Abstract: The status of an under carr iag e at t he touchdow n instant is studied by analyzing the undercar riage par ameters w hich chang e w ith the w heel rotational speed in the drop test. The result indicates that when the spin-up horizo ntal load is the max imum dur ing t he landing , the opposite course residual elasticity of the under carriag e is not finished, and when the opposite course residual elasticity of t he under carr iag e is the max imum, the w heel mov ement ischanged from slide to roll.

Key words: undercarriage, drop test, wheel, rotational speed, horizontal load