Paul, please bear with me, and I promise to get to the point. Like you I&#;m wedded to the Stephenson &#;Jack-pack&#; concept, and have been wrestling with the above and many related issues for some time. For those unfamiliar with the design, the jackpack side arms function totally differently than the Jansport and other packs that use or used sidearms. The latter have little or no connection to the pack at the small of the back, so the pack pulls backwards and down away from the back. With long sidearms, such a pack would be unwieldy and dangerous to the spine. With shorter sidearms, such as Jansport used on the D-2 for example, the packs were functional, but still had the same drawbacks to some extent. They also put the weight of the pack where the shorter arms connected to the belt at the wearer&#;s sides, minimizing any movement of the pack belt with the natural rotation of the hiker&#;s hips. The jackpack belt is connected to the frame at the small of the back, and at the 2 points of the sidearms, so the belt rests on the two points of the hipbone (Iliac) crests closer to the rear, the pack&#;s center of gravity is more forward, and the belt can swivel with the hipbones while walking (but not swivel too much, or the top of the pack will lean too much to the sides). Here&#;s a picture of Jack Stephenson&#;s original Warmlite design:
Link to PFC
There is an upper crossbar above the hipbelt that is not clearly visible in the picture. Note that these two crossbars must be absolutely rigid for the sidearms to hold the hipbelt firmly against the hips. Found this out to my dismay after doing a whole prototype.
All the jackpack type frames I&#;ve made and used successfully were also of 5/8&#; diameter alloy tube, and the lightest came to around 45lbs loaded with food for 7 days and 1-2 quarts of water. Also, the sidearms were designed to cinch the hipbelt against the hips/waist with a pulley arrangement, so there is no need for a buckle at the front.
So as with you, carbon fiber tube came to mind for today&#;s light backpackng. But big concerns remained about the stiffness of CF tube, and the much greater abuse that packs receive compared with tentpole tubes. You mention Paulonia curved CF slats, but all I could find on Google were Pawlonia (spelled with a W) wooden slats. The only precurved CF I could find was through Alibaba. I also have found that CF which is flexible enough to flex into a curve behind a suspended mesh backpanel, and also rugged enough to withstand abuse, makes the backpanel too taut, without the &#;give&#; that is the whole point of a comfortable suspended mesh back panel.
Since Easton .340&#; diameter tent tube is more durable than any CF tent tube I&#;ve found, and is readily available at Quest and others, I looked at its use for an hourglass frame using the best CF solution found; which consisted of a small pultruded CF tube that inserted very snugly into a filament wound fiberglass tube, both from Goodwinds, came to .248&#; outside diameter, was even stronger than the Easton 340 alloy, and had some flexibility. But to use the CF/FG for an hourglass frame, numerous elbows would be required. Or with a ladder frame, numerous Tee fittings and more crossbars. The Fibraplex elbows were just the right size, OK for a tent, and very light, but were not tempered enough to hold the angle under stress. The Easton 340 elbows do not have ferrules as such; but rather consist of one rod of the ferrule diameter that runs right through the whole elbow, and is bent inside the .340 elbow tube, all of which makes for a lot of weight in an ultralight frame with a lot of alloy elbows.
So the decision was to use the .340 elbows (covered under a protective reinforced plastic tubing) just for the bottom two corners of the frame that take the most abuse, possibly with .340 elbows for the top frame corners, inside the pack and protected by reinforcements bonded and sewn on the pack. But what about the rest of the frame? Since the Easton .340 tubing can take long precurves, it would not require a slew of elbows for an hourglass frame. So the relative weights of the frame were roughly calculated and compared using mostly the precurved alloy with few elbows vs the FG/CF composite with more elbows. The prebent .340 alloy came out on top with a significantly lighter weight. With that, the use of CF was abandoned for an hourglass frame that could support sidearms, and withstand abrasion and abuse. Note the Easton .340 alloy weighs less than half the lightest 5/8&#; alloy tube around, so considerable weight savings can be had with it.
Your description sounds like some form of the CF Zpacks frame, or a ladder-shaped frame like Roger&#;s, and you might able to use CF for the crossbars. But CF light enough to flex as you describe might not be robust and stable enough for a pack; and it is also nice to have prebends in the upright rails of the ladder, a la Jansport and others, so the frame will better fit the back&#;s contours. (Don&#;t quite get your nonuse of side rails, especially on a frame that will support rigid sidearms.) I chose an hourglass-shaped frame as it uses less tube length overall than a ladder shape, so can be built lighter. I think it also does a better job of keeping the pack contents from protruding against the backpanel and the back.
With the hourglass frame constructed to have short rails in the lower corners, either that or a ladder frame of .340&#; Easton alloy tube can be built up to take Jansport fittings for a bit less than 5/8&#; tube. This is fine, because another decision was to make just the sidearms out of tubing taken from the lower ends of X-C ski poles that taper from 5/8&#; diameter to around half that at the baskets. .340&#; tube had been tried for sidearms, but I wanted something much ruggeder. So a weight penalty has been accepted just for the sidearms.
Hope to get something done this year, but unlike your greyhound speed drizzle, I go slower than grass grows, although do actually finish and post a project now and then. And hope the above will be helpful to those wrestling with the same issues.
Carbon fiber vs aluminum, a common choice faced by manufacturers. To make the decision easier, we put together this post to compare these two materials.
Keep reading to learn more about aluminum and carbon fiber so you can determine which will work best for the project you&#;re working on.
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There are a number of factors engineers need to consider when designing a project and choosing a material. Let&#;s look at some of those and see how carbon fiber and aluminum compare.
Rigidity refers to how much an object retains its shape even when acted upon by other forces. Carbon fiber is between two and five times more rigid than aluminum at the same thickness. The difference depends on the overall quality of the carbon fiber.
It&#;s also important to compare the strength of two materials which have the same thickness. Aluminum has a strength of about 500 kilonewtons compared to carbon fiber which can have up to kilonewtons of strength.
The weight of a material is particularly important when trying to make a vehicle that&#;s faster or more fuel-efficient. It&#;s particularly important for getting aircraft into the air.
Replacing the aluminum in an object with carbon fiber can reduce its weight by nearly half without compromising strength or rigidity.
Since nearly everything uses electricity to some degree, it&#;s important to look at how well your materials will conduct it. Aluminum is a great conductor of electricity which can make it dangerous in some applications.
Carbon fiber, on the other hand, does not conduct electricity well and can often be used as an insulator to protect against electric shocks.
As a result of exposure to weather or the heat of the engine caused by friction, a material has to resist expanding or failing under heat. Aluminum can always resist high temperatures but carbon fibers can only resist moderately-high temperatures when properly cured.
Despite the many advantages of carbon fiber, there are a few instances in which aluminum will work better.
You&#;ll most likely need to use aluminum in areas that will be exposed to large amounts of heat since carbon fiber can fail in these situations. Aluminum also conducts electricity better and should be used in applications where this is essential.
If you need something to be rigid, strong, and lightweight, carbon fiber is the best option. This is why it&#;s already being used in aircraft, vehicles, and medical and manufacturing industries.
Now you know the difference between carbon fiber vs aluminum. As you can see, each has unique qualities but carbon fiber outperforms aluminum in the majority of the most important areas.
If you want to learn more about how we can help you incorporate carbon fiber into your manufacturing project, contact us today. We would love to help you no matter what part of the design or manufacturing process you&#;re in.
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