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Comparison of Wind-tunnel and Flight Measurements of Stability and Control Characteristics of a Douglas A-26 Airplane

出版	NACA, 1946
URL	http://books.google.com.hk/books?id=OzAD3qm3454C&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN

註釋Summary: Stability and control characteristics determined from tests in the Langley 19-foot pressure tunnel of a 0.2375-scale model of the Douglas XA-26 airplane are compared with those measured in flight tests of a Douglas A-26B airplane. Agreement regarding static longitudinal stability as indicated by the elevator-fixed neutral points and by the variation of elevator deflection in both straight and turning flight was found to be good except at speeds approaching the stall. At these low speeds the airplane possessed noticeably improved stability, which was attributed to pronounced stalling at the root of the producion wing. The pronounced root stalling did not occur on the smooth, well-faired model wing. Elevator tab effectiveness determined from model tests agreed well with flight-test tab effectiveness, but control-force variations with speed and acceleration were not in good agreement. Although some discrepancy was introduced by the absence of a seal on the model elevator and by small differences in the determination of elevator deflections, correlation in control-force characteristics was also influenced by the effects of fabric distortion at high speeds and by small construction dissimilarities such as differences in trailing-edge angle. Except for the wave-off condition, in which the tunnel results indicated rudder-force reversal at a higher speed than the flight tests, agreement in both rudder-fixed and rudder-free static directional stability was good. Model and airplane indications of stick-fixed and stick-free dihedral effect were also in good agreement, although some differences in geometric dihedral may have existed because of wing bending in flight.