Analysis of Trailing-Edge Flap Control for Minimum Vibrations Using CFD/CSD Analysis

The capability to minimize vibratory loads with trailing edge flaps on a helicopter rotor is explored in this paper. Predictions with computational structural dynamics (CSD) codes coupled to a lifting-line (LL) aerodynamic model and a computational fluid dynamics (CFD) code are compared. Open and closed-loop controls are explored with both aerodynamic models. Moderate nonlinearities in the CFD/CSD simulation are shown to be present by illustrating that the extracted T-matrix, from open-loop actuation, varies with actuation phase. For example, for a purely linear system, identical T-matrices would be obtained from open-loop phase sweeps with different combinations of positive/negative cosine and sine inputs. However different T-matrices were obtained for these actuation phase permutations for the CFD/CSD simulation. The predictions showed that trailing-edge flaps are capable of simultaneously reducing vibratory thrust, pitch and roll moments by 90%. The rotor performance (L/De) was shown to be reduced for flap inputs which minimize vibratory hub loads; however the predicted performance reduction is less for CFD/CSD than LL/CSD simulations. Calculations were performed to minimize control loads by reducing 3p-5p push-rod loads.