Aerodynamic Coupling between Lateral and Longitudinal Degrees of Freedom

Abstract

An oscillatory technique for routine measurement of the direct, cross, and cross-coupling moment derivatives due to pitching and yawing has been developed and a series of comprehensive results at Mach numbers 0.7 and 0.25 and at angles of attack up to 40 deg has been obtained in a large wind tunnel. It was found that some of the dynamic cross-coupling derivatives, which at low angles of attack were all insignificant, at higher angles of attack could reach values that rendered the pertinent cross-coupling terms in the equations of motion comparable in magnitude to the well-established damping terms. This applied in particular to results obtained at Mach number 0.7. Large nonlinear variations with angle of attack were observed in many of the measured derivatives including the important damping-in-pitch and damping-in-yaw derivatives. It was concluded that it may be desirable to include certain dynamic cross-coupling derivatives in the equations of motion, and to consider all of these equations simultaneously, rather than in separate longitudinal and lateral groups.