Flight Control Systems Overview

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Questions and Answers

What is the primary function of a torque tube in a basic control system?

To guide control cables through a structure member

To maintain constant tension on cables

To connect cockpit controls to control surfaces

To change linear motion to rotary motion (correct)

What role do cable guards or guard pins play in a flight control system?

They dampen vibration of the control cables

They maintain constant tension on the cables

They prevent cables from jumping out of pulleys (correct)

They stabilize the control surfaces during flight

In a direct cable control system, what is associated with the control column's operation?

Imparting tension to the steel cables (correct)

Changing the direction of control cables

Altering the internal structure of the fuselage

Adjusting the length of the cable

How does a cable tension regulator function in a flight control system?

It maintains constant cable tension across varying temperatures Signup and view all the answers

Which type of mechanical control system is characterized by the use of bell cranks, levers, and torque tubes?

Push-pull rod system Signup and view all the answers

What happens to the force the pilot feels on the control column as airspeed increases in a direct cable control system?

The force increases in correspondence to airspeed Signup and view all the answers

What is the purpose of fairleads in a flight control system?

To guide control cables and dampen vibrations Signup and view all the answers

Which of the following systems is not recognized as a type of mechanical control system used in aircraft?

Servo and actuator systems Signup and view all the answers

What is a primary advantage of cable systems over push-pull rod systems in a flight control system?

Cables have less mechanical play and provide more accurate transmission. Signup and view all the answers

In the hydraulic power flight control system, what role does the servo valve play?

It amplifies the pilot's mechanical input by directing hydraulic fluid. Signup and view all the answers

Which of the following statements about the behavior of cables and push-pull rods in cold weather is true?

Cables experience decreased tension due to differences in material contraction. Signup and view all the answers

Which component is NOT part of the hydraulic circuit in a hydraulic flight control system?

Mechanical linkages Signup and view all the answers

What is a significant disadvantage of the push-pull rod system compared to the cable system?

It lacks warning signs before failure. Signup and view all the answers

What mechanism assists the pilot in controlling larger and heavier aircraft?

The power boost control system using hydraulic actuators. Signup and view all the answers

Why are cables considered a safer transmission system than push-pull rods?

They show warning signs, such as stretching, before breaking. Signup and view all the answers

Which of the following is true regarding the mechanical circuit in the hydraulic flight control system?

It connects cockpit controls with hydraulic circuits through physical linkages. Signup and view all the answers

What happens to the input from the flight deck during a hydraulic power failure in a power-assisted flight control system?

The hydraulic actuator is bypassed and input goes directly to the control surface. Signup and view all the answers

In a power-operated type hydraulic system, what is directly connected to the flight control surface?

The servo unit. Signup and view all the answers

What role does the artificial feel unit play in a hydraulic transmission system?

It simulates the effect of air load for the pilot. Signup and view all the answers

Which type of feel dominates at low speeds and high deflection control demands?

Spring feel Signup and view all the answers

How does the input force from the control column affect elevator movement in the power-assisted type system?

The bottom part of the control lever moves in the opposite direction from the column. Signup and view all the answers

In a power-operated flight control system, what must the pilot do to control the aircraft?

Move the control lever and control valve piston. Signup and view all the answers

Which characteristic is present in the power-operated type hydraulic system concerning pilot feedback?

The pilot does not sense the air load effects directly. Signup and view all the answers

Which scenario describes when the Q feel is expected to dominate in an aircraft control system?

At high speeds with low control deflections. Signup and view all the answers

What is one main advantage of fly-by-wire systems over traditional mechanical control methods?

Reduced maintenance time due to replaceable units Signup and view all the answers

What factor is most concerning regarding the reliability of fly-by-wire systems?

Total loss of flight control computers leading to immediate failure Signup and view all the answers

In fly-by-wire systems, what role do electrohydraulic valves play?

Convert electric signals into hydraulic fluid flow Signup and view all the answers

Which component primarily directs hydraulic fluid to control actuators in a fly-by-wire system?

Main control valve Signup and view all the answers

What does the elimination of traditional connecting methods in fly-by-wire systems result in?

Improved fuel efficiency and reduced weight Signup and view all the answers

What is the primary purpose of hydraulic actuators in large aircraft control systems?

To assist the pilot in moving control surfaces Signup and view all the answers

What material are aircraft control cables generally fabricated from?

Carbon fibre or corrosion resistant steel wire Signup and view all the answers

What is the function of a pulley in an aircraft control system?

To change the direction of a cable Signup and view all the answers

Which component is primarily used for adjusting the tension of control cables?

Turnbuckles Signup and view all the answers

How is a bell crank utilized in an aircraft control system?

To transmit and allow for changes in force direction Signup and view all the answers

What is the correct description of a push pull rod in an aircraft control system?

A component transmitting force and motion between members Signup and view all the answers

What is the function of a quadrant in a flight control system?

To impart force and motion to a cable system Signup and view all the answers

What determines the types and complexity of control mechanisms in an aircraft?

The aircraft size, speed, and mission Signup and view all the answers

Study Notes

Aircraft Hydraulic Systems

Aircraft size, speed and mission dictate the complexity of control mechanisms
Small or low-speed aircraft have cockpit controls directly connected to control surfaces via cables or pushrods
High-performance aircraft use hydraulic actuators to move control surfaces relieving pilot fatigue
This reduces pilot fatigue and improves system performance

Hydraulic Power - Flight Control System Components

Cables

Made from carbon fiber or corrosion-resistant steel wire
Aircraft mechanical cables use 7 strands, each with multiple wires, helically twisted
Cable size is determined based on the circumscribed circle, number of strands, and wires per strand

Pulleys

Used in aircraft control to change the direction of a cable

Turnbuckles

Commonly used to adjust the tension on control cables
Length (threads flush with ends of barrel)
Swaged terminal
Barrel
Pin eye
Turnbuckle body
Locking clip

Bell Cranks

Used to transmit and change the direction of force
It transmits and permits change in the direction of the force.

Push Pull Rods

Used to transmit force and motion between components
It is used between bell crank to torque arm to transmit the force and motion from one member to the other.
Push pull rods are also called control rods.
- Checknut
- Threaded rod end
- Tube
- Adjustable antifriction rod end
- Rivets
- Adjustable rod end clevis

Quadrant

Used at the base of control columns or sticks to impart force and motion to a cable system
Imparts force and motion to a cable system

Torque Tube

A hollow shaft that converts linear motion to rotary motion
A torque arm or horn is attached to the tube, either by welding or bolting, imparting twisting motion

Cable Guards / Guard Pins

Installed on pulley brackets to prevent cables from jumping out of pulleys
Prevents cables from jumping out

Fairlead

Guide control cables through structure members
Dampen cable vibration, maintain alignment and seal openings (e.g., bulkheads)

Cable Tension Regulator

Ensures constant cable tension at various temperatures
Tension is checked using a tensionmeter

Types of Mechanical Control Systems

Push-pull rod system
Cable and pulley systems
Chain and sprocket system

Direct Cable Control System

High-strength steel cable connects cockpit controls directly to control surfaces
Pulleys support the cable through the fuselage
Directs the cable; used in low-speed aircraft
Pilot force on the control column matches the airspeed

Push Pull Rod Control System

Uses bell cranks, levers, and torque tubes
Cockpit controls connect to a hollow aluminum tube with threaded inserts and a clevis or rod bearing

Cable & Pulley vs Push-pull Rod Systems

Cables are lighter than push-pull rods
Cables only transmit pull forces, while push-pull rods transmit both push and pull
Cable systems have less connections for less mechanical play and more accurate transmission
Cables show warning signs before breaking, while push-pull rods break suddenly. Cables are safer
Cable tension decreases with cold weather, while push-pull rod material is similar to aircraft structure
The pilot may feel air load effects differently in different types of systems

Hydraulic Power Flight Control System

As aircraft increase in size, control becomes more difficult
Power-boost control systems operate similarly to power steering in automobiles (hydraulic actuator in parallel) and directs hydraulic fluid to actuate the surface
Mechanical circuit connects cockpit controls to hydraulic systems
Hydraulic circuits use pumps, reservoirs, filters, pipes, valves, and actuators
Actuators convert hydraulic pressure into control surface movement.

Hydraulic Power Flight Control System - Continued

Servo valves control actuator movement
The pilot's input is transmitted to the servo control unit through the mechanical linkages
Servo control moves and controls the surface in proportion to input signal
The Servo valve amplifies mechanical input by directing high-pressure hydraulic fluid
Different modes of operation (power-assisted, power-operated).
Power-assisted type: steering column and control surface are disconnected - Hydraulic actuators bypass and force goes to the control surface if power fails
Power-operated type: the pilot's control connects only to the control lever, servo connects to control surface

Artificial Feel Unit

In a hydraulic transmission system, the pilot does not directly feel the effects of air load
Artificial feel unit simulates air load
Two types: spring feel (low speed, high deflection), Q-feel (high speed, low deflection)

Electrical and Fly-By-Wire Systems

Modern aircraft use electric wires to connect flight controls instead of physical components
Pilot inputs are converted into electric signals
A computer processes flight characteristics
Processed signals convert to hydraulic signals to move control surfaces
Advantages: reduced weight and maintenance time

Fly-By-Wire Systems Concerns

Reliability is a major concern; computer failure results in immediate loss of control
Systems often include backup system

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Description

Test your knowledge on the various components and functions of flight control systems. This quiz covers topics such as torque tubes, cable guards, and hydraulic power systems. Perfect for aviation enthusiasts and students studying aircraft mechanics!