The pylon, shown in figure 1-18, is of aluminum semimonocoque construction. It has beams, bulkheads, stringer, formers, and channels. Various gauges of aluminum skin located on the sides of the box structure are part of the primary pylon structure. Reinforced plastic fairings in the leading and aft surfaces form the airfoil contour of the pylon and are secondary structures. The pylon houses an intermediate gearbox and a tail gearbox. The pylon is attached on the right side of the aircraft to the main fuselage by hinge fittings. These hinge fittings also serve as the pivot point for the pylon to fold alongside the right side of the fuselage. Folding of the pylon reduces the overall length of the H-3 helicopter by 7 1/2 feet, thereby aiding shipboard handling.

Rotary Rudder Head 

The rudder head is usually located on the left side of the pylon. It produces antitorque forces, which may be varied by the pilot to control flight heading. The

Figure 1-19.-Five stresses acting on an aircraft.

rotary rudder head is driven by the tail gearbox. Change in blade pitch is accomplished through the pitch change shaft that moves through the horizontal shaft of the tail gearbox. As the shaft moves inward toward the tail gearbox, pitch of the blade is decreased. As the shaft moves outward from the tail gearbox, pitch of the blade is increased. The pitch control beam is connected by links to the forked brackets on the blade sleeves. A flapping spindle for each blade permits flapping of the blade to a maximum of 10 degrees in each direction.