No abstract

Aircraft performances at landing or takeoff depend strongly on runway surface conditions. There is a need to provide aircraft pilots with reliable information in view of determining landing performance. Currently, this information is based on a description of the type and depth of contaminants on the runway surface. This paper presents a new method to improve the correlation between friction coefficients and braking coefficients measured respectively by ground vehicles and aircraft. A three-step approach is proposed, using a friction model developed by the Engineering Sciences Data Unit (ESDU), to weight the measured coefficients by factors taking into account the characteristics of the devices and the contaminants. The friction ESDU model is used on contaminated surfaces. The methodology is applied to data collected from extensive friction tests conducted between 1996 and 2003 (in the Joint Winter Runaway Friction Measurement Program). Characteristics of ground friction measuring devices and aircraft are provided as inputs for the ESDU model. It was found that the correlation between weighted ground friction and braking coefficients is improved significantly compared with the correlation between unweighted coefficients. Advantages of the newly proposed method are discussed in terms of using ground friction coefficients as a promising alternative to determine the runway condition code for aircraft pilots. Nomenclature C D = drag coefficient F B , F R = braking and rolling force, N F m , F v = measured horizontal and vertical force, N F Drag , F Displacement , F Compression = contaminant, displacement, and compression drag force, N g = gravity, m∕s 2 p, p a = tire inflation pressure (absolute) and atmospheric pressure, N∕m 2 R = wheel radius, m T = torque, N · m V, v = ground and slip speed, m∕s Z = vertical load, N μ Total , μ Slip , μ Roll , μ Drag , μ Ref = total deceleration coefficient, braking coefficient, rolling resistance, contaminant drag coefficient, reference friction coefficient ξ 0 , ξ 1 , η 0 , η 1 , η 2 , γ 0 = empirical constants;N −1∕3 , m −1 · N −1∕3 , N 1∕3 , N 1∕3 · m −1 , dimensionless, m −2 σ, ρ = contaminant specific gravity (dimensionless) and density, kg∕m 3

The paper deals with the modeling of friction between aircraft tires and contaminated runway surfaces. Wet-, snow- and ice-covered surfaces are considered. A tire Brush model developed for aircraft braking on dry runways is adapted to take into account the effect of contaminants. Compared with a dry surface, contaminants are assumed to affect the static and dynamic friction coefficients, the tire stiffness, the tire slip ratio and the length of the contact patch. Linear relationship is established between static and dynamic friction coefficients. The dynamic friction coefficient is reduced using an empirical model for wet surfaces and experimental fitting for snow- and ice-covered surfaces. The tire stiffness is modified considering the frequency and temperature dependence of the tire mechanical properties. Values on snow and ice are lower than those on wet and dry surfaces. A physical model is developed to calculate the length of the wet contact patch. Finally, it is assumed that the aircraft effective slip ratio is surface dependent; values are determined for each of the studied contaminants. Theoretical friction-slip curves are realistic in terms of shape and differentiation between surface conditions. The model is applied to a Falcon 20 aircraft and a runway monitoring device called IMAG. Friction-slip and friction-speed curves are calculated and compared to experimental data. It was found that the model can be used to relate ground friction to aircraft braking performance with enough reliability