The spring-loaded rotor brake accumulator permits manual operation of the master cylinder handle during automatic blade folding operations. Applying the automatic brake unseats the accumulator sequence valve. The open valve permits actuation of the master cylinder handle. The hydraulic fluid flows through the sequence valve and compresses the accumulator spring. Releasing the automatic brake causes pressure to flow from the accumulator to the panel package shuttle valve, and repositions it. Simultaneously, the panel package accumulator maintains hydraulic pressure that was trapped from the automatic application in the rotor brake. The rotor brake accumulator additionally compensates for thermal expansion and contraction of the fluid, and aids in dampening pressure surges.

The master cylinder is gravity fed by hydraulic fluid from the utility fluid tank. Move the brake handle down and forward to apply pressure to the system. A spring latch on the cylinder linkage automatically locks the handle in the ON or PARK position. To release the brake, pull the latch and place the handle in the DETENT position. The pressure gauge indicates the amount of pressure produced by the master brake cylinder. The check valve provides a means to pressure bleed the system. A minimum pressure of 320 psi is required to effectively operate the rotor brake.

An automatic blade folding system of a representative helicopter is shown in figure 10-12. This system is capable of automatic blade folding of one of the two rotary blades from cockpit controls.

The No. 1 blade does not fold, but it automatically positions over the tail pylon. The only hydraulic actuation of the No. 1 blade is damper positioning. The hydraulic portion of the system positions the blades and folds the No. 2 blade. The electrical portion of the system provides the sequencing of operation of the various hydraulic components. It acts to prevent accidental operation of the system. Warning and indicating lights show the status of the system at all times. Safe operation is maintained by a series of electrical interlocks.

You should perform blade folding operations with the pylon locked in the flight position and the engine operating at 104 percent. The rotary-wing head must not be operating. The accessory drive switch is placed in ACCESS DRIVE. The safety valve switch is placed OPEN, and the master switch is placed ON. The blade switch is placed in the FOLD position. Hydraulic pressure from the utility hydraulic system is 3,000 psi. The pressure flows through the motor-operated safety valve. This pressure flows to the blade positioner control valve, and is sent to the blade positioner drive unit for engagement with the rotor brake disc. This action turns the rotary-wing shaft.

Pressure is sent through the blade rotation control valve to the blade positioner hydraulic motor. The motor revolves the blade positioner, causing the rotation of the rotary-wing head. When the No. 1 blade is properly positioned aft, the blade positioner control valve is energized in the opposite direction. The action stops positioning and disengaging of the blade positioner drive unit. Fluid is also sent to engage the rotor brake at this time.

On later models, the rotor brake applies manually. The blade fold control valve is energized, sending hydraulic pressure through the rotor coupling to each damper-positioner. The blades move against their autorotative stops. The mechanical action of positioning the blades operates the damper-positioner sequence valves. These valves cause hydraulic fluid to operate the control lock cylinder, locking the controls. With the rotor head controls locked, pressure is sent to the blade fold lock cylinder. The lockpin is retracted, and fluid is sent to the blade fold cylinder.

Figure 10-12.Automatic blade folding system schematic.

Figure 10-12.Automatic blade folding system schematicContinued.

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.