Aircraft Autopilot and Servo Systems

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Questions and Answers

What type of actuators do large modern aircraft typically use?

Electro-mechanical actuators

Electro-pneumatic actuators

Hydraulic-only actuators

Electro-hydraulic actuators (correct)

How are electro-pneumatic servos designed to operate when no electrical signal is present?

Pistons are locked in place

Only one valve opens

Both valves remain open (correct)

All valves are closed

What generates the position and rate feedback signals in an electro-mechanical servo for AC motors?

Position sensor only

AC motor only

Servo motor and clutch

Tachogenerator and potentiometer (correct)

What is the key difference between power assisted and power operated flight control systems?

Connection method of actuators to control surfaces Signup and view all the answers

In a power assisted system, what initiates the movement of the control surface when the pilot pulls back on the control stick?

Movement of the control lever Signup and view all the answers

What role does the potentiometer play in the electro-mechanical servo?

It provides position feedback Signup and view all the answers

Which component is primarily utilized in power assistance to help the pilot move the control surface further?

Control lever Signup and view all the answers

What is the primary function of the electro-magnetic valve in an electro-pneumatic servo?

To open and close the pressure ports Signup and view all the answers

What is the purpose of applying feedback in command signal processing?

To ensure corrective control is proportional to command signal inputs Signup and view all the answers

What distinguishes the E and I bar sensors from traditional transformers?

Presence of adjustable components and counter wound windings Signup and view all the answers

How do moving vane sensors differ in operation compared to E and I bar sensors?

They require two out-of-phase signals for excitation Signup and view all the answers

What does the output signal of an E and I bar sensor depend on?

The lateral motion of the I bar relative to the E section Signup and view all the answers

What phenomenon do I bar sensors measure in relation to flight attitude?

Acceleration related to attitude change Signup and view all the answers

In what condition does a moving vane transducer output no signal?

When the aircraft is in level flight Signup and view all the answers

What role does programming play in aircraft control systems?

It helps produce precise maneuvers based on control modes Signup and view all the answers

What happens in an I bar sensor when there is no external motion sensed?

It produces output directly related to attitude change Signup and view all the answers

What happens to the Failure Sensor piston when a transfer valve is blocked?

It is driven from neutral and indicates failure. Signup and view all the answers

Which component is primarily responsible for detecting faults in the hydraulic actuator system?

Failure Sensors Signup and view all the answers

What is the role of the remaining non-failed half of a duplex actuator when one half fails?

It continues to function normally to drive the control surface. Signup and view all the answers

Before an automatic control system can be engaged in an aircraft, what must be fulfilled?

All preliminary operating requirements must be met. Signup and view all the answers

Which of the following components is NOT part of the hydraulic duplex servo-actuator schematic?

Static Pressure Regulator Signup and view all the answers

Gain scheduling is performed by which component in the actuator system?

FCC processor Signup and view all the answers

What condition occurs when P1 + P4 is greater than P2 + P3?

The failure sensor detects a fault. Signup and view all the answers

What is an important feature of the duplex actuator during a failure?

It maintains functionality using the non-failed half. Signup and view all the answers

What role does the servo unit play in a power operated control system?

It supplies power to move the control surface. Signup and view all the answers

What is one main advantage of directly operating the hydraulic power unit?

It requires less computer power output. Signup and view all the answers

In a power operated control system, what addition is necessary to provide pilot feedback?

An artificial feel mechanism. Signup and view all the answers

Which component operates the main control valve in an electro-hydraulic actuator system?

The autopilot actuator. Signup and view all the answers

What effect does the absence of cable slack have in an electro-hydraulic actuator system?

It results in higher sensitivity and accuracy. Signup and view all the answers

What initiates the movement of the control input quadrant during manual operation?

Pilot pulling the control column backwards. Signup and view all the answers

What is monitored by the Linear Variable Differential Transducer (LVDT) in the electro-hydraulic system?

The movement of the actuator. Signup and view all the answers

Which component connects the control column to the control surfaces in a power operated control system?

Control lever. Signup and view all the answers

What is the main purpose of the aircraft autopilot?

To control vertical speed, attitude, and heading Signup and view all the answers

Which mode of operation does not involve control in the roll channel?

Yaw dampening mode Signup and view all the answers

How does the Yaw Damper primarily function?

By maintaining directional stability Signup and view all the answers

In helicopters, what is the primary function of the Stability Augmentation System (SAS)?

To assist the pilot in maintaining control Signup and view all the answers

What does automatic trim control achieve in an aircraft?

It helps in maintaining the desired flight attitude Signup and view all the answers

Which of the following is not a category of the Automatic Landing Systems?

Altitude Signup and view all the answers

What is a crucial function of the Autothrottle system?

To automate engine power adjustments Signup and view all the answers

An essential part of the Flight Management System (FMS) is:

The navigation database Signup and view all the answers

What does the inner loop of autopilot primarily control?

Roll Signup and view all the answers

What is a common outcome when engaging an autopilot system?

Reduced fatigue during flight Signup and view all the answers

Which system is designed to maintain control surface stability?

Yaw dampers Signup and view all the answers

Which mode of autopilot allows for navigation without manual heading input?

Automatic navigation mode Signup and view all the answers

What is the main purpose of the glideslope function in Automatic Landing Systems?

To assist in maintaining a proper descent path Signup and view all the answers

Study Notes

Autopilot Purpose

The aircraft autopilot controls the aircraft in vertical speed, attitude and heading
The autopilot reduces workload and fatigue on the flight crew.
The autopilot provides improved flight comfort and stability.
Aircraft that use autopilot systems do not use fly-by-wire; they typically use electro-hydraulic actuators controlled electrically.

Electro-Pneumatic Servo

An electro-pneumatic servo consists of an electro-magnetic valve with dual poppet ports.
The valve ports are connected via pressure ports & orifices to two cylinders containing pistons sealed against pressure loss.
The valves are controlled by electrical command signals from the autopilot.
When no signal is present, both valves are open.

Electro-Mechanical Servo

This mechanism contains an AC or DC motor and gear train, coupled to the flight control system via an electro-magnetic clutch.
The electro-magnetic clutch is connected via a gear train and a sprocket and chain drive.
Feedback is given by a potentiometer in a DC motor or a CX synchro & tachogenerator.
The feedback provides position and rate feedback signals.

Powered Flight Controls

Powered flight controls are used in high performance aircraft.
There are two types of controls; power assisted and power operated.
The main difference between the two systems is in how the actuators are connected to the control surfaces.

Power Assisted Control

The pilot's control stick is linked to the control surface via a control lever.
The control lever pivots about a point when the pilot pulls back on the stick to begin a climb.
The lever begins moving the control surface up.
At the same time, the control valve pistons are displaced allowing hydraulic fluid to flow to the left side of the actuating jack.
The pressure exerted on the piston causes the whole servo unit and control lever to move to the left.
The pilot is assisted in moving the control surface further because of the greater control effort produced.

Power Operated Control System

The pilot's effort is only required to move the control lever and control valve piston, as the servo unit provides the power to move the control surfaces.
The pilot doesn't feel the loads acting on the control surfaces, requiring artificial feel mechanisms.

Electro‐Hydraulic Actuators

The transfer valve is electrically controlled and operates a piston assembly which in turn operates the main control valve for the actuating cylinder.
The movement of the actuator is monitored by an LVDT (Linear Variable Differential Transducer) which provides feedback to the computer.
The system is sensitive and accurate due to the absence of cable slack, stretch, and drag.

Manual Operation

The control column moves the control quadrant, which relates to a back stick input to move the elevators.
Pulling the stick backwards initiates a climb, turning the control input quadrant and moving the upper end of the control valve actuator to the left.

Duplex Actuator

Duplex actuators have redundancy: if one half of the actuator fails, the other half continues operating normally.
Failure Sensor piston drives from neutral and indicates failure, de-energizing the SOV (Solenoid Operated Valve).
This system prevents uncommanded flight control input.

Quadruple Redundant Duplex Hydraulic Servo Actuator

The system incorporates SOVs, EHV (Transfer Valves), DPs (Failure Sensors), System Selector valve, Mechanical input – mode selector valve, MCV, Bypass Damper, CAS LVDT (Rate feedback), and RAM LVDT (Position feedback).

Interlocks

Pre-flight checks must be conducted to ensure the system is safe before engaging with the aircraft's flight controls.
These checks include setting system parameters, automatic programming for handling qualities, and applying feedback.

Autopilot Sensors

E and I bar sensors use an AC signal for excitation of the primary winding, operating based on AC transformer principles.
The I bar's movement relative to the E section varies the air gap, resulting in output signals.
Additionally, these sensors can be used to sense acceleration in a plane by aligning them with the sensing axis.

Moving Vane Sensors

They use two square wave signals as excitation inputs, 180 degrees out of phase.
In the null position, there is no output.
If mounted on a vertical gyro, they sense pitch and roll attitude changes, outputting only during attitude changes.

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Description

This quiz covers the fundamental principles of aircraft autopilot systems and their components, including electro-pneumatic and electro-mechanical servos. Explore how these systems enhance flight stability, reduce crew workload, and improve overall comfort during flight.