A look at an old Jansport external frame pack
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Another thread drifted to external frame packs and I came across an old Jansport yesterday and thought it would be interesting to look at it with 21st Century eyes.
I don't know the exact model on this one. I did find a label that identified it as a medium size.
Specs and features:
Frame:
Tubular aluminum with machined aluminum joints. Approximately 33.5" tall and 14.25" wide. It has two cross bars plus the bag mounting frame. The bag mount mounts via two machined blocks and spring/ball detents. The lower cross bar is fixed at 14.5 inches above the bottom of the frame. The lower section of the frame is a U-shaped section of tubing that completes the rounded rectangle shape of the frame and attaches with the same pins used for the lower attachment of the shoulder straps. There is a top cross bar that forms the upper attachment for the shoulder straps and can be adjusted using sliding aluminum blocks with cam-action locks
Suspension:
The shoulder straps are closed cell foam padding with nylon fabric covering and molded plastic mounts at each end, attaching to the frame with aluminum pins and split rings. The top mount can be adjusted for width by moving the pins to one of two holes drilled in the top crossbar. The crossbar is adjustable to suit torso height. There is no sternum strap on this version, although I have seen other models with one.
Back band:
There is a 6" tall soft mesh and foam back pad held in place with web straps and ladder locks. I recall seeing back bands that were a plain sheet of mesh, almost like window screen. The back band keeps the user's back from sinking too far into the frame and making contact with the tubing. It hits me at the lower ribs, with the lower edge about 2.5" above the waist belt. It can be adjusted for tension and height; the pack back mounts and the center cross bar form some limitations to the placement of the back band.
Waist belt:
It feels like open cell foam with a Cordura-like covering. There are 1-7/8" straps sewn to it that couple in a big side-release buckle. It is attached to the frame sides using a horizontal 3" wide webbing band sewn to the back of the padding. There are no adjustments on this band; it simply slides onto the tubing when the bottom section has been removed. There is a 1.5" webbing strap that runs from the horizontal band and goes around the bottom of the frame and is adjusted with a ladder buckle. There are two 3/4" webbing strap that run from the top of the horizontal band up to the middle cross bar. This arrangement allows the waist belt to slide up and down the frame rails to adjust to the user's torso length.
Pack bag:
Coated nylon pack cloth, measuring roughly 21" tall by 13" wide and 8" deep, totaling 2184 cubic inches or about 36 liters. I estimate that the top side pockets are 2 liters each and the lower side pockets look like simple water bottle pockets, so I would add another liter for each, for a total capacity of about 42 liters (I think I'm being very conservative with that). The left top side pocket has panel behind, forming a sleeve to allow long poles to be carried. The main pack body has two panel-loading compartments with zippered openings; the upper compartment is about 31" tall and the lower one is 8" tall. There are no openings between the compartments. There is a flat zippered pocket on the door of the lower compartment with a mesh outer panel. There are four plastic loops on the bottom of the bag to attach web straps to lash on large bulky items like a sleeping bag, pad, or tent. There are also two lash tabs on the top panel for the same purpose. There is a single compression strap across the top compartment with a side release buckle.
The pack bag mounts to the frame using the U-shaped tubing bar that snaps into the top aluminum blocks and runs through a channel sewn in the top edge of the bag. There are also three Velcro straps on each side that simply wrap around the side frame rails. The bulk of the weight is carried by the top bar, much like a curtain.
The pack weighs 59 ounces (3lbs 11oz) total. The bag is 19 ounces and the frame with suspension is 40 ounces (2lbs 8oz). I didn't tear it down further to get the weight on the bare frame or suspension parts.
What is good about this pack:
My general impression is that the design is very simple with a minimum of buckles and hardware.
I think the tubing mount for the top of the bag is genius. By hanging the weight from the top, there is no need for compression straps or reinforcements to keep the bag from collapsing on itself. The rest of the bag mounting (which amounts to about 24" of 1/2" Velcro) is mostly to stabilize it on the frame and the bag simply hangs like a curtain. The pack bag is basically a big cube with a couple panel loading compartments. There is no padding, just the coated pack cloth and one mesh pocket. The side pockets are very straightforward zippered compartments.
The frame is light and relatively low tech aluminum tubing, with no apparently exotic materials or manufacturing techniques. The cam/lock blocks for the shoulder strap top bar are probably the most complex parts to manufacture. There are no welds in the design. Most of the plastic hardware can be found in any catalog. The top mounts for the shoulder straps are the only specialized plastic parts and don't look complex to manufacture.
Although the pack bag is about 46 liters, the carrying capacity extends far beyond that. There is 5" between the top of the bag and the top of the frame and the load could be extended past that. It looks perfect for placing a bear can or a tent. There is an 11" space between the bottom of the bag and the frame bottom. It was common to stow a sleeping bag, pad or tent (or all three) horizontally in that spot.
What can be improved with modern materials and techniques:
Frame materials: I think aluminum has a great cost/weight ratio, but titanium and carbon fiber tubing certainly come to mind. It could be pulled off with square tubing too.
Smaller frame size: Dana Design made an external frame pack where the frame closely followed the perimeter of the pack bag, avoiding the extensions found on this Jansport. If you don't need to lash bulky items to the frame, dropping the top of the frame would clean things up a bit. The current Jansport Carson model has a much larger (80-90L)pack bag that extends to the top of the frame, but the bottom is much the same as the example here. I think that begs for a top heavy load, not to mention encouraging the user to attempt to fill all that space. It can catch on brush and makes crawling under a log difficult. The bottom frame extension does help protect the bottom of the pack and it gets that massive load up another 11"-12" towards picking it up to get it on your back. Some of that space is used for torso adjustment, but not nearly that much. This frame could be shortened 8" without changing the suspension geometry.
Pack bag materials and design: it begs for Dyneema or Cuben fabric. There is the panel/top load debate and I would keep to the panel loading, but with a 1/2 height zippered door and a good stretchy mesh pocket on the lower half for wet gear and daily trail goodies. I would drop the upper side pockets and re-work the lower pockets into good water bottle carriers. I would definitely keep the bag top mounting bar.
Suspension: I take advantage of newer 3D mesh and padding materials and construction techniques, using more ergonomic designs. Waist belt pockets and a sternum strap would be welcome.
Why bother? The external frame design is simple, well ventilated, and very efficient at weight transfer. It lends itself to multiple interchangeable bag designs and is excellent for hauling bulky items like bear cans, inflatable boats, photographic equipment, tools, or scientific instruments. I think smaller packs are better suited to internal frames, but once the 50 liter mark is reached, an external frame can be lighter and handle the bulky or heavy load more comfortably. The ability to adjust the frame to a wide range of torso sizes can make them useful for families and outdoor organizations.
Note: the orange and black rod is a trekking pole to prop it up for the photo:
If you're not careful, and you keep pushing this external frame idea to its ultra-light pinnacle of design, you may just end up with an Osprey Exos pack.
Coming from the bicycle industry which uses lots of both aluminum and carbon fiber, there is no doubt the carbon fiber rocks in modern bicycles. Why? Great strength to weight, kinda like aluminum, and better vibration damping than aluminum. Vibration damping isn't a big deal in pack frames. Flex can be. Lower end carbon fiber technology actually doesn't save weight over the much less expensive and easier to work with high-end aluminum. So, to build a carbon fiber pack frame that has any real advantage over an aluminum counterpart is going to require the highest end carbon fibers ($100's worth of raw material) and custom layup and molding ($10,000's in tooling and design). Pre-made carbon tubing, cut and bonded or clamped, will NOT outperform aluminum in this application in my opinion. And, any advantages of the highest end, best designed carbon, will be slight if measurable, and prohibitively expensive.
P.S. I have an old squeaky bolted together external frame Jansport backpack that we still use. They were and are, great bags if renowned for brackets coming loose, weak zippers and thin fabric . . . our's hasn't completely failed yet.
"If you're not careful, and you keep pushing this external frame idea to its ultra-light pinnacle of design, you may just end up with an Osprey Exos pack."
I already have one :) My Exos 46 is 2lbs 4oz, but it doesn't have the hauling capacity of the Jansport. We're 1.5 pounds apart as is. The Exos design is guilty of complexity. IMHO, the design team should be taken to the woodshed for piling on all the gadgets and geegaws to the excellent core design of the Exos. It reeks of marketing types co-opting the committee
I would lean to the Osprey style ventilated shoulder and waist straps. It crossed my mind to just buy spare suspension parts from one of the packs that offer interchangeable sized hip belt and shoulder straps.
I agree on the carbon fiber issues. Anyone who has the resources and capital to go after a similar design will run a gamut of patents, so this is probably a MYOG endeavor at best. The frame on the Jansport is easily adapted with common home workshop tools and so well executed that I would concentrate on pack bag and suspension to lighten this thing. If you dissected the components of a good Cuben pack (in design), and add them to a bare Jansport frame, you could end up with a big hauler in the neighborhood of 2.5 pounds. The economics would be questionable unless this is a budget MYOG project; otherwise, I could see it gobbling cash in big bites. I will probably approach it as a Frankenstein project, waiting to find a trashed backpack with adaptable suspension components. REI has the Crestrail 70 shoulder strap module for $22 and the women's version is just $8 — less than the hardware alone would cost.
The whole project only makes sense if someone wants to haul heavier, bulkier loads, which is rather antithetical to general UL principles in the first place. If you shrink the frame on the Jansport significantly, you will indeed end up with an Exos-like pack; it would certainly look like a Dana/Mystery Ranch external.
One thing that inspired this post was a recent acquisition of a Gregory Z65, which is the antithesis to the Jansport design. The Gregory is big and complex, festooned with straps, buckles, zippers and padded panels. It weighs another 7oz over the Jansport too.
I was happy to find a garage sale Jansport pack that I could hack up with no guilt if the project failed. I was able to eliminate three of the cross bars and with a new simple bag and hipbelt, it weighs 3 lbs. 4 oz. I am thinking this will be good on trails for winter and in summer when I have to use a bear can. I may go back and make a smaller bag for summer.
ScottI found the Zen website with some external frame info at http://zenbackpacking.net/Backpacks.htm . They note that Evernew made some titanium load frames for sale in Japan. My searches came to dead ends.
More to the thrift store side of things, they claim the the Outdoor Products frame is the same as the Coleman Peak 1 Ram-X plastic frame. I have seen many more used Outdoor Products version and passed on them, assuming they were inferior copies (I may still be correct) I've thought this frame style had good UL potential because of the multiple attachment points and the design used to make the attachments: a metal toggle that sldes into the slots in the frame. I'll have to keep an eye out for one.
Outdoor Products Enduroflex frame from their Saturn backpack:
I found a photo of another Jansport that has a top design I haven't seen before:
Note the bend in the tubing at the top X. This eliminates the machined blocks and the ball detent/frame piece to hold the top of the bag. The lower X is at the joint that allows the top section of the frame to be removed/replaced, allowing it to be threaded through the sewn channel in the bag. It's not as elegant as the machined blocks, but this is much more approachable for a MYOG builder with a conduit bender and some tubing. The bag is still suspended in the same way.
Imagine melding this with something like the plastic frame from the Outdoor Products/Coleman frame above.
Here's what you get when you hang a Jansport bag on my myog carbon fiber frame.
Weights
Jansport bag 18 ounces
Everything Else 5.6 ounces
TOTAL about 1 1/2 poundsThis Jansport bag has about 2400 cubic inches in the main bag and 300 cubic inches in the pockets for a total of about 2700 cubic inches.
Tent, sleep pads, etc. can be strapped to top bar of frame (say 700 to 1500 cubic inches?)
I also use a front bag with at least 600 cubic inches.
So this set-up could carry anywhere from 2700-5000 cubic inches (44-81 liters).
The Jansport bag is a bit smaller than the 1-4 ounce bag I usually use on this frame.
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