Experimental Investigation of the Static and Dynamic Stability Derivatives Using a Novel 3-DoF Mechanism

The U.S. Air Force Academy (USAFA) Dynamic Pitch Mechanism (DPM) was designed and fabricated to expand testing capabilities into 3-DoF and open the potential for analyzing coupled effects between longitudinal and lateral-directional stability derivatives. In this study, the kinematics of the mechanismwere validated through both measurements and comparison to wind tunnel data of the AGARD-B Standard Dynamics Model (SDM) from prior experimentation. Surface plots were developed for the aerodynamic forces and moments to quantify the influence of cross-coupling in stability derivatives. The analysis indicated a significant lateral-longitudinal coupling through off-diagonal terms. Both forms of analysis yielded consistent results, and the coefficients produced a predictive model of the static stability of the SDM which matched experimental results and can be used to predict the response of the aircraft at flight conditions not directly tested. The pitch dynamic stability of the SDM was evaluated through a series of sinusoidal forced oscillation tests. The results were in agreement with comparison data. Finally, dynamic cross-coupling effects were evaluated by a pitch oscillation at constant sideslip angles.