OBTAUED BY THE TRANSONIC-Bl.JhTMETHOD

An investigation has teen made in the Langley high-speed 7- by 10-”foot tunnel using the trensonic-bumy method to determine the longitudinal stability end control characteristics at transonic speeds of a semispan airplane model having a 45 ° sveptback wing and tail. The results of the investigation indicated an increase in the rate of change of pitching-moment coefficient with lift coefficient at a L)a-cmconstant Mach number-E ~ through the transonic range that was attributed to a rearward snift of the wing-fuselage aerodynamic-center location at subsonic speeds and to a rapid decrease in dowmwash at supersonic speeds. At a Mach number of about 0.95 a moderate decrease occurred in both the lift-curve slope and in the stabilizer effectiveness. The high angle of sweep was effective in delaying the drag rise at zero angle of attack up to a Mach number of about 0.95. The curve of stabilizer incidence required for trim against Mach number had an unstable variation between a Maoh number of 0.90 and 1.20, but trim could be maintained throughout the Mach number range with a stabilizer deflection of only slightly more than 1°