Assessment of Numerical Approaches for Modelling Tilt-Rotor Ground Effect stability in Hover and Near Hover Conditions

The paper proposes a process which, starting from the outcomes of dedicated CFD high fidelity simulations, is able to synthetize accurate ground effect modeling for complex rotorcraft configurations (specifically addressing tilt-rotor case), suitable both for real time pilot in the loop and design/configuration trade-off analyses. The effect of complex aerodynamic interactions between the rotor wakes, nacelles, fuselage, wing, and ground may consistently alter the rotorcraft dynamic response. In this regard, specific design choices as shape and dimensions of movable nacelle parts, rotor blades twist and thickness, wing and tail geometry may have consistent impact on the nature of the rotorcraft aeromechanic response, especially for near-ground operations, with consequent need to capture such phenomena at early stage of design. This picture is even more complex in case of Fly-By-Wire configurations where control laws, generally synthetized out of ground effect, should guarantee their effectiveness in ground effect as well. Specifically, the paper addresses the development of a ground effect modeling based on the outcomes of high fidelity aerodynamics (addressing Next Generation Civil Tiltrotor Technology Demonstrator NGCTR-TD) in the framework of FLIGHTLAB tool. Then, the effects of proposed modeling strategies on the bare aircraft and closed loop system are assessed in terms of the rotorcraft trim conditions and stability features. Investigation of the complete workflow toolchain, starting from aerodynamics modelling up to physical trends and control laws impact analysis provided the opportunity to consolidate an industrial based optimized approach, that carefully merge feasibility/time consumption/accuracy requirements, thanks to which both pilot in the loop simulation and design trade-off analysis are accomplished together, increasing the level of safety of flight for novel rotorcraft configuration.