Carbon fiber or Ti tubes for Flexlite Air?

[Pithawat V]

Based on Ryan’s review it looks like the majority of the chairs weight is from the aluminium tubes. I’m considering buying carbon fiber / Ti tubes to replace them, except for the folding ones supporting the back. Does anyone know what the drawbacks may be, and if anyone has attempted this before? I’m guestimating the weight saving to be around 4oz.

[Bill in Roswell]

I wonder what factor temp range would play out over rime in regard to expansion/cintraction of different materials? A few science/engineer members will know.

[Sam Farrington]

Even best quality filament wound carbon fiber has less resistance to crushing then alloy, but it is much more expensive than other layups of carbon fiber tube.  Check out Rockwest, Dragonplate and Clearwater.  The cloth wrapped carbon fiber tubes are OK, but even less resistant to crushing.  Easton makes strong carbon fiber sections for flexible tent poles, but they and the better arrow shafts are smaller diameter than the tubing used in pack chairs.  I did use some higher diameter carbon tube to stiffen an alloy chair based on canoe chairs:  https://backpackinglight.com/forums/topic/81152/

Can’t help you re Ti tubing, but am sure it would be more durable than carbon fiber.  The problem with nearly all the pack chairs is that they have hubs under the seat that the tubes plug into in order to connect them to the legs.  When you move around in one of those chairs, the pressures on those tubes where they join the hubs is enormous and too much for any carbon tube of same diameter.  That is why I used the hubless canoe chair type design, because you can kick back in it, or swivel around on it to reach items when cooking.  Some believe that the canoe chair type is not high enough, but believe that around 4″ off the ground is plenty to prevent body heat from radiating into the ground, and freezing the butt.  I like to be low anyway to reach different items, and find it more relaxing.

Maybe Ti could compete with alloy for hub connections, and someone can advise you about that.  The canoe chair type I built is of aluminum alloy taken from ski touring poles, so is quite durable.  But having seen the failure of a steel LaFuma chair, added a couple of snug but loose internal carbon tubes to stiffen the tubing on each side of the butt, at only a moderate weight penalty.  It is discussed in the link noted above.  And I’m never without the chair, still going strong.  And suspect a Ti chair would be heavier than the alloy tube found in most pack chairs.

Agree with Matthew K’s post in the companion chair thread about the flaws with the ‘air chair’ designs that use your sleeping pad.  Keep my pad in the tent, especially in foul weather.  The canoe type chair is designed with mesh surfaces so it can be used in the wet.

Hope this is helpful.

[edvin mellergård]

I made a chair with carbon fiber tubes last year, to avoid crusing the tubes where they join the plastic connector I reinforced that area with a small piece of aluminium tubing epoxied on the inside. It worked the first two times but then the cf snapped where the aluminium ended instead :(

To make it work I think youd have to redesign the whole frame or do a much more thorough job of reinforcing the ends of the tubes than I did.

[Jan Rezac]

Titanium is not the way to go – the best alloy is about two times stronger than 7075-t6 aluminum, but also almost two times heavier. When it comes to a tube, aluminum one of the same weight would likely have better overall properties because you can afford larger diameter and thicker wall. The advantage of titanium is e.g. its higher melting point, but you don’t need that in a chair.

Quality carbon fiber tubes would save some weight if the interface to the hubs is solved. What about using pieces of the original tubing as ferrules inserted into the hubs, and using CF tube of larger diameter glued onto these ferrules for the main section of the tube?

[Craig]

<p style=”text-align: left;”>From my experience in bikes, fly rods, and paddle shaft design, its would be very hard and $$$ to get carbon weave tubes that would be better for this application  (as strong in compression and tension but with thin walls to shave resin weight without increasing diameter) than easton alloy – possibly if you change the leg design completely to use a different configuration that doesnt punch the rods 8nto rapid compression so much eg wider angles. To transfer loading more into tension</p>

[Craig]

You know what would probably work ?

The carbon fibre tube that black diamond and zpacks use in their walking staffs. If you could source the tubing it measures close and seems pretty good for high compression part tension loading  I haven’t checked pole diameters cf the socket holes yet

 

 

[Scott H]

I am now the owner of two of the Helinox chair zero chairs as I have one for myself and one for my son for an upcoming camping canoe trip to canada.  Normally I have not bothered with a chair, I previously purchased a crazy creek which actually also happens to weigh as much or more  as a Helinox.  Last year I and my son took a cut up the therm-a-rest folding pad and I had their sit pad.  I don:t know yet if i will decide these chairs are essential or a waste of time.  However going to be trying them out this hiking camping and canoe trip and will know by the end of the year.  However I suspect the best answer to light weight is a therm-a-rest zpad cut in half or less that you can lean against a tree, rock or whatever and improvise a chair but it weighs a lot less.  I don:t see how you can make something elaborate and light weight that is going to beat just something simple and super light with no chair frame to get in the way.  Carbon fiber probably could be designed to work but it kind of becomes the Rube Goldberg complex solution to a simple problem.

[Pithawat V]

Thanks everyone for your responses, especially @Sam @Edvin @Jan and @Craig. Sounds like this project isn’t worth pursuing without extensive changes or a lot of dynamic testing. Too bad!

[Scott H]

I suspect you need a whole new form factor for a carbon fiber camp chair to work.  You might need some sort of integration concept with a back pack in which the pack frame is carbon fiber and removable then folds out into a chair.  It almost needs to be multipurpose as I don:t think carbon rods alone into the helinox type single use design offers enough improvement to matter.

However if you have one pound of weight with two significant uses then you have saved weight in the overall system.  So in my opinion you need a 1 pound carbon fiber chair that also serves as the frame of your pack.

[Craig]

That was interesting

Just ran a micrometer over the helinox zero tubing and a Black Diamond ultra distance carbon trekking pole

helinox tube outer diameter 12.77mm, wall thickness 0.77mm – and they use a smaller diam aluminium tube glued in as the internal ferrule joining piece  to the next tube section

BD carbon trekking pole – as expected more variance even though this clearly uses great technology pressure die moulding with advanced weave lamination and resins – outer diam 13.1 mm for main tube, with an extra weave external layer on ends to reinforce the ferrule joint, with an internal aluminium ferrule piece glued in adjoining piece  – OD 13.97-14.02mm:
wall thickness 1.31mm

i.e. tubing would needs ends cut off to fit in plastic corner pieces of the chair

i don’t have a dead pole to cut up and experiment (these things are nigh on indestructible, despite my abuse – I use them as wading staffs – rock scarred and used as a machete with blackberries)

I suspect however that the carbon tubing will weigh similar and possibly more than the helinox aluminium tubing due to resin.
I do think though the carbon tube would hold up to the application , based on a stress test on one section invoking worst possible application – sudden application of high force in pure comoression

i suspect as some one else found the failure will occur as is normal with carbon where they join with the corner connectors as this creates a high stress point when the tube is in tension

 

[Sam Farrington]

Re:  Edvin’s post

Faced with lightening a friend’s Hubba tent, wanted to replace the long hoop section with CF, (but not the bottom spread struts).  So made the alloy reinforcements external and increased the diameter of the holes in the hub to fit snugly over the reinforcement tubes.  That way, the CF walls were not directly exposed to the crush forces, which were spread out over a larger area.  But suppose that this would be a hassle with replacing a bunch of larger dia.. but shorter ALU alloy tubes used in most take-apart pack chairs.

Assume that the take-apart chairs are valued because the pieces go into a stuff sack that stuffs into the pack.  But again, please consider the canoe style design shown in the link in my post above.  Of course those are metal, being ALU alloy (even tho reinforced with internal carbon tubes on each side of the seat).  But consider a few things:

It is no hassle at all to strap the canoe style chair to the back of the pack.  The chair helps to maintain the vertical shape of the pack, and keep the pack’s center of gravity forward.  Also, when the chair is folded, the part that sticks up over the top front panel zip opening is open, without mash; so the top zip on the panel loader can be opened without undoing the chair from the pack. When I had occasion to meet some SAR veterans at a trailhead on the CDT, they went ga-ga over the chair.  Also, the front support lip of the chair, makes a nice shelf for attaching the foam pad with the folded CF tent poles slipped in for protection.  Neither of those is very heavy, so they do not move the center of gravity backward the way large rear mesh stuff pockets would.  The mash portion of the chair also makes a good place to dry out sox.  So the chair has been a boon, not a hassle, like finding where to carry all those metal parts of pack chairs.

Of course, alloy may be heavier than CF; but it makes a ruggeder chair that will last.  Have several older CF trekking poles that could be cut up to make a canoe style chair; but the alloy one weighs just over a pound, probably not much more than a CF chair would, and sitting on the chair, it somehow just feels like it will take more abuse than CF would.  So see no reason to make a change.

To get down to around a half pound chair, like the ones that fit over sleeping pads, is OK; but still agree with the flaws mentioned in the companion thread cited above.  Suggest that in order to get lighter, we sometimes try to pack too many functions into one item of gear.  So for example, we use trekking pole tents even though we really have no use for a second trekking pole, which becomes just another vestigial item which is a nuisance to lug.  And when we want to leave the tent for any reason, the treking poles are already busy holding up the tent.  When all the while we would be more comfy in a super light dome.  So dual use has its limitations and disadvantages.  Just one more of my two cents.

[Sam Farrington]

Please excuse the references in the above post to “mash,” which should have been to “mesh.”

[Author]

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