A Kinematical Investigation of Some External Wind Tunnel Force Measurement Systems

A discussion on the fundamental concepts associated with wind tunnel forces measurement systems (balances) is presented. Detailed static analyses are performed on the six component pyramidal, six component floating beam, and three component strain gaged strut balances. These static analyses lead to a dimensional uncertainty investigation of the pyramidal and strain gaged strut balances. The critical dimensions for the pyramidal balance are found to be the lengths of the pyramidal links, like platform half-width, and the model attachment strut. No single dimension on the strain gaged strut is more critical than the others. A new method for the classification of wind tunnel force balances is presented. This method uses two defined quantities: the degree of coupling, and a hardware parameter based on the number of areas where tolerances are of a concern. The versatility of the method is demonstrated through a number of classification examples. The following recommendations are made: determine the effects of component deflection on the pyramidal force balance readouts and investigate the uncertainties associated with low strains on the three component strain gaged strut