ESDU 00018:2010

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.