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Due to the limitation of the size and power, micro unmanned aerial vehicle (MUAV) usually has a small load capacity. Aiming at the problems of limited installation space and easy being interfered in flight attitude measurement of the small-scale unmanned helicopter (SUH), a low-cost and lightweight flight control system of the SUH based on ARM Cortex-M4 core microcontroller and Micro-Electro-Mechanical Systems (MEMS) sensors is developed in this paper. On this basis, in order to realize the autonomous flight control of SUH, firstly, the mathematical model of the SUH is given by using the Newton-Euler formulation. Secondly, a cascade flight controller consisting of the attitude controller and the position controller is developed based on linear active disturbance rejection control (LADRC) and proportional-integral-derivative (PID) control. Furthermore, simulations are conducted to validate the performance of the attitude controller and the position controller in MATLAB/SIMULINK simulation environment. Finally, based on the Align T-REX 470L SUH experimental platform, the hovering experiment and the route flight experiment are also carried out to validate the performance of the designed flight control system hardware and the proposed control algorithm. The results show that the flight control system designed in this paper has high reliability and strong anti-interference ability, and the control algorithm can effectively and reliably realize the attitude stabilization control and route control of the SUH, with high control accuracy and small error.

In order to simulate the flight state of the helicopter effectively, it is necessary to trim the helicopter during the forward flight in a wind tunnel test. Previously, due to the lack of an internal-control closed loop in the test rig, the helicopter-wind-tunnel-test trimming was carried out manually, with low test efficiency, unstable data quality, and high labor intensity. With the continuous development of computer technology and automatic control technology, the helicopter-wind-tunnel-test trimming technology has been developing in the direction of automation and intelligence. The helicopter wind tunnel test automatic trimming system is a typical multi-input–multi-output (MIMO), strongly coupled, and complex nonlinear system, involving data acquisition and a processing system, rotor control system, tail-supported mechanism control system, wind-tunnel-speed pressure control system, and other subsystems, which is difficult to describe with an accurate mathematical model. Therefore, in order to meet the needs of a 3 m diameter rotor model aerodynamic performance evaluation and noise characteristics research wind tunnel test, an error feedback variable step automatic trimming algorithm is proposed based on the fuzzy-control principle to realize automatic trimming of aerodynamic loads of rotor model in the forward flight state. To verify the effectiveness and reliability of the trimming strategy, a series of wind tunnel tests on a 3 m diameter scaled rotor model of a helicopter were conducted in the FL-17 aeroacoustics wind tunnel of China Aerodynamics Research and Development Center (CARDC) based on the Φ3m tail-supported helicopter rotor model wind tunnel test rig. The wind tunnel test’s results show that the proposed automatic trimming algorithm has the characteristics of fast trimming speed and high efficiency, which can realize the automatic trimming of rotor model aerodynamic loads under different test states in the wind tunnel test effectively and reliably and greatly improve the intelligence level of helicopter wind tunnel test.

Based on the scattering attenuation theory of loaded polycrystalline metals, a bolt axial stress measurement method using ultrasonic echo attenuation is proposed for the problem that the conventional TOF method is difficult to measure the stress of high-strength short bolts. Firstly, the attenuation coefficients of body-centered cubic crystalline materials in the Rayleigh scattering range are described, and the mathematical model between the ratio of the peak of the two bottom echoes and the axial stress of the bolt is further derived. Then, the effects of the transducer wafer diameter, mounting eccentricity and bolt thread on the ultrasonic signal were analyzed by finite element simulation, to provide a strategy for transducer selection and mounting. In addition, a magnetic ring clamping device was designed to ensure a tight fit between the transducer and the bolt, and to improve the alignment of both. Finally, a bolt axial stress ultrasonic measurement system was built, and a comparison experiment between TOF method and attenuation method was conducted to predict the axial stress of bolts. The experimental results shown that the average relative measurement error of the attenuation method proposed in this paper is 4.42%~5.76% lower than that of the conventional TOF method, which is more suitable for measuring the axial stress of bolts.