Main Beams Assembly

The main beams assembly is manufactured almost entirely from light alloy and comprises two parallel main beams bridged by top and bottom crossbeams. Bolted to the inside face of each main beam are three slippers, which engage in the guide rails on the catapult. Two-seat bucket runner guides are attached to the front face of each main beam and accommodate the top and bottom seat bucket slippers. The slippers provide smooth movement of the seat bucket and incorporate threaded studs for attachment of the seat bucket to the main beams. Friction pads are incorporated in the studs to damp out lateral movement of the seat bucket. Drogue bridle retaining channels are secured to the rear of both main beams. Locating pins for the parachute container hooked brackets are bolted to the upper outside face of each main beam. Interference blocks on the right-hand (RH) beam (forward seat) or left-hand (LH) beam (aft seat) correspond with interference devices on the catapult and the seat bucket to ensure that only the correct assemblies are installed in forward and aft cockpits.

TOP CROSSBEAM.- The top crossbeam accepts and locates the top of the catapult, and

takes the full thrust of the catapult during ejection. Incorporated into the crossbeam is the upper drogue bridle release unit. A dowel in the top crossbeam locates in one of the catapult breech V-grooves when the seat is installed in the aircraft.

BOTTOM CROSSBEAM.- The bottom crossbeam retains and separates the main beams at the bottom end. Incorporated into the crossbeam is a gas passage that forms part of the drogue bridle release system.

TOP LATCH ASSEMBLY.- The seat structure is secured to the catapult by the top latch assembly (fig. 5-6) fitted to the LH main beam. The assembly consists of a housing that contains a spring-loaded latch plunger, one end of which is shaped to engage the catapult piston. The plunger may be withdrawn by using the top latch withdrawal tool (handwheel). Passing through the center of the latch plunger is a spring-loaded indicator plunger. When the ejection seat is fitted

Figure 5-6.-Operation of top latch assembly.

Figure 5-7.-Shoulder harness control system.

to the catapult and the handwheel removed, the latch plunger passes through the top crossbeam and engages with the barrel latch. The shaped end of the plunger protrudes still further to engage the groove of the catapult piston.

SHOULDER HARNESS CONTROL HAN-DLE.- The shoulder harness control handle (fig. 5-7) is located on the left side of the seat bucket. The handle is connected to the inertia reel. In the aft position, the reel is allowed to rotate freely. When the forward position is selected, straps will ratchet in, allowing no forward movement.