AFCS Flashcards
NATOPS Chap 2
AFCS System
The flight control system can be divided into 3 sections:
- Mechanical Control system
- Flight control servo system
- AFCS
NATOPS Chap 2
AFCS System
Where are the mechanical control systems routed?
The Cyclic, collective, and pedals are routed aft and outboard of each pilot seat. From there, vertically up the aircraft and are combined with overhead torque shafts in the hyds bay
NATOPS Chap 2
AFCS System
What do the overhead torque shafts do?
They transfer control inputs and trim inputs thru the pilot assist servos and the mixing unit. From the mixing unit, fore, aft, and lateral inputs are transferred to the sqashplate assembly via the primary servos and the bridge assembly. Yaw inputs to the tail rotor servo are transferred from the mixing unit aft to the tail rotor quadrant through the tail rotor cables
NATOPS Chap 2
AFCS System
If both tr cables are severed, what happens?
The two separate centering springs will counter the tr servo pilot valve positioning the tr servo for a neutral setting to provide a fly-home capability
NATOPS Chap 2
AFCS System
Functions of AFCS (5 Holds, 5 Hovers, 3 Stabs, 2T’s, AABD)
- Pitch and roll att hold
- Arspd Hold
- HDG hold
- BarALT hold
- RADALT hold
- Pitch/roll hvr aug/gust alleviation
- Auto approach to hvr
- Hvr coupler
- Crew HVR
- Cable Angle HVR
- Pitch, roll, yaw stability augmentation
- Maneuvering Stability
- Stabilator Control
- Turn coord
- Cyclic, collective, pedal trim
- Automatic Depart
- Automatic Preflight Check
- Blade Fold Assist
- Diagnostics
NATOPS Chap 2
AFCS System
What two loops does the AFCC Employ?
1) Inner Loop- employs a rate damping to improve
dynamic helo stability. This is fast in response,
limited in authority, and operates without movement
of the flight controls
2) 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% authority, at a limited rate of 10%
per second.
NATOPS Chap 2
AFCS System
What positions the STAB?
Two electric jackscrew actuators that operate in series.
Each actuator provides 1/2 the input to position the Stab and is controlled by a separate, redundant stabilator amplifier
NATOPS Chap 2
AFCS System
What inputs position the stab?
Collective position
Lateral Acceleration
Arspd
Pitch rate
NATOPS Chap 2
AFCS System
What does SAS 2 have that SAS 1 does not?
Hover augmentation, and Alt hold/hover coupler features.
NATOPS Chap 2
AFCS System
With both SAS engaged…. (what is the control authority)
Pitch, roll, and yaw actuators have 10% control authority with each channel providing +-5%. If one fails, the other operates at twice the gain
NATOPS Chap 2
AFCS System
Trim system uses..
Two high-torque electric servos for yaw and collective, and two hyd servos for pitch and roll
NATOPS Chap 2
AFCS System
The trim actuators are limited to..
10%/sec.
NATOPS Chap 2
AFCS System
Attitude and arspeed hold
<50KIAS= attitude hold.. using 4 way trim= 5*/sec
> 50KIAS <30* AOB= arspeed hold.. 4 way trim= 6KIAS/sec
NATOPS Chap 2
AFCS System
HDG Hold
<50KIAS= a/c slewed at 3*/sec using the HDG trim
> 50= Actuation of switch for <1 sec= 1* HDG change for
>1 sec = 1* coordinated turn
HDG hold is reengaged follow a turn when the following
conditions are met for 2 sec:
a/c roll attitude is within 2* of wings level
Yaw rate is < 2*/sec
NATOPS Chap 2
AFCS System
Turn Coordination
Provided at airspeed > 50 and is engaged when roll attitude is > 1* and:
- ) Lateral cyclic displacement is > 3%
- ) Cyclic Trim REL button is pressed
- ) Roll attitude exceeds 2.5* bank angle using 4-way trim
- ) Collective HDG TRIM switch is toggled for more than 1 second.
NATOPS Chap 2
AFCS System
Maneuver Stability
Cyclic commanded forwward 1% for every 1.5* AOB in between 30-75* AOB
NATOPS Chap 2
AFCS System
WARNING for Auto approach
Initiating an auto approach while in a trimmed turn may result in a spiraling approach that will continue thru selected altitude
NATOPS Chap 2
AFCS System
Hover coupler
Engages when longitudinal groundspeed is w/i 1 kgs, or w/i 5 kgs if engaged manually, and a/c alt is w/i 2 ft of selected altitude
NATOPS Chap 2
AFCS System
Hover coupler torque limit
Torque will be limited to 116%
NATOPS Chap 2
AFCS System
Approach profile..
Above alt= 360 ft/min descent
Below alt= 2.5 kt/sec decel
On profile >40 kt= 215 ft/min and 2.5 kt/sec
On prof <40 kt= 130 ft/min, 1.5 kt/sec
NATOPS Chap 2
AFCS System
Auto depart
Aims for 120kt and 150ft. Will climb at 240 ft/min and accelerate at 3 kt/sec below 85kt.
> 100KIAS = 1 kt/sec acceleration
NATOPS Chap 2
AFCS System
Describe the 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 the blade pitch angle through the pitch-change links
NATOPS Chap 2
AFCS System
How does the Tail rotor quadrant system work?
It transmits tail rotor cable movement to the tail rotor servo. Two spring cylinders connected to the quadrant allow cable tension to be maintained if either tial rotor cable becomes severed.
NATOPS Chap 2
AFCS System
What activates teh TAIL ROTOR QUADRANT caution?
When either cable is broken, 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 postioning the tail rotor to a neutral setting to provide a fly-home capability
NATOPS Chap 2
AFCS System
What is the AFCS Voltage Sensor Relay?
The VSR is mounted on the forward side of the cockpit canted bulkhead and is designed to select the source of the single phase, 115 VAC, phase B power to be applied to the AFCC. Only one source can feed the AFCC at a time.
The VSR also controls the AC Essential bus relay. The AFCC is powered by the No. 1 AC primary bus but if the volatage is not within tolerance, the VSR deenergizes and the AC Essential bus and the AFCC are powered from the No 2. AC Primary bus
NATOPS Chap 2
AFCS System
What is the primary purpose of the Stab?
The primary purpose is to provide angle of attack stability.
NATOPS Chap 2
AFCS System/Cable Angle
When the ALFS is airborne (being lowered/raised) how does the Cable Angle system measure the angular displacement?
It is measured in reference to the center of the funnel relative to the aircraft orientation.
NATOPS Chap 2
AFCS System/Cable Angle
When the ALFS is in the water with a DOME WET indication, how does the Cable Angle system measure the angular displacement?
The AFCS uses inputs to maintain the cable perpendicular to the water surface while keeping the aircraft in a stable hover.
NATOPS Chap 2
AFCS System/Cable Angle
How long does the decoupling last each time dome raising/lowering is stopped or started in the water?
the decoupling lasts for approximately 9 seconds, during which time the cable angle signal received form the RMIU is subject to a 1 deg/second rate of change limit in the AFCC
NATOPS Chap 2
AFCS System/Cable Angle
When does Cable angle hover mode disengagement occur?
Disengagement occurs automatically when teh dome is reeled up through the 27 +- 12 foot water depth, or when the pilot presses the CABLE ANGLE pushbutton switch.
NATOPS Chap 2
AFCS System
When is the Automatic preflight check initiated? (BREWS)
1) Both EGI attitudes valid
2) Rotor Brake On
3) Engine Torques below 10%
4) Weight on wheels
5) SAS 1 pushbutton engaged (after AFCC on for at
least 20 sec)
