By: Michael Traskos

Impact of Secondary Wire Harness Protection on Heating

December 10, 2019 Michael Traskos

If you are standing outside on a cold winter day, would you be warmer in a T-shirt or in a jacket? The answer is obvious, but somehow that ‘obvious answer’ is obscured when thinking of aircraft wire harness design. A common question of OEMs and aftermarket modifiers is: how much of an impact (if any) does secondary harness protection have on wire harness heating?

Lectromec took time this last week to put together a representative harness and run tests to generate data on the thermal impact of three secondary wire harness protection schemes. While this data is not representative of every wire harness configuration, it does provide a basis for determining if additional testing (or simulation) are needed for your application.

Getting the Right Bonds

November 22, 2019 Michael Traskos

Things were so much easier with aluminum aircraft structures. The structure acted as an EMI shield, electrical grounding could be done right to the structure without additional effort, and the electrical mating of the structure was straight forward. Now, with composite structures, aircraft design concepts such as electrical bonding, particularly in the case of handling lightning strikes, becomes more important.

When done right, the impact of a lightning strike should have a limited impact.

In this article, we review the concepts around primary aircraft bonding, its requirements, and the implementation as they relate to lightning strike.

Non-Standard Standard Part Performance

November 11, 2019 Michael Traskos

Standardized products made by different manufacturers through different processes will undoubtedly yield variable product performance. The expectation is that each ‘qualified’ product should perform comparatively well, but anecdotal evidence suggests that this is not the case. This paper reviews recent work performed by Lectromec investigating the qualified wire/cable performance variability in both qualification tests as […] Read more

SAE Wire and Cable Committee Meeting Update – Fall 2019

November 3, 2019 Michael Traskos

The SAE wire and cable committee held their fall 2019 meeting in San Diego this year. As with every committee meeting, a lot of technical areas were discussed, progress was made, and some new ideas/problems are emerged. As we do after all these meetings, we put together a highlight of some of the talking points from the meeting.

Determining Voltage Drop

October 11, 2019 Michael Traskos

If voltage is applied to a circuit and the attached equipment does not turn on, then there is an issue with either the circuit or the applied voltage (assuming the device is fully functioning). Sometimes glossed over in circuit design, the length and gauge of a wire can impact the voltage to the load; this is known as “voltage drop”. Just as the current carrying capacity of a wire/wire harness is impacted by the system and environment, so too is the voltage drop.

In this article, we go over the idea of voltage drop, guidance on its application in design, and an example of quantifying the voltage drop on a wire/cable.

Wire Diagnostic Equipment

September 17, 2019 Michael Traskos

Finding wire faults/damage is not an easy task; now consider that problem across an entire aircraft. In-situ testing of wires/cables has always been viewed as something of a challenge to the industry. Given the branching that most harnesses undergo, the various wire lengths, splices, and numerous termination conditions, it can be difficult. Attempts to automate some of the testing has come to the development of Automatic Wire Test Sets (AWTS [pronounced “Eh-Wits”]).

Because there are so many ways to test a wire harness, the US military sought to create a performance standard to cover the general ideas and best practices of this equipment. Here, we review the standard and some of the performance features that can be expected when using equipment in compliance with the standard

Checking a Coaxial Cable for Damage with a Multimeter – Part II

September 11, 2019 Michael Traskos

In the last article, Lectromec introduced a damaged coaxial cable and tried three techniques to distinguish it from an undamaged cable. The standard multimeter tests (capacitance, inductance, and resistance measurements) found no appreciable difference.

The idea of this evaluation was to demonstrate that the classic multimeter, while a great tool, is not suitable for detecting damage to coaxial cables.

But we cannot run an article and leave it without a solution. In this article, we continue the testing of a damaged coax cable to see what technology, if any, can identify and perhaps locate the damaged section of cable.

Checking a Coaxial Cable for Damage with a Multimeter

August 23, 2019 Michael Traskos

The electronic multimeter is a great tool; invented in the 1920s, the multimeter has been used by millions of technicians and engineers seeking to measure circuits and troubleshoot electrical issues. So common are these tools now that it is almost impossible to consider a toolbox complete without one.

While these are great tools and can be employed in a million situations, they are not the magic tool that can diagnose every circuit. If only one thing is remembered from this article: multimeters are not the tool to use for coaxial cables

EWIS Physical Hazard Assessment

August 14, 2019 Michael Traskos

Aircraft system safety assessments are not a new concept. These safety assessments have a defined process for evaluating an aircraft which involve identifying its failure modes, top-level events, and eventual means to achieve an unsafe condition. Documents such as the SAE ARP4761 provide guidelines and methods for conducting the safety assessment process on civil airborne systems and equipment.

To follow the typical development cycle, the aircraft failure hazard assessment (FHA) is followed by the system failure hazard assessment and performed in parallel with the preliminary system safety assessments (PSSAs). This then evolves into the system safety assessments (SSA) and common cause analyses (CCAs). For those with a systems reliability background, this should all be second nature. For the rest of the community, these are often terms that we come across because of our work in this field.

Wires and Fuel Compatibility

August 7, 2019 Michael Traskos

Whether by design or by accident, some wires in an aircraft will be exposed to jet fuel. Because of this, it is necessary to be prepared and select wires/cable types that will not suffer adverse effects of the exposure. Considering the impact of fuel on wiring is not idle musing about wiring systems; to quote the FAA AC120-97A, “Since 1959, there have been 18 fuel tank explosions on transport category airplanes”. Read more