NATOPS CH2.9 Flight Control System Flashcards
Into what sections can the flight control system be devided?
- Mechanical control Section
- Flight Control Servo Section
- Automatic Flight Control Section
How do the mechanical control inputs get to the Swashplates?
Cyclic, collective, and trail rotor pedal inputs are routed aft and outboard of each pilot seat and vertically up the side of the aircraft (in the broom closet) where they are combinedat the overhead torque shafts inside the hyd bay
The overhead torque shafts transfer inputs from the from the trim servos and pilot controls through the pilot assist servos and mixing unit
From the mixing unit Fore/Aft/Lateral inputs are transfered to the stationary swashplate via the bridge assembly
Trim and Control Inputs -> Pilot Assist Servos -> Mixing Assembly -> Primary Servos -> Bridge Assembly -> Swashplates
How is the Tail Rotor System Actuated?
The Tail Rotor Servo is mechanically actuated (Tail Rotor Quadrant) but requires hyrdaulic pressure to operate the pitch change shaft (Tail Rotor Servo)
Describe the Primary servos
What if one fails?
Three primary servos have two stages that are indipendent and redundant.
Looking aft on the aircraft they are (from left to right think “Fat A Lady”) Forward, Aft, Lateral
Should one stage become inoperative the other will pick up the slack and the approriate PRI SERVO PRESS will illuminate
Which pumps operate which stage of the Tail Rotor Servo?
The No.1 Hyd system powers the first stage TR servo, the Backup Pump will operate the second stage in the event of a leak or if the TAIL SERVO switch is placed in backup
What does the Pilot Assist Servo Assmebly contain?
Which require Hyd power?
- Boost Servos
- SAS Actuators
- Hydraulic (pitch and roll) actuators
Controls are operable without hydraulic power but movements in the collective and Yaw inputs will require considerable effort. Primary servos require hydraulic pressure to operate
Name the Boost Servos and their order
There are three boost servos Collective, Yaw, and Pitch. All three plus the roll channel include SAS actuators
From left to right looking forward (think “Your Ready Plane Captain) Yaw, Roll, Pitch, Collective
Describe the Mechanical Control Compensations
- Collective to Yaw
- Increase in torque drives Nose right when collective is increased so TR thrust is increased
- Collective to Lateral
- TR Prop effect causes Helo dirft to right when collective is increase so MR disk is tilted left
- Collective to Longitudinal
- MR downwash on Stab pitches nose up when collective is increased so MR disk is tilted fwd
- Yaw to Longitudial
- TR lift vector pitches nose down with Left pedal applied so MR disk is tiled aft
Describe the electronic Control Compensation
The Camber of the trail rotor pylon varies side load with airspeed causing the nose to yaw left as airspeed increases so a portion of the trim MR torque compensation is washed out as airspeed increases
(pylon becomes more effective so less TR trim input is required)
Describe what the AFCC does and its control channels (Inner/Outer)
The Automatic Flight Control Computer commands the SAS actuators and trim actuators in all four channels. It employs two types of control the inner-loop system and the outer-loop system
The Inner-Loop system employs rate dampening (fast in response, limited in authority) it operates without flight control input. Think of this as the behind the scenes system that keeps you from over controlling
The Outer-Loop system provides long term inputs by trimming the flight controls to the position required to maintain the selected regime. This is the system that you will feel make inputs to hold alt/spd or conduct approaches
How much can the Outer-Loop move controls?
It is capable of moving the controls through the full control range, however it is limited to 10% per sec
What are the 19 functions of the Automatic Flight Control system?
- Automatic Preflight Check
- Blade-Fold Assist
- Cyclic, Collective, and Pedal Trim
- Pitch and Roll Attitude Hold
- Airspeed Hold
- Heading Hold
- Pitch and Roll Hover Augmentation/Gust Alleviation
- Turn Coordination
- Maneuvering Stability
- Radar Altitude Hold
- Barometric Altitude Hold
- Automatic Approach to a Hover
- Hover Coupler
- Crew hover
- Automatic Depart
- Pitch, Roll, and Yaw Stability Augmentation (SAS)
- Diagnostics (failure Advisory)
- Stabilator Control
- Cable Angle Hover
What is required to execute the preflight checks?
- Weight on Wheels
- Rotor Break On
- Engine Torque below 10%
- Both EGI attitude valid
- SAS 1 Push button Engaged (after AFCC on for 20 sec)
How does the AFCS contribute to the blade fold system?
The AFCS will position the cyclic, collective, and tail rotor pedals prior to the blade fold sequence
How many trim servos are there?
How much control do they have?
There are two high-torque electric servos (yaw and collective) and two hydraulic servos (pitch and roll)
They command full control authority but are rate limited to 10% per sec
How is setting pedal trim different from the others?
Below 50 KIAS pressing the trim release switches on the pedals will release the trim hold, however above 50 KIAS both the pedal trim and the cyclic trim release switches must be pressed to disengage/reengage pedal trim
When is Attitude Hold employed and what happens as you accelerate?
How much can you change attitde with the trim hat?
At airspeeds less than 50 KIAS the attitude hold feature is used. A wing leveling feature is added retrimming the aircraft as the aircraft passes through 50 KIAS
Using the trim hat you can change the pitch 5° per sec, and you can change the roll 6° per sec
When is airspeed hold used?
How much can you change the airspeed?
Airspeed hold is used above 50 KIAS and angles of bank less than 30°
Airspeed can be changed at a rate of 6 KIAS per sec
How much is heading hold slewed with the HDG TRIM switch? (Above and Below 50)
When is it reengaged?
Below 50 KIAS
Slewed 3° per sec
Above 50 KIAS
Less than a sec results in 1° heading change, greater than a sec results in a 1° per sec coordinated turn
Reengaged
After a turn, it is reengaged when the following conditions are maintained for 2 sec:
- Aircraft roll attitude is within 2° of wings level
- Yaw rate is less than 2° per sec
What does the Pitch & Roll Hover Augmentation and Gust Alleviation do?
Improves aircraft stability at low airspeeds bu using attitude retention, longitudinal acceleration, and leteral acceleration to eliminate drift
What does Turn coordination provide?
When is it engaged?
Turn coordination allowed the pilot to fly a coordinated turn at airspeed above 50 KIAS
It is engaged and heading hold is disengaged with roll attitude is greater than 1° and any of the following exist:
- Lateral cyclic displacement is greater than 3%
- Cyclic TRIM REL is pressed
- Roll attitude exceeds 2.5° AOB using the trim hat
What does Maneuvering Stability do?
It displaces the cyclic forward to increase pilot effort required to maintain a given pitch rate at bank angles greater than 30°
It provides 1% forward cyclic for every 1.5° AOB between 30-75° AOB
When can Radar Altimeter hold be engaged?
What happens if it fails?
It can be engaged between any altitude from 0-5000ft AGL and at any airspeed
If Radalt Hold fails, Baralt hold is automatically engaged
When may Barometric Hold be engaged?
Baralt Hold may be engaged at any altitude and airspeed
How does the AFCC deal with torque when moving the collective?
The computer monitors engine torque and will stop increasing the collective in the event that torque reaches or exceed 106% or 120% (above/below 80 KIAS)
When can you engage the Automatic Approach to a hover?
When should you not engage it?
The Auto Approach to a Hover can be engaged at any airspeed and any altitude less than 5000ft
Initiating an approach to a hover while in a trimmed turn may result in a spiraling approach that will continue through the selected altitude. Pilot action will be required to avoid water impact
What is the Auto Approach to a Hover Profile?
How much can it be altered?
- Above Profile: 360 ft/min, Spd hold
- Below Profile: 2.5 kt/sec, Alt hold
- On Profile >40 KIAS: 2.5 kt/sec 215 ft/min
- On Profile <40 KIAS: 1.5 kt/sec 130 ft/min
The deceleration can be controlled up to ±1 kt/sec, A 2 sec trim hat input will result in a full 1 kt/sec change
When will the Hover Coupler Enagage?
The Hover Coupler will engage with longitudinal groundspeed is within 1 KGS of selected speed after an automatic approach or within 5 KGS if engaged manually and when within 2 ft of the selected altitude
How much can you manipulate Ground Speed while in a hover with the Trim hat?
How fast will you climb and Descened using the POTS?
The Trim Hat will allow you to adjust longitudinal and lateral ground speed up to ±10 Knots
You can climb at 1000 ft/min and descend up to 200 ft/min
When can Crew hover be engaged and how much control authority does the creman have?
The CREW HVR pushbutton can only be activated if the hover couple mode is already engaged.
They have control authority of ±5 KGS laterally and longitudinally
What does the Auto Depart feature do?
When is it available?
The Automatic depart feature performs an automatic departure from a coupled hover or from an automatic approach to an airspeed of 120 KIAS and an altitude of 150 ft AGL.
It is available any time the auto pilot is engaged, airspeed is below 50 KIAS and RAD ALT hold is operational
What is the departure profile?
How do you cancel it?
Climb: 240 ft/min
Accel: 3 kt/sec (<85 kts) and 1 kt/sec (>100 kts)
When passing through 50 KIAS the aircraft will assume a wings level attitude if angle of bank is less than 5°, otherwise it will maintain a coordinated turn
Pressing the Cyclic trim release will cancel the acceleration, pressing the Collective trim release will cancel the climb. Double tapping the depart button will cancel both
Describe the Stability Augmentation system (loop and types)
How are they different?
How much authority does it have?
SAS is a part of the Inner-Loop system with two separate and independent channels. SAS 1 is an analogue system and SAS 2 Digital
The two systems are identical except for SAS 2 which also includes Hover Augmentation and the Altitude hold/coupler features
With both channels engaged, the Pitch, Roll, and Yaw actuators all have ±10% control authority with each channel providing ±5%
What happens when one of the SAS channel fails?
How much authority remains?
If SAS 2 fails the AFCC will automatically disengage the affected axis, if SAS 1 fails it must be manually disengaged
The remaining channel is still limited to ±5% authority but it will operate at twice the normal gain to make up for the failed SAS channel
Whats the purpose of the Stabilator?
It provides angle of attack stabilty
During forward flight the stab stabilizes the aircraft in both angle of attack and maneuvering stabilty helping to maintain a level attitude in forward flight
in low speed flight, the stabilators variable angle of incidencec functionality is to eliminate undesired nose up attitudes caused by rotor downwash impinging on the stabilator
(It keeps the nose level in forward flight, and changes pitch to prevent nose high attitudes when going slow)
What moves the Stabilator and how far will it move?
Two electric Jackscrew Actuators acting in series position the stabilator.
It travels from 42° trailing edge down for hover and low speed flight (below 30 KIAS) to 10° trailing edge up for cruise and maneuvering flight
What are the inputs to the stabilator?
CLAP
- Collective Position
- Lateral Acceleration
- Airspeed
- Pitch Rate
What happens if the system detects a fault?
What are the travel restrictions in the event of an actuator failure?
Any system malfunction caused by a difference in the two stabilator actuator positions will result in an Auto Mode Failure. If this occurs the pilot still have the ability to manually control the Stab using the MAN SLEW switch.
If one of the actuators fails, the stab travel will be restricted to 35° is an actuator fails in the full down position or to 30° if an actuator fails in the full up position
Will you always be warned if the Stab fails?
What happens if you reengage Auto Mode after a failure?
It is possible for the Stab to fail without illumination of the STABILATOR caution and associated aural tone. In this case the first indication will be an uncommanded pitch change
Reengagement of the Auto Mode after shutdown will result in the Auto mode operating for 1 sec.
If a handover signal caused the initial shutdown then the system will shutdown again. Subsequent reengagement SHALL NOT be attempted in this case since it may result in additional stab movement
What is the purpose of the Cable Angle Hover Mode?
How does it work?
While the ALFS is submerged the AFCS will maintain the cable angle perpendicular to the waters surface and keep the aircaft in a stable hover
There are ALFS cable sensors in the ALFS funnel which measure the angular displacement of the cable and provides longitudinal and lateral corrections to the AFCS which then created the appropriate control inputs
What happens to the Cable Angle Signals when moving the dome?
Each time the dome raising/lowering is stopped or started int he water the cable angle signals are decoupled from the AFCS for approximately 9 sec
During this time the cable angle signal is subject to 1° per sec of change limit in the AFCC to prevent erratic helicopter movement
Describe the scale of the Cable Angle Display
What are the risks associated with each ring?
There are tick marks at every 2° and an inner ring at 4.25°, and an outer ring at 8.5°
If the inner ring is reached when the dome is leaving the water there is an increased risk of the sonar dome striking the aircraft which may result in equipment damage
If the outer ring is reached 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 and/or death
When will the Cable Angle At Limit appear?
What is the risk, and what should you do if it happens?
When the cable angle has exceeded 7.5° total deflection
Changing depth of the dome which at the angle limit may cause cable and/or funnel damage from contact friction
The crewman should stop the dome, and verify the alert is valid visually, the pilot at the controls should then input the appropriate corrections to prevent the alert.
When can you engage Cable Angle Hover?
When ground speed is ±5 knots, altitude hold is withing 10 ft of selected altitude, and you have a dome wet indication (27±12 ft of water depth)
When does the Cable Angle Hover disengage?
What happens when it disengages?
Cable angle hover mode will disengage automatically when the dome is reeled up through 27±12 ft of water depth or when the pilot presses the CABLE ANGLE push button
The aircraft will then transition back to HVR mode
What does Submerge Override do and when should you use it?
What are some risks associated?
The SUBM OVRD push button allows the pilot to defeat the 27±12 ft water depth requirement for engaging the cable angle. This may be required for shallow water dips or if the cable angle hover mode fails to engage
The cable angle hover mode will not automatically disengage when the dome leaves the water, if not manually disengaged sever oscillations of the aircraft may occur
What do the Long/Lat Fail advisories indicate?
A failure in either the LAT or the LONG axis. If only one if illuminated you still have automatic control authority in the non-illuminated axis
How long does it take the AFCC to come up with a nulling solution?
What if the dome is still out of limits?
It takes the AFCC 25 sec after engaging the Cable Angle Hover mode in order to come up with a nulling solution
Corrects must be made in the following order (Trim, Lat, Trim, Long)
- Trim Hat
- Fly against the Lateral trim only
- Depress the Trim button and reposition the Aircraft
- Fly against the Longitudinal trim
The pilot making longitudinal correction against trim of 3% for 2 sec or more will cause the AFCS to remove the Cable angle hold solution and will require another 20 sec to fully reincorporate a solution
