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The WE Cross-Frame

The WE assymetric cross-frame is the structural platform used in all the big-capacity backpacks. The sophisticated Synchro-FORM harness system integrates directly with it. We have used this simple, outstanding frame system for nearly 30 years. The fact that the cross-frame configuration has been adopted in this decade by some well-known, international brands for their high volume, expedition pack models says something. The only reason we can see that it is not more commonly used is that the cross configuration requires a more involved construction of the pack harness panel where the frame locates. Here is the explanation of it's simple brilliance...

What Does a Backpack Frame Need to Do?

The most important function is to provide "prop-up" stiffness to the pack bag so that load carried in the pack can be effectively loaded through the pack hip harness onto the wearer's hips. Without adequate stiffness the pack bag will simply sag and re-load the shoulders.

The next function of the frame is to form an (adjustable) surface in the harness panel of the pack bag that follows the shape of the wearer's back. In this way the pack load can be carried as close to the back as possible. This was not possible with the original, external backpack fixed shape frame designs.

If the frame is stiff enough to maintain its given shape once formed to the wearer's back profile then it can maintain a small but highly effective contact-free, ventilation clearance, an function where original, pre-seventies, external backpack frames over-achieved.

Another function of the frame is to help define and control the shape of the pack bag, particularly at the top where it usually opens. At the base of the bag the cut of the fabric panels do this job well enough. At the top, if the frame structure extends out to the edges of the pack harness panel then this rigidity will reduce the tendency for the top of the pack bag to round-out away from the wearer.

Finally, here is a nice, second-order possibility linked to the cycle of body dynamics that define walking. To maintain dynamic balance when walking, our hips and shoulders rotate slightly in opposite senses, following the swing of opposing arms and legs. If the pack frame system has built-in torsional springiness it can constantly recycle some of the energy associated with deforming it one way then the other. Frame systems that are "dead" transmit this energy to the pack bag where it is absorbed and lost.

The WE Cross-Frame

This simple frame consists of two light-weight, tempered, high-tensile aluminium bars. The cross-section of the bar material has a slight curvature. This increases the bar stiffness without adding weight. The frame bars are pre-curved in production, according to their pack size length, so they approximate the curvature of a typical human back profile. Even under rough handling these bars retain the essential curves built into them. Despite this, it is still possible to adjust their shape to individual profiles by applying firm hand pressure.

The bars form a cross in the pack harness panel, located in separate fabric channels. At their top ends they reach almost to the outer corners of the harness panel. Their bottom ends are located closer together and stop well above the base of the pack bag. (This makes the assymetric-cross). The exact geometry at the bottom is part of the Synchro-FORM hip harness system design. Hip harness components fasten through the pack bag directly into threaded fittings built into the bottom ends of the frame bars. This arrangement also eliminates the possibility of the frame wearing a hole in the base of the pack bag, something you see on some well used packs where the frame extends to the base panel seam.

This simple frame system achieves every function identified in the previous section. It is the cross arrangement of the separate bars that is responsible also for excellent torsional springiness. The profile arc shapes of the frame bars also add resiliency and cushioning to the system in just the same way as the curvature of the human spine protects against shock when jumping down a step.

 

 

 
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