This Data Item describes both the origins of, and how to apply in practical applications, the empirical models defined in ESDU 10015, Model for performance of a single aircraft tyre rolling or braking on dry and precipitate contaminated runways, which is summarised in ESDU 05011, Summary of the model for performance of an aircraft tyre rolling or braking on dry or precipitate contaminated runways and ESDU 13007, Side-force coefficients on aircraft tyres in yawed and unbraked motion on dry and wet pavements.

The model for a tyre in linear motion is valid for runways contaminated with water, slush, snow and ice but can also be applied to runways that are free from any contaminant. In order to calculate decelerating forces, in addition to an approximation to the operating slip ratio for the braking system, it is necessary to know values of nine variables, all of which are used in customary calculations of aircraft performance. These are

• depth of macro-texture of runway surface

• depth of contaminant (where applicable)

• density of contaminant (where applicable)

• ground speed

• tyre inflation pressure

• normal (to runway) load on tyre

• nominal tyre width

• nominal tyre diameter

• runway surface temperature.

For a tyre in yaw, the yaw angle is also required.

The Data Item serves as an introduction to a series of worked examples which analyse the retarding forces acting on tyres which operate in braked and unbraked states on both dry and contaminated runway surfaces. Additionally, the problems associated with operating on such surfaces and relevant regulatory requirements are also considered.