Parachute Canopy and Drogue

During the ejection sequence, the parachute deployment rocket motor fires, extends the withdrawal line, and withdraws the parachute in its bag. The parachute canopy emerges from the bag, periphery first, followed progressively by the remainder of the canopy and the drogue. The extractor rocket and bag clear the area. The drogue and crown bridle impart a force on the canopy, proportional to airspeed, to inhibit full canopy inflation until g-forces are reduced.

Rotation of the emergency restraint release handle to permit emergency ground egress will rotate the cross shaft of the lower harness release mechanism to release the lower harness locks, leg restraint line locks, and negative-g strap lock. Full rotation of the handle to withdraw the sear of the firing unit is prevented by the pin puller engaging the rear end of the slot in the emergency restraint release operating link.

During ejection, gas from the RH seat initiator impulse cartridge enters the pin puller plunger housing and lifts the plunger out of engagement with the groove in the piston. Movement of the plunger allows gas to enter the cylinder and withdraw the piston out of engagement with the slot in the emergency restraint release operating

link, the piston being held in the operated position by residual gas pressure. The operating link is then disengaged from the lower harness release cross shaft by the action of a spring-loaded plunger in the operating link guide bracket mounted on the seat bucket side.

Seat Survival Kit

The seat survival kit (SKU-7/A) operates automatically upon seat ejection. Kit components are maintained by the PR rating. The SKU-7/A contains new equipment. Specific information on the new items was not available at the time of development of this manual.

EJECTION SEQUENCE

When the ejection control handle is pulled (fig. 5-34), the sears are withdrawn from the seat initiator firing mechanisms and the two impulse cartridges are fired.

Gas from the RH cartridge is piped as follows:

1. To the pin puller, which withdraws a piston from engagement in the lower operating link of the emergency restraint release mechanism.

2. To the inboard connector of the command sequencing quick-disconnect on the RH ballistic

Figure 5-34.-Ejection seat gas flow (block diagram). 5-34

manifold to operate the command sequencing and canopy jettison systems.

3. To the 0.30-second delay cartridge-actuated initiator (aft seat only) on the RH ballistic manifold. Gas from the initiator passes to the RH inlet of the catapult manifold valve to initiate the catapult.

4. To the breech of the shoulder harness reel, where it fires the impulse cartridge to pull the seat occupant into the correct position for ejection.

5. To the thermal batteries.

6. Via a check valve to the 0.75-second delay cartridge-actuated initiator on the LH ballistic manifold. Gas from the initiator passes to the LH inlet of the catapult manifold valve to initiate the catapult.

7. If the seat (F/A-18D only) is command ejected (i.e., the ejection control handle on the other seat has been pulled), gas from the command sequencing system enters the RH seat initiating system through the inboard connector of the command sequencing quick-disconnect on the RH ballistic manifold, and operates as described in 1 through 6 above. On the forward seat only, gas pressure also enters the outboard connector of the command sequencing quickdisconnect and is passed to the catapult manifold valve to initiate the catapult. This gas pressure is also piped, via a check valve, to the shoulder harness reel and thermal batteries.

Gas from the LH cartridge is piped as follows:

1. To the thermal batteries.

2. To the 0.75-second delay, cartridgeactuated initiator on the LH ballistic manifold. Gas from the initiator passes to the LH inlet of the catapult manifold valve to initiate the catapult.

Gas from the delay initiator is piped to the ejection gun initiator via the manifold valve. Gas pressure developed by the initiator passes down the catapult to operate the ballistic latches, retaining the IMP lanyard end fittings. As the pressure increases within the catapult, the catapult piston rises, releases the top latch, and begins to move the seat upwards. Further movement of the piston uncovers the catapult secondary impulse cartridge, which is fired by the heat and pressure of the ejection gun initiator gas. Staggered firing of the catapult cartridges provides a relatively even increase in gas pressure during catapult stroke to eliminate excessive g-forces during ejection.

As the seat goes up the guide rails:

1. The IMP lanyards begin to withdraw.

2. Personal services between seat and aircraft are disconnected.

3. The emergency oxygen supply is initiated.

4. The URT-33A beacon is activated.

5. The leg restraint lines are drawn through the snubbers and restrain the occupants legs to the front of the seat bucket. When the leg restraint lines become taut, the special break ring incorporated in each leg line fails, and the lines are freed from the aircraft. Forward movement of the legs is prevented by the lines being restrained by the snubbers.

Near the end of the catapult stroke, the IMP lanyards become taut and operate the firing mechanisms. Gas pressure from the IMP cartridge passes:

1. To the start switch plungers. Closure of the start switches commences sequencer timing.

2. To the barostatic release unit release piston (from the RH IMP only).

3. To the pitot mechanisms to deploy the pitot heads.

4. Via the LH ballistic manifold and trombone tube to the underseat rocket motor. The rocket motor ignites, sustaining the thrust of the catapult to carry the seat clear of the aircraft.