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Chinook CH-47D > AFCS > Flashcards

AFCS Flashcards

1
Q

What must the AFCS have to operate?

A

(a) AC electrical power, − No. 1 and No.2 AC bus.

(b) DC electrical power, − No.1 and No.2 DC bus.

(c) Hydraulic pressure, − No.1 and No.2 flight control hydraulic systems.

(d) Two vertical gyros.

  1. Copilot’s for No.1 AFCS.
  2. Pilot’s for No.2 AFCS.
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2
Q

AFCS provides what functions?

A

BAAAH P LASH

Bank angle hold
Airspeed hold
Altitude hold
Attitude (pitch) hold
Heading hold

Positive stick gradient

Longitudinal Cyclic Trim
AFCS trim
Stability about all axes.
Heading select

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3
Q

What happens when the centering device release switch is pressed?

A

The magnetic brakes in the pitch, roll, and yaw axes are released.

Heading hold and bank angle hold are momentarily disengaged.

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4
Q

How many CCDA’s in flight control closet? What are they used for?

A

Two
1 for pitch (Airspeed hold or AFCS trim). This one can operate independently of the AFCS.
1 for Thrust (altitude hold)

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5
Q

When heading select is engaged, what will be disengaged?

A

AFCS trim

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6
Q

When is Bank Angle Hold disengaged?

A

Bank angle hold will be disengaged UNTIL the roll rate is less than 1.5º degrees per second

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7
Q

What will be disengaged above 40 kts when lateral AFCS trim is used?

A

Heading hold

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8
Q

What triggers the AFCS light (outside of using the selector knob)?

A

Hydraulic pressure.

Electrical power.

Vertical gyro.

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9
Q

Pitch, roll, and yaw extensible links provide for what functions of the AFCS?

A

Stability.
Bank angle hold.
Bank angle trim.
Heading hold.
Heading select.
Coordinated turns.

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10
Q

DASH actuators provide for what functions of the AFCS?

A

The DASH makes the control inputs for: AIRSPEED HOLD, PITCH ATTITUDE HOLD, and POSITIVE STICK GRADIENT.

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11
Q

What do the CPT’s do?

A

Provide control position information to the AFCS

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12
Q

How are the landing gear proximity switches activated?

A

When the shock strut is compressed with the weight of the helicopter.

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13
Q

What do the left and right landing proximity switches do?

A

Reduces the No.1 (left) or No. 2 (right) AFCS pitch stabilization signal by 50%.

Cancels the longitudinal CPT input to the No.1 or No. 2 AFCS computer.

Both switches must be closed (both aft gear on the ground) to position the LCT actuators to the GND position.
Both are inoperative during water landings.

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14
Q

What sensors does the AFCS system use to process info?

A

PSS GGG CHRAF

Pitot tubes (airspeed).
No.1 AFCS/Left tube and No.2 AFCS/Right tube.

Static ports (barometric altitude).

Sideslip ports (sideslip stability).
The ports are located on the left and right side of the nose. No.1 AFCS/Upper. No.2 AFCS/Lower.

Yaw rate gyros.
One yaw rate gyro is located in the base of each AFCS computer and provides a rate of motion signal for motion dampening.

Vertical gyros.
Right vertical gyro signal goes to the No.1 AFCS. Left vertical gyro signal goes to the No.2 AFCS.
The gyros produce pitch and roll attitude signals and a rate of motion signal for motion dampening and turns is derived by the AFCS computers.

directional gyro
provides the signals for heading hold and the Horizontal Situation Indicator (HSI). The controls for the Gyro-magnetic compass are on the overhead panel.

CPT’s

HSI
Heading select

Radar Alt
Radar Altitude Hold

Feedback signals from the actuators

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15
Q

Where does the AFCS send its command signals?

A

ILCA’s in the pitch, roll, and yaw axes (extensible links).

Thrust CCDA (100% travel authority).

DASH.

LCT.

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16
Q

What is positive stick gradient?

A

stick position in proportion to airspeed from hover to V-max.

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17
Q

What AFCS signals are canceled when ground contact lights come on?

A

The longitudinal CPT input to the AFCS is canceled when the aft landing gear is on the ground.
The vertical gyro signal is not canceled.

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18
Q

The AFCS consists of the following components:

A
  1. Cockpit control panel
  2. Two (2) AFCS computers
  3. Three (3) integrated lower control actuators (ILCA)
  4. Two (2) differential airspeed hold (DASH) actuators
  5. Two (2) longitudinal cyclic trim (LCT) actuators
  6. Two (2) magnetic brakes (yaw and roll), a longitudinal cockpit control drive actuator (CCDA) and a collective cockpit control driver actuator.
  7. Three (3) control position transducers (CPT)
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19
Q

What does the centering device release button “turn off”?

A

Used to release yaw pedals, lateral cyclic and longitudinal cyclic magnetic brakes and provide a momentary heading hold and attitude hold disengage signal to the AFCS unit.

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20
Q

When only one AFCS system is engaged, certain functions controlled by the disengaged AFCS system continue. What are these functions?

A

These are the cyclic trim functions for each system and the barometric and radar height hold functions for the No. 1 system. When neither AFCS system is engages, only the cyclic trim functions continue.

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21
Q

What does the swivel switch do in flight?

A

When set to unlock, it decouples the directional gyro from the AFCS

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22
Q

Do not mess with the compass slaving unless what?

A

The swivel switch is in the unlock position

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23
Q

The HDG button on the AFCS panel does not latch unless what?

A

The airspeed is above 40 kts and the HDG command button is engaged.

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24
Q

With the helicopter on the ground, the signal to the DASH is cancelled. What happens once airborne?

A

Upon takeoff, AFCS opens the pitch CPT circuit to the dash and the AFCS computer increases pitch rate back to 100%.
When proximity switches close upon landing, the pitch CPT signal to the DASH actuator is removed and the other circuit reduces pitch rate by 50%.

More complicated answer:
With the aircraft airborne, a “logic switch” is closed which connects the CPT signal via two paths to a “summing amplifier”. These paths provide for longitudinal control augmentation. One path is direct. The other path, a higher gain path, is through a “velocity limit” circuit. This circuit limits the rapid signal increase that occurs with quick stick movement and which would otherwise result in over response. The output of this summing amplifier is the resultant longitudinal CPT signal.

When proximity switches close upon landing, one circuit opens up the pitch CPT to the DASH actuator and the other circuit reduces pitch rate by 50%.

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25
Q

How does the AFCS command the dash for positive stick gradient?

A

The AFCS uses the longitudinal CPT information (pitch) and airspeed to deliver a proportional relationship between the stick position and airspeed.

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26
Q

What do the LCT’s do?

A

Reduces flap-back to relieve bending stresses particularly on rear rotor shaft and helps to reduce drag.

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27
Q

What does AFCS need to operate?

A

AC and DC power. (Plus hydraulic pressure and vertical gyros)

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28
Q

Does selecting AFCS system off turn AFCS off?

A

Selecting a system off disengages most of the AFCS OUTPUTS to the flight controls, however, the AFCS continues to follow up inputs. The AFCS can be isolated only by pulling the relevant circuit breakers.

29
Q

What may happen to DASH when landing with one AFCS system selected?

A

One DASH actuator section is disabled which may lead to abnormal stick position during landing.

30
Q

How does heading select operate?

A

The AFCS computer directs the bug error signal (difference between the present heading and the HSI bug heading) to the roll ILCA extensible link.

The roll rate signal is then applied to the yaw ILCA extensible link.

31
Q

How does stability augmentation work?

A

The rate gyros in the pitch, roll, and yaw provides a signal to the AFCS which talks to the extensible links.

32
Q

With heading hold, the heading stays within what of the heading selected?

A

5 degrees

33
Q

How does heading hold function?

A

The directional gyro provides heading info to AFCS which talks to the Yaw extensible link.

34
Q

Will altitude hold work if the number one AFCS system is turned off?

A

Yes, it only doesn’t work if the #1 computer is broken

35
Q

What is the max altitude for radar alt hold?

A

1500 ft

36
Q

What must you NEVER do with alt hold engaged?

A

Never move the thrust rod without pressing the thrust brake trigger switch with altitude hold engaged.

To change Altitude press thrust brake, come to new altitude, then release break.

37
Q

What is the range of programming (kts) at sea level for the LCT’s?

A

60-150kts

38
Q

When are rotors perpendicular to the rotor mast?

A

When LCT’s are in GND

39
Q

What is the forward tilt of the rotors with fully extended LCT’s?

A

4 degrees on both

40
Q

How high up are the LCT’s altitude compensated?

A

Both actuators are altitude compensated up to 15,000 feet PA to provide more forward tilt of the rotor systems at lower airspeeds.

Three knots per 1,000 feet.

Actuators will not begin to program below 40 knots.

41
Q

What must you NOT do below 60 knots with the LCT’s?

A

Do no extend LCT’s beyond GND position below 60 kts…it will cause high aft shaft stress.

42
Q

How do you know your LCT’s have failed in cruise flight?

A

As you slow down, you’ll tend to have more pronounced nose up attitude.

43
Q

How will a vertical gyro failure affect AFCS?

A

AFCS may go off or pitch and roll transients.

44
Q

What features of AFCS are disengaged while the centering device release switch is pressed?

A

Heading hold, heading select, bank angle hold

45
Q

What are the 3 AFCS functions are provided by the DASH actuator?

A

Airspeed Hold, Pitch attitude Hold, Positive Stick Gradient

46
Q

Which mode of LCT operation should you select during flight in turbulence?

A

Manual

47
Q

The BASIC ILCA has two basic functions:

A

Provides hydraulic (boost) assist for the elimination of control friction forces and component weight

Converts the AFCS electrical input into a mechanical output using hydraulic actuation in three axis

*The thrust ILCA only provides hydraulic (boost) assist

48
Q

What is the operating pressure of the ILCAS?

A

1500 PSI

49
Q

Single extensible link % of control travel or authority covers?

A

Pitch 12.5%

Roll 13%

Yaw 24%

50
Q

What gives the controls a force feel

A

Centering spring and mag breaks

51
Q

With AFCS on, where are the outputs sent from and where do they go to?

A

They are sent from the extensible links to the upper flight controls without moving the lower control actuators.

52
Q

When the pilot selects only one AFCS system on, only one extensible link will extend or retract. What part of the ILCA does this displace?

A

The output arm of the lower control actuator

53
Q

What does each extensible link consist of?

A

A piston, cylinder, a lock piston, an electro hydraulic valve, and a self feedback LVDT

54
Q

What is the purpose of the servo valves on the ILCA’s?

A

The valves direct pressure to vary the length of the extensible links. Each hydraulic system serves one section of a dual extensible link for redundancy.

55
Q

Can a pilot override and AFCS input?

A

Yes. Each extensible link provides a certain amount of control authority (authority covers) to the flight control of the helicopters. By limiting the amount of the authority, the pilot is able to override any AFCS control input.

56
Q

What is the extensible link range of movement limited by?

A

By the authority covers

57
Q

What does extension of the #1 roll, pitch and yaw extensible link cause?

A

2 does the opposite.

It causes pitch up, roll right, and yaw right

58
Q

How do extensible link behave with no hydraulic pressure (AFCS off)?

A

With no hyd pressure a spring loaded piston and return hyd pressure in each section of the dual extensible link assembly centers and locks its respective cylinder at a null position. The extensible link in this state, functions as a fixed rod in the flight controls.

59
Q

What happens if one ground contact light stays on after pickup or doesn’t go off after landing?

A

Should either or both L or R GND CONT indi-cating lights on the MAINTENANCE PANEL not illuminate after landing, there will be no reduction in pitch gain of the Automatic Flight Control System (AFCS), stick input to the DASH actuators will not be cancelled, and the LCT actuators will not be cancelled, and the LCT actuators will not program to the GND position.
Basically AFCS inputs will not be nulled/reduced.

60
Q

There are 3 electrical connections on each ILCA. What are they?

A

1 self LVDT and 2 summing LVDT’s (1 for each AFCS):
Individual servo valve and self feedback wiring pass directly through the link connector. The summed LVDT passes its signals through two summed LVDT connections and then through the link connector.

61
Q

What does the “artificial feel” system consist of?

A

Mag brake, centering spring, balance spring, and viscous dampener.

62
Q

What provides control dampening with the mag breaks on? How about off?

A

Centering springs provide control dampening with mag breaks on. Viscous dampeners provide it with them off.

63
Q

Why is the artificial feel system in the controls required?

A

Because the ILCAS block any feedback from the rotor system.

64
Q

Why are viscous dampeners required in the flight control closet?

A

They provide a dampened rate of movement to the ILCA Pilot valves which reduces stress on the helicopter and prevents rapid input into the rotor system.

65
Q

What is the summing link? The swing link?

A

The summing link combines the #1 and #2 AFCS extensible link inputs into one output.
The swing link provides a pivot point if one AFCS has failed. It allows the summing link to provide additional required control movements.

66
Q

Where are the AFCS temperature probes located?

A

Under the nose of the aircraft near the search lights.

67
Q

What is something to remember while landing AFCS off?

A

Move cyclic as much as needed to a position that makes ground contact lights come on. Remember, the dash is in a locked position so control position will most likely be unusual when landing.

68
Q

How might you tell that a proximity switch is broken?

A

If you only have one ground light on, it may or may not mean that the LCTs will retract or that the dash will be programmed.

69
Q

What might you want to avoid as a consequence of the Dash?

A

A nose low attitude. The dash has about 44% authority, but if it drives too far forward, you may not be able to overcome it.

Chinook CH-47D (15 decks)

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