LEADING EDGE TEMPERATURE AND OVERHEAT CIRCUIT

controlled by three switches on the bleed-air section of the ice protection panel. When the solenoid is energized, it admits filtered, regulated, bleed-air pressure to one side of a diaphragm chamber in the valve. The other side of the diaphragm chamber is spring-loaded to the closed position. Movement of the diaphragm operates a main line butterfly valve. When the valve opens, hot air is admitted to the leading edge distribution system. The hot air goes through the modulator valve to the ejector manifold, out the jet nozzles, and into the wing leading edge plenum area. The bleed air is then directed across a pneumatic thermostat. Increased temperature across the thermostat actuates the sensor and opens a bleed passage from the diaphragm chamber. This reduces the pressure on the diaphragm and allows a spring to close the main valve. THERMOSTATS.— The wing leading edge pneumatic thermostat is installed adjacent to each modulating valve. (See fig. 3-2.) The thermostat controls air pressure on the modulating valve diaphragm, and thereby controls the valve opening. The unit is composed of a probe and a valve assembly. (See fig. 3-3.) The probe is a core made of layers of high- and low-expansion material that is locked to a sliding piston. In addition, the piston contains an override spring and ball-type metering valve. Airflow from the leading edge flows over the core and causes the materials to expand or contract. As temperature rises, the core pulls the piston and metering ball from the seated position. This allows pressure from the modulating valve diaphragm to vent. Increasing temperature causes more air to be bled from the diaphragm chamber. Because of spring action, the modulating valve moves toward the closed position. This restricts flow through the modulator valve and drops the skin temperature. LEADING EDGE TEMPERATURE AND OVERHEAT CIRCUIT.— To monitor the overheat warning system, six skin temperature sensors (one in the inboard section, one in the center section, and one in the outboard section of each wing) form a part of an amplifier circuit. When the wing leading edge skin temperature rises in excess of 230°F at any one or more sensors, the airfoil temperature control unit amplifier completes a caution light circuit, thus illuminating the leading edge caution hot light. Also, there are three ducting overheat thermal switches installed in each wing and three installed in the fuselage adjacent to the bleed-air duct. These switches form a part of a loop that is connected to a signal light control assembly. When any one of the thermal leak detector switches closes, its respective caution light illuminates. Also, when the test switch is placed in the TEST position, both lights illuminate through their respective loop circuit. The ducting overheat switches are single-pole, single-throw, explosiveproof, thermally actuated electrical switches with an integral temperature Figure 3-3.-Wing leading edge thermostat. 3-4