On the use of load-transformation matrices when working with internal wind tunnel balances

Internal wind tunnel balances are often classified by the design as 'force', 'moment' or 'direct-read' balances. Only the direct-read balances can immediately yield the total loads; with other designs, balance-type-specific transformations of actually measured loads to total loads are necessary. It is shown that a representation of these transformations in matrix form, as a 'load transformation matrix', beside being a convenient method to perform the calculations, enables significant generalizations in data processing, practically dispensing with the 'type' of a balance. The use of a transformation matrix also facilitates exchanges of balance calibration data or the balances themselves between wind tunnel communities using different axes- and component-sign conventions. It is proposed that, because of the advantages it offers, the load transformation matrix be generally used to describe balance designs and to accompany a balance together with a calibration matrix.