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Old 01-28-2004, 13:59   #1
Razor
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Ruck Frame Considerations

More info I originally posted over at www.geardo.com:

External Frame Rucksacks
External frame rucksacks are a good choice for carrying very heavy or awkward loads. Some external frames, such as the US Army issued LC-series (aka the ALICE), have a protruding bracket on the lower ‘waist’ end that lifts the rucksack ‘bag’ off ones back, allowing a great deal of airflow between one’s back and the bag that helps keep a user cool. The rigid construction of an external frame rucksack allows one to lash boxy or bulky loads (such as ammunition cans, water cans, and radio sets) directly to the frame. This keeps the hard, sharp edges off the user’s back to enhance comfort. External frames are often built from tubular metal, which provides a great deal of strength and durability in all directions, making them less prone to bending and lighter than solid beam members of the same dimensions.
Because many external frame rucksacks partially lift the load away from a user’s back, external frame rucksacks can be more difficult to use in situations where balance is important, such as skiing and rock climbing. The user’s center of gravity shifts away from the body, moving more to the user’s rear. With very heavy loads, a user may have to compensate for this shift by leaning forward, causing strain on the neck from angling one’s head up to see forward (this strain is obviously exacerbated when wearing a helmet or NVGs on one’s head).
There are a number of after-market sources for enhanced shoulder straps and waist belts for the ALICE frame. These items go a long way in making the ALICE rucksack more comfortable to carry. Ergonomic shoulder straps provide more padding than issued straps, and their shape aids in preventing blood-flow cutoff to the arms. A sternum strap helps keep the shoulder straps from shifting to the outside of the chest and shoulders, which helps reduce shoulder fatigue and also assists in prevent blood-flow obstruction. A full, padded waist belt helps bring the load closer to a user’s back, reducing the center of gravity shift, and when worn correctly goes far in transferring the weight of the load from the shoulders to the hips, where it is more easily borne by the body’s skeletal frame.

Internal Frame Rucksacks
Internal frame rucksacks use a system of stiffeners—called stays—that are often built into the rucksack bag itself (or are in contact with the bag’s outer surface), and run parallel to the long (vertical) axis of the rucksack. They nearly always employ a waist belt, which shifts the load from the stays to a user’s hips. Without the belt, the ‘frame’ is useless, and the load is borne solely by the shoulders.
As the stays are very close to or are built into the bag, the load rides very nearly in full contact with a user’s back. While this can trap a great deal of heat, the trade-off is that the load doesn’t shift the user’s center of gravity nearly as much as an external frame. This, combined with a slimmer front-to-back profile, makes the internal frame rucksack a good choice for those needing a greater degree of balance during movement.
Internal frame rucksacks are not the best choice for hard, boxy loads. Items cannot be directly lashed to the stays, and they must be able to fit inside the bag. Additionally, as the bag rides nearly in contact with the user’s back, the load must be carefully packed to ensure sharp edges and corners do not come in contact with the user’s back and cause discomfort or injury. Internal frames are generally not a good choice for very heavy loads, either. The stays of an internal frame rucksack are almost always flat ‘shims’ of metal (often aluminum, due to its strength-to-weight ratio), with their long axis oriented parallel to the surface of the bag. In this orientation, the stays are prone to bending under heavy loads, or under hard use.

Hybrid Frame Rucksacks
Some rucksacks utilize a hybrid frame system, incorporating the best features of both external and internal frames. Kifaru builds one such hybrid system. Both the Extended Mission Rucksack and Multi-Mission Rucksack feature a frame system consisting of flat aluminum stays and a full waist belt that brings the load close to the user’s back (like an internal frame), but is completely removable from the rucksack bag so the user can lash boxy, heavy loads directly to it (like an external frame). The versatility of this frame system makes it an excellent choice for those with widely varying needs, such as a soldier that may find himself carrying the rucksack during a technical rock ascent one day, and toting a 5 gallon water jug or ammunition cans several miles the next.
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