Design and Verification of Multi-Mode Variable Camber Wing Trailing Edge ^†

Abstract

By changing the aerodynamic shape of the trailing edge of its wing, an aircraft can achieve lift and drag reduction during takeoff and landing and continuously achieve better aerodynamic efficiency while cruising, which plays an important role in the whole flight process and has always been a research hotspot in the field of aviation structure. Firstly, the principle scheme of wing trailing edge deformation based on a two-stage multi-link mechanism was designed and realized, and then the mechanical structure was designed in a way that ensured the machining feasibility of the prototype. Secondly, a control system scheme was designed to realize synchronous and differential deformation movement of single and double mechanisms. Finally, power drive device selection and prototype manufacturing verification were carried out. The experiments show that the designed and manufactured variable camber wing trailing edge prototype can achieve two modes of wing trailing edge deformation, namely the overall deflection of the variable camber wing trailing edge +5°~−20° and the wing tip deflection +10°~−10°. The deformation error is measured within 5%.

1. Introduction

The variable camber trailing edge is used throughout the flight of the aircraft. In the process of takeoff and landing, the lift function takes place through the lower side of the trailing edge. During cruising, the smooth and continuously variable camber wing trailing edge plays various roles: (1) it deals with the aerodynamic efficiency caused by the change in aircraft weight; ② it slows down wind gusts; ③ it improves the aerodynamic characteristics of trans-supersonic flight; and ④ it reduces the radar reflection area [1]. A large number of studies have shown that the finger-type scheme of the wing trailing edge with variable curvature has the characteristics of a simple scheme, reliable stiffness and strength, and is suitable for large aircraft, and is currently a widely used scheme [2,3,4,5,6]. Although the finger-type scheme can only achieve segmental bending and drooping, it has been found through research that, usually, approximately three “knuckles” can meet the demand for airfoil bending from the aerodynamic perspective [7,8]. Based on this, a multi-mode bending wing trailing edge design scheme is proposed in this paper, and a control scheme for multi-mode deformation of a wing trailing edge is designed to realize multiple deformation modes. In addition, through rational material selection and power plant selection, the multi-mode variable bend wing trailing edge sample is manufactured, which verifies the feasibility of the design scheme in this paper.

2. Design of Deformation Principle

In this paper, the motor rocker arm is used to drive the two-stage multi-link mechanism to drive the rear edge of the wing to change the bending motion. By changing the size, angle and hinge point position of the connecting rod, the angle of the three sections of the wing can be evenly changed to avoid a sudden aerodynamic change in the wing. At the same time, according to the three-center theorem and the instantaneous center method, the ratio of input and output torque is calculated and optimized to minimize the input torque and maximize the output torque to the greatest extent possible.

The variable bending rear edge is designed in three sections: B1, B2 and B3, among which the string length of B1 is 435 mm, the string length of B2 is 430 mm and the string length of B3 is 435 mm. The three variable modules are hinged together by cylindrical hinges. The outline of the rear edge and the initial position of the rod are shown in the Figure 1 below. The digital mark line in the figure is the two-stage linkage mechanism that has been designed to drive the variable bending trailing edge to achieve target deformation, and the circle part is the location of the driving device of the two-stage linkage mechanism.

In the case of mode 1, the two-stage drive motor operates at the same time, driving the two-stage connecting rod mechanism to move, so that the overall deformation angle of the wing surface of the variable bending back edge is 5° up and 20° down. In the case of mode 2, the first-stage drive motor does not move, while the second-stage motor operates, so that the wing tip of the variable bending back edge is 10° up and 10° down. The deformation principle is shown in the following Figure 2.

3. Design of Mechanical Structure

The multi-mode variable camber trailing edge wing deformation mechanism is mainly composed of a trailing edge wing bracket, a two-stage linkage mechanism, a driving device, a trailing edge support platform, measurement and control hardware, etc. The three-dimensional effect design of the variable camber trailing edge platform is shown in the following Figure 3.

The trailing edge wing comprises a fixed module, B0, and three movable modules, B1, B2 and B3, (the deformed trailing edge part), wherein the fixed module B0 is helically connected to the trailing edge platform, the movable modules B1, B2 and B3 are hinged with each other and B1 is connected to the fixed module B0 through a pin shaft, and the power drive device is placed between the two ribs of the trailing edge B1 and B2 modules.

4. Design of Control Scheme

The network topology of the system controller and the operating touch screen and the driver is as follows in Figure 4:

The control of the biplane control system is split into two parts: (1) the CODESYS platform development part, which complies with the PLCope motion control specification, through CoDeSys_SoftMotion, to achieve a good range of motion; and (2) application design: HMI configuration and SCADA interface.

The platform development part is based on the actual function and performance of the mechanical action of the two wings so as to meet the functional and actual performance requirements of the design. The inclinometer /SERVO motor encoder data acquisition and SERVO driver are used to realize output and data feedback functions, and two control modes of automatic control and manual control are designed. At the same time, in the application design part, the man–machine operation interface of the control system, data formula loading, remote operation of the upper computer and data recording are implemented according to the action mode and speed and accuracy requirements of the biwing robot arm. CODESYS hierarchical data structure programming design is adopted to avoid the serious loss of system functions caused by a single fault, and data synchronization design is based on the bus and software. This ensures that single-machine, single-axis, and dual-axis switching can be performed without disturbance.

The controller communicates with the driver via the extended EtherCAT bus protocol, which is sent to the driver as a real-time control command.

(1) Single machine control mode:

When the controlled motor in the single system is moving independently, the absolute positioning mode of the driver will be activated, the target inclination value will be input, and the set inclination value will be directly converted to the target position value through the conversion relationship between angle and position, and the target position value and start instruction will be sent through the EtherCAT bus. During operation, the actual inclination value collected by the AI channel is compared with the final stopping angle, and the final operation correction is carried out to achieve accurate positioning.

(2) Synchronous operation or differential operation of the motor in the mechanism:

In the motor synchronous operation or differential operation mode in the mechanism, the main motor is set to bus control mode, the secondary motor is set to follow mode and the following ratio can be set in the servo drive. In the synchronous mode, the following ratio is 1. In the differential operation, the corresponding following ratio will be converted according to the user-set differential ratio. Synchronous or differential movement of the slave machine is driven directly by PTO output of main machine.

(3) Synchronous or differential operation of two mechanisms:

The synchronous or differential operation of the dual mechanism is the same as the synchronous or differential operation of the two motors in the mechanism, and in the hardware design, the four drives form a PTO ring.

By setting the following ratio between different motors, the following driver is driven by PTO to realize the synchronous or differential operation of the two mechanisms.

5. Sample Manufacturing and Functional Testing

The selection of the torque of the trailing edge drive motor depends on the output load of the mechanism, the benefit of the mechanism, the reduction ratio of the harmonic reducer and the efficiency of the drive mechanism, etc. The calculation of the motor torque size is shown in Formula 1 below.

$$T_{qd}={\displaystyle \frac{T_{out}}{i_{xb}•MA•\eta }}$$

(1)

where T_qd is the output torque of the drive motor; i_xb is the reduction ratio of the harmonic gear reducer; MA is the benefit of the connecting rod mechanism, and 3.35 is taken here; η is the driving mechanism loss factor, and 0.7 is taken here.

The output load of the mechanism includes two parts: the aerodynamic load of the trailing edge airfoil and the self-weight of the module. The first-stage linkage mechanism needs to overcome the aerodynamic load and self-weight of the entire trailing edge airfoil, while the second-stage linkage mechanism only needs to overcome the self-weight and applied aerodynamic load of module B3. When the first stage uses a speed ratio of 1:160 for the harmonic reducer, and the second stage uses a speed ratio of 1:120 for the harmonic reducer, it can be calculated by formula 4 that the output torque of the first stage motor is 9.77 N•M, and the output torque of the second-stage motor is 0.89 N•M. Therefore, after investigation, the trailing edge power unit is made of a double-rod servo motor and harmonic reducer, of which the rated torque of the two servo motors is 11.5 N•M and 1.27 N•M, respectively.

The wing material is made of aluminum alloy 7075. As shown in Figure 5, the deformed rear edge contains two connecting rod mechanisms and each connecting rod is hinged together by a pin shaft. The two connecting rods are made of aluminum alloy 7075 and the pin shaft is made of stainless steel 2Cr13. Sample and functional test results are shown in the Figure 6 below:

The test results show the following:

(1)

The motion stroke of a multi-mode variable camber trailing edge connecting rod mechanism meets the requirements of wing trailing edge variable camber, and the selection of the power drive device is reasonable.

(2)

Variable camber trailing edge principle The prototype can achieve two modes of deformation. The overall deflection of the variable camber wing trailing edge is +5°~−20°, and the deflection of the wing tip is +10°~−10°, and the deformation error is measured within 5%.

6. Discussion and Conclusions

In this paper, the structure and control scheme of a wing trailing edge based on a multi-mode variable bending mechanism are proposed, and a physical prototype is manufactured for functional testing, which verifies the feasibility of the design scheme. The following conclusions are drawn:

(1)

A finger-shaped design scheme is adopted for the creation of a multi-mode variable camber wing trailing edge. The motor rocker arm drives a two-stage multi-link mechanism to drive the wing trailing edge to carry out variable camber movement, and the optimal design scheme is realized by optimizing the connection point position to improve the torque output efficiency.

(2)

The trailing edge control system of variable camber wing adopts CODESYS hierarchical data structure programming design and realizes data feedback function through the inclinometer so as to realize single-machine control, single and double mechanism synchronization and differential operation.

(3)

The variable bending wing trailing edge principle is as follows: The prototype can achieve two modes of deformation. The overall deflection of the variable bending wing trailing edge +5°~−20°, and the wing tip deflection +10°~−10°.