Longitudinal Stability Characteristics of a 1/40-Scale Model of a Proposed Configuration of the XF-91 Airplane Measured by the Wing-Flow Method

This report presents the results of an investigation in the transonic speed range of the longitudinal stability characteristics of a proposed configuration for the Republic XF-91 airplane. The tests covered a Mach number range of 0.55 to 1.05 and a Reynolds number range from 400,000 to 1,375,000. Lift, pitching-moment, and rolling-moment characteristics of the half model and the hinge moments on the all-moving tail were measured. The downwash factor delta x epsilon / delta x alpha at the tail was determined from the pitching-moment data. A calculation of the elevator deflection and stick force required for trim was also made. It was found that the variation of force and moment coefficients was linear through the test angle-of-attack range of -1 deg to 8 deg at any Mach number; that the stability increased markedly at Mach numbers above 0.85; that the effectiveness of the tail in producing pitching moments decreased about one-third with increasing Mach numbers and that the value of the downwash factor, delta x epsilon / delta x alpha, at the tail decreased from about 0.35 at a Mach number of 0.85 to about zero at a Mach number near 0.95 and became slightly negative at higher Mach numbers. The calculated values of stick force per g and elevator deflection per g, assuming no aerodynamic balance, increased rapidly above a Mach number of 0.85