Harold F. Kleckner
Published: 1945
Total Pages: 22
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Summary: The NACA is conducting flight tests of an all-movable horizontal tail installed on a Curtiss XP-42 airplane because of its possible advantages as a longitudinal control for flight at high Mach numbers. The results are presented for some preliminary tests in the low-speed range for which the tail was very closely balanced aerodynamically and a bobweight was used to obtain stable stick-force variations with speed and acceleration. For these tests, the tail was hinged at 0.24 chord and was tried with two arrangements of servotab control. The elevator control was found to be unsatisfactory with the control arrangements tested. Although there were sufficient variation of stick force with acceleration in steady turns and a stable stick-force variation with speed, the near-zero variation of stick force with stick deflection resulted in an extremely sensitive control that required continuous attention in order to avoid motions of the airplane due to inadvertent movements of the control stick. For subsequent tests, the servotabs are being connected as geared unbalancing tabs in order that more conventional elevator hinge-moment characteristics may be obtained. The expected advantages of the all-movable tail with a control system utilizing tabs would of course be limited to flight at Mach numbers below those for which severe compressibility effects are encountered on the tail itself. For higher Mach numbers, the all-movable tail would require an irreversible power-boost control in order to handle the large hinge-moment increases that are expected.
