Main Beams Assembly

overcoming the springs and retaining the multi- purpose initiator lanyard spigots (fig. 5-3). PISTON.— The piston consists of a light alloy tube, attached to the lower end of which is a necked end fitted with piston rings to provide a gas seal between the piston and the barrel. At the upper end of the piston is a breech, into which the cartridge-activated initiator is inserted. The breech has a groove machined around its outer diameter, into which the plunger of the top latch mechanism on the seat main beams engages when the seat is installed on the catapult. A V-groove in the top of the breech engages a dowel on the seat top crossbeam when the seat is installed in the aircraft (fig. 5-3). CATAPULT MANIFOLD VALVE.— The catapult manifold valve provides an interface between the ejection seat and the catapult. The catapult manifold valve is mounted on the top of the catapult. The valve is locked onto the cartridge-activated initiator by a spring-loaded plunger and a retaining pin. The valve contains two inlet ports that connect the hoses from the time delays. 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. 5-7