INTRODUCTION

This Data Item provides a method for representing – and, if necessary, relating – the braking performances of aircraft and ground-test machines in wet conditions. The method 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.

Section 3 defines the model used to represent wet runway braking friction. Section 4 describes procedures for generating a Friction Data Base for aircraft and ground-test machines and introduces examples based in existing test data. Section 5 discusses several ways in which Friction Data Bases can be used. Within the context of this Data Item the primary uses are,

to represent measured aircraft braking performance data on a statistical basis,

to provide means of relating the braking performances of ground-test machines and aircraft.

Section 6 addresses the possibilities of interpreting existing Friction Data Bases for use elsewhere.

Section 7 reviews the limitations of the method and various aspects of its implementation.

If the method 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 from day-to-day measurements from the ground-test machine.

ESDU 99016 and ESDU 99017 (References 7 and 8) provide two examples of the derivation of Friction Data Bases for individual aircraft. 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. Reference 9 provides a detailed example for a ground-test machine.

See Reference 42 for methods appropriate to runways contaminated with significant depths of water, slush, snow or ice. Reference 3 gives a general introduction to many aspects of aircraft ground performance.