Fam 6 Discuss Items

=Hydraulic System= The hydraulic system, as shown in figure 6-1, consists mainly of a power pack, filter, pressure switch, solenoid valve and servos. This highly efficient system reduces pilot workloads by reducing control pressures and vibrations generated by the main rotor system. Since the main rotor is where the heavy control loads exist, hydraulic assisted control is provided only for the cyclic and collective control systems. Our discussion will deal with the major components mentioned above and will begin with the power pack.

Power Pack
The power pack is located on the forward port side of the transmission and is driven by the transmission accessory drive shaft. The power pack consists of the reservoir area, pump section, pressure regulator valve and rotor tachometer generator mounting pad (figure  6-2). Because the system generates heat, the reservoir is finned and has air directed from the engine oil cooler blower to aid in cooling. The capacity of the reservoir is approximately one pint and it has a scupper and drain line to drain vented fluid overboard. Fluid level is checked through a sight gauge in the reservoir. Hydraulic fluid is gravity fed from the reservoir to the pump assembly which pressurizes the fluid and sends it through the pressure regulator valve. This valve regulates system pressure to approximately 600 +/-50 psi. Next, the fluid is pumped to the hydraulic filter.

[on a side note, also look in the systems book on page 6-6 to get the actual servo-actuator system]

Filter
The purpose of the filter is to remove foreign matter that has contaminated the hydraulic fluid. The filter assembly in figure 6-3 consists of a head, filter element, and body. Since there is no bypass system, unfiltered fluid cannot enter the servos if the filter becomes clogged. A popped filter indicator means filter stoppage and the filter element should be cleaned or  replaced by maintenance before flight.

Pressure Switch
The pressure switch, shown in figure 6-4, is located downstream from the filter. This switch continually monitors system pressure and will close if the pressure falls below 300 psi. A hydraulic pressure light illuminates when the switch closes and goes out when the pressure  rises above 400 psi.

Solenoid Valve
The next component in the system is the hydraulic solenoid valve, located on the service deck forward of the transmission. The valve is spring-loaded to the open position and requires electrical power to the solenoid to move the valve to the bypass position. This fail-safe design feature ensures the valve is open at all times, unless bypass is selected. The hydraulic ON/OFF switch (figure 6-5), located on the pedestal (TH-57B) or near the center of the  instrument panel (TH-57C), controls the solenoid valve. With the hydraulic control switch ON, no power is applied to the solenoid valve and it springs to the open position. With a hydraulic system failure, such as a servo malfunction, setting the switch to OFF causes the solenoid valve  to move to the bypass position. This action removes pressure from the servos and terminates hydraulic boost to the flight controls. Circuit protection is provided by the hydraulic boost circuit breaker located on the overhead console. With the valve in the open (ON) position, hydraulic fluid is routed to the three servos (see figure 6-6).

Servo Actuators
The major servo actuator components are the sequence valve, pilot valve, and differential relief valve (figure 6-7). With the system operating, fluid at 600 psi enters the servo pressure port and the flow is stopped until a control input is made. Hydraulic pressure on the sequence valve pushes down on the poppet valve and spring, thereby opening a return port for fluid to return to the reservoir. If pressure is lost, the sequence valve closes, trapping fluid in the servo which will continue to  dampen main rotor feedback (vibrations). The function of the differential relief valve is to cause fluid to be routed to the return line if back pressure exceeds system pressure. Heavy main rotor loads are one possible source of excessive back pressure. The heart of the servo is the pilot valve. The pilot valve is mechanically connected to the flight controls and receives input from movement of the controls. This causes the pilot valve to move and allow fluid under 600 psi pressure to enter the actuator, which then moves the flight controls. When the flight controls reach the desired position, the pilot valve centers and fluid flow to the actuator is stopped. Again, in the event pressure is lost, the sequence valve will trap fluid in the servo. In this case, movement of the pilot valve will allow fluid to flow from one side of the actuator through the  valve body to the other side of the actuator. This allows control movement and dampens rotor system vibrations felt through the controls. Under normal pressurized operation, the fluid is routed from the servo back to the reservoir, where it is cooled and the cycle repeated.

=Hydraulic System Failure= INDICATIONS: PROCEDURES: 1. Airspeed — Adjust (to obtain most comfortable control movement level). 2. HYDRAULIC BOOST switch — Check ON. 3. HYD BOOST circuit breaker — Out. If system is restored: 4. Land as soon as practicable. If system is not restored: 5. HYD BOOST circuit breaker — In. 6. HYDRAULIC BOOST switch — OFF. (C)7. FORCE TRIM (FT) — ON. (C)8. AFCS STAB — ON. (C)9. AFCS ALT — OFF. 10. Land as soon as practicable.
 * HYDRAULIC PRESSURE light
 * Increased force required for control movement Feedback in control.

=Hydraulic Power Cylinder Malfunction= INDICATIONS:
 * Cyclic/collective ctrl displaces to abnormal posn
 * Pilot ctrl of cyclic/collective difficult or imposs

PROCEDURES: 1. HYDRAULIC BOOST switch — OFF. WARNING Hydraulic system will not secure if HYD BOOST circuit breaker is out. 2. Helicopter — Regain Control. 3. Adjust airspeed as desired to obtain most comfortable control movement level. 4. Land as soon as possible. WARNING In the event of a complete power failure in the TH-57B or a failure of the ESS No. 2 bus in the TH-57C, the hydraulic system will reenergize in the malfunction mode. The pilot will be unable to override the hydraulic boost solenoid.

=Mast Bumping= NATOPS 11.5 Mast Bumping:

Mast bumping occurs when the rotor exceeds its critical flapping angle and the underside of the rotor hub contacts (bumps) the rotor mast. If contact is severe, mast deformation can occur and cause mast structural failure. Excessive rotor flapping can also cause rotor blade contact with the tailboom or cockpit. Mast bumping generally occurs at, but is not restricted to, the extremes of the operating envelope. The most influential causes are (in order of importance): Less significant causes are maximum sideward/rearward flight, sideslip, and blade stall conditions.
 * 1. Low g maneuvers (below +0.5g)
 * 2. Rapid large cyclic motion (especially forward cyclic)
 * 3. Flight near longitudinal/lateral cg limits
 * 4. High-slope landings

WARNING: Should mast bumping occur in flight, catastrophic results are highly probable. Since conditions causing rotor flapping are cumulative, improper pilot response/recovery techniques to flight situations approaching or favorable to mast bumping can aggravate the situation and lead to in-flight mast bumping and mast separation.

INDICATIONS: Sharp two-rev knocking (but really you're going to hear one knock, and then your mast will separate, your rotor leaves the scene, you go down and crater).

PROCEDURES:

-Max slope we can land on in the TH-57 is 7.5 degrees.

=CRM: Situational Awareness= What is Situational Awareness? Situational Awareness refers to the degree of accuracy by which one's perception of his current environment mirrors reality.

PERCEPTION VERSUS REALITY
 * View of Situation
 * Incoming information
 * Expectations & Biases
 * Incoming Information versus Expectations

FACTORS THAT REDUCE SITUATIONAL AWARENESS
 * Insufficient Communication
 * Fatigue / Stress
 * Task Overload
 * Task Underload
 * Group Mindset
 * "Press on Regardless" Philosophy
 * Degraded Operating Conditions