The F-14 aircraft uses the clamshell canopy system. This pneumatic system is operated by setting any one of the three canopy control handles, This action positions valves within the pneumatic control module to route pneumatic pressure to or from the system. The modes of operation that can be selected are normal opening mode, holding mode, normal closing mode, boost closing mode, and auxiliary opening mode. The function of all three control handles is the same.

Normal Opening Mode

Figure 2-2 (a foldout at the end of this chapter) shows a schematic of the F-14 pneumatic canopy system. Setting the pilot canopy control handle to open pulls the lock lockpin and positions valves No. 1,2, and 6 within the control module to direct nitrogen at 325 psi through the C 1 and C3 ports of the module, to the timer check valve, and to the unlock port of the canopy-lock pneumatic actuator. Simultaneously, the shutoff valves in the open and close modules of the canopy hydraulic actuator are vented to the atmosphere through the C5 port of the actuator, through the canopy pneumatic timer, and through valve No. 3 in the control module. The lock port of the canopy-lock pneumatic actuator is vented overboard through the pneumatic timer. The piston of the actuator extends and, by means of a torque tube, cranks, and links, moves the canopy aft to unlock it from the sill locks. When the extending piston reaches the end of its stroke, ball locks engage to hold it in that position. The extended piston also actuates the timer check valve, which directs the 325-psi nitrogen to the C1 port of the canopy hydraulic actuator. The nitrogen that enters the hydraulic actuator acts against the piston of the open transfer cylinder. This pressure, acting against the piston, causes the hydraulic fluid on the opposite side of the piston to extend the ac-tuator. The extending actuator rotates the canopy on the aft hinge to open the canopy. As the ac-tuator extends, fluid displaced from the close side of the actuator acts against the piston of the close transfer cylinder. The nitrogen on the opposite side of this piston is vented overboard through the C2 port of the hydraulic actuator and through valve No. 4 of the control module. Pulling the lock lockpin at the beginning of the opening cycle closes the canopy switch, which provides 28 volts from the essential dc No. 2 bus, through the CAN/ LAD CAUTION/ EJECT CMD IND circuit breaker, to the canopy caution indicator light on the pilot and NFO caution advisory indicators.

Holding Mode

The HOLD position stops canopy motion at any desired opening. Valve No. 3 in the control module directs 325-psi nitrogen through the C5 port of the module, through the pneumatic timer, to the C5 port of the hydraulic actuator. The nitrogen that enters the C5 port closes the shutoff valves in the open and close modules. The closed shutoff valves trap hydraulic fluid on the open and close side of the actuator piston, stopping piston travel.

Normal Closing Mode

Setting the control handle to CLOSE positions valves No. 1, 2, 4, and 5 in the control module to vent both transfer cylinders and the unlock port of the canopy-lock pneumatic actuator overboard. The weight of the canopy closes it; pneumatic power is not required. The closing time, approximately 10 seconds from the fully open position, is controlled by the flow regulators in the open and close control modules of the hydraulic actuator. The final closing motion of the canopy actuates the pneumatic timer to direct 325-psi nitrogen from valve No. 2 of the control module to the lock port of the canopy-lock pneumatic actuator, unlatching the ball locks. The actuator piston retracts and, by reverse action, moves the canopy forward to engage the canopy hooks in the sill locks. With the canopy in its full forward positions, the lock lockpin engages and prevents aft movement of the canopy. The final motion of the lock lockpin opens the canopy switch, breaks the circuit to the canopy caution indicator light on the caution advisory indicators, and the lights go off.

Boost Closing Mode

To close the canopy under high headwind conditions, the canopy control handle must be moved to BOOST. On aircraft not modified by AFC 95, the control handle must be rotated out-board to move the handle pasta stop to BOOST. Valve No. 4 in the control module is positioned to direct 790-psi nitrogen through the C2 port of the canopy hydraulic actuators to the close transfer cylinder. This nitrogen, acting against the transfer cylinder piston, causes the hydraulic fluid on the opposite side of the piston to retract the actuator. The other valves in the control module are positioned the same as when CLOSE is selected, and the system functions in the same manner to lock the closed canopy. The closing time for this mode of operation is also controlled by the flow regulators in the open and close control modules of the hydraulic actuator.

Auxiliary Opening Mode

The auxiliary opening mode is used to unlock the canopy when normal pneumatic system reservoir pressure drops below 225 psi. To prevent further depletion of nitrogen pressure in the normal system, a low-pressure sensor repositions valves No. 5 and No. 6 in the control module. The canopy must now be unlocked by activating the auxiliary opening mode. To set the canopy control handle to AUX OPEN on aircraft not modified by AFC 95, the handle must be rotated outboard to move past a stop (the handle will remain in the AUX OPEN position). When the control handle is set to AUX OPEN, the auxiliary unlock pneumatic release valve releases pressurized nitrogen from the auxiliary pneumatic reservoir. Nitrogen pressure from this reservoir flows through a 325-psi pressure reducer, through the release valve and pneumatic unlock shuttle valve, to shift position of the shuttle valve internal spool. This directs nitrogen pressure to the unlock port of the canopy-lock pneumatic actuator, unlocking the canopy. Valve No, 1 in the control module directs reservoir pressure to the open transfer cylinder of the canopy hydraulic actuator. This low-pressure nitrogen, acting against the transfer cylinder piston, counter-balances the weight of the canopy. The canopy can then be easily opened and closed manually. The canopy cannot be locked closed under these conditions. To return the system to normal operation, the control handle must be set to OPEN and, on aircraft not modified by AFC 95, rotated outboard to move past a stop. The release valve eccentric cam must be manually reset to block auxiliary nitrogen pressure flow to the shuttle valve and to vent the pressure in the canopy-lock pneumatic actuator.