scope:

INTRODUCTION

General

Accumulations of water on airfield runways affect aircraft operations in three ways.

(1) In damp conditions, although there is no measurable depth of water, there is a loss of adhesion between tyre and surface that follows from a masking of the sharpness of the micro-texture. In terms of braking action, on a runway constructed with adequate sharpness, this loss of adhesion can be trivial, especially when the surface is well-maintained.

(2) As rainfall rate rises and becomes significant, accumulations of water arise that inhibit the drainage effect due to macro-texture. Braking action further diminishes and planing ultimately occurs so that braking action and (non-aerodynamic) directional control is lost.

(3) Furthermore, accumulations in troughs and tyre-tracks may be such that impingement of spray on to an airframe, together with ingestion of spray into intakes, may result in unacceptable loss of take-off performance.

This Data Item is an analysis of the available, relevant experimental data for accumulation on ungrooved surfaces†. An algebraic, empirical model is developed from laboratory experiments that is confirmed to be applicable to an operational surface. Statistically, the modelling is shown to be adequately precise; experimental data are described to within one half millimetre.

† Grooved surfaces will be considered in a further Data Item.