These pictures are the underneath of a rucksack I bought some time ago:

I've never figured out what this arrangement of velcro flaps, cord loops and webbing is supposed to be for. I think I did try asking the firm I bought it from but got no reply.
From top to bottom in the pictures (which is from back to front when wearing the pack) there is:
Has anyone seen this arrangement before, or care to make a guess at what it's for? The two flaps would wrap around some sort of tube I guess, and then you could lace a cord back and forth through the cord loops either side, to stop the velcro coming undone maybe? But then why the velcro "ears" either end of the flaps, or the bit of 2" webbing?
My two best guesses were that it's for a pack frame, or for pulling a sled of some sort (the pack does have a hip belt). Neither of those feels convicing though. There are no other apparent fixings for a pack frame, and would you even use one on a rucksack that's only about 30-35 litres? Towing a sled feels a pretty niche requirement and I don't know why you'd want it integrated into a rucksack.

I've never figured out what this arrangement of velcro flaps, cord loops and webbing is supposed to be for. I think I did try asking the firm I bought it from but got no reply.
From top to bottom in the pictures (which is from back to front when wearing the pack) there is:
- A row of PALS webbing
- A strip of 2" webbing stitched like a carry handle, but there's only room to fit 2 fingers through the loop. It seems designed to carry significant load because it's reinforced with another strip of 2" webbing inside the pack.
- A line of 4 loops of cord
- A pair of flaps, with velcro that allows them to be joined together to form a tube about 1" in diameter. The velcro on the outer flap extends beyond the ends of the flap by about 2.5" either side, and when you stick that velcro down it partially closes off the ends of the tube.
- Another line of 4 loops of cord
- Another row of PALS webbing.
Has anyone seen this arrangement before, or care to make a guess at what it's for? The two flaps would wrap around some sort of tube I guess, and then you could lace a cord back and forth through the cord loops either side, to stop the velcro coming undone maybe? But then why the velcro "ears" either end of the flaps, or the bit of 2" webbing?
My two best guesses were that it's for a pack frame, or for pulling a sled of some sort (the pack does have a hip belt). Neither of those feels convicing though. There are no other apparent fixings for a pack frame, and would you even use one on a rucksack that's only about 30-35 litres? Towing a sled feels a pretty niche requirement and I don't know why you'd want it integrated into a rucksack.
