Aircraft Control Cables Standards and Materials

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Questions and Answers

What is the primary method of moving flight control surfaces in commuter and general aviation aircraft?

Digital flight control technology

Electronic servos

Hydraulic systems

Flexible control cables (correct)

Which material is more suitable for aircraft control cables in corrosive environments?

Plastic composites

Stainless steel (correct)

Carbon steel

Aluminum alloy

What type of cable is limited to straight runs without pulleys?

Extra-Flexible 7 × 19

Flexible 7 × 7

Hybrid cables

Non-Flexible 1 × 7 or 1 × 19 (correct)

Which cable construction type is most commonly used in aircraft flight controls?

7 × 19 Signup and view all the answers

What defines the tensile strength of an aircraft control cable?

The size, material, and construction Signup and view all the answers

Which type of cable is used where cables must change direction over relatively small-diameter pulleys?

Extra-Flexible 7 × 19 Signup and view all the answers

What is a characteristic of all aircraft control cables?

They are pre-formed. Signup and view all the answers

Which of the following stresses are commonly encountered by cables in service?

Bending and sudden shock loads Signup and view all the answers

What is the primary function of a turnbuckle in aircraft control systems?

To provide adjustable cable tension. Signup and view all the answers

Which of the following statements about Bowden cables is correct?

They are designed to only pull. Signup and view all the answers

What is the maximum number of threads that should be visible at the turnbuckle ends after adjustment?

Three threads. Signup and view all the answers

What feature do broken cable compensators provide in aircraft control systems?

They prevent false control input from a broken cable. Signup and view all the answers

What is the primary purpose of cable drums in aircraft?

To actuate the continuous-loop cable. Signup and view all the answers

How does a swivelling coupling function in an aircraft control system?

It allows angular movement for the sliding end fitting. Signup and view all the answers

What are the characteristics of Teleflex cables in comparison to Bowden cables?

They are designed to both pull and push. Signup and view all the answers

In an aircraft control system, when should the primary stop contact occur?

Before the secondary stop is contacted. Signup and view all the answers

Which cable system is designed specifically to handle tracking and friction limitations?

Bowdenflex cables. Signup and view all the answers

What is the function of cable quadrants in control systems?

To change direction of cable movement. Signup and view all the answers

What is an important aspect of installing modern clip-type locking devices?

They need to be inserted into a groove on the cable terminal end. Signup and view all the answers

Which type of wire is used to lock primary control cables?

Stainless steel wire. Signup and view all the answers

What should be avoided when adjusting turnbuckles?

Lubricating the turnbuckles. Signup and view all the answers

What is the minimum bend radius for Bowdenflex cables?

3 inches. Signup and view all the answers

What is the safety factor of a cable with a strength of 10,000 lb and a total working load of 2,000 lb?

5 Signup and view all the answers

What are the two factors that cause cable stretch under load?

Structural stretch and elastic stretch Signup and view all the answers

What is the primary purpose of Lockclad cable assemblies in aircraft?

To eliminate sagging and prevent wear Signup and view all the answers

What does a Nicopress termination achieve with respect to cable strength?

100% of the cable strength Signup and view all the answers

During the swaging process for aircraft cables, what indicator is used to ensure proper compression?

A before and after gauge Signup and view all the answers

What material are shackle pins primarily made from?

High-tensile steel and high-tensile stainless steel Signup and view all the answers

What is the purpose of the proof load test after cable installation?

To load the cable to 60% of its breaking strength Signup and view all the answers

What should be used at points where a control cable contacts the aircraft structure?

Fairleads made from soft plastic or fibre Signup and view all the answers

What material are control cable pulleys typically made from?

Hard fibre, aluminum, or stainless steel Signup and view all the answers

How is cable tension typically measured in aircraft systems?

Using a cable tensiometer Signup and view all the answers

What is required to maintain proper cable tension across varying conditions in large transport aircraft?

Cable tension compensator assembly Signup and view all the answers

Where do cables typically wear or break during operation?

At the points where they pass over pulleys or through fairleads Signup and view all the answers

What must be done after the swaging process is completed to indicate any subsequent slippage?

Apply a colored paint ring around the terminal Signup and view all the answers

What is not a method of termination for aircraft control cables?

Bowline knot Signup and view all the answers

Study Notes

Equipment and Testing Standards

Aircraft control cables must comply with CASA's Civil Aviation Order CAO 108.41.
Control cables remain primary for moving flight control surfaces in commuter and general aviation, despite the rise of digital flight control technology.

Materials Used

Two main materials for aircraft control cables are carbon steel and stainless steel.
Stainless steel is more expensive, has lower tensile strength, but is preferred in corrosive environments, such as agricultural aircraft and seaplanes.

Types of Steel Cable

Non-Flexible Cables: Types 1 × 7 (7 wires) and 1 × 19 (19 wires) for straight runs, without pulleys.
Flexible Cables: 7 × 7 type, suitable for straight runs or large pulleys.
Extra-Flexible Cables: 7 × 19 type, used over small-diameter pulleys; most common in flight control and trim systems.

Cable Strength and Safety Factor

Cables endure various stresses: direct tension, shock loads, bending, and multiple simultaneous forces.
Tensile strength is determined by cable size, material, and construction, as specified in maintenance manuals.
Safety factor: ratio of cable strength to working load (e.g., strength 10,000 lb, working load 2,000 lb leads to a safety factor of 5).

Cable Stretch

Cable stretch impacts output movement due to structural and elastic stretch, related to load, length, and material properties.

Lockclad Cable

Lockclad assemblies combine aluminium alloy tubing with galvanised or stainless steel cables to prevent sagging and wear.

Cable Termination Methods

Nicopress Process: Uses copper sleeves compressed onto cables; creates strong bonds and maintains full cable strength.
Swaged Terminals: Predominant method requiring specialized training; terminals fit snugly post-compression and are marked to prevent slippage.

Components and Testing

Shackle Pins: High-tensile steel pins securing joints; tested under shear loads and secured with split pins.
Proof Load Test: Conducted at 60% of breaking strength for at least 3 minutes to validate safety and integrity.

Cable Installation Practices

Cables are routed directly with pulleys for direction changes; fairleads prevent contact with the structure while allowing cable movement.
Pressure seals ensure aeroplane pressurisation at bulkhead cable transitions.

Control Cable Pulleys

Constructed from hard materials; must align accurately to avoid misuse and ensure cable security in grooves with guards to prevent jumping out.

Cable Tension

Type Certificate Data Sheet (TCDS) defines required deflection; cable tension adjustments are made using a cable tensiometer.
Cable tension compensators regulate tension in response to changes in airframe dimensions.

Control and Adjustment Devices

Turnbuckles: Allow cable tension adjustments; must show no more than three threads visible after adjustment, with various lock methods.
Cable Drums: Used in trim tab systems to control movement in response to user input via control wheels.
Quadrants: Serve to change motion direction or convert linear to rotary motion.

Special Cable Types

Bowden Cables: Designed for pulling; commonly used in various applications.
Teleflex Cables: Handle both pulling and pushing, providing enhanced strength with an inner rod mechanism.
Swivelling Couplings: Enable angular movement; essential when a control lever synchronizes with component motion.

Operational Considerations

Bowdenflex Cables: Push-pull design transmitting loads with a flexible central load rail, capable of operating in extreme temperatures and requiring no lubrication.
Minimum bend radius and stroke range are defined to avoid excessive wear due to incorrect bending angles.

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Description

Explore the equipment and testing standards for aircraft control cables, including compliance with CASA's regulations. Learn about the materials used, types of steel cable, and the safety factors related to cable strength in aviation. This quiz covers essential knowledge for those involved in aviation maintenance and safety.