Balancing Flexibility, Strength, and Fatigue in Aircraft Cable

Aircraft cable works like a machine, wherein the characteristics of strength, flexibility, and fatigue work together to create balance. Modifying one characteristic inherently impacts the other two, and these changes influence the construction, functionality, and performance of a cable. When determining the correct aircraft cable for your application, or comparing different cable configurations, it is essential to understand how these factors work together to create a product that is flexible when it needs to be, and strong when it matters most.

Flexibility
In general, the more wires or strands a cable has per a given diameter, the more flexible it is. The more flexible it is, the less quickly it fatigues through repeated bending. Comparatively, cables with fewer wires or strands offer greater strength, but with a lesser tolerance to fatigue, and they are typically less flexible. 7x19 aircraft cable, for example, is extremely flexible compared to 1x7 strand, and 1x7 is more susceptible to the effects of bending.

Strength
Aircraft cable that is correctly specified for an application should be able to withstand abrasive wear, repeated bending, and other forms of stress. 1x7, 7x7, 1x19, 7x19, and 19x7 cables are all configured to excel in different applications given their corresponding configurations, diameters, and break strengths; and while a certain cable may be appropriate for one application, it may not be the best choice for another. In general, lower wire or strand counts result in a higher strength cable. Let’s compare 7x19 cable to 1x7 strand again. 7x19 aircraft cable performs well when flexibility and fatigue are concerns, which is why it is used commonly in winches and garage doors, yet it is not as strong as 1x7 strand, which has a higher breaking strength and performs best in stayed rigging, structural supports, and push-pull applications.

Fatigue
Cable fatigue is triggered by small cracks in the wires due to repeated bending and straightening over sheaves or drums. Often referred to as the cable’s cycle life, this wear is inevitable with time but can be delayed by employing appropriately sized sheaves, ensuring the cable is appropriately lubricated, and limiting the number of different directions a cable bends.

• Sheaves: In general, larger sheaves are a more effective choice for larger cable, faster operating speeds, and heavier loads, because large cable with small sheaves typically accelerate damage. Smaller sheaves can be used without causing early stress if the operating speed is slow, the cable is smaller, or the loads are lighter.
• Lubrication: Aircraft cable is lubricated to reduce friction and provide protection against corrosion. Corrosion and abrasive wear can shorten the cycle life of a cable, especially when the cable travels around sheaves.  
• Bend directions: It is best practice to avoid reverse bends whenever possible. Reverse bends, where a cable bends in one direction and then the opposite direction, can expedite damage and reduce the lifespan of a cable. If reverse bends are unavoidable, larger sheaves and thicker cable will offer a longer cycle life.

Strand Core manufactures flexible and non-flexible aircraft cable to meet commercial and military specifications. Built to accommodate a variety of different applications, our cable is available in stainless steel and galvanized alloys. For more information about our aircraft cable, visit https://strandcore.com/products/aircraft-cable/.