Model Load Measurement
ARA has extensive experience in the design and manufacture of balances. The mechanical force and moment balance is the most commonly used item of equipment used to measure the aerodynamic forces and moments applied to a model under test. Sections of the balance deform under load and these deformations are converted into electrical outputs by strain gauges. Applied loads are calculated from these electrical outputs using coefficients obtained during a pre-test calibration of the balance.
Main Model Balances
Main model balances are used to measure the overall loads on a wind tunnel model. As with most measurement devices, there is a trade-off between the load range a wind tunnel balance can be subjected to without damage, and the accuracy with which the balance can measure a given load. Typically, the most sensitive balances are used for performance or “drag” tests where the applied loads tend to be moderate, and the strongest balances are used for stability and control tests where accuracy is less important than the available load range.
Store and Panel Balances
Smaller balances are used to measure loads on parts of the model of particular interest like stores (such as external fuel tanks or missiles), control surfaces (such as ailerons or rudders) or parts of the aircraft model (such as winglets).
Technical Information
Measurements such as lift, drag and pitching moment are derived from the balance loads and non-dimensionalised using model reference dimensions (wing area, span, and chord) and flow parameters (dynamic pressure).
Standard tunnel corrections are then applied to obtain the final fully corrected data values. Typical standard tunnel corrections include corrections for the presence of the tunnel walls and corrections for thermal changes in the force and moment balance.
For further information, please download the documents attached to this page.
