The development of a three-axis trim program for aerodynamic data

This thesis presents the development of a three-axis trim program. The goal of three-axis trim is to position airplane or missile control surfaces at deflection angles which result in zero aerodynamic moments about three orthogonal axes through the vehicle center of gravity. The moment about each axis can be expressed as a single equation in terms of control effectiveness derivatives, deflection angles, and residual moments resulting from the deflections. Therefore, the essence of the problem is the solution of three equations with three unknowns (the deflections at trim). Gaussian Elimination is used to solve the equations with the control derivatives being the matrix of coefficients and the residual moments completing the augmented matrix. The solution is iterative with the control derivatives and residual moments changing for each new estimate of the trim deflections. The values of other aerodynamic parameters at the trim deflections are also available for output. The methods of updating the control effectiveness and residual moments are presented, and an example case is given.