Abstract
Control allocation is still a challenge for tiltrotor aircraft due to effectors’ redundancy, dramatic nonlinearities and cross-coupling. Besides this, the external disturbance caused by the unique configuration of tiltrotor such as larger wing area and tiltable mechanism puts forward extra security requirement on control allocation method. Thus, this paper proposes an innovative control allocation framework from the perspective of flight safety to address this problem. Firstly, an effector distribution management scheme based on remaining control ability index (RCAI) is developed to reduce the effector saturation and ensure flight safety. Secondly, the energy consumption models for two classes of effectors: thrust vectoring and aerodynamic surfaces are introduced respectively for the subsequent optimization problem mathematically. Then, the null space transition is used to find the minimum-energy control input of effectors. Finally, key parameters of energy consumption model are identified by experiments. The real-time hardware-in-loop simulation platform is adopted to demonstrate the effectiveness of the proposed control allocation framework. Experimental results show that the energy consumption of proposed method can reduce by about 63.5% comparing to traditional control allocation method.
Highlights
During recent years, tiltrotor aircraft has gained remarkable attention on aviation industry [1-4] due to the broad flight envelope: from hover state, typical of rotorcraft, to high cruising-speed characteristic of fixed-wing aircraft
Many control allocation methods have been proposed to solve the problem of redundantly-actuated unmanned aerial vehicles (UAVs). [10] proposes a control allocator for a fully-actuated tilting quadrotor platform to decouple the platform’s rotation and translation by mapping the attitude and position commands to the unique actuator
From the analysis of effectors’ control effectiveness, we have found that the proper selection of switch point between the thrust vectoring and aerodynamic surfaces can effectively guarantee the control ability of tiltrotor, leading to certain anti-interference ability and ensure flight safety
Summary
Tiltrotor aircraft has gained remarkable attention on aviation industry [1-4] due to the broad flight envelope: from hover state, typical of rotorcraft, to high cruising-speed characteristic of fixed-wing aircraft. The advantage of redundancy effectors allows to optimize some objectives such as minimum energy or drag, and provides the possibility of improving flight safety Most research work such as [33-35] focus on fault tolerant control after actuator faults happened, which not exploits the potentiality of redundancy effectors before the failure of actuators. The larger wing area and tiltable mechanism of tiltrotor will bring more external disturbance and model uncertainty, which put forward higher security requirement on control It seems that few literatures take flight safety into consideration during the design process of control allocation. (3) Control allocation method based on null space transition is proposed to find minimum-energy control input of effectors by using the energy consumption model.
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