AFCS (OFT 8) Flashcards
What is the AFCS?
- automatic flight control system
- electrohydromechanical system
- 3 subsystems: SAS, Stab System, AFCC
What is the AFCC?
- commands SAS and trim actuators in C/P/R/Y channels
- located in nose bay
- 2 types of control: inner-loop and outer-loop
What is inner-loop control?
- SAS actuators
- fast control response
- limited to 10% authority
- does not move cockpit controls
What is outer-loop control?
- trim actuators (or autopilot)
- limited to 10% per second of rate response
- has full authority (100%)
- moves cockpit controls
What does the SAS do?
- Senses rate acceleration in P/R/Y
- inputs rate dampening for improved stability
What is SAS 1?
- analog
- P/R/Y only
What is SAS 2?
-digital
Same as SAS 1 but also has:
- hover augmentarion
- gust alleviation
- altitude hold
- coupler features
- turn coordination
- roll attitude hold
What kind of pressure and from what does SAS get px?
- SAS actuators get hyd px from PAS module via SAS shutoff valve
- controlled by SAS/BOOST pushbutton
When and why does the SAS caution illuminated?
- during loss of px OR when actuators lose electrical power (manual disengagement or power server)
- sensed by SAS px switch
With both SAS actualtors what is control authority?
-P/R/Y have +/- 10% authority
———–thats’s +/- 5% authority from each channel
What happens to control authority if either SAS fails?
What happens if SAS 1 fails?
What happens if SAS 2 fails?
- AFCS DEGRADED caution and SAS on fail cube
- remaining SAS works at +/- 5% control authority but at 2x the gain to compensate
- if SAS 1 fails: AFCC automatically disengaged affected axis
- if SAS 2 fails: pilot must manually disengage via AFCS panel
5 “Holds”
19 functions
- Attitude hold
- Airspeed hold
- Heading hold
- BARALT hold
- RADALT hold
5 “Hovers”
19 functions
- Auto approach
- Coupled hover
- Cable angle
- Crew
- Auto depart
3 “ations”
19 functions
- Turn coordination
- Hover augmentation and gust alleviation
- Stability augmentation (system)
Last 6
19 functions
MT DABS
- M = maneuvering stability
- T = trims
- D = diagnostic cubes
- A = auto pre-flight check
- B = blade fold assist
- S = stabiliator
Trim (19 functions)
-cyclic, collective, pedal
- pitch and roll have hydraulic trim servos (1000psi)
- collective and yaw have electric servos
-actuators command 100% control authority BUT are rate-limited to 10%/sec (outer-loop)
How do you disengage yaw trim?
A/S < 50 KIAS = pedal microswitch
A/S > 50 KIAS = pedal microswitch AND cyclic trim release
How do you disengage yaw trim?
A/S < 50 KIAS = pedal microswitch
A/S > 50 KIAS = pedal microswitch AND cyclic trim release
Maneuvering stability
-engages by pushing AUTO PLT pushbutton on
-in AOB > 30°……..
longitudinal trim actuator pushes cyclic forward in a turn to “increase pilot effort” (i.e. false g-loading)
- 1% of fwd cyclic per 1.5°AOB (between 30-70° AOB)
- @ 70° AOB = 30% fwd cyclic
Heading hold
Requirements, airspeed, re-engage
- to turn on: weight OFF wheels and AUTO PLT on
- disengaged with: WOW/on deck
- A/S < 50 KIAS: 3°/second
- A/S > 50 KIAS: 1°/click (less than a sec) OR 1°/sec
- to re-engage HH after turn, 2 things must be maintained for 2 seconds:
1. 2° of wings level
2. Yaw rate < 2°/sec
RADALT Hold
- any airspeed and 0-5000’ AGL
- RADALT, SAS 2, TRIM, AUTO PLT must be on
- to change altitude, collective trim must be held until at new alt.
- in hover coupler mode: altitude controlled with HVR ALT knob will be limited to 1000 fpm climb and 200 for descent (starts automatically within 2ft of selected altitude on HVR ALT)
BARALT hold
-turned on when BAR ALT, SAS 2, TRIM, AUTO PLT are on
- AFCC monitors engine Q and will stop collective increase if Q is pulled to:
- —‐—-106% (> 80 KIAS)
- ——–112% (< 80 KIAS)
-change altitude with collective trim release button (when depressed)
Attitude hold
- A/S < 50 KIAS and AUTO PLT engaged
- 4 way trim switch changes 5°/second
Airspeed Hold
Engaged with:
- AUTO PLT
- A/S > 50 KIAS
- AOB < 30°
-4 way teim switch controls at 6 KIAS/sec
Pitch/roll hover augmentation and gust alleviation
- controlled by SAS 2
- improved stability by maintaining attitude, lat/long acceleration to stop drift
Turn coordination
- allows pilot to fly coordinated turns with directional control from AFCS at > 50 KIAS
- udes lateral acceleration and roll rate to determine if in balanced flight
- done by yaw SAS and yaw TRIM
- engaged when heading hold off, and roll attitude is > 1° AND any of the following:
- ———–lateral cyclic > 3%
- ———–cyclic trim release pressed
- ———–roll attitude > 2.5° (using 4-way trim switch)
Hover coupler
- engaged after end of auto approach within 1kt of set airspeed OR manually within 5 kts
- with SAS 2, TRIM, AUTO PLT, APPR/HVR
- provides LAT/LONG groundswell control via LAT/LONG velocity potentiometers
- AFCC monitors dual-engine Q to prevent collective increase if Q reaches 116%
- warning, pay attention to airspeed, if you go above 50 KIAS you’ll be put on air speed hold
- limitednto 50kts fwd, 20 kts aft, 20 kts sideways
- cannot exceed 1000 fpm clim or 200 fpm descent
Crew hover
- allows aircrewman to contro/position hover when coupled
- aircrww cyclic authority rated at +/- 5 KIAS
- activatrd by CREW HVR pushbutton, but must be in coupled hover
