Tent for snow camping?

[Cherian Thomas]

@jamesdmarco

Cherian, I was an admin for a major university doing research analysis on many different projects. I used to run a few different programs against the actual values collected during my time there before I retired (about 10 years ago,) mostly in an effort to debug or apply various corrections to apparatus/data loggers. The diagrams were just some morphs of the primary structural component, the poles. I got very good at eyeballing a lot of that stuff from all the analysis I did. The diagrams were some quickie drawings of what I expect would happen at pole failure since I no longer have access to the programs.

Looking at them again, They likely exaggerate the billowing effect somewhat…but not real bad, likely close to 20% variance on the vectored angle.

Hi James, I asked because I was wondering how you produced those pictures.

I think you need to remember that the whole reason Roger chose the gambrel shape was to use carbon fibre pole sections. CF is, pound-for-pound, much stronger and stiffer than Al.

Also note what Roger said earlier – he designed his poles to be under some bending stress at rest, which does reduce deflection under sideways loads. I have no doubt that Roger’s tent poles are much stronger and stiffer, per pound, than Al hooped poles. Merely comparing shapes isn’t taking the whole picture into account.

[Sam Farrington]

Thank you, Roger.  Now I get why you needed the CNC machine.

Cherian, +1.

But when choosing alloy or carbon poles for snow or other stressful use, please note that carbon fiber tubes come in many different qualities.  Before I threw up my hands like Bernie and started break testing, I was often having to replace carbon pole sections made from arrow shafts.  Easton has posted on BPL that arrow shafts are not suited for tent poles; but has now made carbon tent poles available to consumers.  And I have carbon poles made from arrow shafts that tested the highest in break tests, cost a lot less, and have never again had any breaks, though carry a couple carbon repair sleeves just in case.  So all is good.

[Roger Caffin]

In addition, oils ain’t oils.

Some vendors sell what look like carbon fibre arrow shafts but in reality they are a pultruded glass fibre core with a light dusting of graphite on the surface. Naturally, as soon as you bend the shafts, the pultruded extrusion splits full-length. I think the brand was ‘Carbon Express’. Note: they make make fine arrow shafts: I wouldn’t know.

Some vendors make and sell wrapped CF tubing. That is CF woven fabric inpregnated with some sort of resin, and wrapped moderately tightly around a polished mandrel. They work, but they are ‘soft’ and bendy. Other vendors create a ‘2D Wrap’ using a great big machine which laminates longitudonal fibres with layer of tightly wrapped CF fibres around them. If you (Cherian) search here at BPL with ‘2D wrap’ you should find other threads about this.

I use 2D wrapped CF poles. They are extremely robust: I have even stood on the ends of them on solid rock and they did not break at all. They are also extremely stiff, which is why my tunnel tent designs start with a specified radius of curvature for the poles, rather than taking whatever comes out.

The weather closed in later in the evening. It did not worry us.

Cheers

[James Marco]

Cherian, I assumed equal pole strengths of no particular design.

As Roger says, poles can vary. Diameter, lengths, materials, construction, temperature, etc…just a generic morph.

[Eric Blumensaadt]

Roger said “tarp tents, in their infinite variations, just don’t compare.” (as winter tents)

I kinda agree if we are talking about heavy winds and even higher gusts, say steady 40 mph. and 60 mph gusts.

But I’ve “winterized” my Moment DW and Scarp 2 with the optional X-ing poles run beneath the fly and attached to it with Velcro wraps. And I’ve tested both in very high winds as described above. They both have done very well in high winds with both rain and snow.

Guyed out at sides and ends is vital but also one must absolutely stake down the fly hems to avoid flapping and the wear it involves.

With the Moment DW Henry Shires has revised the main pole arch guy setup to two guys instead of the former single guy. This is “belt and suspenders” and would work very well in high winds. As well the improved Moment DW fly has a hem that has been lowered and comes with two stake loops per side.

Seeing as how I’ve lost my Moment DW fly (don’t ask) and ordered the new fly I’ll be even better prepared for winter camping in the nearby Spring Mountains outside of Las Vegas. Winds at 9,500 ft. can be a bit challenging.

 

[Cherian Thomas]

@rcaffin

Some vendors make and sell wrapped CF tubing. That is CF woven fabric inpregnated with some sort of resin, and wrapped moderately tightly around a polished mandrel. They work, but they are ‘soft’ and bendy. Other vendors create a ‘2D Wrap’ using a great big machine which laminates longitudonal fibres with layer of tightly wrapped CF fibres around them. If you (Cherian) search here at BPL with ‘2D wrap’ you should find other threads about this.

Hi Roger, what you call 2D-wrapped is more commonly referred to as pullwinded (or pullwound?) tubing. The tightness of the wrap with either roll-wrapped fabric or any kind of winding operation (be it pullwinding or filament winding) doesn’t add strength – the tensions in a winding operation are controlled to ensure accuracy of the wind (by preventing fibre slippage) and avoid voids.

The choice of fibre directions determines the distribution of strength and stiffness, and you can vary properties of the end products widely with all forms of composites. Pullwound tube and roll-wrapped fabric are both great choices for tent applications, provided they are bending-optimised. With roll-wrapped tube this is often called unidirectional tube which, despite the name, tends to have a layers of circumfrentially-oriented fibres thrown in for some crush/splitting resistance. Either one is fine, though. Fabric-wrapped tube shouldn’t be more flexible than pullwound tube – that would suggest a difference in fibre orientations to me.

A practical consideration is that it is pretty hard to find pullwound tube with <1mm wall thickness. If you want thinner-walled tube, roll-wrapped unidirectional tube is generally the only option.

There are also many fibre and resin choices when you really get into it…

[Roger Caffin]

Yes, you could call it ‘pullwound’ if you want. I prefer 2D-Wrap as it seems less clumsy.

The difference between 2D-Wrap and fabric wrap is two-fold.
* The fabric tubing has a higher percentage of plastic resin compared to the 2D-Wrap, and this materially alters the bulk strength.
* The much higher tightness in the circumferential fibres in a 2D-Wrap mean the whole thing is more tightly bound and more rigid.

While you can wind the circumferential fibres very tightly in a 2D-Wrap construction (with a large machine), you simple cannot get the fabric to wrap nearly as tightly. This is another way of expressing the first two factors. The fabric stuff on the other hand can be made in a backyard.

I have both sorts, and I have measured both sorts. If I wanted greater flexibility, I would go for good fabric-wrapped tubing, but I want strength.

it is pretty hard to find pullwound tube with <1mm wall thickness.
My standard 2D-Wrap CF tent tubing has a >6.0 mm ID and a 7.5 mm OD. That gives it a wall thickness of under 0.75 mm. This stuff is widely available, most easily from better quality archery suppliers.

Cheers

[Cherian Thomas]

Yes, you could call it ‘pullwound’ if you want. I prefer 2D-Wrap as it seems less clumsy.

It’s a lot easier to find pulwound/pulbraided tube through a Google search :)

The difference between 2D-Wrap and fabric wrap is two-fold.
* The fabric tubing has a higher percentage of plastic resin compared to the 2D-Wrap, and this materially alters the bulk strength.

Agreed. Pultrusion/pulwinding/pulbraiding generally runs at 60-65% fibre volume fraction, while the prepreg fabric typically used for fabric rolled tube is typically ~55% fibre volume fraction once cured.

* The much higher tightness in the circumferential fibres in a 2D-Wrap mean the whole thing is more tightly bound and more rigid.

I don’t think this matters. Once you take the mandrel away, the circumferential stresses disappear as there is no longer anything to react against.

While you can wind the circumferential fibres very tightly in a 2D-Wrap construction (with a large machine), you simple cannot get the fabric to wrap nearly as tightly. This is another way of expressing the first two factors. The fabric stuff on the other hand can be made in a backyard.

Nobody is making commercial-grade prepreg tube in their backyard, unless they happen to have an autoclave.

I have both sorts, and I have measured both sorts. If I wanted greater flexibility, I would go for good fabric-wrapped tubing, but I want strength.

I think you can’t generalise from fabrication method to strength/stiffness. There are far too many variables besides fabrication method that affect the performance of the end product. Layup schedules being chief among those.

it is pretty hard to find pullwound tube with <1mm wall thickness.
My standard 2D-Wrap CF tent tubing has a >6.0 mm ID and a 7.5 mm OD. That gives it a wall thickness of under 0.75 mm. This stuff is widely available, most easily from better quality archery suppliers.

Fair enough. I have never looked at arrow shafts, because I’m only interested in tube 9mm OD and up.

[Sam Farrington]

Am glad we have another person on BPL who is well versed in matters related to carbon tent poles.  Using break tests has been adequate for me to determine which carbon arrow shafts and tent poles have the greatest strength, but I  do not have the engineering background for a technical discussion.  But will venture to say that the fabric rolled shafts, such as those made by SkyShark, do not compare with some, but not all, of the multilayered shafts.  I assume this is because the filaments are bonded in different directions, but cannot say without the training and lab equipment to find out.  And as with anything, the quality of the manufacture and materials, as well as the design, affect the outcome.  Just know what works best for tent poles, but certainly appreciate the technical discussions to learn why, because very strong carbon tent poles relate directly.and in substantial measure, to the weight of tents made for snow camping.

[Roger Caffin]

The problem with wrapped fabric is that the weave is never straight (it is woven after all) and the fibres are never really tight. The 2D-Wrap I use manages both of those very well.

Mind you, if you NEED greater flexibility for your design, then wrapped fabric is probably the way to go.

My 2c
Cheers

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