A New Method of Longitudinal Control for Aircraft by Use of an Adjustable Angle of Attack Balance

Abstract

THE PRESENT-DAY TYPE of large airplane has approached a definite limit in two respects: first, it must be loaded over a restricted center of gravity range (e.g. range); second, as the airplane size and gross weight are increased, the control forces become too great unless properly reduced, which so far has been a troublesome problem. The e.g. range of the airplane has the forward limit fixed by the maximum control force that can be produced by the horizontal tail to meet a given landing or maneuvering requirement and the rearward e.g. limit established by the ability of the airplane to meet certain stability requirements. Lately, these stability -requirements have offered much discussion, mainly because airplanes may still be flown at e.g. positions further aft than the position generally limited by the requirements. In this paper, the author presents a new method of aircraft longitudinal control which it is believed will permit the e.g. range of the airplane to be substantially increased, as well as reduce the control forces in a more satisfactory manner than is customary. This method essentially provides a cockpit control by which the pilot may regulate the elevator hinge moment characteristics according to an estimate of the airplane e.g. and enables the pilot to make the airplane stable during a climb or in level cruising flight or maneuverable when he so desires. The cockpit control is a means for regulating the amount the elevator hinge moment changes for a given change in angle of attack of the airplane horizontal tail as expressed by the elevator hinge moment coefficient derivative c>CHe/(>at = CHea. To obtain this regulation a method is proposed whereby the forward part of the stabilizer is made movable and is connected to the elevator by an adjustable linkage system such that it may move in a regulated manner with the elevator. A second method consists of allowing a small surface within the stabilizer to move in an adjustable relation to a tab attached to the elevator, the internal surface being vented to the airfoil surface.