The blade fold cylinder is found inside the sleeve spindle of the No. 2 blade. See figure 10-13. It connects to sector gears, which cause the folding actions. When the No. 2 blade reaches a certain angle, a microswitch turns on the blade folded light in the cockpit. The lock valve traps hydraulic fluid in the rotary-wing head to keep the damper-positioners in the autorotative position. It also keeps the No. 2 blade in the folded position. With the fold sequence completed, the SAFETY VALVE OPEN, the FOLD PWR ON, the No. 1 BLADE POS, the CONT LOCKPIN ADV, and the BLADES FOLDED warning and indicating lights are lit. NOTE: You may have to move the cyclic control stick around the neutral position to engage the control lockpin. If excessive movement of the cyclic stick is necessary, troubleshoot the system for possible mal- adjustment. Blade Spreading Operations The spreading operation requires the same conditions as the fold operation. The primary exception is that the blade fold switch is in the SPREAD position. Pressure is sent through the motor-operated safety valve and through the positioning unit pressure reducers. Pressure is sent to the blade positioner drive unit for rotor brake disc disengagement and the engagement of the rotor brake. With the rotor brake on and the blade fold valve energized, 3,000 psi hydraulic fluid is sent through the rotor coupling. From the coupling, pressure is sent to the damper-positioners. The damper-positioners drive the blades against their autorotative stops. Pressure is then sent to the blade fold cylinder. The blade fold cylinder operates the gear sector and spreads the blade. As the blade starts to spread, the lock valve solenoid is de-energized, releasing fluid in the rotary-wing head. When the blade is completely spread, hydraulic fluid is sent to the blade lock cylinder, engaging the blade lockpin. Engagement and locking of the blade lockpin causes the internal sequencing mechanisms to direct pressure to the control lock cylinder. The control lock cylinder, in turn, locks the controls. The spread sequence is completed. The FOLD PWR, BLADE SPREAD, and SAFETY VALVE OPEN warning and indicating lights should be lit. Figure 10-13.—Blade fold cylinder. Blade Folding System Components Hydraulic components of the blade folding system are conventional type, solenoid-operated selector valves, check valves, pressure reducers and snubber, sequence valves, and actuating cylinders. Of special interest are the safety valve, the blade positioner drive unit, the rotor coupling, the control lock cylinder, and the blade fold accumulator. SAFETY VALVE.—The safety valve is a two-position, motor-operated selector valve. The purpose of the unit is to prevent hydraulic pressure from entering the blade fold system during flight. The motor provides a camming action to move the poppet valve within the selector valve. With the rotor stopped, electrical interlocks allow the safety valve to send fluid to the blade folding system. This action occurs when the safety valve switch is placed in the OPEN position. In the CLOSED position, pressure is blocked at the pressure port. The system vents through the lock valve.    The venting eliminates the possibility of damage to the system by thermal expansion of the hydraulic fluid. The safety valve will not close if the blade spread interlock relay malfunctions. The safety valve will not close if the blades are folded. The safety valve motor opens a limit switch. The switch cuts electrical power to the motor when the safety valve reaches the fully open position. BLADE POSITIONER DRIVE UNIT.—The drive unit is found on the upper surface of the main gearbox input cover. It consists of a gear train, a sequence valve, a tiller plug, a sight gauge, and a hydraulic motor. The gear train rotates because of the hydraulic motor. The gear train turns the rotary-wing 10-18