Section 14 - Finck Aviation · PDF fileSection 14 . Autopilot . This ... the system ensures...

Section 14

Autopilot This chapter provides a general introduction to the standard 3-axis autopilot system fitted to the majority of BHL AS332Ls. Further reference to BHL FM supplement No. 12 is necessary for information on RNAV coupling and co-pilot mode selection. For information on the 4-axis system fitted to a small number of company machines, refer to the FM supplement 10.15 (section 10). Note that the 4-axis Autopilot is fundamentally different in several respects and a specific EOP checklist is issued to each 4-axis aircraft.

Section 14 Autopilot 1 of 23


(After reading this chapter, the look on your face will be……)

INTENTIONALLY BLANK


INTRODUCTION The SFIM Type 155 Autopilot (AP) is fitted as standard in the Tiger. It is a 3-axis system that provides stability in pitch, roll and yaw – each axis being controlled by two mutually monitored lanes. The provision of two lanes gives a layer of redundancy in normal operation – Lane 1 (the “Governing” lane) providing inputs to the flying controls and Lane 2 (the “Shadowing” lane) is used as a comparison to verify integrity of the AP computer signal. In certain failure conditions, one lane alone can provide appropriate inputs. The Autopilot acts through the autopilot hydraulics unit which provides control inputs in series to the flight control linkages – the system having approximately 5% mechanical control authority in pitch and roll, but up to 100% authority in yaw. The hydraulics unit is housed at the base of the “broom cupboard” (in the bulkhead behind the right-hand pilot’s seat) and joins the control run immediately downstream of the lower bellcranks. Hydraulic pressure is provided by the left-hand hydraulic system to give assistance to the pilot in moving the controls. The pressure is reduced from 175 bar to 103 bar and 4.3 bar by the AP hydraulic power unit. An isolation (NORMAL-OFF) control is provided via a switch on each pilot’s collective lever. The Autopilot control panel is located on the top right corner of the centre console. The following functions are provided by the SFIM 155 Autopilot: 1. Stability around the Pitch and Roll axes. 2. Gradual variations around the Pitch and Roll axes by use of the 4-way “Beep trim” switch (also

known as the “coolie hat”) located on each cyclic. 3. Major attitude reference changes in one cyclic axis only (either Pitch or Roll) by “Stick and Beep”

pilot action. 4. Major attitude reference changes in both cyclic axis simultaneously (both Pitch or Roll) by “Stick

Trim Release” pilot action. 5. Stability around the Yaw axis. 6. Co-ordinated turns by action of the cyclic stick in roll (airspeed above 60 knots and bank angle

above 4º). 7. Directional Attitude Hold and Pedal-controlled turns. (Heading reference will be maintained when

movement in yaw axis reduces to less than 1½º per second.) 8. “Fly-through piloting” available at all times so that the pilot retains aircraft control, even with the

system engaged. In addition, the following “higher” functions are also available: (i) Altitude Hold: Aircraft maintains altitude at time of selection. (ii) Airspeed Hold: Aircraft maintains airspeed at time of selection. Note - As both these holds are functions of the Pitch channel, only one can be selected at a time. (iii) Selected Heading Hold: Controlled by heading “bug” on pilot’s and co-pilot’s HSI. The aircraft

will turn (20° bank maximum) onto and will then maintain the heading selected. The autopilot has two modes of operation: ASE and SAS, depending on the position of a selector switch on the control panel. In SAS mode (Stabilisation Augmentation System), the system ensures short term damping of aircraft oscillation, without returning the aircraft to its original attitude. In ASE mode (Automatic Stabilisation Equipment) both short term damping and long term attitude stabilisation are ensured: the aircraft is returned to the pilot’s desired attitude. Note - The “higher” functions listed above are only available in ASE mode.

A Note on Stability & Damping The helicopter, by nature, is a dynamically unstable machine. Whilst the designer will try to produce an aircraft that will fly with the minimum amount of effort from the pilot, external forces (e.g. turbulence) will affect the flight path and attitude of the helicopter throughout its flight. Without appropriate assistance and correction, the pilot’s workload would be significantly increased. A helicopter without a stabilisation system will be hard work to fly since all aerodynamic forces acting on the aircraft will affect its attitude and will need to be corrected manually by the pilot. Since the pilot must try not to over- or under compensate for the required control input, the workload is high and the flight path variable.


A helicopter that has an SAS-based stabilisation system will damp out any external aerodynamic forces that tend to deviate the aircraft from the intended flight path. The rate of that deviation is minimised and corrective inputs are made by the Autopilot computer to maintain the pilot’s chosen attitude. Such an aircraft flying in a wings-level attitude, which is affected by turbulence, will be returned to a similar attitude, but in a position offset from the original flight path. A helicopter that has an ASE-based stabilisation system can be flown so that specific flight parameters (such as altitude, airspeed etc) are corrected for and maintained even though external forces cause deviations from the flight path.

Figure 1 – Autopilot Damping

Intended flightpath

Intended flightpath

PRINCIPLES OF OPERATION Each of the three channels (pitch, roll and yaw) constitutes a slave control based on the following philosophy. The Autopilot tries to maintain the aircraft attitude selected by the pilot. This “datum” attitude is stored as a result of where the pilot positions the cyclic stick or yaw pedals. A sensor detects aircraft movement away from the “datum” position and sends an electrical signal based on the amplitude and rate of change of that movement to the AP computer. This deviation information is compared to the memorised information (i.e. the attitude desired by the pilot – the “datum”) and a corrective output signal relative to the detected deviation is sent to the servo-controls in the AP hydraulics unit. This output actuates the flying controls, attempting to re-establish the aircraft at its initial attitude.

AP Computer

Datum

Reference

Flight Servo ComparatorSensor Controls Controls


“Feedback loop”

Figure 2 – Schematic of Autopilot Philosophy

The system assumes that the desired attitude (the “datum”) is unchanged as long as the pilot makes no physical input to the cyclic stick or yaw pedals. When an input is made to either of these controls by the pilot, the computer’s memory goes into “synchronisation” and waits until a new attitude is selected and then stores this attitude as the new “datum”. The following notes describe the system in the AS332L and then show how they relate to the above philosophy.

System Control The Auto Pilot control panel on the central pedestal is the main interface with the AP system for the pilot. The system can be engaged, disengaged and monitored via buttons and indicating lights on the control panel. In the event of malfunction, various functions of the system may be deselected via switches on the same panel in order to allow continued use. A number of system controls are also located on the cyclic sticks and collective levers. Figure 3 illustrates the Autopilot control panel and the table opposite gives a description of the functions available on the control panel. The red numbers on the Autopilot panel relate to the numbers in the key.


Figure 3 – Autopilot Control Panel Item Description Function

P R Y

Yd P R

Lane

Lane

TEST

RUN

A.S.E. AUTO-TRIM NORM COLL LINK CYCL TRIM

S.A.S. PITCH RELEASED ROLL TURB OFF

6 8

1

7

OFF

2 9

13

18 17 14 12 10

16 15 11

P 19 20 21 22

5 4 3

Individual Button


1 & 2 Push button Lane 1 and Lane 2 Activates Lane 1 and Lane 2 (Pitch, Roll and Yaw)

3 Two position push buttons (push-in, push-out)

Activates “PITCH” channel on Lanes 1 and 2 respectively when lane is engaged


Activates “ROLL” channel on Lanes 1 and 2 respectively when lane is engaged


Activates “YAW” channel on Lanes 1 and “YAW DAMPER on Lane 2 when lane is engaged

6 TEST display window Displays defective sequence numbers after running pre-flight test

7 Red light Flashes during test running sequence

8 TEST switch When set in RUN position it actuates a self-test sequence

9 Lighting rheostat Adjusts indicator lighting brightness on control panel

10 CYCLIC TRIM RELEASE switch Simultaneously releases trim on pitch and roll channels when in RELEASED position

11 COLLECTIVE LINK switch Inhibits the collective pitch/roll coupling when selected OFF

12 Amber warning light Indicates a malfunction in collective link system – Switch OFF collective link switch

13 NORM/TURB switch In “TURB” assists the elimination of “dutch” roll by sending correcting yaw and roll signals

14 Amber warning light Indicates a malfunction in the automatic roll trim system – Switch OFF automatic trim roll switch

15 AUTO TRIM ROLL/OFF switch Allows engagement of automatic trim function via roll trim actuators

16 AUTO TRIM PITCH/OFF switch Allows engagement of automatic trim function via pitch trim actuators

17 Amber warning light Indicates a malfunction in the automatic pitch trim system – Switch OFF automatic trim pitch switch

18 Two position switch Selects piloting mode. Mode ASE to maintain attitude and stability. Mode SAS to provide stability alone.

19 Button Identifier

20 Mechanical Indicator Indicates white if the button is depressed (engaged)

21 Green Engaged Light Indicates that the channel in engaged and operating correctly

22 Amber Fault Light Indicates that a fault has occurred in that channel.


DIRECT VERTICAL VERTICAL DIRECT GYRO 1 GYRO 1 GYRO 2 GYRO 2

OFF OFF OFF OFF ON ON ON ON FAST SLAVE FAST SLAVE

Figure 4 – Autopilot Component Location in the Cockpit

Central Warning Panel

A.P. A.P. HT

YRO G

Higher Function HSI HSI

HSI & Rotary Selector for setting heading ‘bug’ in

conjunction with heading hold

IAS ALT HDG RNAV

IAS ALT HDG RNAV

Higher Function

AP.HTº P R Y

Y

P R

TES

Lane 1

Lane 2

RUN

A.S.E. AUTO-TRIM NORM COLL LINK CYCL TRIM

S.A.S. PITCH ROLL TURB OFF RELEASED OFF

Autopilot Control and Monitoring

Autopilot Heat Selector

Other controls found on the pilot’s and co-pilot’s cyclic and collective levers are illustrated below.


Figure 5 – Flight Control Autopilot Switches

4-Way Beep Trim Switch (Coolie Hat) Used to modify pitch and roll reference positions

Stick Trim Release Push-Button Temporarily releases the stick force trim Anchoring point

Autopilot Disengagement Push-Button When pressed both Lane 1 and Lane 2 will be disengaged To re-engage the autopilot, both Lane 1 and Lane 2 push-buttons on the control pane must be pressed.

Autopilot Hydraulics Isolation Switch (Normal = Forward and OFF = Rearwards)

Autopilot BARAN Release Temporarily Releases BARAN reference for Altitude

or Airspeed Hold when button is pressed

System Components The Autopilot system comprises several other components, which are illustrated below:

1 2

3

4

5

6


7

8

9

11 10

Figure 6 – Location of Autopilot System Components

1. Gyroscope control unit : operating and slaving switches for vertical and directional gyros

2. Collective pitch potentiometers – ANTICIPATOR (These supply collective/cyclic channel precontrol signals to prevent attitude variations due to collective pitch modifications

3. AP hydraulic servocontrol unit

4. Yaw channel microswitch actuator link

5. Roll channel microswitch actuator link

6. Pitch channel microswitch actuator link

(The microswitch contacts open to permit “fly-through” manual override control whilst retaining reference attitude information)

7. No 2 vertical gyro unit (VG2) – transmits pitch and roll attitude data to AP lane 2

8. Autopilot computer - Receives data inputs from peripherals – shown here – and processes output signals to the auxiliary servocontrols in the AP hydraulic unit. Also houses yaw rate gyro which transmits signals to yaw damper lane 2 and a lateral accelerometer

9. No 1 vertical gyro unit (VG1) – transmits pitch and roll attitude data to AP lane 1

10. No 2 gyro magnetic compass (DG2) - Transmits heading data to AP yaw channel lane 1

11. Air data module (BARAN unit) - Monitors pitot and static pressures from co-pilot’s systems and transmits airspeed and barometric altitude signals to AP computer

12. Flux valve (in tailboom) – NOT SHOWN HERE. Senses magnetic north and sends signal to compass control unit to align DG1 and DG2

Rear View Front View

5 4 10 6 Pressure 3 9 4.3 Bar 7 2 Pressure


1 4.3 Bar

9 1 8

Figure 7 – Components of the Autopilot Servo Pack Key to Figure 6 1. Servovalves – where AP computer makes automatic input to controls. 2. Collective servocontrol output rod (connects to collective/yaw coupler and anticipator) 3. Pitch servocontrol output rod (connects to phasing unit) 4. Pitch channel beeper valve 5. Roll channel beeper valve – Items 4 and 5 operate together when cyclic trim release is pressed and operate independently when large attitude change is required and demanded through the 4-way beep trim switch - “coolie hat” 6. Roll servocontrol output rod (connects to phasing unit) 7. Yaw servocontrol output rod (connects to collective/yaw coupler) 8. Yaw channel open loop system – allows large scale inputs to yaw controls 9. Servocontrol bypass valves – isolate servocontrols in the event of hydraulic pressure failure 10. Yaw channel damper

The Autopilot hydraulic unit contains four auxiliary servocontrols (pitch, roll, yaw and collective) inserted in series in the flight control linkages. They actuate by amplifying the pilot’s control loads in manual operation (rather like power steering in a car), and converting AP electrical signals into hydraulic commands when the autopilot is operating. Note - There is no servovalve or electrical input to the collective channel in the standard autopilot. In the absence of hydraulic pressure, the bypass valves (9) in Figure 7 operate and the servocontrols act as simple mechanical relays in the flight control linkage, directly actuated by the pilot’s control inputs. The controls operate normally, but will feel very heavy to the pilot. (Refer to EOP checklist 5/7) – AP HYDRAULIC FAILURE. The AP hydraulic unit does not use full left-hand hydraulic system pressure. A hydraulic power unit (found in the base of the ‘broom cupboard’) reduces left-hand pressure from 175 bar to 103 bar for the servocontrols. A further reduction to 4.3 bar is made for the supply to the beeper trim valves (4) and (5)in Figure 7. The servovalves require extremely pure hydraulic fluid so a 15-micron filter is fitted to the hydraulic power unit. The filter includes a ‘pop up’ clogging indicator which is visible through an inspection window just above the cockpit floor behind the right-hand pilot’s seat. Components & Functions of the Cyclic (Pitch & Roll) Servocontrols

Beeper Valve Electrical Control Signal 2 1 Main Rotor Input R

3

103 Bar Safety Pin Servo Valve Electrical

Control Signals A

4 103 Bar

14

5 B 13

6 R 12 R

Input Play P 11


7 8

9 10

Input Play

Pilots Control Input C

Figure 8 – Pitch and Roll Servo Control


Manual Operation with Hydraulic Assistance. The numbers in the following text relate to Figure 8. Hydraulic pressure separates the bypass pistons (12) and (14): power actuator chambers (A) and (B) are isolated, and the roller (11) is free within the limits of the input play. Initially, the distribution slide valve (6) is centred, shutting off the pressure inlet lines to the actuator chambers (A) and (B), and the output rod (9) is stationary. A pilot control input at (P) pivots the input lever (10) around point (C). The motion is transmitted by the link (8) to the stirrup (7) controlling the distributor slide valve (6). The slide valve pressurises one actuator chamber and opens the second to the hydraulic fluid return line (The figure shows chamber (A) pressurised and (B) open to the fluid reservoir.) The power actuator piston moves accordingly. The piston movement tends to re-centre the slide valve by means of lever (10), link (8) and stirrup (7). When the pilot action ceases, the slide valve re-centres and the actuator stops moving. Note that the operation of the auxiliary servocontrols in the AP hydraulic unit is similar to the main servocontrol operation covered in the Flight Controls chapter. Also note that in the absence of an electrical control input signal, servo valve (5) is inoperative (control vane (4) is centred). Manual Operation without Hydraulic Assistance In the event of an autopilot hydraulic system failure, the pilot closes off the autopilot cut-off solenoid valve, simultaneously opening the hydraulic unit supply circuits to the return line. The bypass piston (14) is moved by spring pressure (no longer opposed by hydraulic pressure), locking roller (11) and interconnecting power chambers (A) and (B). In this configuration, a pilot control input at (P) is transmitted directly with out play by lever (10) to the output rod (9), which is driven with minimum effort in the absence of opposing pressure in chambers (A) and (B). In the trim actuator (13) the lower chamber is open to the return line, but the upper chamber is isolated by the beeper valves. The trim actuator is thus hydraulically immobilised: it cannot move downward since cavitation phenomena prevent any increase in the upper chamber volume. This arrangement maintains the initial anchoring point and the simulated trim loads. Automatic Operation The electrical control signal actuates the servo valve (5): the vane (4) moves according to the signal direction and amplitude. The movement of the vane creates differing pressures either side of the distributor slide valve (6). The slide valve moves, pressurising one actuator chamber and opening the other to the return line. (The figure shows chamber (A) pressurised and chamber (B) open to the fluid reservoir). The movement of the output rod (9) tends to re-centre slide valve (6) by means of stirrup (7). The output rod motion is not felt by the pilot. When the electrical input signal disappears, the vane (4) re-centres, as does slide valve (6): the servo control stops moving. Note - For a high amplitude electrical input signal, the Autopilot computer causes a beeper valve to open, moving the cyclic stick and modifying the stick anchoring point.

Components & Functions of the Yaw Servocontrol

1 2

103 Bar

Control Signal

Servo Valve

Distributor Slide Valve R

7

9

C 10 P

Input play (a)

12

6

5

4

A

B

103 Bar

Figure 9 – Yaw Servo Control



Manual Operation with Hydraulic Assistance A pilot control input at (P) causes lever (10) to pivot around point (C), since the servocontrol actuator is initially immobilised. Lever (10) first moves freely moving roller (6) within the limits of the open loop play (a), then compresses spring (4), causing the pilot to feel a control load inversely proportional to the aircraft turning radius (i.e. a tight turn produces a heavy control load). The remaining operation sequence is the same as for the cyclic servo channels: stirrup (7) moves the distributor valve off centre, pressurising one actuator chamber and opening the other to the return line. The movement of the output rod (9) tends to re-centre the slide valve and the open loop system (4). The yaw damper (1) slows the input action of rod (P) in the event of excessive yaw pedal movement. Automatic Operation The servo valve drives the power actuator in the same way as the cyclic channel servocontrols. As long as the actuator travel does not eliminate the play (a) in the open loop, the yaw pedals are not affected. If the actuator travel exceeds the input play, the input rod (P) is driven and the yaw pedals follow the motion through the damper action. This input rod (P) movement reinforces the servo valve action by slowing the re-centring action of the distributor slide valve. Manual Operation without Hydraulic Assistance Chambers (A) and (B) are interconnected by the bypass valve piston (12). Roller (6) is hydraulically locked. Slide valve (2) is pushed by spring pressure, interconnecting the two chambers in the damper. This allows the pilot to move the power actuator with no input play and with minimal yaw pedal loads. Note – in this configuration the yaw damper protection is removed.

SUMMARY OF SYSTEM OPERATION IN BRISTOW AS332L


Figure 9 – Summary of Pitch and Roll Channel Operation. How are the required functions of the autopilot provided? (1) Stability in pitch and roll – Vertical gyro signals provide sensing signals to the Autopilot

computer, which are compared with the “datum” reference. (2) Gradual variations in pitch and roll – A 1 second input to the 4-way “coolie hat” changes the pitch

attitude by 2° or the roll attitude by 4° (via the servovalve). This function is known as BEEP TRIM and is available whenever lane one is operating. If the input is of a high magnitude, the servovalve may run out of authority and the AP computer operates the beeper valves in order to make its input more effectively. (NB - The cyclic will move.) A new “datum” is generated.

(3) Major changes to pitch and roll attitudes (one axis only) – The cyclic should be positioned to the

desired attitude in pitch or roll (the beeper trim actuator spring will provide artificial feel). The spring pressure can be released by operating the 4-way “coolie hat” in the direction of the attitude change. This method is known as “Stick and Beep”. A new “datum” is generated.

(4) Major changes to pitch and roll attitudes (both axes simultaneously) – The Trim Release button

on the cyclic should be depressed, the cyclic repositioned and the Trim Release button released. All 4 beep valves open during the control input. A new “datum” is generated.

(5) Collective/Pitch coupling and collective/roll coupling is achieved through the Collective Link

function. As the collective is raised, the aircraft’s nose tends to want to pitch up and roll left (down and right when collective is lowered). The AP computer sends corrective signals to the pitch and roll channels whenever the collective is moved.

TRIM LOAD

SPRINGSERVO VALVE

VERTICAL GYRO 1 VERTICAL GYRO 2 (Normally “Governing”) (Normally “Shadowing”)

CYCLIC STICK

MICROSWITCH LINK

TRIM ACTUATOR

(100% control authority) SERIES

ACTUATOR (Limited authority)

BEEP VALVE

MAIN SERVOCONTROL

Hydraulic Unit

AUTO AP AP TRIM LANE 1 LANE 2


(6) Fly-through piloting – The micro switch actuator links operate whenever the pilot makes a control input (the beeper trim actuator provides artificial feel) and the beeper trim actuator function is temporarily inhibited. The servocontrol moves the control linkages. The old “datum” is maintained.

(7) Stability in yaw – The Pilot’s compass (supplied by DG2) and the yaw rate gyro provide sensing

signals to the AP computer that are compared with the “datum” reference. (8) Heading hold and pedal controlled turns – The heading provided by DG2 is maintained unless

the aircraft is yawing at a rate of more than 1.5° per second. (9) Co-ordinated turn function – Above 60kts, operation of the cyclic leading to more than 4° roll

results in the aircraft performing a balanced turn. The AP computer uses a lateral accelerometer to calculate the amount of yaw input required. The pilot should leave his feet off the pedals. If he places his feet on the pedals, the yaw micro switch actuator operates and a co-ordinated turn is not performed. The pilot must keep the aircraft in balance himself.

(10) Turbulence function – In cases of bad turbulence, external forces may be felt on the tail fin,

inducing a roll movement. Selecting the NORM-TURB switch to TURB sends ½ the yaw correction signal to the roll channel to counter this effect.

(11) Altitude Hold – The “datum” is the altitude at the time of engagement of the ALT hold (sensed in

the BARAN unit) and can be changed by adjusting altitude whilst depressing the BARAN release switch on the collective. The datum altitude is maintained by making corrections via the pitch servovalve, or if large corrections are required, via the beep trim actuator (and the cyclic moves) if the AUTO TRIM is functioning in pitch. ALT hold gives a warning if altitude varies more than 150 feet from the datum.

(12) Airspeed Hold - The “datum” is the airspeed at the time of engagement of the A/S hold (sensed

in the BARAN unit) and can be changed by adjusting airspeed whilst depressing the BARAN release switch on the collective. The datum airspeed is maintained by making corrections via the pitch servovalve, or if large corrections are required, via the beep trim actuator (and the cyclic moves) if the AUTO TRIM is functioning in pitch. ASI hold gives a warning if airspeed varies by more than 15kts from the datum.

(13) Selected Heading Hold – The “datum” is the heading set on the HSI bug. Either pilot may select

Heading Hold and the aircraft will respond to the most recent selection. (i.e. control will “flip-flop” between the two pilots if each engages this function in turn.) This function should not be used below 60kts as the co-ordinated turn function will not be available. If a heading correction of more than 2° is required, the aircraft performs a co-ordinated turn onto the required heading. For a required heading change of less than 2°, the AP corrects the heading by “slewing” the aircraft in yaw.

Autopilot Heating In order to maintain viscosity of the hydraulic fluid in the AP hydraulic unit, the unit should be kept warm when flying in the colder temperatures of the normal operating range. This will maintain normal speed of operation of the beeper trim valves and prevent build up of pressure in the yaw damper. Heating is achieved in two ways:

1: A hot air supply is ducted from P2 bleed heating system into the base of the “broom cupboard”. It comes on whenever the heater is selected on in the cockpit or cabin.

2: An electrical heating system for the hydraulic power unit, beep trim valves and yaw

damper. The heaters take the form of resistors embedded in mats wrapped around the appropriate sensitive components. The resistors are powered by 115V AC and are selected ‘ON’ via a guarded switch on the centre console marked AP HEAT. Whilst the system is selected on and functioning correctly, a green light illuminates in the switch. Heating is controlled to not exceed 80°C. A red warning light AP.HT° is located on the CWP to warn of a malfunction.

The electrical heating system is operated in the following way. Prior to each start-up, the AP HEAT is selected ‘ON’. After start:

a) If the OAT is above 0°C, AP HEAT is deselected. b) If the OAT is between 0°C and -5°C, AP HEAT should remain ‘ON’ for 20 minutes. c) If the OAT is less than -5°C on the ground or in flight, AP HEAT should be selected ‘ON’.

Heating Resistors for


Figure 10 – Autopilot Heating System

Heating Beeper valves

Hot Air from Cabin Heating System for

Heating Yaw Damper & Trim Actuator

P2 Air Manifold


Electrical Power Supplies A number of different electrical supplies are involved in the AP system. A CB on the appropriate panel protects each supply.

1XP2B - 115v ac for AP heater resistors

1XP2C - 115v ac for powering VG1 and DG1

2XP2C - 115v ac for powering VG2 and DG2

1XP4 - 26v ac for powering AP Lane 2

2XP4 - 26v ac for powering AP Lane 1

1PP6 - 28v dc for system selection, lighting, beeper trim valve operation and mode selection

1PP5 - 28v dc for system selection and mode selection


Normal Operating Procedures (NOPs) Pre-start, the AP HYD switches on each collective lever should be checked in the NORM position. On the AP control panel, all 6 channels should already have been selected with the white indicators showing. All switches on the panel should be forward. The autopilot is engaged immediately prior to flight by pushing the Lane 1 and Lane 2 buttons on the AP control panel. Six green lights should illuminate (one in each channel button). The “higher” functions (Altitude Hold, Airspeed Hold and Selected Heading Hold) can be selected by pressing the appropriate button. A green light in the button (“ALT, “ASI” or “HDG”) shows that the mode has been selected. If the mode drops out or is deselected by the pilot (using the same button) an amber “Mode Warn” light flashes in the button for 10 seconds. The autopilot, when fully operational in flight, is a “Hands Off” system and will fail passive, i.e. if one lane fails there will be no major loss of control. The autopilot is normally disengaged as soon as the aircraft has landed and is stable on the ground. The system is disengaged by the button the either pilot’s cyclic. Any time the autopilot is engaged with the aircraft on the ground the pilot must keep hands and feet on the controls in order to prevent the autopilot making “corrective inputs” to the main and tail rotors. Pre-flight Tests Prior to the first flight of the day, the AP system test should be performed. The aircraft should not be on a moving platform. The autopilot should be engaged via Lane 1 and Lane 2 buttons on the AP control panel. AP hydraulics should be selected “OFF” and the “test” switch on the AP control panel moved to the “RUN” position. The test takes about one minute, during which time the lights on the control panel illuminate in sequence and a red dot flashes in the L.E.D. window. (The test sequence may be inhibited if the nose wheel is not central.) At the end of the test, a “0” should appear in the L.E.D. window. The test switch should be reset, the AP hydraulics reinstated and the AP released. If a figure other than a “0” appears then the pilot should take the appropriate action as listed in the Flight Manual FM (Section 3). Prior to every flight, the Beep Trim test should be performed. With Lane 1 engaged, the pilot should make an input on the 4-way “coolie hat” in each direction (fore and aft, left and right). The input should be large enough to saturate the series actuator and operate the beep trim actuator in the appropriate direction. The cyclic should move. Movement is cancelled by pressing the Trim Release button on the cyclic.

Emergency Operating Procedures (EOPs) With any degradation of the autopilot, the pilot must fly the aircraft with hands and feet on the controls and should limit collective pitch to 15.5º (see FM section 3). Refer to FM section 2 for IMC Flight Envelope limitations, which are affected by the serviceability of the AP. Note - With the Autopilot inoperative all manoeuvres must be made gently. Visual warnings: CWP (32α) panel warnings: Illuminates for 10 seconds in the event of an

autopilot system fault or if the autopilot is disengaged.

A P

Illuminates in the event of gyro malfunction (in association with an amber light on the gyro panel).

GYRO

Illuminates in the event of AP heating unit overheating (>120°C) or resistor short circuit. A.P. HT

Hydraulic sub-panel warning: Illuminates when hydraulic pressure

A.P. H.P. at the autopilot hydraulics unit is less than 70 bar.

For diagnosis of amber warning lights or other indications of a malfunction on either the AP control panel or the overhead gyro control panel, read the following notes and refer to Section 7 of the EOPs which outlines the necessary remedial action. (See also EOP checks 5/7 – AP HYDRAULIC FAILURE and 5/9 – JAMMED YAW PEDALS from the Hydraulics Section of the checklist.) Notes on the nature of Autopilot Failures General If a channel input fails, the pilot should deselect that channel on the control panel if is not capable of being restored. Individual Lane Failures: When a whole Lane fails, the remaining Lane continues to provide stability, however the input to this Lane is no longer being compared with anything. Pitch, Roll and Yaw channels should be deselected in the failed Lane. Because of the mechanical authority given to the Yaw channel, pilots must also deselect the remaining Y or YD channel since it is unchecked and has the ability to move the yaw pedals through 100% of their range. The unchecked Pitch and Roll channels have only a limited mechanical authority and single channels may be left engaged to provide normal stability. Depending on which Lane fails, certain functions of the AP will be lost. VG and DG Failures: Failure of a vertical gyro results in the loss of pitch and roll inputs to one Lane (VG1 for Lane 1 and VG 2 for Lane 2). The appropriate VG should be switched off. Certain functions of the AP are lost. Loss of DG2 means that Lane 1 Y has no input. HEADING HOLD is lost and the pilot’s compass is no longer supplied with heading information. DG2 should be switched off. Lane 1 Y should be deselected and, for reasons given above, so should Lane 2 YD. A failure of DG1 has no effect on the AP since it only provides heading information to the co-pilot’s HSI.



Channel Discrepancies Remember that when both Lanes are operating, Lane 1 is the “governing lane” and Lane 2 is “shadowing” – providing comparisons and verifying the Lane 1 input. It is the input to Lane 1 that is translated into aircraft movement. If the Pitch or Roll inputs from VG1 and VG2 differ, a warning light appears in the pitch or roll channel selector buttons. The “rogue” channel must be deselected and the remaining channel allowed to continue to provide stabilisation. The EOP’s method for diagnosing the “rogue” channel can be confusing. Instead, you might consider the following. By definition, both lanes must be operating for a discrepancy to occur. A “rogue” signal in Lane 1 will immediately translate itself into aircraft movement away from the desired “trimmed” attitude. Deselection of the appropriate channel in Lane 1 should restore the aircraft to the desired attitude as Lane 2 takes over. If a “rogue” signal occurs in Lane 2, no attitude change will be seen at the time of the warning, but if the Lane 1 channel is subsequently deselected, the “rogue” signal from remaining Lane 2 channel will cause an aircraft attitude deviation. A channel discrepancy in Yaw requires no diagnosis since, for reasons stated earlier, both yaw channels must be deselected. BE AWARE: AFTER ANY FAILURE THAT RESULTS IN THE AIRCRAFT BEING FLOWN “AP OUT” OR IN “SAS” MODE, AN EXTREMELY POWERFUL YAW/ROLL COUPLE IS GENERATED BY EVEN SMALL AMOUNTS OF RIGHT PEDAL INPUT. AFTER A SHORT DELAY, THE AIRCRAFT CAN ROLL VIOLENTLY TO THE RIGHT AND COULD BE DISASTROUS SHOULD THE PILOT NOT REGAIN CONTROL OF THE AIRCRAFT IMMEDIATELY.


How to use the Autopilot and Trim system

If you take nothing else away from this chapter, at least use the following maxims as you develop your flying technique on the AS 332L.

• Provided the Autopilot is engaged and fully serviceable, it is recommended to fly with

hands and feet away from controls.

• The handling pilot should keep hands and feet on the controls when the aircraft is on

the ground anyway, but especially when the Autopilot is engaged. When handling the aircraft:

• Always trim to required pitch attitude. • Make gradual pitch and roll attitude changes via the 4-way switch on the cyclic. • Major large pitch and roll attitude changes using “Stick and Beep” method. • It is recommended that the aircraft is trimmed to “wings level” in roll - especially IMC.

Any turns should be made against the artificial “feel” springs so that if the pilot becomes disoriented, letting go of the cyclic should result in the aircraft righting itself to “wings level” again.

Section 14 - Finck Aviation · PDF fileSection 14 . Autopilot . This ... the system ensures...

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