MISCELLANEOUS COMPONENTS

Other systems and components that are related to the canopy system are the canopy electrical system, air-cycle air-conditioning system, maintenance status display and recording system, mission computer system, and the multipurpose display group.

The F/A-18 aircraft electrical system supplies 28-volt dc power for canopy operation. Because the bus distribution system varies, depending upon the bureau number of the aircraft, refer to the maintenance instruction manuals to determine the applicable configuration. (See electrical system schematic shown in figure 2-9.)

The air-cycle air-conditioning system supplies partially cooled bleed air for the inflation of the canopy pressure seal to maintain cabin pressurization.

The maintenance status display and recording system, mission computer system, and multipurpose display group all receive inputs from the canopy system. Inputs are processed and supplied to the left digital display indicator and master caution light. The inputs are also processed, recorded, and displayed as maintenance codes on the nosewheel well digital display indicator. Canopy caution and warning indicators

Figure 2-8.-Canopy position switch and latch retainer. 2-6

are made up of the following components: canopy caution light on the cockpit left digital display indicator, master caution light on the left-hand advisory and threat warning indicator panel, and the maintenance code display on the nosewheel well digital display indicator.

NORMAL OPERATION

Learning Objective: Identify the canopy normal mode of operation to include the manual backup mode.

The canopy is operated electrically by the external or internal canopy control switches in the normal control mode. The canopy can also be operated manually in the backup manual control mode if electrical power is not available.

NORMAL CONTROL MODE

The canopy may be operated with the external canopy control switch. To open the canopy, the switch is held in the OPEN position. The canopy stops automatically when the full open position is reached. To close the canopy, the switch is held in the CLOSE position until the canopy closes, moves full forward, and locks. The canopy stops automatically when the closed and locked position is reached. Motion may be stopped at any point during opening or closing by releasing the switch. The switch returns to the HOLD position when released.

To open the canopy internally with weight on the wheels, the internal canopy control switch is set to OPEN and released. The switch is magnetically held in the OPEN position until the canopy raises to full open and stops. The switch then returns to HOLD. Canopy motion may be stopped at any point during canopy opening by manually setting the switch to the HOLD position, which overrides the magnetic holding coil. The internal canopy control switch opening circuit is equipped with a weight-off-wheels relay that deenergizes the magnetic holding coil when the aircraft is in a weight-off-wheels condition. With the holding coil de-energized, the switch must be manually held to the OPEN position when opening the canopy.

When the canopy closes, moves full forward, and locks, the No. 4 right canopy latch depresses the canopy position switch plunger. Simultaneously, the canopy actuator arm rotates overcenter and depresses the canopy locked switch plunger. Depressing both switch plungers causes the master caution light and the canopy display on the left digital display indicator to extinguish, indicating the canopy is fully closed and locked. If both switches are not fully depressed or a failure occurs in either switch, the master caution and canopy caution indicators will remain illuminated. If both switch plungers are not depressed within 15 seconds, the canopy switches disagree and the maintenance code (889) will be displayed on the nosewheel well digital display indicator.

Electrical inputs supplied to the canopy actuator are transformed into mechanical motion used to raise and lower the canopy. The actuator is equipped with an up-travel-limit switch, which automatically interrupts power to the actuator when the full open position is reached. With no aircraft generator power or external power applied, a utility battery supplies power for at least five open and close cycles of the canopy. On some F/A-18 aircraft, a logic circuit in the battery and charger unit secures the canopy control power when the battery voltage drops below 191 volts.

Due to decreased battery capacity at low temperatures, canopy operation using battery power is not recommended when ambient temperature is below 0F. Under these conditions, external electrical power should be used. When external power is not available, the canopy can be operated using the backup manual control mode.

To further understand how the opening and closing cycles function, refer to figure 2-9.