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Aircraft Control Systems: Autopilot and Feedback Mechanisms

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30 Questions

What is the purpose of the follow-up system in an autopilot system?

To provide position feedback and return the control surface to neutral

What type of systems does the autopilot mode select panel belong to?

Command element

What is the primary function of the computer amplifier in an autopilot system?

To compute, amplify, and process signals from the sensing and command elements

What is the ultimate goal of the autopilot system's correction process?

To return the control surface to its neutral position

What type of systems do the attitude gyros, rate gyros, accelerometers, and pitot static systems belong to?

Sensing element

What is the role of the output element in an autopilot system?

To move the control surfaces of the aircraft in response to the computer demands

What are the possible types of autopilot actuators?

Pneumatic, electric servomotors and electromagnetic transfer valves

What is the minimum requirement for an autopilot system?

Pitch and roll attitude, and heading information

What is the purpose of using airspeed and altitude information in an autopilot system?

To alter the gain programming of the pitch, roll, and yaw autopilot channels

What is the function of an angle of attack sensor in an AFCS?

To compute approach path

What is the purpose of a radar altimeter in an AFCS?

To provide automatic landing control

What type of information is provided by inertial navigation systems, radio receivers, and global positioning systems in an AFCS?

Flight path and navigational data

What is the typical range of overpowering force on the control wheel?

25 to 35 pounds

What does the trim indicator provide?

A visual display of the magnitude and polarity of the signal

What happens when a pointer on the trim indicator remains continuously deflected?

The servo amplifier needs to produce a continuous correction signal

What is the purpose of the autopilot disengage switch?

To rapidly disengage the autopilot system

Where are the autopilot disengage switches typically located?

On the control yoke

What happens when the servo commands are satisfied?

The pointers on the trim indicator return to their zero trimmed positions

What is the normal autopilot engaged mode where the pilot does not touch the controls?

Command mode

What is the purpose of the transducer on the control wheel in control wheel steering mode?

To convert the input force into an electrical signal

What is the primary function of the Mode Select Panel in an aircraft?

To interface with the flight crew and automatic flight control systems

What happens when the pilot applies a reasonable amount of pressure on the respective flight control?

The autopilot's actions are overridden by the pilot

What is the purpose of the Fail Operational feature in an aircraft's autopilot system?

To allow automatic landing to continue despite a single input failure

What is the main difference between manual mode and command mode in an autopilot system?

In manual mode, the pilot can change the attitude and heading of the aircraft

What is the function of the autopilot in control wheel steering mode?

To assist the pilot in flying the aircraft

What type of sensing device is used in the control wheel steering transducer?

E-and-I-bar assembly or LVDT or piezoelectric-type

What is the relationship between the flight director and the autopilot system?

The flight director relies on the autopilot system

What is the term for the mode where the pilot sets the autopilot to assist in flying the aircraft?

Control wheel steering mode

How many autopilot systems can be engaged during normal flight conditions?

One

What navigation modes are selectable through the Mode Select Panel?

Lateral and vertical navigation modes, including VOR/ILS, heading hold, and others

Study Notes

Autopilot System

  • Control surface movement causes a change in aircraft attitude, which is then corrected by the sensor output, returning the control surface to its neutral position.

Autopilot Elements

  • A basic autopilot consists of sensing, command, and output elements.
  • The sensing element detects uncommanded movement of the aircraft about its three flight axes and the rate of that movement.
  • The command element includes the autopilot mode select panel, flight controller, control wheel steering, and navigation systems.
  • The output element consists of units that move the control surfaces of the aircraft in response to computer demands.

Sensing Elements

  • A minimum of pitch and roll attitude, heading information, and airspeed and altitude data are required for autopilot function.
  • Additional sensors can improve autopilot function, including pitch, roll, and yaw rate sensing, vertical acceleration, and air data information.
  • A fully operational AFCS (Automatic Flight Control System) uses data from inertial navigation systems, radio receivers, global positioning systems, flight management systems, and radar altimeter information.

Command Elements

  • The autopilot mode select panel is the primary interface between the flight crew and the automatic flight control systems.
  • The panel contains switches and logic circuits for on/off control and mode selection for autopilot/flight director channels and the Autothrottle system.
  • The mode-select panel autopilot engage switches have CWS (Control Wheel Steering) in place of MAN (Manual).

Control Wheel Steering

  • The pilot can set the autopilot to control wheel steering mode, where the pilot's input is measured and used as an input signal to the flight control computer.
  • The autopilot stays engaged and helps to move the control surfaces.
  • The transducer on the control wheel converts the input force into an electrical signal.

Autopilot Override

  • The pilot can overpower the autopilot at any time by applying a reasonable amount of pressure on the respective flight control.
  • A typical overpowering force would be 25 to 35 pounds of turning force on the control wheel or 40 to 50 pounds of force on the control column.

Trim Indicator

  • The trim indicator provides a visual display of the magnitude and polarity of the signal being applied to the flight control actuator or servomotor.
  • Each pointer represents a primary flight control, and a pointer is deflected each time a servo amplifier command signal is applied to the actuator.
  • The pilot can manually trim the aircraft until the pointer returns to the zero position.

Understand how autopilot systems work in aircraft, including the role of control surfaces, sensors, and feedback mechanisms in maintaining stable flight. Learn about the process of correcting aircraft drift and returning to a selected attitude.

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