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A Preliminary Flying Qualities Evaluation of a Variable Sweep Fighter Type Aircraft

The F-111A is a two-place (side —by-side) long-range fighter bomber built by
General Dynamics, Fort Worth Division. The airplane is designed for all-weather
supersonic operation at both low and high altitude. Power is provided by two TF30 —P—1
axial—flow, dual -compressor turbofan engines equipped with afterburners. The wings,
equipped with leading-edge slats and trailing—edge flaps, may be varied in sweep angle
between 16° and 71. 5". The empennage consists of a fixed vertical stabilizer with
rudder for directional control and a horizontal stabilizer (rolling tail) that is moved
symmetrically for pitch control and asymmetrically for roll control. Wing spoilers
augment roll—control power for wing—sweep angles of less than 47°. The main—
landing-gear door acts as a speed brake.

The aircraft tested in this investigation was F—lllA airplane number 6 (S/N
63—9771), a pre —SWIP (Super Weight Improvement Program) configuration. Al-
though differences exist in the inertia characteristics and certain physical dimen—
sions between airplane number 6 and SWIP aircraft, the results from these tests
are believed to be generally representative of this class of variable —sweep aircraft.

Other features of the test aircraft include individual ejection seats, standard
pre -SWIP engine inlet duct, translating inlet cowls, and production vortex gen—
erators in the inlet. The test aircraft does not have a low-speed trim compen—
sator, an adverse yaw compensator, or inlet cone bleed.

A two-view drawing of the aircraft is shown in figure 1, and pertinent physical
characteristics are listed in table I. Figure 2 shows the changes in wing geometry
with wing—sweep angle, and figure 3 details the variable —geometry features of
the wing. It should be pointed out that the flaps cannot be extended at wing sweeps
greater than 26° and the total spoiler system is inoperative at sweep angles greater
than 47°.

The F-111A flight control system incorporates pilot-assist modes, command
augmentation (rate command) and adaptive —gain scheduling in pitch and roll, and
a fixed~gain yaw damper. In pitch and roll, command augmentation and adaptive
gains are designed to provide invariant aircraft response for pilot control through—
out the operational envelope within the limits of control—system authority. A
manual mode is available on the test aircraft that allows gains in pitch and roll
to be selected manually. The gain levels are displayed on cockpit indicators.