AFCS and MMU Flashcards
What is the purpose of the Mechanical Mixing Unit (MMU)? Explain.
Designed to reduce inherent control coupling and reduce pilot workload.
Increasing collective will cause the nose of the helicopter to turn to the right due to increased torque . This one of many examples of inherent coupling.
What are the different inputs provided by the mechanical mixing unit?
Collective to Pitch mixing compensates for the downwash on the aft fuselage and stabilator. As COLLECTIVE is INCREASED the MAIN ROTOR tilts FORWARD slightly. As COLLECTIVE is REDUCED the MAIN ROTOR tilts AFT slightly.
COLLECTIVE to ROLL compensates for translating tendency. As COLLECTIVE is INCREASED the MAIN ROTOR is tilted slightly LEFT. As COLLECTIVE is REDUCED the MAIN ROTOR is tilted slightly RIGHT.
COLLECTIVE TO YAW compensates for the torque effect of the main rotor. As COLLECTIVE is INCREASED TAIL ROTOR PITCH is INCREASED. As COLLECTIVE is REDUCED TAIL ROTOR PITCH is DECREASED.
YAW to PITCH compensates for tail rotor lift vectors. As TAIL ROTOR PITCH INCREASES the MAIN ROTOR DISK is tilted slightly AFT. As TAIL ROTOR PITCH DECREASES the MAIN ROTOR DISK is tilted slightly forward.
Describe electronic coupling.
COLLECTIVE TO AIRSPEED TO YAW mixing is NOT A FUNCTION OF THE MMU. IT IS A FUNCTION OF THE SAS/FPS computer. Electronic coupling helps compensate for the torque effect of the main rotor along with collective yaw mixing of the MMU, by increasing or decreasing tail rotor pitch through the yaw trim actuator. The yaw trim actuator varies its inputs based on the collective position and airspeed signals.
Max mixing occurs from 0 to 40 KIAS and is reduced as airspeed increases above 40 KIAS until 100 KIAS is reached and mixing is reduced to zero. At airspeeds above 40 KIAS the tail rotor and cambered vertical fairing become more efficient to where electronic coupling is no longer required.
SAS/FPS may override this function as need to maintain heading hold or turn coordination.
Describe Stability Augmentation System (SAS)
The H60 has two SAS systems (SAS 1 & 2) that help maintain a stable platform in flight by providing short term rate dampening in the pitch roll and yaw axes.
SAS 1 is analog and SAS 2 is digital meaning SAS 2 has self diagnostic capabilities while SAS 1 does not. A failure of SAS 1 is indicated by erratic rotor tip path and “knocking” of the controls. A failure in SAS 2 results in illumination of the SAS/FPS fault advisory lights.
SAS provides control inputs to the flight control surfaces without moving cockpit controls. Each SAS has 5% control authority for a combined 10%. Control authority is the amount of input a system can make compared to how much the pilot can move those controls.
Both SAS utilize hydraulic pressure from the #2 system which is applied to the SAS actuators in the over head cowling.
If one SAS malfunctions the other SAS will double its gain or sensitivity. The effect is the pilot wont notice much difference in the handling qualities of the aircraft.
What controls SAS 1? From where does SAS 1 receive its signals?
SAS 1 is controlled by the SAS 1 amplifier located in the avionics compartment.
SAS 1 receives a PITCH signal from the #1 STABILATOR AMPLIFIER, a ROLL signal from the PILOT’S VERTICAL GYRO, and a YAW signal from an INTERNAL RATE GYRO.
What controls SAS 2? From where does SAS 2 receive its signals?
SAS 2 is controlled by the SAS/FPS computer located aft of the lower console.
SAS 2 receives a PITCH signal from the #2 STABILATOR AMPLIFIER, a ROLL signal from the ROLL RATE GYRO, and a yaw signal from the YAW RATE GYRO.
Describe Flight Path Stabilization (FPS)
The FPS provides long term rate dampening in the pitch roll and yaw axes.
FPS also provides basic auto pilot functions using the trim actuators to maintain attitude hold in the pitch and roll axes, and heading hold and turn coordination in the yaw axis. When coupled with TRIM, FPS has 100% control authority.
How does FPS use the PITCH axis?
Utilizes PITCH TRIM ASSEMBLY to make pitch attitude adjustments.
PITCH TRIM ASSEMBLY is ELECTRO- HYDROMECHANICAL, meaning is it is electronically controlled and converts hydraulic pressure into mechanical movement.
BELOW 60 KIAS provides ATTITUDE HOLD.
How does FPS use the ROLL axis?
Utilizes the ROLL TRIM ACTUATOR to make roll attitude adjustments.
ROLL TRIM ACTUATOR is ELECTRO-MECHANICAL and utilizes an electric motor to drive its output linkage.
ATTITUDE HOLD provided REGARDLESS OF AIRSPEED.
How does the FPS use the YAW axis?
Utilizes the YAW TRIM ACTUATOR to make yaw adjustments.
The yaw trim actuator is ELECTRO-MECHANICAL
BELOW 60 KIAS provides HEADING HOLD
ABOVE 60 KIAS provides HEADING HOLD and TURN COORDINATION.
To enter turn coordination the cyclic must be displaced 1/2 in. and a roll attitude of 1.5 degrees or greater.
What is needed for FPS to function properly?
SAS 1 and/or SAS 2, BOOST, AND TRIM. The STABILATOR enhance FPS but is not required.
How is an FPS failure detected and what are the indications and response?
SAS 2 FPS computer constantly monitors the trim actuators when FPS is on.
If a failure is detected both MASTER WARNING CAUTION LIGHTS, FPS, and TRIM caution lights will illuminate.
If of an INTERMITTENT nature POWER ON RESET. If continuous the affected axis can be controlled manually with no FPS or force gradient in that axis.
What components comprise the TRIM system? What does TRIM provide?
PITCH TRIM ASSEMBLY (ELECTRO-HYDROMECHANICAL)
ROLL TRIM ACTUATOR (ELECTRO-MECHANICAL)
YAW TRIM ACTUATOR (ELECTRO-MECHANICAL)
TRIM by itself provides a force gradient in the pitch roll and yaw axes.
What does proper operation of the YAW TRIM ACTUATOR require?
The yaw boost servo must be pressurized and operational
What do the ELECTRO-MECHANICAL ACTUATORS provide that allow the pilot to overcome an internal jam of the actuators?
Slip clutches allow the pilot to break though the clutches in the even of an internal jam. Force required to break through the clutch is 80 lbs. max (yaw) and 13 lbs max (roll).
