G41365
Leading Edge Flap Actuator 500
27-81-0 Figure 2 Dec 15/70
Page 8
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
5. Leading Edge Flap Actuator
A. A two-position hydraulic actuator mounted on the front spar of the wing is used to extend and retract each leading edge flap. (See figure 2.) A self-aligning bearing at each end of the actuator allows the actuator to rotate about its mounting bolts. The actuator housing contains two identical blocking valves and a piston and rod assembly. The blocking valves will hydraulically lock the actuator pistons in position if hydraulic pressure drops below 2000 psi. If a loss of pressure occurs, a compression spring moves the blocking valve slide to prevent flow of hydraulic fluid through the valve. One blocking valve is used for hydraulic system A while the second blocking valve is used for the standby hydraulic system.
B. External ports in the actuator housing are provided for an actuator retract pressure line, an actuator extend pressure line and a standby system pressure line. The actuator retract pressure line provides system A pressurized fluid from the leading edge flap and slat control valve. With the hydraulic system pressurized, system A pressure is ported at all times to the retract side of the actuator piston. System A hydraulic pressure from the control valve extends the actuator by acting upon a larger piston area than the pressure attempting to retract it. When the control valve is closed, pressure from the extend side of the piston is ported to return. The flap will then retract due to hydraulic system A pressure on the retract side of the piston.
C. During standby hydraulic system operation, standby pressure is ported to both the extend and retract sides of the actuator piston. Since hydraulic pressure is acting on a larger piston area on the extend pressure side, the actuator extends. The actuator will remain in the extended position until system A hydraulic pressure is restored.
6. Leading Edge Slat Actuator (See figure 3.)
A. A three-position hydraulic actuator mounted on the front spar of the wing is used to extend and retract leading edge slats 1 through 6. The three actuator positions are retracted, intermediate extension and full extension. Each actuator housing contains two identical blocking valves, an internal mechanical locking mechanism, an outer piston and an inner piston and rod assembly. A reed switch i s installed in the actuator inner piston rod and is actuated by movement of the locking piston within the inner rod. The actuator outer piston slides within the actuator housing and the inner piston slides within the outer piston . The internal mechanical locking mechanism consists of a spring-loaded piston and locking segments. It locks the actuator in the retracted position in the absence of extend pressure. When extend pressure is applied, the locking piston moves against spring force to retract the locking segments and allow the actuator to extend. The blocking valves hydraulically lock the actuator pistons in position if hydraulic pressure drops below 2000 psi. If a loss of pressure occurs, a compression spring moves the blocking valve slide to prevent flow of hydraulic fluid through the valve. One blocking valve is used for hydraulic system A while the second blocking valve is used for the standby hydraulic system.
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May 15/71 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 27-81-0 Page 9
B. External ports in the actuator housing are provided for an actuator retract pressure line, two actuator extend pressure lines and a standby system pressure line. The actuator retract pressure line provides pressurized fluid directly from hydraulic system A. The two actuator extend pressure lines provide system A pressurized fluid from the leading edge flap and slat control valve. With the hydraulic system pressurized, system A pressure is ported at all times to the retract side of both actuator pistons. System A hydraulic pressure from the control valve is directed to the slat actuator in two progressive steps. As the control valve moves to its intermediate position, pressure is ported to extend the inner piston and rod assembly. This allows the actuator to move to the intermediate position. In the second step, the control valve ports hydraulic pressure to extend the outer piston while pressure is still ported to the inner piston. This allows the actuator to move to the fully extended position. Actuator extension results from system A pressure acting upon a larger area on the extend pressure side of the pistons than on the retract pressure side. When the control valve is returned to the intermediate position, the outer piston extend pressure is ported to system A return. Hydraulic pressure on the retract side of the outer piston then causes the outer piston to retract. When the control valve closes, the inner piston extend pressure is also ported to system A return. Hydraulic pressure on the retract side of the inner piston then causes the inner piston to retract.
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