Implementation and Use of a Convergence Test for Iterative Wind Tunnel Balance Load Predictions

Abstract

A modified and extended version of a convergence test for wind tunnel strain–gage balance load iterations was implemented. The test uses an upper bound of the Lipschitz constant to assess convergence characteristics of balance load predictions if the Iterative Method is applied. Convergence is expected within the use envelope of the balance whenever this upper bound is less than the threshold of one. It is explained in great detail how the convergence test can be applied to the two load iteration equation types that are currently being used in the aerospace testing community. In addition, the application of the test to balances with bi–directional output characteristics is discussed. It is also shown how numerical differentiation can be used to obtain partial derivatives that are needed for the calculation of the Lipschitz constant. Finally, machine calibration data of NASA’s MC60E six–component force balance is selected to demonstrate both implementation and use of the convergence test.