Inelastic collision dynamics of alkane (CH4 and C2H6) molecules at highly-corrugated surfaces is studied by the molecular beam scattering technique. For the azimuthal direction such as the [110] or the [100] of the impinging molecules on a LiF(001) surface, a wide variety of surface corrugation can be realized. Angular distributions of the reflected molecules realized in our experiment are found to qualitatively agree with those predicted by such simple classical collision models as hard cube [R. M. Logan and R. E. Stickney, J. Chem. Phys. 44, 195 (1966)] and washboard [J. C. Tully, J. Chem. Phys. 92, 680 (1990)] models. The surface corrugation experienced by C2H6 molecules is found much less than that experienced by CH4 molecules, due to the effectively large size of a C2H6 molecule. The surface corrugation decreases as the kinetic beam energy of the impinging molecules increases. This is caused by the difference in energy dependence of the repulsive potential energy surface of Li and F ions which independently interact with the incoming molecules.