Designed and made an ultralight 55litre aluminium framed backpack coming in at 535 grams in order to lighten my pack weight on two 8 day through tramps in New Zealand's south island. The pack successfully lasted the NZ test although the base was slightly holed and roughed by the rocks.
I'll dot point the main items which may assist anyone in making a similar backpack.
Main goal as light a backpack as possible to carry around 13kg or more with a 55litre capacity, plus front mash pocket. The pack must be strong and not fail
Chose materials as shown in the list. The HyperD used for the base and up the sides for 11cm or so and the back up to the top of the frame.
Made brown paper patterns of the 5 main sides
Dimensions are - my neckbone to hip ledge about 43cm. Pack base to top frame 60cm and extention to 35cm. Bottom of lower hip webbing to shoulder hinge - 42cm and to top of frame 56.5cm Width between hip hinge flaps - 24cm. At base of pack sides 17cm front and back 30cm. At top of frame pack sides 20cm and front and back 33cm and this continued to the top of the extension.
Made all attachments first and stitched them to the different flat panels, this includes, shoulder straps, waist belt, rear mesh pocket etc. In other words everything is firmly stitched onto the seam width before you think about assembling the 5 panels
Stitch (inside out) the 4 panels to the back/base panel. this whole assembly is still flat.
Stitch the side panels together.
made the frame from 10mm aluminium tube from local hardware store, $6 for 3m length. Plug one end by hammering in a piece for garden cane, fill with running table salt, tap and refill. Hammer in another piece of cane to compress the salt (this inhibits the tube from kinking). Hand bend over a childs rubber rimmed wheel in a vice, cut over length, try and cut to the correct size. Hammer in two plastic furniture stoppers inot the frame feet to stop the frame ends cutting into the fabric.
That's about it. It worked well. I would make the following changes if I make another pack
Use a heavier tougher fabric for the base, say Cordura
Increase the seam width to greater than 12mm, either 16mm or 20mm. This will facility better anchoring of all of the attachments to the seams.
increase the frame top level by 25mm or so.
Possibly use the HyperD rather than the silpoly for the pack as it only increases the weight by 50 grams or so.
leave all webbing long until you try the pack with weight on
Things that worked well
The waistband was a great success, no buckles, two means of tensioning, all you had to do was to thread the ladderlocks when you put the pack on
the top tie down system
the frame, never looked like bending.
the pack was very comfortable with all or most of the weight on my hips.
