Aircraft Electrical Equipment Bonding

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Questions and Answers

What is the primary function of the dielectric in a coaxial cable?

To reduce the loss of RF power during transmission

To provide shielding from external interference

To maintain the position of the inner conductor and keep the capacitance between the two conductors at a constant value (correct)

To increase the characteristic impedance of the cable

What is the typical material used for the inner conductor in a coaxial cable?

Tin

Aluminum

Copper (correct)

Silver

What is the purpose of a double outer conductor in some coaxial cables?

To increase the characteristic impedance of the cable

To improve the flexibility of the cable

To reduce the cost of the cable

To provide extra shielding (correct)

What is the characteristic impedance of most coaxial cables?

50 Ω Signup and view all the answers

What is the main function of RF connectors in a coaxial cable assembly?

To carry RF power from one point to another with a known rate of loss Signup and view all the answers

What type of coaxial cable is being studied in this context?

Flexible (braided), solid dielectric type Signup and view all the answers

What is the typical material used for the outer conductor in a coaxial cable?

Copper braid Signup and view all the answers

What is the difference between a plug and a jack in a coaxial cable connector?

A plug has a male contact, while a jack has a female contact Signup and view all the answers

What is the primary purpose of providing low-impedance paths to aircraft structure for electronic equipment?

To provide radio frequency return circuits and reduce EMI Signup and view all the answers

Why is it important to conform to the system's installation specification when interconnecting, bonding, and grounding electronic equipment?

To ensure proper operation of electronic equipment Signup and view all the answers

What is the purpose of bonding conducting objects on the exterior of the airframe to the airframe?

To conduct static charges and lightning strikes Signup and view all the answers

What is the exception to bonding conducting objects on the exterior of the airframe to the airframe?

Antenna elements Signup and view all the answers

What is the minimum area requirement for isolated conducting parts inside and outside the aircraft to be bonded to the airframe structure?

3 in.² Signup and view all the answers

What is the maximum resistance allowed for bonding larger objects to the airframe structure?

1 Ω Signup and view all the answers

What is the purpose of bonding isolated conducting parts inside and outside the aircraft to the airframe structure?

To dissipate static charges and lightning strikes Signup and view all the answers

What is the primary focus of a bonding inspection?

To look for electrical connections to the aircraft structure Signup and view all the answers

What provides a good deal of information?

The shape of the echo, the direction of the echo pulse, and the location of the pulse on the screen Signup and view all the answers

What is the result of changing the design dimensions of the coaxial cable and connectors?

Added losses to the RF power and radiation interference Signup and view all the answers

What should be avoided when handling coaxial cable?

Bending it sharply Signup and view all the answers

What should be done when attaching connectors to coaxial cable with a double shield?

Soldering both shields together at the connector Signup and view all the answers

What is the importance of keeping the soldering iron clean, smooth and well tinned?

To ensure a good connection Signup and view all the answers

What should be done to avoid trouble when assembling coaxial cable and RE connectors?

Follow the assembly directions carefully Signup and view all the answers

What happens when the coaxial cable is damaged or might be damaged later?

The efficiency of the system is reduced Signup and view all the answers

What should be avoided when starting the nut into a plug or jack body?

Cross-threading Signup and view all the answers

What is the primary reason for ensuring uniformity of wire sizes in aircraft?

To prevent fires caused by improper selection of wire sizes Signup and view all the answers

What should be done before starting an inspection of the aircraft electrical system?

Turn off all electrical power Signup and view all the answers

What is the specification number for aluminium aircraft wire?

MIL-W-7072 Signup and view all the answers

What is the minimum size of aluminium wire that can be used on aircraft?

No. 6 Signup and view all the answers

Why should aluminium wire be two sizes larger than copper wire when replacing copper wire?

Because of its higher resistance Signup and view all the answers

What is the maximum temperature rating for MIL-W-22759/1 wire?

260 °C Signup and view all the answers

What should be inspected during an inspection of the aircraft electrical system?

The adequacy of support, protection, and general condition of wires and cables Signup and view all the answers

What is the consequence of exceeding the current-carrying capacity of a wire?

Excess heat is generated, which may cause a fire Signup and view all the answers

What is the primary purpose of cable loom support?

To ensure the durability and reliability of the cables and connections Signup and view all the answers

What is the main reason for preventing chafing of cables?

To prevent mechanical strain and damage to conductors Signup and view all the answers

What is the purpose of lacing and tying wire groups and bundles?

To ease installation, maintenance, and inspection Signup and view all the answers

What is the difference between a wire group and a wire bundle?

A wire group is a collection of wires going in the same direction, while a wire bundle is a collection of wire groups Signup and view all the answers

What is the purpose of loops formed by lacing at regular intervals?

To secure the wire group or bundle Signup and view all the answers

Where should wire groups or bundles not be laced?

Except for enclosures Signup and view all the answers

What is the benefit of securing wires and wire bundles routed through bulkheads and structural members?

To prevent mechanical strain and damage to the structure Signup and view all the answers

Why is it important to permit replacement or repair of individual wires without removing the entire bundle?

To simplify the repair process Signup and view all the answers

Study Notes

Equipment Bonding

Low-impedance paths to aircraft structure are required for electronic equipment to provide radio frequency return circuits and reduce EMI.
Components that produce electromagnetic energy should be grounded to structure to ensure proper operation.
Metallic surface bonding is required for all conducting objects on the exterior of the airframe to be electrically connected to the airframe.
Exceptions may be necessary for some objects, such as antenna elements, that require electrical isolation from the airframe.
Static bonds are required for isolated conducting parts inside and outside the aircraft that are subjected to electrostatic charging.

Coaxial Cables

Coaxial cables have a inner conductor (usually copper), a dielectric, and an outer conductor (usually a copper braid).
The dielectric provides low-loss insulation between the inner and outer conductors and maintains the relative position of the inner conductor.
Coaxial cables have a characteristic impedance, typically 50 Ω, but can also be 48, 53, 75, or 93 Ω.

Coaxial Cable Connectors

Coaxial cable connectors are attached to coaxial cables to form a coaxial cable assembly that carries RF power.
Connectors are available as plugs, jacks, panel jacks, and receptacles.
Plugs have male contacts, while jacks and panel jacks have female contacts.

Coaxial Cable Assembly Precautions

Good connection depends on holding coaxial cable and connectors to design dimensions.
Any change in dimensions can cause added losses to RF power and radiation interference.
Assembly directions must be followed carefully to avoid trouble.
Precautions include handling coaxial cable carefully, avoiding damage, and not using pliers to assemble or disassemble RF connectors.

Aircraft Wiring

All aircraft wire must meet the appropriate standard to be considered airworthy.
Wire specifications include MIL-W-7072 for aluminum wire and MIL-W-22759/1, /41, /16, /19, and /1044/9 for copper wire.
Wire characteristics include operating temperature ranges, voltage levels, and general application guidelines.
Important reasons for specifications include ensuring uniformity of sizes and reducing the danger of fires caused by improper selection of wire sizes.

Wiring Inspection Requirements

Wires and cables should be inspected for adequacy of support, protection, and general condition throughout the aircraft.
Inspection requirements include visual inspection for:
- Adequacy of support
- Protection
- General condition
- CAUTION: Turn off all electrical power prior to starting an inspection or performing maintenance.

Cable Loom Support

Wire and wire bundles should be bound and supported to:
- Prevent chafing of cables
- Prevent mechanical strain
- Prevent arcing or overheated wires from damage
- Prevent interference between wires and other equipment
- Prevent excessive movement in areas of high vibration
- Secure wires and wire bundles routed through bulkheads and structural members
- Facilitate re-assembly to equipment and terminal boards
- Permit replacement or repair of individual wires without removing the entire bundle

Lacing and Tying

Wire groups and bundles are laced or tied to ease installation, maintenance, and inspection.
Lacing is securing a group or bundle of wires with a continuous cord forming loops at regular intervals.
Tying is securing a group or bundle of wires with individual ties at regular intervals.
Wire groups are two or more wires tied or laced together to give identity to an individual system.
Wire bundles are two or more wire groups tied or laced together because they are going in the same direction.

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Description

Learn about the importance of low-impedance paths to aircraft structure for electronic equipment, reducing electromagnetic interference and radio frequency return circuits.