INTRODUCTION

This Data Item is the third of a series of examples of the application of a method for representing – and, if necessary, relating – the braking performances of aircraft and ground-test machines in wet conditions. The method, which is given in Reference 11, is essentially statistical and implies that there is a clearly-defined level of probability that can be deduced from test runs of a ground-test machine (or an aircraft) in a given set of wetness conditions on a particular runway. If the runway macro-texture depth is known, then the parameter that defines the variation of coefficient of braking friction in the given conditions can be readily calculated from a pre-determined Friction Data Base. The concept of a Friction Data Base is explained in Reference 11.

This example uses data for the "Mu-Meter" ground-test machine operating both on wetted runways and in self-wetting mode. The background to the tests is described in Section 3. The method of analysis is summarised and results are presented in Section 4. Mu-Meter friction measurements are available from widely differing test series – to the extent that the suitability of the various results for use in predicting aircraft stopping performance can be assessed – see Table 4.1 – as a function of the ranges of runway wetness conditions used.

Two examples of the derivation of Friction Data Bases for individual aircraft are given in ESDU 99016 and ESDU 99017 (References 12 and 13). The former of these considers an aircraft for which an extensive set of test data is available; the latter considers an aircraft for which a limited set of test data is available.

If the method of Reference 11 is to be used to relate the braking performances of a given combination of aircraft and ground-test machine, the procedure comprises two distinct phases. The first is the establishment of separate Friction Data Bases for the aircraft and for the ground-test machine. The second is the prediction of operational braking performance of the aircraft using day-to-day measurements from the ground-test machine.