Analytical investigation of acceleration restriction in a fighter airplane with an automatic control system

James T. Matthews, Jr.
Jan 1958

A theoretical analysis was made to investigate the performance and acceleration-restriction capabilities of a normal-acceleration command control system in a fighter airplane. Several combinations of pitching velocity and pitching acceleration were investigated as feedback quantities in combination with normal acceleration. The flight conditions considered were airspeeds of 600 and 1,000 feet per second, at sea level and an altitude of 20,000 feet, and maneuver margins of 3.3, 13.3, and 23.3 percent of the mean aerodynamic chord. The most desirable transient responses (10 percent or less overshoot) to acceleration commands were obtained when pitching velocity was fed back in a manner that increased the damping of the airplane and pitching acceleration was fed back in a manner that increased the effective inertia of the airplane. In order to obtain satisfactory performance, all the systems investigated required a compensating network which reduced the phase lag of the power control in the vicinity of its natural frequency. The analysis also included the normal-accelleration response of the controlled airplane to simulated rough air. The normal-acceleration response of the controlled airplane to rough air was somewhat reduced as compared with that of the basic airplane, particularly at the lower maneuver margins. The magnitude of the pitching-velocity response was greater for the controlled airplane, as might be expected.

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