Friction Characteristics of Landing Gear Tires on Sand-Contaminated Runways

Sand contamination alters the direct contact between aircraft tires and runway pavement and introduces particle-scale interactions that cannot be adequately represented by a constant friction coefficient alone. To examine this transient tire–particle–runway interaction, a two-way coupled discrete element method–multibody dynamics (DEM–MBD) model of a dual-wheel main landing gear assembly was developed using RecurDyn 2024 and EDEM 2022. In contrast to conventional single-wheel models with directly applied loads and predominantly steady-state conditions, the present model retains the load-transfer path through the landing gear structure and axle and considers the decelerating ground-roll phase after stable main-wheel contact. The effects of sand surface density and normal load on longitudinal resistance, friction coefficient, and particle motion were evaluated. As sand surface density increased, the longitudinal resistance decreased from 700.0 to 517.6 N, corresponding to a reduction of 26.1%, while the friction coefficient decreased from 0.0355 to 0.0275. Increasing the normal load from 10 to 30 kN raised the longitudinal resistance from 265.1 to 845.6 N, whereas the friction coefficient increased only from 0.0248 to 0.0288. The left and right wheels also exhibited non-synchronous transient responses. At the particle scale, higher normal loads were associated with lower local particle velocities and a smaller high-velocity region. These results show that the proposed coupled framework can capture both the structural load-transfer characteristics of dual-wheel landing gear and the particle-scale mechanisms governing transient tire friction on sand-contaminated runways.