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Title: Fire Scout Launch and Recovery Considerations in Parametric-like Roll Conditions

Author(s): Dr. Bernard Ferrier, Andrew Silver, Robert Ernst

Abstract: The MQ-8 (Fire Scout) unmanned aircraft system (UAS) is the U. S. Navy’s primary ship-based helicopter UAS. The current Concept of Operations (CONOPS) calls for the MQ-8 to be based aboard any suitably equipped air capable ship, i.e. any ship installed with Mission Control Station (MCS), Tactical Common Data Link (TCDL), Unmanned Aerial Vehicle Common Automatic Recovery System (UCARS), associated radios and other helicopter handling systems. In particular, the Littoral Combat Ship (LCS) is the main platform for MQ-8 operations. LCS has two variant classes of ships, the Freedom and Independence class which MQ-8 will be deployed on. As part of the Navy deployment process, a ship suitability assessment is conducted in the form of Dynamic Interface (DI) testing. DI testing evaluates all aspects of shipboard helicopter suitability and compatibility, including the adequacy, effectiveness, and safety of MQ-8 shipboard Flying Qualities and Performance (FQ&P), aviation support facilities and procedures for all ship-based helicopter types. A significant component parameter centers on the ship’s motion characteristics. In the course of MQ-8B and LCS envelope expansion DI trials, unexpected ship motions have been measured and recorded. These motions were almost exclusively observed to be large roll. These roll motions may have been induced by a seaway, or may have been induced by non-linear interaction with pitch and heave motions. Since seaway measurements were not available, there was no way of knowing with certainty the cause of these motions. On further study it was shown that all of the axial traces were in phase. The ship speed with notable exception of angular roll displacement, all the other degrees of freedom, their rates and their accelerations, were low. Since the ship speed was low, and the pitch and heave motion was low, a possible cause of these motions was a low period swell coming on the beam of the ship. With shallow draft and streamlined hull without traditional rudder or stabilizing surfaces, the LCS can be made to roll without much wave energy. The implications for Fire Scout operations encountering parametric-like roll events are discussed. The need for careful definition of the ship’s motion characteristics are being driven by the combination of limited manpower availability and a requirement to reduce the time needed to execute aircraft launch and recovery (L&R) or to maintain deck tempo. To facilitate the upcoming ship-suitability assessment, a parallel effort was initiated to determine the feasibility of applying simulations and plug-and-play mission module options in support of unmanned DI at-sea testing and experimentation. Initial analysis indicates traditional linear ship motion models do not predict the presence of parametric roll. Real time measurements appear to offer one of the few choices available to detect the on-set of these roll cycles. At-sea preliminary study results are discussed and compared with simulated scenarios.