Pack Design Question

Here are a few thoughts from my limited experience with the design.

The design is simple and elegant. There are fewer pieces to cut and fewer seams to sew or fail.

The design limits your ability to pick material for specific purposes. For instance, texture of the front panel against your back, strength of the material at the shoulder strap attachment points, and abrasion resistance on the bottom panel. I don't think this is much of an issue unless you have those specific needs.

Because there is no bottom seam, the bottom edge of the back pocket must be sewn to the face of the back panel. This isn't really a problem, and it can protect the bottom edge of the pocket from abrasion when you set your pack down.

The design limits your ability to shape the bottom panel. It's a fixed rectangle. Ninety degree corners are hard to sew, so you may want to round the corners of the side panels instead. This in turn can move the bottom shoulder strap mounting points up a bit.

Because the seams will be so long and they negotiate corners, it's more important to use pins or alignment marks to avoid fabric 'creep'.

Here is an illustration showing rounded corners on the side panels, bottom seam of back pocket, and lower shoulder strap attachment points:

Hope this is helpful,
Lance

For years I've made all my packs using one piece of fabric for the front (as in the face that contacts your back) and the bottom, with that fabric wrapping up a few inches of the back. I've done it this way because I want durability on the bottom and texture on the front (so that the pack doesn't slide around on my back). Both of the ends are served by using 160d or 330d cordura, which oddly enough weigh about the same.
Then I use one piece of fabric for the sides and back, which needs neither the texture nor the durability, so I use a lighter fabric for that.

So your idea is fine as long as you don't need or want different fabrics for the front, back, and bottom.

Lance touched on a bunch of the limits. It can also be a pain sewing all the harness components and any pockets/daisy chains/etc on to one 70+ inch piece of fabric. This also points to another issue, that you'll need at least two continuous yards of fabric for a larger pack of this design.

I've made a few smaller packs using one piece of fabric for the back, front, and bottom, but for larger packs the benefits are often outweighed by the downsides.

Thanks everyone! Your help is much appreciated.

It sounds like this will work after all! I was actually planning on the bag having more of D shape instead of a square bottom so the corners shouldn't be a problem.

Another question. I'm 6'4" and 270 pounds. I currently use an REI Flash 30. It's comfy and it works great for my usual 2-3 night trips. I'm a pretty wide guy though and it feels like the bag is only about half as wide as my back. I think it's actually like 11" wide. My back is closer to 16". I know how to determine the length of a bag, Illialic (sp?) crest to knot on the back of your neck. Is there and optimal width, though? Honestly I think I'd rather have a wider pack that keeps thing closer to my back. If that makes sense.

David,

My myog backpack bag is typically 14-16" wide, depending on how I stuff it.

My old MSR frame pack was 14" wide.

Not specific to your original question (because I use a stuff sack design for my back bags) but I use a single piece of fabric for my back bags.