AFCS / STAB SYS Flashcards
The AFCS is what type of system?
electrohydromechanical
Define inner-loop.
Inner-loop is our SAS capability which employs rate dampening to improve stability.
It has fast response and limited authority.
Operates without movement of the flight controls.
Define outer-loop.
Outer-loop (auto-pilot) provides long term inputs by trimming the flight controls with 100% authority to move the flight controls through their full range of motion, at a limited rate of 10% per second.
What is the CILA? What is it commanded by?
the collective inner-loop actuator (CILA) is commanded by SAS 2.
the collective SAS operates with RADALT, BARALT, APPR/HVR, and DEPART modes engaged and is limited to +/- 10% control authority.
What is the difference between SAS 1 and SAS 2?
SAS 1 is an analog system. SAS 2 is a digital system.
Their functions are identical except that SAS 2 also provides: hover augmentation/gust alleviation, altitude hold/coupler features, turn coordination, and roll attitude hold.
SAS 1 is not linked to the AFCC.
With both SAS channels engaged, the pitch, roll, and yaw actuators have ______ control authority with each channel providing ______.
+/- 10%, +/-5%
When does the [SAS] caution appear?
if SAS 1 and SAS 2 lose electrical power or when hydraulic pressure is lost to the actuators
What happens when one SAS channel fails?
if either channel malfunctions, the [AFCS DEGRADED] caution appears.
if SAS 2 fails, the AFCC will auto-disengage the affected axis. if SAS 1 fails, the pilot must manually disengage SAS 1.
the remaining operable SAS channel is limited to +/-5% control authority, but operates at 2x it’s normal gain to partially compensate for the failed channel.
List the 19 functions of the AFCS.
5 Holds: Attitude Hold Airspeed Hold Heading Hold RADALT BARALT
5 Hovers: Automatic Approach Automatic Departure Hover Coupler Crew Hover Cable Angle Hover
3 "-ations": Stability augmentation Hover augmentation / gust alleviation Turn coordination
MTDABS: Maneuvering stability Trim Diagnostics (fail advisory) Automatic preflight checks Blade fold Stabilator control
Attitude Hold
engaged with the autopilot pushbutton.
attitude hold is used < 50 KIAS and commanded through cyclic trim release or 4-way trim.
auto-leveling transitions helo from left wing down in a hover to wings level at 50 KIAS.
Airspeed Hold
engaged with the autopilot pushbutton above 50 KIAS and AOB < 30 degrees.
Heading Hold
engaged with autopilot and WoffW.
trim switch on collective will slew HDG at 3 deg/sec. when < 50 KIAS.
> 50 KIAS: 1 sec. click = 1 deg. HDG change or 1 deg/sec coordinated turn
Altitude Hold (BARALT / RADALT)
engaged with SAS 2, trim, and autopilot engaged.
AFCC monitors torque and will stop collective increase if <80 KIAS torque rises to 120% or >80 KIAS torque rises to 106%.
BARALT: AFCC uses the air data transducer as the reference altitude
RADALT: AFCC uses radalt info as reference, can be engaged at any altitude 0-5000’ AGL
Automatic Approach
can be initiated at any airspeed and altitude < 5000’ AGL
On profile >40kts: 215fpm descent / 2.5kt/sec decel.
On profile <40kts: 130fpm descent / 1.5kt/sec decel.
Above profile: 360 fpm descent / airspeed hold
Below profile: RADALT hold / 2.5kt/sec. decel.
Automatic Departure
can be performed from a coupled hover or automatic approaching will terminate at 150’ / 120kts
Profile:
< 85kts: 3kt/sec accel. / 240fpm climb
>100kts: 1kt/sec accel. / 240fpm climb
AFCC monitors torque to prevent increase >120% below 80kts and above 106% above 80kt.
Hover Coupler
engages when:
- within 1 KGS of longitudinal velocity selected
- within 5 KGS if manually engaged
- RADALT engaged within 2’ of hover altitude selected
AFCC monitors torque to prevent increase above 116%
Crew Hover
aircrew able to position aircraft in a coupled hover with +/- 5 KGS of authority from lat/long velocities selected
Cable angle hover display references
submerged: cable’s vertical angle relative to the surface of the water
not submerged: cable’s vertical angle relative to the center of the funnel
Cable angle hover display associated numbers and cautions/warnings:
Inner ring = 4.25 degrees
Outer ring = 8.5 degrees
Tick marks = 2 degrees
If the 4.25 inner ring is exceeded as the dome is leaving the water, there is an increased risk of the transducer striking the aircraft which may result in aircraft damage.
If the 8.5 outer ring is exceeded while the dome is leaving the water there is a significantly increased risk of the dome striking the aircraft, including the rotors which may result in aircrew injury or death.
How long does it take the AFCS to calculate a solution for current, winds, sea state, etc. in cable angle hover?
25 seconds
Hover Augmentation / Gust Alleviation
provided by SAS 2 and further improves the aircraft’s stability at low airspeeds by using attitude retention and lat/long acceleration to eliminate drift
Turn Coordination
provided > 50kts.
turn coordination is engaged and heading hold is disengaged when roll attitude > 1 degree and:
- lateral cyclic displacement > 3 degrees
- cyclic trim release depressed
- roll attitude > 2.5 deg. bank angle
- collective heading trim toggled > 1 second
Maneuvering Stability
as the aircraft exceeds 30 degrees AOB, increased pilot effort is required to maintain pitch rate.
higher pitch control forces are used to alert the pilot to G-loading during flight between 30-75 degrees AOB.
Trim
provided through two electric trim servos (yaw and collective) and two hydraulic trim servos (pitch and roll)
command full control authority, limited to 10%/sec.
trim is an outer-loop autopilot function
Diagnostic Fail Advisory
fail cubes in AFCS panel can be acknowledged via the red button and cleared by pushing the cubes
Automatic Preflight Checks (requirements)
“BREWS”
on AFCS ground check we check SAS 1 for 10 seconds to ensure the rate gyros are functioning properly.
following conditions must be present (BREWS):
- both EGI attitudes valid
- rotor brake on
- engine torque < 10%
- WOW
- SAS 1 engaged
Blade Fold
AFCS commands trim actuators to drive flight controls to a predetermined position.
at that position, electromechanical pitch-lock actuators lock the pitch change horns and then the sequence starts.
The stabilator is what type of system?
automatic fly-by-wire system
What is the primary purpose of the stab?
to provide AOA stability by maintaining a level attitude in forward flight and eliminating undesirable nose-up attitudes caused by rotor downwash at low airspeeds
There are ___ _______ ______ actuators in series that each provide ____ the input and are controlled by separate stab amplifiers.
two electrical jackscrew, 1/2
Name the four control inputs required to position the stab.
“CLAP”
- Collective postion
- Lateral acceleration
- Airspeed
- Pitch rate
If there is a difference in stab actuator positions, what will happen?
that will result in an automatic shutdown to both actuators
How many degrees is the stab limited to if it’s failed full-down? Full-up?
full-down = restricted to 35 degrees full-up = restricted to 30 degrees
The stab indicator is powered by what system? The ability to slew the stab?
stab indicator = AC powered
slew the stab = DC powered
Cable angle corrective pilot action (in order)
- Use cyclic trim (4-way).
- Fly against lateral trim.
- Use trim release button.
- Fly against longitudinal.
