Balances can be divided into two main groups: internal and external. The group names are derived from their location relative to the test model and wind tunnel test section internal balances reside inside a test model, while external balances reside outside the test section. During the early years of wind tunnel testing, Forces and Moments were literally measured through pan-type balances. Internal Force/Moment balances are almost universally used for measurements in supersonic and transonic tunnels. However, they are also becoming popular in subsonic tunnels. Although technology has advanced dramatically since those early days, the term balance is still applied to the devices used for Force and Moment measurements today.
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