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.