The Effects of Static Margin and Rotational Damping in Pitch on the Longitudinal Stability Characteristics of an Airplane as Determined by Tests of a Model in the NACA Free-flight Tunnel

John P. Campbell · John W. Paulson

Jan 1944 · National Advisory Committee for Aeronautics

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Summary: The effects of static margin and rotational damping in pitch on the longitudinal stability characteristics of an airplane have been determined by flight tests of a model in the NACA free-flight tunnel. In the investigation, the rotational damping in pitch was varied over a wide range by using horizontal tails that varied in area from 0 to 24 percent of the wing area. A range of static margins from 2 to 16 percent of the mean aerodynamic chord was covered in the tests. For each test condition the model was flown and the longitudinal steadiness characteristics were noted. It was found in the investigation that longitudinal steadiness was affected to a much greater extent by changes in static margin than by changes in rotational damping. The best longitudinal steadiness was noted at large values of static margin. For all values of rotational damping, the steadiness of the model decreased as the static margin was reduced. The model was especially unsteady at low values of static margin (0.03 or less). Reduction in rotational damping had little effect on longitudinal steadiness, except that with low values of static margin (0.03 or less) the longitudinal divergences were sometimes more violent with the tailless (low rotational damping) condition.