Vertical take-off and landing operations of aerial vehicle on ship’s deck enhance mission capabilities for military and civilian users. Anyway, these operations are the most dangerous flight phases for helicopters. Indeed, with reference to a Rotorcraft Unmanned Aerial System, a remote pilot has to deal with an invisible ship air wake, poor visible cueing and a landing spot which is heaving, rolling, pitching and yawing; at the same time the pilot shall also monitor vehicle’s structural, aerodynamic and control limits. Moreover, operations take place in close proximity to the superstructure of the ship, that means there is little margin for error and the consequences of a significant loss of positional accuracy by the pilot can be severe.
The availability of Guidance Navigation and Control algorithms for automatic operations can help the remote pilots to face these tasks by significantly reducing operator workload, improving safety level and flight handling qualities. The design and verification of such algorithms require the availability of a suitable simulation environment that shall be as simple as possible, to enhance physical understanding and lower the computational load. On the other hand, the simulation models shall be sufficiently accurate for catching all the relevant phenomena that can affect helicopter behaviour.
CIRA dealt with these issues within the framework of the MISE project, where two products were developed in collaboration with the Helicopter division of Finmeccanica: a numerical simulation environment of the Rotorcraft Unmanned Aerial system and a library of FMS routines specifically designed to be integrated into a ‘standard’ FMS system and to completely and automatically manage the phases of Taking-off and of Landing on the deck of a ship carrier.
The simulation environment includes helicopter flight dynamics, on board sensors and actuators, the motion of the ship for the given sea state, the influence on the helicopter of the ship air wake and of the environment in general. Key original contribution of this environment is the development of a mixed empirical and physical formulation of the equations, so that the resulting simulation model only reproduces the main effects to take into account to design and validate the GNC algorithms.
The FMS routine are provided into a modular architecture characterized by a clear distinction between mission dependent block and mission independent block. The mission dependent block generates the flight plan Way Points depending on the specific mission task (Auto Landing, Auto Take Off, Missed Approach, etc.), the vehicle current state and commands/information sent by the Ground control station. It also activates the correct Autopilot mode. The mission independent block computes the vehicle trajectory between the waypoints, which is generated in step distinguishing between horizontal trajectory, vertical trajectory and speed profile. Moreover, this block computes the steering commands and the tracking errors sent to the Autopilot.
The use of the proposed simulation environment dramatically reduced the FMS module design time, risks and costs, by limiting the required flight test activities. Finally the module was successfully demonstrated in flight, by means of a full-size optionally piloted helicopter: the Finmeccanica SW-4 SOLO.