Development and Application of a Comprehensive Simulation for Modeling Helicopter Ship Landing

Abstract

This work presents a comprehensive first principles physics-based simulation capability for helicopter ship landing, denoted as "HeliUM2-umich." The simulation incorporates key components of the ship-helicopter dynamic interface including: 1) a high fidelity flight dynamics model with coupled rotor-fuselage-landing gear dynamics, 2) an aerodynamic model for the complex Wind Over Deck (WOD) that results from wind interacting with the superstructure of a moving ship, 3) a ground effect model that captures aerodynamics in proximity of the deck, 4) a ship deck motion model for a given sea condition, and 5) a Linear-Quadatric Regulator (LQR) based Flight Control System (FCS) to stabilize the vehicle dynamics and maintain a desired approach trajectory.

Initial portion of the work was focused on developing a WOD model and integrating it into the flight dynamics code in order to examine the influence of WOD on the UH-60A helicopter response during approach and landing flight segments. The WOD velocities were generated using unsteady Detached Eddy Simulation of flow over a full-scale Simple Frigate Shape Version 2 ship. The flight trajectory consisted of steady level flight followed by descent along a straight inclined trajectory to a specified hover position. Subsequently, the main rotor collective is gradually decreased to enable vertical descent and landing. Gain scheduling was used to track the approach trajectory. The effect of the WOD on vehicle response was examined for two cases: WOD affecting the rotor only, and WOD affecting the entire helicopter including the fuselage, empennage and tail rotor. The controller was shown to be effective in maintaining the desired approach and landing trajectory. However, additional control effort was needed in the presence of WOD. High frequency oscillations were noted in the CG position coordinates and attitude angles due to WOD. Oblique WOD conditions required greater control effort than the headwind case. A larger effort was also required when WOD affected the entire helicopter as compared to the rotor alone. The combined influence of WOD and ground effect during approach and landing was also examined. The ground effect, which was modeled using a simple scaling factor, caused a decrease of approximately 11.3% in power consumption.

Next, a finite-state ground effect model was implemented to study the influence of static deck inclination and deck motion on helicopter dynamics. Rotor performance predictions showed good agreement with results from literature for hover over a level and stationary ground plane. Hover and landing simulations were performed with the deck inclined at constant roll and pitch angles, as well as with the deck excited in isolated roll, pitch and heave motions. For hover over a deck with constant roll inclination, an increase in the lateral inflow coefficient and the longitudinal cyclic control input was noted. Deck heaving motion produced an additional 7.5% change in power requirements relative to static ground effect, thus highlighting the importance of modeling dynamic ground effect. Simulations were also performed to examine the combined influence of WOD and deck motion. The representative ship motion data was extracted from the Systematic Characterization of the Naval Environment (SCONE) database. The controller was capable of maintaining a stable landing on level, inclined and moving decks in the presence of WOD and ground effect.