THERMAL RADIATION PROTECTION UTILITY SYSTEMS-Cont.

of the flak curtains prior to takeoff will depend upon mission requirements. The radiation protection system on the A-7 aircraft is similar to that of the A-6 except that it may be opened or closed manually or closed automatically using pneumatic system pressure. The A-7 protective closure consists of one fixed and three movable fiber glass segments, which enclose the entire cockpit viewing area when extended. The forward segment of the closure presses against the instrument panel cowl so that a windshield curtain is not necessary. In the open position, the movable segments are retracted within the contour of the fixed segment so that they do not restrict the pilot’s vision. An overcenter spring on each side of the closure holds the panels in either the open or closed positions. The automatic closing sequence is accom- plished in 0.2 second. A lock on the left-hand canopy frame locks the closure open and prevents extension until it is manually released. Interference tolerances between the ejection seat and the closure panels require that the seat be within 1/4-inch of the full down position prior to closure operation. Manual actuation of the system is initiated by placing the thermal closure switch to the CLOSE position. This will cause the ejection seat to be automatically lowered to provide proper clear- ance. As the seat lowers, it actuates a seat posi- tion switch, which directs current to the closure selector valve. The energized valve releases 1,000 psi pneumatic system pressure through a restrictor to the two closure actuators, rapidly extending the closure panels. When the thermal closure switch is released, it returns to the OFF position, de-energizing the closure selector valve and blocking pneumatic system pressure to the actuator extend lines. De- energizing of the selector valve also vents the extend lines so that the closure panels may be manually opened or closed as necessary. In the automatic mode of operation, the thermal closure system operates in the same manner except the solenoid of the closure selector valve is grounded through a switching demodulator unit rather than the thermal closure switch. The switching unit energizes the closure selector valve and turns on the white cockpit floodlights when the system is initiated (triggered) by a nuclear flash sensor. The nuclear flash sensor is mounted on the pilot’s flight helmet. When activated by high- intensity light, such as that created by a nuclear blast, the sensor energizes the closure selector valve for approximately 3 seconds. The closures extend, are held closed for the 3-second interval, and then the valve is de-energized and the actuator lines are vented to allow manual opening and closing of the panels. NOTE: When flying a special weapons mission in the A-7, the pilot’s helmet is equipped with a flash-blindness protective (ELF) lens. When the nuclear flash sensor that closes the radiation panels is activated, current is also directed to detonate a very small explosive charge contained in the lens. The exploding charge releases a light- blocking graphite suspension to the inner core of the lens to protect the pilot’s eyes from thermal flash while the closure panels are extending. The ELF lenses are normally stored in containers in the cockpit when not in use. 1-35