NATOPS Flashcards
Primary Fuel
A fuel that the aircraft is authorized to use for continuous unrestricted operations.
Restricted Fuel
A fuel that imposes operational restrictions on the aircraft.
Emergency Fuel
A fuel which may be used for a minimim time when no other primary or restricted fuel is available in case of emergency or operational necessity.
What are our primary fuels?
JP-5, JP-8, A++ (F-24), TS-1
What are our restricted fuels?
A1, A, JP-4, B
What are our emergency fuels?
JP8+100, F-27
What engine does the MH-60R have?
T700-GE-401C engine
5 sections: inlet, compressor, combustion, turbine, and exhaust.
Compressor Section
5 stage axial, single stage centrifugal
Where is TGT sensed?
Between the gas-generator and power turbine.
Engine Airflow Distribution
30% of total airflow used for the combustion process. The rest is utilized for:
- Compressor inlet temperature (T2) air
- Compressor discharge pressure (P3) air
- Combustor and turbine cooling
- Engine oil seal pressurization
What engine governing is retained with PCLs in LOCKOUT?
Np overspeed protection
TGT limiting, Np governing, and load shading are deactivated
Functions of the Engine-Driven Fuel Boost Pump
- Provide reliable suction feed from the aircraft fuel tank to the engine
- Provide discharge pressure to satisfy the minimum inlet pressure requirement of the HMU or high-pressure fuel pump.
HMU fuel is tapped off for what purposes?
- Positioning a metering valve to ensure proper fuel flow to the engine.
- Position a servo piston that actuate the variable geometry van servo and start bleed valve.
- Amplifying various signal (T2, P3, Ng) that influence fuel flow and variable geometry servo position.
HMU responds to the PCL for what?
- Fuel shutoff
- Setting engine start fuel flow with automatic acceleration to ground idle
- Setting permissible Ng up to maximum
- Fuel priming
- EDECU override capability (LOCKOUT)
Why is power available in FLY normally more than required?
- Fail-safe to high power (loss of torque motor electric signal)
- Power available with OEI (gas generator can increase power up to its limit
Functions of the HMU
RANNAF
- Rapid engine transient response through collective compensation
- Automatics fuel scheduling for engine star
- Ng overspeed protection (110 +- 2%, centrifugal valve secures fuel flow)
- Ng governing (T2, P3, Ng governing through 3D cam)
- Acceleration limiting (Ng governor protects PCL motion from damaging engine)
- Flameout and compressor stall protection (via VGV and AI/SBV position)
Functions of the ODV
- Provide main fuel flow to the 12 fuel injectors during engine start and operation
- Purge the main fuel manifold overboard, after engine shutdown, through a shutoff and drain valve to prevent coking of the fuel injectors
- Traps fuel upstream, which keeps the fuel/oil heat exchanger full, so that system priming is not required prior to the start
- Returns fuel back to the HMU if the Np overspeed is energized or if the EDECU hot start preventer is activated
Engine limiting definitions
Protect engine components and/or reaching a max possible outcome based on ambient conditions and collective setting
TGT-limiting is defined by reaching either IRP or CRP functions within the EDECU.
HMU-fuel flow limiting is defined by engine control system limiting the max power output under the following:
- Max fuel flow limited by the physical size of the fuel lines within the HMU and ODV
- HMU protecting compressor section by limiting fuel flow as a function of Ng and ambient temp
Increasing the collective during either of these will result in a droop in rotor speed below 100%, no increase in Ng or TGT, and a slight increase in torque within the range of continuous Np limits.
Engine limit condition definition
Torque limited condition is a transmission limit defined by reaching a Chapter 4 limit.
TGT-limited is an engine limit defined by reaching a Chapter 4 limit prior to reaching EDECU IRP, MRP, or CRP functions
Ng limited is an engine limit defined by reaching a Chapter 4 Ng limit.
If an engine is Ng limited and the collective is increased further, Nr will remain at 100% and Ng will increase (along with TGT and torque).
EDECU Operations
4N CHEF TASTEE
- Np governing - Actual Np compared to reference Np to compute speed error input signal
- Np overspeed protection - When Np>120%, ODV diverts fuel to inlet of HMU, causing flameout
- Np overspeed test - A/B buttons that re-reference Np to 96%
- Ng decay relight feature - turns on igniters for 5 seconds to attempt restart if Ng deceleration rate exceeded (>63%)
- Contingency power
- Manual: C-power switch on - TGT-limiting increased to 903, no further fuel flow increase at 891 +- 10
- Auto: enabled in OEI conditions (when one eng <50% torque); reset from 861 to 891 +- 10
- Dual-engine auto: requires Np <96%, greater than 3% droop between Np actual and reference, or 5%/sec Np droop rate - Hot start prevention - stops fuel flow when TGT >900 when Ng <60% and Np <50%; restored after TGT <300 or 25 sec
- Engine load sharing - torque matches lower torque engine by increasing power without affecting higher engine
- Fault diagnostic - displayed numerically on torque indicator (4 sec on/2 sec off); verify clear with TGT >425, PCL in IDLE/FLY
- TGT limiting - prevents further fuel flow to engine when TGT 866 +-10; Np/Nr will droop <100% and Ng governing will be sacrificed to protect against overtemp
- Auto-ignition system - turns on igniters for 5 sec when Np overspeed condition reached; will continue until Np/Nr controlled
- Cockpit Signals - provides Np, TGT, and torque to VIDS
- Transient droop improvement (TDI) - initiates power turbine acceleration why using anticipatory signals from TDI Nr sensor (good for autos)
- Eng speed trim - INCR/DECR switch, adjust Np between 96-101%
- EDECU lockout - PCL manually controls Ng and Np; deactivates TGT limiting, Np governing, and load sharing; keeps Np overspeed protection
CEDECU Operational Modes
incorporates a discrete application selection (DAS) plug, which mates with the E-4 connector
Navy code: 35 +-2.9%
Army Black Hawk code: 15 +-2.9%
EDECU: 0%
Ways to anti-ice the engine
- Vent bleed air from engine swirl vanes and engine IGVs by the engine AI/SBV
- Vent bleed air into the airframe engine inlet by the engine inlet anti-ice valve
- Continuously pump engine oil through scroll vanes
What indicates a malfunctioning anti-ice/start bleed valve?
- Appeareance or disapperance of the ENG ANTI-ICE ON advisory when outside of the range specified in the chart (<80.5: Off, 80.5 - 96.5: On, >96.5: Off)
- No illumination of ENG ANTI-ICE ON advisory when switch is selected on
- No rise in TGT when ENG ANTI-ICE turned on (30-100 increase)
Max torque available is reduced by up to 18% per engine with ENG ANTI-ICE on
How to tell in engine inlet anti-ice valve is not working properly?
Appearance of INLET ANTI-ICE On when OAT >13 (should be fully closed by 13, variable between 4 and 13, fully open <4)
The resultant loss of torque could be a maximum of 49%
Advisory comes on when inlet temp reaches 93
Engine Parameter Sensing
Np and Torque - two pairs of teeth induce electrical pulses that measure torsion or twist of Np shaft, which is proportional to output torque (left provides Np signal to EDECU and VIDS, right feeds torque compensation circuit and Np overspeed protection)
Ng - alternator provides signal to VIDS
TGT - thermocouple harness of 7 thermocouples, signal has -71 bias; located between gas generator and power turbine
What is the path of flight control inputs?
Cockpit inputs –> out, upwards, and aft –> pilot assist servos –> mixing unit –> primary servos –> bridge assembly –> swashplate assembly –> pitch change rods –> pitch change horns –> spindle assembly –> blade
When are anti-flap restraints and droop stops activated?
Anti-flap restraints:>35% Nr
Droop stops: out at >70% Nr, seat at <50% Nr on shutdown
Main Rotor Blade description
Each blade has a pressurized hollow spar, honeycomb core, outer skin, abrasion strips, electrothermal deicing mats, and a removable swept-back blade tip fairing. The 20° swept tips provide both sound attenuation and increased rotor blade efficiency. An electrothermal blanket is bonded into the leading edge for de-ice capability. The abrasion strips bonded to the leading edge of the spar extend the useful life of the blades. The spar of the main rotor blade is pressurized with nitrogen.
Tail Rotor System
A bearingless, crossbeam tail rotor blade system provides antitorque action and directional control.
The tail rotor head and blades are installed on the right side of the tail pylon, canted 20° upward, and provide 1 2.5 percent of the total lifting force in a hover.
With a loss of both tail rotor control cables, a spring-tension feature of the tail rotor control system will provide positive pitch on the tail rotor equivalent to the antitorque requirements (left pedal) for a midposition collective power setting.
The tail rotor indexing system positions the tail rotor blades during pylon fold operations and prevents the tail rotor from windmilling in winds up to 60 knots with the tail in the folded position.
Tail Rotor Quadrant
Transmits tail rotor cable movements into the tail rotor servo. Two spring cylinders are connected to the quadrant. In the event a cable is broken, the quadrant will operate normally by controlling the remaining cable against spring tension.
AVCS
Consists of an AVC Computer (AVCC), ten feedback accelerometers sensors, and a Vibration Control Actuation System (VCAS).
The AVCS implements a closed-loop feedback control algorithm utilizing accelerometers as the feedback sensors and airframe-mounted force generators as actuators.
8 vertical, 2 lateral accelerometers
(4 pair) 1000 lb force generators
(1 pair) 500 lb force generator
Functions of XMSN System
The primary function of the transmission system is to take the combined power from the two engines, reduce the rpm, and transfer it to the main and tail rotors. The secondary function is to provide a drive for electrical and hydraulic power generation.
Main Transmission System Components
The MGB drives and supports the main rotor. It is of modular design with a built-in 3° forward tilt. The main transmission consists of five modules: two accessory modules, two input modules, and a main module.
The input module provides the first gear reduction between the engine and the main module.
The engine output shaft provides drive from the engine to the input module via the diaphragm coupling. The diaphragm coupling is designed to allow for slight angular or axial misalignment of the engine output shaft during operation.
Each accessory module provides mounting and drive for an ac electrical generator and a hydraulic pump module.
Nr Sensor Locations
An Nr sensor for the vertical instruments is mounted on the right accessory module.
The Nr sensor for the TDI and the main transmission low-oil pressure sensors are mounted on the left accessory module.
Main Transmission Lubrication System
The main transmission incorporates an integral wet sump lubrication system that provides cooled, filtered oil to all main transmission bearings and gears). The ac generators on the accessory modules also use transmission oil for cooling.
The PDI is visible above the sonobuoy launcher. An extended PDI button is an indication that maintenance is required after the last flight of the day; it is not a lubrication system malfunction indication.
Transmission Lubrication Pressure and Temperature Sensors
MAIN XMSN PRESS LOW - activated when psi <14, located on No. ! accessory module (arthest point from the pumps)
VIDS pressure reading - taken at MGB manifold inlet
MAIN XMSN HOT - activated when temp > 117°C, located at the oil
cooler input to the MGB manifold
VIDS temperature reading - sensed in the sump using a temperature
sensor that is embedded in the main module sump chip detector
Transmission Lubrication System Cautions and Advisories
- MAIN XMSN OIL HOT caution (yellow) — Generated when the oil temperature sensor is activated.
- MAIN XMSN OIL HOT advisory (white) — Generated when the main transmission oil temperature is >105 °C and the MAIN XMSN OIL HOT caution is not activated. The main transmission oil temperature vertical instrument tape may be yellow or red, depending on oil temperature value:
a. Yellow tape — If the oil temperature is greater than or equal to 105 °C and less than or equal to 120 °C.
b. Red tape — If the oil temperature is greater than 120 °C. - MAIN XMSN PRESS LOW caution (yellow) — Generated when the oil pressure sensor is activated.
- MAIN XMSN PRESS LO advisory (white) — Generated when the main transmission oil pressure is less than or equal to 30 psi, the rotor speed (Nr) is greater than or equal to 25 percent, and the MAIN XMSN
PRESS LOW caution is not activated. The main transmission oil pressure vertical instrument tape may be yellow or red, depending on the oil pressure value:
a. Yellow tape — If the oil pressure is greater than or equal to 20 psi and less than or equal to 30 psi.
b. Red tape — If the oil pressure is less than or equal to 20 psi. - MAIN XMSN PRESS HI caution (yellow) — Generated when the main transmission oil pressure is >130 psi. The main transmission oil pressure vertical instrument tape will be red.
- MAIN XMSN PRESS HI advisory (white) — Generated when the main transmission oil pressure is between 65 -130 psi and the MAIN XMSN PRESS HI caution is not activated. The main transmission oil pressure
vertical instrument tape will be yellow.
Main/IGB/TBG Chip Detection System
The main transmission chip detector system consists of five chip detectors, each with a corresponding caution. The accessory chip detectors are located in the return lines of the No. 1 and No. 2 accessory modules. The chip detectors for the input modules and main module are located in the main module.
Each chip detector has a burnoff feature, which eliminates false warnings created by fuzz and minute particles. The fuzz burnoff feature is deactivated when oil temperature is above 140 °C; however, magnetic detection will remain. The chip detector for the main module sump rests in the lowest point of the oil system, contains an embedded temperature sensor, and incorporates a 30-second time delay to further eliminate false warnings.
The IGB and TGB contain identical chip detectors that contain an embedded oil temperature switch. When the oil temperature reaches 140 °C, the INT XMSN OIL HOT or TAIL XMSN OIL HOT caution will appear. The loss of oil will preclude proper operation of the oil temperature warning system.
CHIP IBIT Test
The CHIP IBIT takes approximately 2 minutes to verify circuitry and checks the individual chip detectors. For approximately the first 40 seconds of the test, 28 Vdc is interrupted and WCAs and MASTER CAUTION lights will not correctly respond.
Fuel System Summary
The fuel system is a crashworthy, suction-type system with a self-sealing main tank. The system is capable of pressure refueling, gravity refueling, and Helicopter In-Flight Refueling (HIFR). It has provisions for priming the engines, dumping fuel, indicating fuel quantity, and warning of low fuel levels.
Main Fuel Cell
The main tank system is composed of two cells interconnected to form one tank. The system capacity is 590 usable gallons (4,012 pounds when fueled with JP-5). The lower one third of the tank is self-sealing. The main cells’ interconnect level is approximately 270 to 600 pounds per side.
Fuel Transfer Fault/Fails
When a single valve or pump fails, the PUMP/VALVE FAIL caution will illuminate and the alternate pump or valve will supply fuel transfer capabilities.
If the AUTO FUEL XFER FAULT caution illuminates, this indicates a lack of fuel transfer from the auxiliary tanks to the main tanks. A lack of fuel flow may be caused by a failed closed transfer valve, both transfer/dump pumps inoperative, FMCP control failure, or a blockage in the associated fuel lines. Fuel in the auxiliary tank may be unavailable with an AUTO FUEL XFER FAULT.
Fuel Transfer Rules
Do not initiate unmonitored manual transfer to the main tank from auxiliary tanks until main tank is below 3,200 pounds. During manual auxiliary tank transfer, the main tank high-level sensor (float valves) should prevent overflow of the main fuel tanks.
When main fuel tank capacity has decreased approximately 300 pounds, check the manual fuel transfer system to ensure proper transfer.
At AUTO, the fuel management logic is not initiated until the main fuel tank fuel level depletes to approximately 2,640 pounds.
External Tank Jettison
Emergency jettison of external fuel tanks via the ALL STORE JETT pushbutton (PB) is inhibited when less than 40 gallons (approximately 272 lbs.) remain in the tank. SEL JETT must be used to jettison when less than 40 gallons (approximately 272 lbs.) remain in the tank. The fuel gauge for the external fuel tank reads in 50 lbs. increments. If the external fuel tank requires jettison and the fuel gauge reads 300 lbs. or less, SEL JETT should be used.
Fuel Quantity System
The fuel quantity indicating system incorporates a fuel probe mounted in each fuel cell. The tank probes are capacitance-type sensors that employ fuel as a dielectric to measure the weight of the fuel in each tank.
When a main tank falls below the Low Fuel Level Sensor caution level, the MAIN FUEL tape and readout turn yellow.
Fuel Low-Level Warning System
The fuel low-level warning system has two separate and independent indications to alert the aircrew of a low-fuel state. When the fuel level in one of the fuel cells reaches 300 pounds, the #1/#2 FUEL LOW caution appears and the associated digital fuel readouts on the mission and flight displays turn yellow. When total fuel reaches 600 pounds, the total fuel display also turns yellow.
In order to minimize aircrew desensitization when fuel washes on and off the sensors, the master caution will be displayed when a fuel low condition is detected for a period > 5 seconds and will be deactivated when the condition is not detected for a period of 20 seconds.
HIFR System
The HIFR system consists of a Wiggins quick-disconnect, pressure-refueling fitting, a pressure-refueling precheck switch to allow the high-level sensors to be checked from inside the aircraft, and a five-element (fuse) GO/NO GO canister.
Flow is reduced to an extremely low level if the fuel is contaminated with water and particulate matter. Once a 20-psi pressure differential exists, fuel flow stops.
APU
The APU is a gas turbine engine consisting of a power section, a reduction gearbox, appropriate controls, and accessories. Fuel consumption at rated power is 150 pounds per hour.
The minimum accumulator pressure required for starting the APU is approximately 2,650 psi. With ac power available, the accumulator is charged by the backup hydraulic pump.
APU Start System
With the FUEL PUMP switch in the APU BOOST position, pressurized fuel is supplied from the right fuel cell by the prime/boost pump. The fuel control governs and meters fuel flow to the APU power section, permitting automatic starting under all ambient conditions and constant speed operation once the APU has accelerated to its normal speed.
Placing the APU CTRL switch to ON initiates the start sequence. The DESU sends a signal to open the APU start valve, releasing the hydraulic accumulator charge to the starter. As the accumulator pressure drops below 2,650 psi, the APU ACCUM LOW advisory and ACCUM LO caution light appears, indicating that the accumulator pressure is low.
The APU ON advisory appears when the APU is on and operating normally.
Placing the APU GENERATOR switch to ON makes electrical power available. If the backup pump is cycled ON then to the OFF or AUTO position, it will remain on for one cycle of 90 seconds (180 seconds with winterization kit installed).
AC Electrical System
Primary ac electrical power is supplied by two oil-cooled 30/45-kVA, 115-volt ac, 3-phase, 400-Hz generators driven by the transmission accessory modules. Secondary ac electrical power is supplied by an air-cooled 35-kVA, 115-volt ac, 3-phase, 400-Hz generator driven by the APU.
Generator Control Unit
A Generator Control Unit (GCU) connects each respective generator to the ac electrical bus system, regulates generator output, and protects system components and circuitry against overvoltage, undervoltage, feeder fault, and underfrequency.
GCU Disconnection
- With WOW, if Nr droops below 94 percent, the GCU removes the main generator electrical input from the entire ac power distribution system.
- In flight, underfrequency protection is disabled and the generators will remain online until the Nr decreases to approximately 80 percent.
- A minimum of 97 percent Nr is required for the GCU to reconnect the generators to the ac electrical distribution system.
External Power Monitoring
External power is monitored for phase rotation, overvoltage, undervoltage, underfrequency, and overfrequency.
AC Bus Distribution
With both main generators operating normally, the No. 1 generator powers the No. 1 AC Primary, ac Essential, and AC Secondary buses; the No. 2 AC generator powers the No. 2 AC Primary and the ac Monitor bus.
If the APU generator is selected while both main generators are operating, the APU generator will not be connected to the ac bus distribution system.
Should either main generator fail, automatic bus switching limits the ac load to the available generator output.
AC Bus Load Priority
- The backup hydraulic pump (major load on the No. 1 AC Primary bus) will always be powered, if required.
- The mission avionics system is the major load on the AC Secondary bus and is the next priority. Tail rotor de-ice power is also supplied from this bus.
- The main rotor de-ice system is the only system powered from the AC Monitor bus and has the lowest priority of the major current-drawing components.
DC Electrical System
Two converters supply 28-volt dc power. The converters are powered by the No. 1 and No. 2 AC Primary buses, respectively. A 24-volt dc battery, located in the copilot seat well, is the primary source of power for APU starting and the secondary source of power for the dc essential bus and the Battery bus. With an 80 percent charge, normal battery life is 11 minutes for day operations and 9 minutes for night operations.
DC Bus Load
The No. 1 converter powers the No. 1 dc primary bus, the dc essential bus, and the battery bus. The No. 2 converter powers the No. 2 dc primary bus. The battery powers the Battery Utility bus.
If a single converter fails, the operating converter will pick up the load of the buses powered by the failed converter via automatic bus switching.
If both dc converters fail, the battery provides a source of emergency electrical power to the Battery Utility bus, the Battery bus (if the BATT switch is ON), and the dc Essential bus (if the battery is above a 35 percent charge). Power to the No. 1 and No. 2 dc Primary buses is dropped.
Battery Power Requirements
A 24-volt dc NiCad battery, located in the copilot seat well, is the primary source of power for APU starting and the secondary source of power for the dc essential bus and the Battery bus.
80% charge: 11 min / 9 min for day / night operations
40%: BATTERY LOW CHARGE caution
35%: DC Essential Bus dropped
30%: battery power may not be sufficient to activate the fire extinguisher (CAD).
Important Components of Each Bus:
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No. 1 Hydraulic System Summary
The No. 1 hydraulic system operates with rotors turning and supplies the first stage of the primary servos and the first stage of the tail rotor servo. System components include the No. 1 hydraulic pump, the No. 1 transfer module, the first stage of the primary servos, and the first stage of the tail rotor servo.
No. 1 Transfer Module
The No. 1 transfer module routes hydraulic fluid from the No. 1 hydraulic pump to the first stage of the primary servos and the first stage of the tail rotor servo. The No. 1 transfer module automatically routes hydraulic fluid from the backup pump if No. 1 hydraulic system pressure is lost.
The components of the No. 1 transfer module include a transfer/shuttle valve, pressure switch, first-stage primary servo shutoff valve, and first-stage tail rotor servo shutoff valve.
No. 2 Hydraulic System Summary
The No. 2 hydraulic system operates with rotors turning and supplies hydraulic pressure to the second stage of the primary servos and the pilot-assist servo assembly. System components include the No. 2 hydraulic pump, No. 2 transfer module, the second-stage primary servos, and the pilot-assist servo assembly.
Backup Hyd Pump
The backup hydraulic pump is identical to the No. 1 and No. 2 hydraulic pumps except that it is powered by an ac electric motor. An internal depressurizing valve reduces the output pressure of the backup hydraulic pump to aid startup of the electric motor.
When power is supplied to the pump, this valve is closed and 3,000-psi pressure is supplied to the hydraulic system. After 4 seconds on APU or external power, or 0.5 second with either main generator on, the pump will energize. The automatic low-level sensing switch, mounted on top of the pump, closes when fluid level is low, causing the BACK UP RSVR LOW caution to appear.
Automatic Backup Hyd Pump Initiation
- Loss of No. 1 hydraulic pump pressure (#1 HYD PUMP caution).
- Loss of No. 2 hydraulic pump pressure (#2 HYD PUMP caution).
- Loss of No. 1 hydraulic reservoir fluid (#1 RSVR LOW caution).
- Loss of pressure to the first stage of tail rotor servo (#1 TAIL RTR SERVO caution).
Utility Module
The utility module routes hydraulic fluid from the backup hydraulic pump to the No. 1 and No. 2 transfer modules, second stage of the tail rotor servo, rescue hoist, and APU accumulator. A pressure switch is located on the module sensing backup hydraulic pump output pressure and, if above a prescribed value, closes a circuit causing the BACKUP PUMP ON advisory to appear.
A priority valve is installed between the utility module and the rescue hoist to restrict hydraulic fluid to the rescue hoist in the event that backup hydraulic pressure decreases below a prescribed value. The utility module incorporates a velocity fuse, which secures fluid flow to the APU accumulator if flow rate exceeds a prescribed limit.
1 LDI Test
- # 1 RSVR Low Caution- Assume No.1 TR Servo; Backup Pump On; #2 TR Servo Openeda. #1 TR Servo Caution, Backup Pump On and #2 TR Servo On Advisory
2a. Leak Stops
a. Leak in #1 TR Servo: #1 Hyd supplies #1 servo, Backup supplies #2 TR servo
b. Cautions: #1 RSVR LOW, #1 TR SERVO; Advisories: BACKUP PUMP ON, #2 TR SERVO ON
2b. Leak Does not Stop
a. Complete Loss of #1 Rsvr Hyd Fluid: #1 HYD Caution -> flicker #1 PRI SERVO PRESS
b. Backup Hyd Pump supplies #1 Pri and TR Servo
Pilot Action
3a. Yes (Servo Switch 1st Off)
a. Loss of #1 PRI Servo; Backup Pump supplies #1 TR servo
b. Cautions: #1 HYD PUMP, #1 PRI SERVO PRESS, #1 RSVR LOW; Advisories: BACKUP PUMP ON
3b. No
Does Leak Stop?
4a. Yes (Leak upstream of #1 Transfer Module)
a. Backup Hyd supplies #1 Pri Servos, #1 TR Servos
c. Advisory: BACKUP PUMP ON
1 LDI Test
- # 1 RSVR Low Caution- #1 TR Servo off; Backup Pump On; #2 TR Servo Openeda. #1 TR Servo Caution, Backup Pump On and #2 TR Servo On Advisory
2a. Leak Stops
a. Leak in #1 TR Servo: #1 Hyd supplies #1 servo, Backup supplies #2 TR servo
b. Cautions: #1 RSVR LOW, #1 TR SERVO; Advisories: BACKUP PUMP ON, #2 TR SERVO ON
2b. Leak Does not Stop
a. Complete Loss of #1 Rsvr Hyd Fluid: #1 HYD Caution -> flicker #1 PRI SERVO PRESS
b. Backup Hyd Pump supplies #1 Pri and TR Servo
Pilot Action?
3a. Yes (Servo Switch 1st Off)
a. Loss of #1 PRI Servo; Backup Pump supplies #1 TR servo
b. Cautions: #1 HYD PUMP, #1 PRI SERVO PRESS, #1 RSVR LOW; Advisories: BACKUP PUMP ON
3b. No
Does Leak Stop?
4a. Yes (Leak upstream of #1 Transfer Module)
a. Backup Hyd supplies #1 Pri Servos, #1 TR Servos
c. Cautions: #1 HYD PUMP, #1 PRI SERVO PRESS, #1 RSVR LOW; Advisory: BACKUP PUMP ON
4b. No
a. Leak in Pri Servo 1st Stage; Partial Loss of Backup Hyd Rsvr fluid; Total loss of Backup Rsvr Hyd Fluid
b. Loss of #1 Pri Servos and #1 & #2 TR Servos
c. Cautions: #1 HYD PUMP, #1 PRI SERVO PRESS, #1 RSVR LOW, BACKUP RSVR LOW
2 LDI Test
- # 2 RSVR Low Caution- Pilot-Assist Servos Off;a. Boost servo Off; Cautions: SAS & AFCS DEGRADED
2a. Leak Stops
a. Leak in Pilot-Assist Servos: #2 Hyd supplies #2 servo, Pilot-Assist Servo function lost
b. Cautions: #2 RSVR LOW, BOOST SERVO OFF, SAS, AFCS DEGRADED
2b. Leak Does not Stop
a. Complete Loss of #2 Rsvr Hyd Fluid: #2 HYD Caution -> flicker #2 PRI SERVO PRESS
b. Backup Hyd Pump turned on, Pilot-Assist Servos turned on
Pilot Action
3a. Yes (Servo Switch 2nd Off)
a. Loss of #2 PRI Servo; Backup Pump supplies Pilot-Assist servos
b. Cautions: #2 HYD PUMP, #2 PRI SERVO PRESS, #2 RSVR LOW; Advisories: BACKUP PUMP ON
3b. No
Does Leak Stop?
4a. Yes (Leak upstream of #2 Transfer Module)
a. Backup Hyd supplies entire #2 Hyd system
c. Cautions: #2 RSVR LOW, #2 HYD PUMP; Advisory: BACKUP PUMP ON
4b. No
a. Leak in Pri Servo 2nd Stage; Partial Loss of Backup Hyd Rsvr fluid; Total loss of Backup Rsvr Hyd Fluid
b. Loss of #2 Pri Servos and Pilot-Assist Servos
c. Cautions: #2 HYD PUMP, #2 PRI SERVO PRESS, #2 RSVR LOW, BACKUP RSVR LOW, SAS, AFCS DEGRADED, BOOST SERVO OFF
Hydraulic Leak Test
Requirements to initiate:
1. Ac power.
2. BACKUP HYD PMP switch in the AUTO position.
3. All hydraulic reservoirs full.
4. Weight On Wheels.
5. Rotors engaged.
Satisfactory indications:
1. #1 RSVR LOW.
2. #2 RSVR LOW.
3. BACK UP RSVR LOW.
4. SAS.
5. BOOST SERVO OFF.
6. AFCS DEGRADED.
7. #1 TAIL RTR SERVO.
8. #2 TAIL RTR SERVO ON.
9. BACKUP PUMP ON.
10. MASTER CAUTION.
Flight Control - Mechanical Control System
- The cyclic, collective, and tail rotor pedal flight controls are routed aft and outboard of each pilot seat, vertically up each side of the aircraft, and are combined for each axis at the overhead torque shafts inside the hydraulics bay.
- The overhead torque shafts transfer inputs from the trim servos and flight controls through the pilot assist servos and the mixing unit.
- From the mixing unit, fore, aft, and lateral inputs are transferred to the swashplate assembly via the primary servos and the bridge assembly.
The yaw inputs to the tail rotor servo are transferred from the mixing unit aft to the tail rotor quadrant through the tail rotor cables.
Tail Rotor Control System
The tail rotor servo is mechanically actuated, but requires hydraulic pressure to operate the pitch change shaft, which moves the tail rotor pitch change beam, changing blade pitch angle through the pitch-change links.
The tail rotor servo is powered by either the No. 1 hydraulic system or the backup hydraulic system.
1. The tail rotor quadrant transmits tail rotor cable movement to the tail rotor servo.
2. Two spring cylinders connected to the quadrant allow cable tension to be maintained if either tail rotor cable becomes severed. Microswitches activate the TAIL ROTOR QUADRANT caution when either cable is broken.
3. Directional control of the tail rotor is maintained by the remaining spring. If both cables are severed, two separate centering springs will counter the tail rotor servo pilot valve positioning the tail rotor to a neutral setting to provide a fly-home capability.
Flight Control System Sections
- Mechanical control system.
- Flight control servo system.
- Automatic flight control system.
Primary Servos
There are three primary servos located in the hydraulics bay. Each primary servo has two stages that are independent and redundant with only the input linkage in common. Should one primary servo stage become inoperative due to pressure loss or a jammed input pilot valve, a bypass valve within the affected stage will automatically open, and the #1/#2 PRI SERVO PRESS caution will appear.
Pilot-Assist Servos
The pilot-assist servo assembly contains the boost servos, SAS actuators, and hydraulic (pitch and roll) trim actuators. Flight controls are operable without hydraulic pressure to the pilot-assist servos, but collective and yaw inputs will require considerable pilot effort. Hydraulic power is still required to move the primary servos.
Boost servos - collective, yaw, and pitch — located between the cockpit controls and the mixing unit that reduce cockpit control forces and SAS system feedback.
Control Mixing
Mechanical
1. Collective to yaw - Main rotor torque causes right nose yaw when collective is increased.
-Compensation: TR thrust is increased
2. Collective to lateral: Lateral lead (TR propeller effect) causes right drift when collective is increased
-Compensation: Rotor disk is tilted left
3. Collective to longitudinal: Rotor downwash on the stab causes nose pitch up and drifting aft when collective is increased
-Compensation: Rotor disk is tilted forward
4. Yaw to longitudinal: TR lift vector causes pitch down and forward drift when left pedal is applied
-Compensation: Rotor disk is tilted aft
Electronic
5. Collective/airspeed to yaw: Camber of tail rotor pylon varies side load with airspeed causes left nose yaw as airspeed increases
-Compensation: A portion of the main rotor torque compensation is provided by a trim input that is proportional to collective position and airspeed. The trim input is then progressively washed out as pylon side loads increase with airspeed.
AFCS Functions
19: 5 Hover, 5 Hold, PCSDAMBAT
- Pitch and roll attitude hold.
- Airspeed hold.
- Heading hold.
- Barometric altitude hold.
- Radar altitude hold.
- Pitch and roll hover augmentation/gust alleviation.
- Hover coupler.
- Crew hover.
- Cable angle hover.
- Automatic approach to hover.
- Pitch, roll, and yaw stability augmentation.
- Cyclic, collective, and pedal trim.
- Stabilator control.
- Diagnostics (failure advisory).
- Automatic depart.
- Maneuvering stability.
- Blade fold assist.
- Automatic preflight check.
- Turn coordination.
AFCS Functions
19: 5 Hover, 5 Hold, PCSDAMBAT
- Pitch and roll attitude hold - 5/6 °/sec <50 KIAS
- Airspeed hold - 6 KIAS/sec > 50 KIAS
- Heading hold - 3 °/sec < 50 KIAS, 1°/sec > 50 KIAS (within 2° of wings level, yaw <2°/sec)
- Barometric altitude hold
- Radar altitude hold - 0-5,000’ AGL (climb/descent 1000/200 fpm in hover) - SAS 2
- Pitch and roll hover augmentation/gust alleviation - SAS 2
- Hover coupler - within 1 KGS auto approach or 5 KGS manual; +-10 KGS 4-way. within 2 ft of radalt; max 116 torque
- Crew hover - +- 5KGS
- Cable angle hover - <5 KGS, with 10’ radalt, dome wet
- Automatic approach to hover - 2.5 kt/sec, 215 ft/sec >40 kt; 1.5 kt/s, 135 ft/sec <40; 360 ft/sec if above profile
- Pitch, roll, and yaw stability augmentation.
- Cyclic, collective, and pedal trim.
- Stabilator control.
- Diagnostics (failure advisories)
- Automatic depart - 120 KIAS/150’ AGL; 240 ft/min climb; 3 kt/sec <80 KIAS, 1 kt/sec >100 KIAS
- Maneuvering stability - >30° AOB: 1% fwd cyclic/1.5° AOB, 30-75° AOB
- Blade-fold assist.
- Automatic preflight check.
- Turn coordination - roll >1° and any of: lateral cyclic >3%, TRIM REL pressed, roll >2.5° using 4-way, HDG TRIM > 1sec
AFCC Control - Inner/Outer Loop
The AFCC employs two types of control, identified as inner-loop and outer-loop. The inner-loop (SAS) employs rate damping to improve dynamic helicopter stability. This system is fast in response, limited in authority, and operates without movement of the flight controls.
The outer-loop (autopilot) provides long-term inputs by trimming the flight controls to the position required to maintain the selected flight regime. It is capable of driving the flight controls through their full range of travel, or 100 percent authority, at a limited rate of 10 percent per second.
Stabilator Control
The stabilator is an automatic, fly-by-wire control system with a backup manual slew control. It is completely independent of the other two AFCS subsystems except for common airspeed sensors, lateral accelerometers, collective position sensor, and pitch rate gyros.
In low-speed flight, the purpose of the stabilator’s variable angle of incidence functionality is to eliminate undesirable nose-up attitudes caused by rotor downwash impinging on the stabilator. To accomplish this, the stabilator was designed to program so it aligns with rotor downwash in low-speed flight regimes.
Stabilator Inputs
- Collective position.
- Lateral acceleration.
- Airspeed.
- Pitch rate.
Stabilator Failure Travel Limits
Stabilator travel is restricted to 35° if an actuator fails in the full-down position or 30° if an actuator fails in the full-up position.
Stability Augmentation System
SAS 1 is an analog system; SAS 2 is a digital system that is part of the AFCC. SAS 1 and SAS 2 functions are identical except for the hover augmentation/gust alleviation and altitude hold/coupler features that are incorporated only into SAS 2. SAS 2 also complements the AFCC to provide turn coordination and roll attitude hold. With both SAS channels engaged, the pitch, roll, and yaw actuators have ±10 percent control authority with each channel providing ±5 percent.
Only SAS 2 commands the collective inner-loop actuator (CILA). The collective SAS operates with RAD ALT, BAR ALT, APPR/HVR, and DEPART modes engaged and is limited to ±10 percent control authority.
If either SAS channel malfunctions, the remaining operable SAS channel is limited to ±5 percent authority, but operates at twice its normal gain to partially compensate for the failed SAS channel.
Trim System
The trim system uses two high-torque electric servos for the yaw and collective axes and two hydraulic servos for the pitch and roll axes. The trim actuators command full control authority in all four control axes, but are rate-limited to 10 percent per second.
If cyclic trim is depressed and released while cyclic is in motion then trim is not engaged until cyclic motion stops.
Cable Angle Display
Outer Ring: 8.5°
Inner Ring: 4.25°
CABLE ANGLE AT LIMIT caution: 7.5°
Cable Angle Controls
Cable Angle: disengaged when TA raised through 27+-12 feet
Potentiometers: bias cable away from preset sensor calibration
-45° of rotation equates to 3° of cable angle bias to the AFCS; 90° of rotation equates to 10° of cable angle bias to the AFCS.
Requirements for Cable Angle to engage
Grounds speed +_ 5 kts, altitude hold within 10 feet of selected altitude, and a dome wet indication.
AFCS Preflight Check Requirements
- Weight on wheels signal.
- Rotor brake on.
- Engine torques below 10%.
- Both EGI attitudes valid.
- SAS 1 pushbutton engaged (after AFCC on for at least 20 seconds).