2nd Test Flashcards
What does altitude sensing require?
Use of a reference, which provides datum for pitch, roll, and yaw
In modified aircraft instruments on light aircraft, what is the reference used to sense altitude?
Sensing of the angular movement of gimbals in a gyro to produce differential air pressure (in vacuum gyros) or DC signals (elec gyro)
What do vertical and directional gyro units measure?
Altitude and heading for autoflight.
What references does an IRS use and what data bus signals are used?
sensor inputs, nav databases (GPS), altitude info from AFCS.
- Data bus = ARINC 429, ARINC 629
In what way is the electronic signals amplified?
pneumatic/hydraulic, magnetic, electric
Does an aircraft using parallel hydraulic and pneumatic servo units use powered flight controls?
No
How is the autopilot of a parallel hydraulic and pneumatic servo unit engaged and disenganged?
Controlling the hydraulic or air supply.
Does an aircraft using electric servo units use powered flight controls and how is it engaged/disengaged?
No
- Engaged by closing a clutch
What servo units are used in powered flight controls?
Hydro/Electric servo motors
What is a single axis system?
Only the ailerons are controlled, keeping a wing-level condition
What is a dual axis system? And how is the rudder controlled in these systems?
Controls ailerons and elevator for pitch and roll.
- Rudder is controlled by a yaw damper system
What is a 3 axis system? And what 2 groups do these fall into?
Controls elevators, ailerons and rudder.
- Two Groups:
Ones that control the rudder full time, and ones that only control the rudder during autoland (all other times = yaw damper)
What are the 2 methods to detect attitude changed?
Displacement System: (measures displacement from a datum)
- Used on most autopilots
Rate System: (measures using rate gyro)
- More capable, but more complex
- Yaw dampers
- Time aspect
What is inner loop control?
A stability augmentation section of the AFCS where the servo units will adjust any changed in attitude automatically.
What is outer loop control?
Aircraft position or path is deliberately changed by flight crew.
What is an Unsynchronized auto flight?
When the autopilot is not engaged, the aircraft does not know what the aircraft is doing. It will immediately try to move the aircraft back to a level altitude as quickly as possible.
- Before engaging, pilot must trim the aircraft to fly straight (hands off control)
What is synchronized autopilot?
Can be engaged with the aircraft at any sensible attitude.
- When the autopilot is engaged, the system is powered but not connected to the flight controls.
What are interlocks, and what forms do they come in?
Forms: Hardware, software
Interlocks:
- For the autopilot to engage, the interlock circuit must be complete
- The autopilot will not allow faulty external system to control outer loop (it will be ignored if selected by crew)
- If the failure is to the attitude reference system, autopilot does not engage.
What are the 2 main Cross feed cases?
Versine:
- Versine signal (thus lift compensation) is determined by roll angle.
- In a dual axis system, the yaw damper assist to reduce adverse yaw but does not compensate for loss of lift and drops the nose. To reduce this effect, a signal is produced in the roll channel to produce a nose-up command.
Aileron to Rudder Cross Feed:
- Used in 3 axis systems
- Signal proportional to roll angle is supplied to the rudder channel, causing rudder to be applied when banked.
- Minimizes side slip
What is the purpose of outer loop?
Maintain the aircraft following a specific path
In altitude (ALT) mode, what is measurement is used to hold the aircraft to a altitude?
Barometric pressure from the ADC
What is ALT SEL
- Air data outer loop
Pilot is able to select an altitude which calculates the difference between actual altitude and selected altitude, and corrects for it.
- Automatically switches to ALT HOLD when aircraft levels off.
What is VS mode?
- Air data outer loop
Vertical speed mode
- Pilot selected vertical speed is compared to the actual vertical speed measured by the air data computer.
What is IAS?
- Air data outer loop
Airspeed Hold
- works in similar way to VS mode, but the signal is airspeed error supplied by the ADC
What is VNAV?
- Air data outer loop
The vertical control applied to the pitch system from the FMC.
- Always used with auto-throttle
- FMC has control over aircraft vertical position and engine thrust.
What is pitch attitude hold?
- Fixed datum outer loop
A fixed datum mode to maintain a certain pitch. Often used in turbulence mode.
What is TURB mode?
- Fixed datum outer loop
Turbulence mode:
- Reduce autopilot channel amplifier gain about 50%, slowing the response to disturbance and softening the ride.
- Reduce rapid displacement and structural loads.
What is wing levelling?
- Automatically rolls wing to a level condition if the angle of the aircraft is less than 3-5 degrees.
- NOT SELECTABLE (can be overridden)
- Engage heading hold to keep the aircraft on a constant heading.
What is Roll Attitude Hold?
Opposite of wing levelling
- Removes heading monitoring and wing levelling
- remains at constant roll attitude.
What does CWS (Control wheel steering) and TCS (Touch control steering) do?
Allows control of aircraft when autopilot is engaged
What is CWS?
Only fitted to a/c with powered flight controls.
- Fitted with force transducers
- A dead zone amplifier will not allow the signal to pass through the amp until a certain value is reached.
- When pilot releases the force on control column, a/c will remain in the same pitch attitude as when the force was removed.
What is TCS?
For aircraft without powered flight control.
- Uses a spring loaded press button on control wheel to disengage autopilot
- Puts it into a synchronizing mode and holds attitude when switch is released.
What are the two command modes that the autopilot can be in?
CMD - Command mode
- The FCC uses sensor inputs to calculate the commands to the actuator. The actuators input to the PCU to move aileron and elevator.
CWS - Control wheel steering mode
- Force transducers on control column sends commands to autopilot to move aileron/elevator.
What commands can be calculated with an FCC?
- Radio nav systems
- IRS
- FMCS
- Autopilot/control surface sensors
- Speed/Mach trim
- Altitude alerts
- Disengage warnings
What are the purpose of Yaw dampers?
- Prevent a dutch roll from the rudder channel. A/c becomes speed and altitude limited with a faulty yaw damper
- Turn coordination: Minimal rudder control to assist a swept wing turn
- Modal supression: Body bending about the wing area due to turbulence, causing vibration particularily in long/slender bodies.
What is the difference between Parallel and Series Yaw Dampers
Parallel - Servo motors operate the control column and the control surface e.g. rudder pedal moves when yaw damper activates.
Series - Control inputs add/subtract from any control column inputs. No movement in flight deck.
Do yaw dampers operate full time?
Yes, only disengaged on ground.
What are the components of a yaw damper?
- Yaw damper coupler (contains its own rate gyro)
- Actuator (Uses yaw rate from IRS. May be separate unit or integral to rudder PCU)
What problem does the force trim system accommodate for and how does it work?
Fatigue
- Removes forces on the cyclic and pedals while moved to a new position. When button is released, new location becomes zero point.
What are the 2 types of electro-mechanical actuators?
Series:
- Actuator moves control surface but not cockpit controls
- The cockpit control is prevented from moving by the artificial feel system
- Operates at high speed to counter small disturbances quickly/
- Limited authority (10% total control travel), so not normally suitable for autopilot functions.
Parallel:
- Actuator moves both cockpit control and control surface
- Artificial feel is required
- Full authority through its range of travel
- Stick position pick-off is required
- Combined with artificial feel system to reduce weight/complexity.
What benefits does a combination of series and parallel actuators provide?
- Good short term stabilizations
- Long term attitude retention and autopilot capabilities.
What is Beep Trim?
A 4-way trim switch used for fine adjustments in attitude.
What is the purpose of a leaky integrator in a Stability Augmentation System?
Simulates an attitude signal that can be used as a datum.
- Provides a pseudo attitude by integrating the rate signal.
- Only provides altitude based on the last 20-30 seconds.
- Can overcome the problem of nose dropping during turn
What 2 things determine the SAS’s ability to provide a long-term altitude?
- Sensitivity of the rate gyro
- Time constant of the integrator
What are the limitations to the SAS?
Even when pilot has moved stick, rate damping is taking place but there will be no attempt to return to the datum. The system will only try to maintain an attitude when the helicopter is in trimmed flight.
What is the difference between SAS and SCAS?
- SAS appears sluggish
- SCAS has a crisper response
What is the difference between SAS and SCAS Attitude-Based Stabilization?
Use of attitude gyros and parallel actuators
What is Rate Command Attitude Hold (RCAH)?
Maintains pitch, similar to wing leveler
Below and above 40 knots IAS, is the flying referenced to ground speed or airspeed?
(Due to yaw)
Below 40 knots: Ground speed
Above 40 Knots: Airspeed
Why is trimming an aircraft in pitch necessary?
Affected by changed in center of gravity due to airspeed and fuel use
In aircraft without powered flight controls, how is pitch trim done?
The use of a separate servomotor
Trim Threshold Circuit:
- Detects elevator signals which have been applied for more than a certain time 3-5 seconds
In aircraft with powered flight controls, how is pitch trim done?
By varying the angle of incidence of the horizontal stabilizer
How does Speed Trim work?
Keeps target airspeed by varying TRIMMABLE HORIZONTAL STAB (THS).
Does speed trim work during autopilot use?
No, it is inhibited.
How is Mach Tuck compensated for?
With the Mach Trim system:
- Pitches nose up by either transferring fuel from front of the aircraft to the trim tank, or, using an actuator to move horizontal stab
- Normally forms part of the elevator trim system
What main components make up the Mach Trim system?
- Mach Trim coupler unit
- Mach trim actuator
- Fail lamp
- Test switch
At what speed does the Mach Trim actuator shaft retract?
0.715 Mach - 0.815 Mach
How far away are VOR stations spaced and what frequency do they operate?
50-80 nautical miles.
108-118 MHz
What are the 3 indicating elements on a Horizontal Situation Display Indicator (HSI)?
-VOR
- A bearing scale / Index
- A deviation pointer
- TO-FROM indicator
How is coupling the roll channel of a VOR channel initiated?
By selecting VORLOC
What is the cone of confusion and how is it prevented?
Where radials frequencies converging over a VOR station.
- Prevented by cutting off VOR signal at the entrance of the cone so that the roll channel only responds to heading data signals. Cut-off is automatic and is kept for a preset time.
What are the systems in the roll channel?
- INS
- GPS
- FMC
- FCC
What are the 2 limits for an Auto Thrust system?
Maximum Thrust - max thrust available
Thrust limit (or Thrust REF) - limit for the operating mode in use
What does a potentiometer installed in the EEC cables do?
Measure the thrust lever angle
What is an auto throttle clutch pack?
Fitted to aircraft with conventional engine controls, allows override by the pilot for the servo commands
