on Contaminated Runways. (www.easa.eu.int/doc/Rulemaking/NPA/NPA_14_2004.pdf)
Water 1.0
Slush 0.85
Wet snow 0.5
Note para 7.1.1 (Aquaplaning Speed)
“An aeroplane will aquaplane at high speed on a surface contaminated by standing water, slush or wet snow. For the purposes of estimating the effect of aquaplaning on contaminant drag, the aquaplaning speed, VP, is given by -
Vacq = 9P where Vacq is the ground speed in knots and P is the tyre pressure in lb/in2.
Predictions (Reference 5) indicate that the effect of running a wheel over a low density liquid contaminant containing air, such as slush, is to compress it such that it essentially acts as high density contaminant. This means that there is essentially no increase in aquaplaning speed to be expected with such a lower density contaminant. For this reason, the aquaplaning speed given here is not a function of the density of the contaminant”.
A difference between theory and certification practice? Possibly due to calculated landing performance having additionl margins built in i.e. " for the purposes of ..."