Helicopter Flight Dynamic Simulation with Refined Aerodynamics and Flexible Blade Modeling

Abstract

Acoupled rotor ‐fuselagee ight dynamicmodel thatincludesa maneuveringfreewakemodel and acouplede ap ‐ lag‐torsione exibleblademodel,aswellastheresultsofaninvestigationonsomeeffectsofine owandblademodeling onthefree-e ightresponseofahingelessrotorhelicoptertopilotinputs,aredescribed.Thewakemodelisarelaxation typefreewake, capableofmodelingthewakegeometry changesdueto maneuvers; no assumptionsaremadeonthe wakegeometry,whichisfreetoevolvebased on themaneuver.Theoreticalpredictionsarecomparedwith e ight-test data. The results show that the free-e ight, on-axis response to pilot pitch and roll inputs can be predicted with good accuracy with a relatively unsophisticated model. It is possible to predict the off-axis response from e rst principles, that is, without empirically derived correction factors and without assumptions on the wake geometry. To do so, however, requires sophisticated modeling. Both a free wake model that includes the wake distortions caused by the maneuver and a ree ned e exible blade model must be used. Most features of the off-axis response can be captured using a dynamic ine ow theory extended to account for maneuver-induced wake distortions, for a fraction of the cost of using a free wake model. The most cost-effective strategy, for typical e ight dynamic analyses and if vibratory loads are not required, is probably to calibrate such a theory using the more accurate free wake based model, and then use it in all calculations.