Here are all the details you should know about aerospace wiring harness.
Airplanes, jets, helicopters, and spacecraft navigate challenging environmental conditions during daily or scheduled operations.
So aerospace wiring harnesses should withstand exposure to such conditions without failure because they power and transmit electrical signals to and from critical components.
For instance, they should have chemical-resistant insulations to protect the conductors from engine fluids like fuel and lubricants.
Also, they should be flame-resistant to keep the electronics running in case of a fire. Read on to learn more.
Table of Contents
- What Is an Aerospace Wiring Harness?
- Why Use Electrical Wiring Harnesses in the Aerospace Industry
- Aerospace Wiring Harness Components
- Aerospace Wiring Harness Manufacturing Wire Material
- Wire Gauge Selection in Aircraft Wire Harnesses
- Aircraft Wire Harness Testing
- Wrap Up
What Is an Aerospace Wiring Harness?
This wiring harness is a collection of aerospace cables enclosed in an outer jacket (usually thermoplastic) to insulate the conductors from the harsh conditions outside.
Thermoplastic has the required properties for this application, which include high-temperature resistance, low water absorption, and chemical resistance.
Why Use Electrical Wiring Harnesses in the Aerospace Industry
Let’s focus on the airplane. The first generations of aircraft after their invention were purely mechanical. Initially, they relied on ropes to rotate pulleys to adjust control surfaces on the wings and tail.
Metal cables replaced these ropes as the planes advanced, making the control network system more compact and reliable.
The fly-by-wire system replaced these manual flight controls using electrical signals transmitted via wires to move actuators on all the control surfaces.
In this setup, flight control computers take input from the cockpit and determine the electric signal to send to the actuators to fly the aircraft.
A pilot adjusting the thrust lever during a flight
This system requires a few wires to manage the flight, making the control system compact and lighter. So the airplanes can either be smaller or carry more cargo, which is good for business.
The nerve system for this electrical control system is the wire harness.
Aerospace Wiring Harness Components
When assembling custom aircraft wiring harnesses, you will need components that fall into these categories.
Standard Components
You can’t use any parts for the electrical system when building military or commercial airplanes. Only consider components from government or industry-certified suppliers.
And in the military aircraft category, you must use MIL-SPEC or military-grade parts.
Non-Standard Components
Non-standard components are variants of commercially accessible components that meet the required standards by the military or government.
A teacher and student engineers studying an aircraft’s turbine engine
OEMs can set their standards for these components, leaving you to choose parts from different aircraft wiring harness manufacturers if they meet these standards.
These original equipment manufacturers can also certify and pick suppliers to build these components. If they choose one, the prices can be high due to market monopolization.
Off-The-Shelf Components
These parts are usually cheap because manufacturers make large quantities to meet customer demands. Producers don’t need government or military approval to modify these components.
Manufacturers can make these parts unique and assign them part numbers for quick identification. Also, they can have sole control over their production, giving them price control.
Aerospace Wiring Harness Manufacturing Wire Material
Aerospace wiring harnesses can contain several kilometers of wire and thousands of components, even for small aircraft.
Remember, these harnesses control all the craft’s components, including the landing gear, fuselage, air circulation, computers, and the aircraft engines. So they must cover all aspects to make flights smooth.
The most critical and significant part of this wiring is the conductor. Whether single cables, twisted pairs, or triplets, these conductors contain either copper or aluminum metal strands inside for electrical transmission.
Wiring inside the instrument panel of a small single-engine aircraft
Although copper is a better conductor of electricity, is easier to solder, and has a higher tensile strength, manufacturers prefer aluminum.
The metal is lighter than copper, and weight is critical in overcoming gravity during flight. Most aircraft fuselages are primarily aluminum, signifying the importance of lightweight designs in enabling flight.
Aluminum wires also minimize weight on the wings because they exert little downward pressure. So, airplanes can have longer wings to carry a larger body with more payload.
Wire Gauge Selection in Aircraft Wire Harnesses
The best way to determine an airplane’s wire harness wire size is by looking at the connections from the system diagram level.
A system diagram will show the larger sections of the wiring and their components.
However, this diagram only indicates the wire connections using lines. It does not show the wire gauge.
Also, it does not show wire splits, such as when wire heads use two connectors to go through a bulkhead.
The wiring and mechanical parts of a propeller aircraft engine
But the crucial thing is the schematic shows the signals the wire carries and the locations requiring different wire types.
These include twisted pairs, shielded cables, triplets, quads, etc.
Combining the data about the wire type, maximum current transmitted, and type of signal should help you determine the wire to use.
And since weight is critical in aerospace engineering, pick the thinnest wire (highest gauge) to transmit the required signal reliably.
Aircraft Wire Harness Testing
If aerospace wire harnesses fail, the result can be catastrophic. So, testing them is crucial before installing the wires in the craft.
Aircraft wire harness manufacturers usually use wiring analyzers to assess these cable assemblies.
Special programs run these devices, instructing them to run various tests in different parts at the correct electric current and voltage levels. Also, they direct the tester on the duration to apply the electric current.
Wires and pipes outside the lining of an airplane’s turbine engine
The only manual process during the tests is to join the analyzer to the harness using adapter cables.
Once connected, the tester conducts multiple tests, but the two typical ones are continuity and insulation resistance.
Insulation Resistance (Megohm Test)
This test tries to identify if there are any short circuits in the wires, which indirectly checks the insulation quality.
All cables should have reliable insulations separating the conductors.
So, a failure will indicate insufficient material separating the two conductors.
This failure occurs if the resistance between two disconnected wires is low. It should be high because they are not in contact.
The threshold figure is 100 megaohms. If the resistance exceeds 100 megaohms, the harness passes the test.
A technician working on an airplane’s wiring
Continuity Test
Continuity is more like the opposite of resistance. This test checks if every wire transmits electrical signals to the target with minimal resistance. The analyzer runs this test at 0.5 amps for a minimum of 0.2 seconds at a constant voltage.
Wrap Up
Although aerospace wiring harnesses have the same functions as those in automotive applications, they require special care during construction and assembly.
After assembly, they need rigorous testing to ensure they meet the highest quality standards because failures mid-flight can be catastrophic.
That marks the end of this article. Check out this automotive wire harness manufacturing process to compare it with the aerospace harness above, and comment below if you have any questions. We’ll get back to you ASAP.
