Research On Key Technologies Of Rotor/Ducted Fan Unmanned Helicopter Preliminary Design

Rotor/Ducted Fan unmanned helicopter is an innovative rotorcraft that consists of counter-rotating rotor and ducted fan as lift-generating system and control surface.The fan is protected within the duct fuselage,and the compact structural layout and low height results in facilities for storage and transporting.The control mechanism,similar to single rotor configuration,is simple and highly reliable.The entire vehicle is axially symmetrical.Outstanding resistant capability of wind and landing stability makes it adaptable for shipboard.In order to further improve the performance and mission adaptability,on the basis of previous design,experiments and flight tests,The aerodynamic characteristics of unmanned helicopter with the configuration is researched;the modeling for aerodynamic interference of the integrated lift system is worked out;the method for performance calculation is ameliorated further;the optimization design of preliminary parameters and aerodynamic layout is performed.Considering the configuration natures of the rotor/ducted fan and putting the aerodynamic interaction on an important place,a model for calculating aerodynamic performance is established,and a tethered test for hover performance is carried out.The model is verified by comparing with data of the hover test and previous flight experiment.Based on these works,integrating the optimal of hovering and forward flight performance as objective,a multidisciplinary optimization design of preliminary parameters for this configuration is developed whose effectiveness is verified.To make more improvement on the aerodynamic performance of the ducted fan,a refined analytical model of aerodynamic performance for ducted fan on the ground of CFD and momentum-source method is built.The duct shape is optimized by which the aerodynamic performance of the ducted fan is improved.The aerodynamic principle of small airfoil trailing edge-mounted lift augmentation device is studied.Influences on aerodynamic feature of fan blade airfoil from different lift augmentation are analyzed and that the effective height of lift augmentation device exerts the main influence on increasing airfoil lift is figured out.The results demonstrate that mounting a Gurney flap on the trailing edge of the fan can help improve the aerodynamic performance of the ducted fan effectively,and contributes to reducing the structural size of the ducted fanBased on the time-marching free wake and unsteady panel method,an aerodynamic performance analytic model for primary aerodynamic components including rotor,fan and duct fuselage is developed.The characteristics of coupling flow field by integrating rotor and ducted fan is analyzed.By this model,the characteristic of aerodynamic interaction between the rotor and ducted fan is analyzed.The mechanism degree of aerodynamic interference among rotor,duct and fan is confirmed that due to the aerodynamic interaction,the inflow velocity that rises quickly reduces the effective angle of attack,and then,results in the fan thrust decline.For promoting the use safety of this configuration,a nonlinear flight dynamics model for rotor/ducted fan UAV in low attitude wind shear is established.The impact from the direction and dimension of wind shear on flying feature of this configuration is investigated.The results indicate that the higher dimension of wind shear,the greater influence on the helicopter.In every dimension,lateral wind exerts the least impact on flight state,and in forward flight,the effect from wind shear at low speed is more serious than that at high speed.The influence of constraining stiffness of rotor elastic support is calculated,which indicates an unfavorable effect on the response characteristic of a helicopter in wind shear.In this dissertation,by means of integrating theoretical model and experimental validation,the preliminary design-oriented investigations including aerodynamic performance,parameters optimization design and flight dynamics response features are carried out to form a series of design methodologies and analytical calculating model for preliminary design of the rotor/ducted fan unmanned helicopter,which offers some theoretical basis for developing this configuration.Meanwhile,the research content can be referred to for conceptual,preliminary design and development of unmanned helicopter with relevant or other complicated configuration.