Exploratory Towing Tests of Seaplane Skipping

Recently, there has been significant interest in unconventional concepts such as unmanned aerial vehicles and wing-in-ground effect craft, which require the ability to take-off from and land on water. These emerging focus areas are in addition to the traditional roles of commercial, recreational or civil seaplanes. Skipping is a hydrodynamic instability in heave that can occur on many types of seaplanes and can result in a loss of the aircraft. This paper summarizes exploratory hydrodynamic towing tests intended to isolate skipping from other hydrodynamic instabilities in heave and pitch. The tests show that skipping can initiate in calm water at fixed trim. Pressure taps located aft of the step record large negative pressures during runs in which the seaplane skipped. The addition of passive ventilation tubes aft of the step broke the suction and eliminated skipping, in accordance with past studies on the subject. The relative magnitudes of the forces involved in skipping are discussed, and it is shown that the afterbody suction forces are very large relative to the steady-state hydrodynamic lift. The findings of this study are also applicable for stepped planing hulls, highlighting the significance of proper step ventilation.