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One of the most important issues, which high-speed underwater vehicles (HSUV) deal with, is the so-called planing force. The dynamic of HSUV includes two separate phases called planing phase and non-planing phase. Ideally, in perfect flight, the vehicle should fly within the cavity walls. However, in practice, the vehicle impacts on the cavity boundaries due to disturbances. The magnitude of the planing force is large and has a strong effect on dynamics of HSUV. However, planing force modeling is often too simple and therefore inaccurate, due to the nonlinear interaction among the solid, liquid, and gaseous phases, which is not well understood yet. Consequently, planing force identification is of great importance and should be studied in details. The present paper discusses the identification of the planing force in HSUV. For this purpose, the equations of motion are developed for the HSUV in the planing phase while the tail and the body end impact on the cavity wall. Then, a robust hybrid switching control approach is employed to deal with the highly nonlinear behavior of the underwater vehicle as it is influenced by the liquid-gas boundary interactions. An on-line planing force identification based on Lyapunov function is considered within designing controller procedure, thus the stability of the system is guaranteed. Lateral and longitudinal planing force identification are achieved and discussed. Compared to the proportional-integral-derivative control scheme, the hybrid control scheme seems to increase the stabilization of HSUV, which is useful in avoiding unsteady changes of cavity shape.

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