The wing surface control system controls the military variable geometry wings to increase aircraft performance at all speeds and altitudes. The system also provides high lift and drag forces for takeoff and landing. It provides increased lift for maneuvering, and at supersonic speeds, aerodynamic lift to reduce trim drag.

The wing sweep control initiated at the throttle quadrant provides electronic or mechanical control of a hydromechanical system that sweeps the wings. See figure 9-38. The wings sweeps from 20 degrees through 68 degrees in flight. On the ground, a wing sweep position of 75 degrees is available (through mechanical control) for spotting the aircraft or enabling a wing sweep control self-test. See figure 9-39.

A wing sweep under electronic control is initiated at the throttle quadrant. Four modes are availableautomatic, aft manual, forward manual, or bomb manual. Selection of these modes causes the air data computer to generate wing sweep commands consistent with the aircraft speed, altitude, and configuration of the flaps and slats. The commands are applied through the wing-flap glove-vane controller to the wing sweep control drive servo. They are converted to mechanical rotary force. This force, transferred to the wing sweep/flap and slat control box, causes the wing sweep hydraulic control valve to operate hydraulic motors that are driven by the flight and combined hydraulic power systems to sweep the wings. The flight hydraulic power system positions the right wing, and the combined hydraulic power system positions the left wing. A synchronizing shaft (fig. 9-38) interconnects the wings to ensure symmetrical operation. If a hydraulic system fails, it provides the driving force for sweeping the wing affected by the failed system.

Wing sweep commands generated by the air data computer are limited by the configuration of the auxiliary flaps, maneuver flaps, and slats. With the auxiliary flaps extended, wing sweep is limited to 21.25 degrees. The maneuver flaps, with or without slats extension, limit wing sweep to 50 degrees. To prevent structural damage to the wings during negative-g conditions, wing sweep is interrupted to prevent wing sweep changes until the negative-g condition no longer exists. In the automatic mode, the wings are positioned at a rate of 7 degrees per second.

Figure 9-39.Wing oversweep Positionmanual control.

When wing sweep is under mechanical control, the wing sweep handle positions the wings through the wing sweep/flap and slat control box. Because the minimum wing sweep limiting is not available under mechanical control, the wings can be swept to an adverse position that could cause damage to the wings. Mechanical control is used for emergency wing sweep and wing oversweep.

During emergency wing sweep, the wing sweep handle, mechanically coupled to the wing sweep/flap and slat control box through a cable assembly, positions the wings. The wing sweep can be returned to electronic control by repositioning the wing sweep handle to the stowed position.

Wing oversweep can only be obtained with the aircraft weight on the wheels. Wing oversweep, shown in figure 9-39, reduces the amount of space required for spotting the aircraft. A wing sweep self-test can only be performed while the wings are overswept.