CFD/CSD aeroelastic predictions of a semi-span tiltrotor

This work focuses on steps towards the ability to use tight coupling between computation fluid dynamics (CFD) and rotorcraft comprehensive analysis (CSD) to predict aeroelastic stability of a rotor. First, the Rotorcraft Comprehensive Analysis System (RCAS) analysis is used to carry out traditional linear stability analysis. Next, a method of using trim springs to artificially increase the stability of the wing so that a periodic solution during the RCAS trim procedure is presented. RCAS is then used to complete time-integrated transient analysis using a lifting-line aerodynamic model following a system perturbation through a vertical force located at the wing tip. CFD/CSD coupling is used for the first time to simulate a fully-elastic semi-span tiltrotor model. Loose coupling is used to achieve a trimmed solution for a sweep of airspeeds. Tight coupling is used to observe the transient behavior of the system following a perturbation. Low-speed results are promising and clearly demonstrate differences between the higher-fidelity method and comprehensive analysis indicating Helios is capturing previously missed aerodynamic effects. At higher speeds, the perturbation used here is found to be inadequate for activating the wing beam bending mode. Finally, the tight coupling procedure predicts an unstable rotor mode that is not predicted by comprehensive analysis. The primary objective of this work is to demonstrate new capabilities introduced to the CREATE-AV software Helios and RCAS which allow for a first fully-elastic semi-span simulation of a tiltrotor using high-fidelity analysis through both loose and tight coupling methodologies.