I was toying with the idea of lightweighting an old Kelty External Frame Backpack.
The frame has two large 1" dia 30" lengthwise aluminum (1/16" wall thickness) tubes and a grand total of 6 transverse aluminum tubes about 22" long in diameters of 3/4" (2 of these), 5/8" 3 of these and a top extension of also 5/8".
This frame is way overbuilt, as surely has been noted for years.
I calculate the base aluminum structure to weigh 2.75 pounds out of the total 4.7 pound backpack.
Two of the 5/8" cross tubes can almost certainly be eliminated for a savings of 0.488 pounds.
If the remaining tubes were to be scaled down in size, 1" becomes 3/4", 3/4" becomes 5/8", and 5/8" becomes 1/2", then there would be a slimming down weight savings of 0.409 pounds.
So, elimination of excess cross tubes and slimming down of all remaining tube diameters in an aluminum structure gives 0.897 pounds of weight reduction.
I am winging it on weight reductions in hip belts and shoulder straps, but feel redesign using lighter weight materials and designs could save 0.7 pounds there.
The cloth bag could be fabricated from lighter weight fabrics with as much as a 30% reduction in the roughly 2 pounds of bag weight for another 0.67 pounds lost.
So, with no resorting to radical new design concepts for an external frame backpack, the weight of a 4.7 pound external frame backpack could drop to about 2.3 pounds.
I always liked the air circulation and coolness of the external frame pack. I haven't sampled any recent internally framed packs that attempt to create an airflow path between the pack and the back.
This year, I may just try tinkering with this idea.
I feel sure that others have been down this road long ago. Ideas like this are bound to occur to lots of people.
I have been away from backpacking for over 20 years - the family bit, you know - and am trying to catch up.
My reason for posting is to hopefully tap into the experience of others who have already thought of this and likely have done this.
Reinventing is fun, but bootstrapping on the experience of others is fun too, and rewarding often.