LD Data Generation

The purpose of LD data generation is (1) to establish steady sideslip capability, (2) to determine the crosswind landing capability, (3) to determine the rudder and lateral control hinge moment, (4) to determine the rudder effectiveness (C„s^, and (5) to determine the directional stability (Cn ). LD testing involves two or three axes testing. In a level flight with symmetric thrust, the rudder deflection is given with lateral control such that the flight path is straight and there is no change in heading, with sideslip and bank angle, for various rudder angles. The maximum values of the sideslip angles are obtained by performing tests at gross weights and aft CG. The data are used to obtain the relationships between control deflection and various angles: bank angle, sideslip angle, and angle of attack. Maximum values of the rudder deflection and the sideslip angles, wheel deflections, and bank angles are plotted as a function of Mach number and altitude, and the maximum values of the sideslip angles are obtained at heavy weight and aft CG. The yawing moment produced by the rudder can be computed by knowing the yawing moment produced by the asymmetric thrust and using the rudder to reduce the sideslip angle to zero.

Various dynamic characteristics also need to be established: (1) the Dutch roll (DR), (2) spiral stability, and (3) LD rate derivatives. These characteristics are estab­lished by generating the flight test data by using doublet/3-2-1-1 inputs and performing the appropriate maneuvers as discussed in Section 7.6. Then, parameter estimation methods are used to determine the stability and control derivatives of the aircraft.