Progress and Design Data

In the 1920s and 1930s, researchers in several wind tunnel and full-scale aircraft flight groups at Langley conducted analytical and experimental investigations to develop design guidelines to ensure satisfactory stability

and control behavior.[468] Such studies sought to develop methods to reli­ably predict the inherent flight characteristics of aircraft as affected by design variables such as the wing dihedral angle, sizes and locations of the vertical and horizontal tails, wing planform shape, engine power, mass distribution, and control surface geometry. The staff of the Free – Flight Tunnel joined in these efforts with several studies that correlated the qualitative behavior of free-flight models with analytical predictions of dynamic stability and control characteristics. Coupled with the results from other facilities and analytical groups, the free-flight results accel­erated the maturity of design tools for future aircraft from a qualita­tive basis to a quantitative methodology, and many of the methods and design data derived from these studies became classic textbook material.[469]

By combining free-flight testing with theory, the researchers were able to quantify desirable design features, such as the amount of wing – dihedral angle and the relative size of vertical tail required for satisfac­tory behavior. With these data in hand, methods were also developed to theoretically solve the dynamic equations of motion of aircraft and determine dynamic stability characteristics such as the frequency of inherent oscillations and the damping of motions following inputs by pilots or turbulence.

During the final days of model flight projects in the Free-Flight Tunnel in the mid-1950s, various Langley organizations teamed to quan­tify the effects of aerodynamic dynamic stability parameters on flying characteristics. These efforts included correlation of experimentally determined aerodynamic stability derivatives with theoretical predic­tions and comparisons of the results of qualitative free-flight tests with theoretical predictions of dynamic stability characteristics. In some cases, rate gyroscopes and servos were used to artificially vary the magnitudes of dynamic aerodynamic stability parameters such as yawing moment because of rolling.[470] In these studies, the free-flight model result served as a critical test of the validity of theory.