Research On The Key Tecnologies Of Landing And Taxiing For Leaf Spring Landing Gear UAV

Landing gear system is the key component of the on-ground shock absorber of Unmanned Aerial Vehicle(UAV). The property of the landing gear can directly influence the landing, taxiing dynamic behaviors of UAV, and the safe of takeoff and landing operation. Leaf spring is a classical compression bumper which is mounted in many little type UAVs. The structure performance of leaf spring needs to meet the requirements of stiffness, strength and impact energy absorb etc, so the design of leaf spring is always a very complex process.Therefore, it is necessary to study the kinematics mechanism and modeling method of the leaf spring landing gear system. Then the technique of simulation can be used to direct the design and performance analysis of the landing gear system. This paper focuses on the accurate elastic modeling and rigid-flex multibody analysis of leaf spring landing gear that used in UAVs. The dynamics behavior of the leaf spring structure and landing gear device are analyzed respectively. Simulations and experiments are implemented to test the landing gear which are important for improving on-ground motion performance and reducing the cost of landing gear design. In order to build a more accurate simulation model, this paper also proposed a multidisciplinary simulation environment to study the landing gear dynamics behavior and taxiing control performance during landing and taxiing of UAV. The main contents of this paper include the following aspects:1. A brief overview of leaf spring elastic modeling based on general modal superposition method is summarized. The differential equation in modal coordinate is rewritten in a state space form. The modal reduction method is also given. For the deformation of leaf spring subjected to small deformations but relative large rotations, modal warping method is used to model leaf spring elastic deformations. Kinematics of infinitesimal deformation is investigated to calculate the rotational deformation in modal coordinate. Then modal warping method is used to integrate the rotational deformations into differential equation in order to obtain accurate elastic model. The cantilever beam numerical examples and leaf spring experiments are presented. The results show that the relative errors are below 5% for both the linear modal and modal warping method when the load is less than design landing mass. Even though the load has reached to 180 kg which represents the maximum realistic condition for landing, the error of the modal warping method remains within 10%, while the error of linear modal has been more than 35%.2. The rigid-flex coupling motion of leaf spring is studied. The equations of motion of Lagrangian formalism based on floating frame of reference formulation(FFRF) in multibody systems have been proposed. The use of the mixed set of reference and elastic coordinates in the FFRF leads to a highly nonlinear mass matrix as a result of the inertia coupling between the reference and the elastic displacements. Therefore to increase computational efficiency, a solution strategy called linear theory of elastodynamics is used to simplify the dynamics equations. The rigid-flex multibody model for a leaf spring landing gear system is developed. Both the dynamics behavior of the leaf spring system and the accuracy of the proposed method are examined by drop experiment and simulation.3. The proposed rigid-flex modeling method is also used in the study of multibody dynamics of UAV, a rigid-flex coupling model of UAV including nose and leaf spring landing gear, tire and airframe is built. To deep analysis the dynamics behavior of leaf spring landing gear during UAV landing phase, a multidisciplinary simulation environment is proposed for the simulation of the UAV landing phase. The landing experiment of the physical prototype experiment is conducted after the simulations.4. Differential brake controller is designed to steer the direction of UAV’s on-ground low speed taxiing. Differential brake lateral deviation control law is accomplished based on the genetic algorithms optimization, and the construct of the adaptation function accounts for both the lateral deviation and wind resistance performance. Non-linear mathematics model of on-ground UAV is given to design the lateral deviation controller. Then the multidisciplinary simulation environment is used to analysis the performance of the controller. Differential brake lateral deviation controller shows a good ability to turn the UAV during taxiing, landing, etc. that can move the UAV back to a centerline smoothly without turning over. Meanwhile taxiing controller can guarantee the lateral deviation remains within 1.5m under the fourth lateral wind situation.