Research On The Actuation Technology Of Variable Height And Cant Winglet

Drag reduction is one of the main goals in aircraft design. Although winglet has the capability ofreducing the induced drag of an aircraft, traditional designs of the winglet are only optimized forcruise phase and are inefficient at non-cruise condition, including taking off phase and climbing phase.In this thesis, a new morphing winglet design is proposed in which the height and cant angle of thewinglet can be changed to provide the optimal drag reduction efficiency for both cruise andnon-cruise conditions, overcoming the shortage of traditional winglet at non-cruise condition.The main contents and achievements are as follows.First the deformation modes and the range the parameters of the morphing winglet areinvestigated. Many parameters are employed to describe the performances of the winglet, each ofwhich has different influence on drag reduction efficiency. The main challenges of morphing wingletsare to determine which parameter should be deformed and what is the deformation range. By usingPlackett-Burman test method, the effects of the winglet parameters on drag reduction are analyzed todetermine the key parameters that affected the drag reduction, from which the deformation mode ofwinglets could be obtained. The optimal value of the key parameters and their ranges during takingoff, climbing and cruise are then obtained by using the response curve surface design. The resultsshowed that the key parameters of winglet are height and cant angle, which suggests that themorphing winglet should change its height and cant angle to improve the drag reduction efficiencyduring taking off and climbing.Second actuation techniques of the morphing winglet are studied. Three types of drivingmechanisms are investigated which include the retractable grid for variable height winglet, the activebending beams for variable cant angle winglet and the antagonistic retractable grid for variable heightand cant angle winglet. The kinematics of the three mechanisms was studied by numerical simulationand model experiments to derive the equations of motion and find the control method. The resultsshow that the three kinds of driving mechanisms could meet the requirements of the morphingwinglets.Finally, the aerodynamic benefit of morphing winglet is analyzed. By combining computationalfluid dynamics (CFD) with wind tunnel test, the aerodynamic benefit of morphing winglet isconsidered. The spanwise pressure distribution, the wingtip vortices dissipation, the aerodynamiccharacteristics and root bending moment of a wing before and after morphing were analyzed. Theresult demonstrates that the morphing winglet could significantly improve the aerodynamic performance of an aircraft in the takeoff phase of flight, among which the height deformation mode isthe most efficient in improving the aerodynamic benefit of morphing winglet, the height and cantangle coupled deformation mode is lesser and the cant angle deformation mode is the least.Furthermore, all three ways of deformation modes would induce the pressure augmentation inoutboard wing, which produce extra wing root bending moment. Therefore, the morphing wingletshould be controlled within the optimal range to prevent from wing structure failure.This thesis is accomplished in State Key Laboratory of Mechanics and Control of MechanicalStructures, as well as funded by the National Natural Science Foundation of China under Contract No.90605003.