This paper summarizes the hydrodynamic work that was performed on the Robinson R66 helicopter’s water emergency landings as part of the roadmap to obtain FAA approval. The emergency system consists of two floats that are rapidly inflated as soon as the helicopter touches the water using gas from a high pressure cylinder. This type of design is common in the helicopter industry and is known as a “pop out” float system. The floats have already been shown to provide enough buoyancy to keep the helicopter afloat in calm water.

Recognizing that once the helicopter is in the water, it is subjected to wave forces and behaves as a small water craft, a numerical study was performed using OrcaFlex. Over 500 numerical simulations, each lasting 10 minutes, of the helicopter floating in different wave environments were performed. The helicopter’s 6 degree-of-freedom (DOF) motions were monitored throughout. At the end of the run, if the helicopter had not capsized, the run would report: “no capsizing”. Sensitivity studies were performed by varying parameters individually. This led to an understanding of each parameter’s effects on the overall helicopter floating performance. These parameters included: wind, wave period, initial helicopter relative heading against the waves, wave height, and simulation seed (different random wave sets with the same spectral characteristics). The FAA expects floatation characteristics to be evaluated in “reasonably probable” water conditions and has issued guidance that World Meteorological Organization (WMO) sea state 4 is one acceptable definition of reasonably probable. A wind speed of up to 21 knots is also associated with sea state 4.

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