Flight Dynamics Modeling & Coupling Investigation Of A Helicopter Suspended By A Slung Load

When a helicopter is flying with a slung load under-suspended,it could break through the restrictions from ground transportation and helicopter cabin size.And it has been applied to military & civil fields widely with distinct advantages.Meanwhile in such flights,there are very complicated flight dynamics couplings,which have severe effects on flight safety.The research of this thesis,concentrating on couplings in helicopter suspended flights,is carried out systematically including fully coupled flight dynamics modeling of a helicopter suspended by a slung load,quantitative analysis on coupling properties in such flights,and coupling refactoring via natural property modification based on quantitative coupling analysis.A fully coupled flight dynamics model for a helicopter suspended by a slung load is the foundation of coupling research.First,a helicopter flight dynamics model specifically used for slung-load transportation research is developed.The dynamics model of main rotor blade flap & lead-lag motion,aerodynamic models of components,the rigid-body dynamics model of helicopter fuselage aerodynamic interaction models among components,and the interface used for suspending flight modeling are all integrated.Then,the dynamics model of the suspending system mainly composed of a slung load and cables is built,and both quasi-steady and unsteady airloads are highlighted in slung load aerodynamic modeling.On this basis,fully coupled modeling,contentrating on kinematic,inertial,and aerodynamic couplings between helicopter and suspending system,is presented with the modeling of main rotor wake interaction on slung load,the derivation of couplings between helicopter and suspending system in varous conditions,and the establishment of a fully coupled model reflecting all prominent problems in helicopter suspended flights.The models are verified with the comparison between calculated values and flight test data about trim states and frequency responses of both a single helicopter and a helicopter with a suspending system.A method is developed for quantitative analysis of coupling property in a flight dynamics system.Parameters,including magnitude property and integration property,used for coupling quantitative analysis are put forward.The strength of couplings can be evaluated by the magnitude property,and the rate of state converging/diverging affected by couplings can be measured by the integration property.Couplings of a helicopter,a suspending system,and the couplied system of them are all elaborated on.It concludes that there are complicated longitudinal-lateral couplings in helicopter modes,that lateral pendulum motion and slung load yawing motion are coupled in suspending system modes,and that both the couplings of suspending system on helicopter angular rate and the couplings of helicopter on suspending system pendulum motion exist significantly in the modes of helicopter suspended flights.Coupling refactoring is explored systematically based on quantitative coupling analysis,and a synthetic coupling refactoring method for helicopter flights with a suspending system is formed with flight safety improved.The couplings of a helicopter are refactored by explicit model following control with better stability and controllability obtained.With a vertical stabilizer fin,the coupling in lateral & yaw motions of a suspending system is refactored,and the unstable slung load yaw damping is stabilized.With delayed feedback and input shaping,the coupling between helicopter and suspending system in pendulum motion is refactored,and the convergency propery of pendulum motion is promoted.