Keywords wind tunnel testing; Strain balance; Moment balance; Force balance; Force measurement principle; Scale calibration.

Wind tunnel strain balance is the most commonly used and critical high-precision force measurement device in conducting ground experiments on aircraft aerodynamics [1-2]. The development of advanced aircraft requires solving key aerodynamic problems, therefore, there is an urgent need for high load-bearing force measuring scales with large longitudinal and transverse load ratios and highly mismatched torque loads [3-4]. The load capacity of the strain balance is directly related to the testing ability of the wind tunnel, and is one of the main factors restricting the ground simulation testing ability of advanced combat aircraft and large passenger aircraft. Since the 1960s, the United States has been developing high load-bearing assembly force balances (hereinafter referred to as force balances) for continuous wind tunnel force testing. Technologies such as the design, manufacturing, and calibration of multi-component assembly balance have been proposed and developed, and these scales still serve wind tunnel testing in the United States to this day. In order to promote the establishment and development of assembly force balance technology for future 2 m and 4 m wind tunnel tests, this article collects and sorts out the current status and hot issues of application research on assembly force balance abroad through a large amount of foreign literature research, summarizes and extracts the key technologies for the development of this type of balance, and provides reference for the construction and development of force balance technology system..

The wind tunnel strain balance senses the deformation of the model after being subjected to force in the aircraft force test through the strain gauge on the surface of the measuring element, and converts it into electrical signals in real time through the Wheatstone bridge. Then, the aerodynamic force of the research object is iteratively obtained using the calibration matrix. Aerodynamics consists of three forces and three moments in space, namely lift (Normal Force, NF), side force (SF), drag (Axial Force, AF), pitching moment (PM), yawing moment (YM), and rolling moment (RM). The definition of each measuring component of the balance is shown in Figure 1..

Fig.1 Diagram of Wind Tunnel Model with a Balance.

Among them, the torque balance corresponds to the most widely used double bridge force balance based on the bending deformation principle. The lift and pitch torque are calculated by combining the front and rear pitch torque components (PM1, PM2) and their respective bridge outputs (rPM1, rPM2). The lateral force and yaw torque are calculated by combining the front and rear yaw torque components (YM1, YM2) and their respective bridge outputs (rYM1, rM2)..

Plate Bolt Anchor

The direct reading balance corresponds to some single bridge force measuring balances that are still based on bending deformation. Its structural form is exactly the same as the torque balance, with the only difference being that after the direct reading balance is electrically decoupled, each bridge output directly corresponds to each measurement component, without the need for secondary calculations..

Litianping is a type of high load-bearing force balance based on tension compression deformation that is rarely used in China. It calculates the lift and pitch moment by combining the front and rear lift components (NF1, NF2) and their respective bridge outputs (rNF1, rNF2).