INTRODUCTION

This Data Item is the second 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
4, is essentially statistical and implies that there is a
clearly-defined level of probability that can be deduced from test
runs of an aircraft (or ground-test machine) 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 effective 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 4.

The Item uses test data collected from a short trial on a small
combat aircraft to illustrate the way in which a very limited
amount of information can be used to establish a Friction Data
Base. For this aircraft the data were limited in so far as the
tests were made on a single runway and the measured quantities were
"brakes-on" speed and stopping distance. The background to those
tests is described in Section 3. The methods of analysis are
summarised and results are presented in Section 4.

The first example, for an aircraft where an extensive set of
test data is available, is given in Reference 5. An example of the
application of the method to ground-test machine data is given in
Reference 6. Many other examples are considered in Reference 3.

If the method of Reference 4 is to be used to relate
the braking performances of a given combination of aircraft and
ground-test machine, the procedure is comprised of 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.