This Data Item summarises the empirical model defined in ESDU 10015, Model for performance of a single aircraft tyre rolling or braking on dry and precipitate contaminated runways, which describes the decelerating forces acting on an aircraft type tyre when rolling or braking on hard surfaces typical of runways and taxiways. The model 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.

The model is founded on experiments with aircraft type tyres analysed in the context of observations based in rubber technology. It has been substantiated over a range of experimental data so that aircraft and ground-test machine performance can be predicted for a wide range of operational envelopes. Where values are known for all the variables listed above, the model provides estimates of the decelerating forces due to rolling or braking. However, in cases where, say, runway conditions are unknown, the model can be used to deduce those conditions from ground-test machine measurements. Subsequently, those conditions can be re-applied to the model to predict aircraft performance. In the particular case of winter precipitation, the model includes the statistical variation of the mechanical properties of snows and the frictional characteristics for runways that are completely covered with ice or snow.

Application of the method to multiple-wheel undercarriages is also considered.