Lateral tunnel tent?

[Roger Caffin]

Ah – Gotcha.
Cheers

[R]

I’ve been noodling on this a bit more, focusing on wind loading, as that appears to be a weak point of the concept.

I realized that if you have a big, head-to-toe arch, you can stick a trekking pole up in the middle of it with guys out to each foot of the arch. This should stiffen it considerably to a lateral wind load, or vertical snow load.  Typical internal guy lines put an X right in the middle of you doorway, but this is no worse than a half-mid pitch.  You can even leave the guys in w/o the pole in milder conditions and still realize some benefit as they prevent the windward side from elongating as the arch rolls to lee.

Another stiffening trick is to run a guy line from one foot of the arch, to about 12″ up the opposite side.  A pair of these will cross in the middle of the doorway 6″ above the ground – right about at the top of a good bath tub floor, so again, they can be permanent.  This will help keep the leeward side of the arch from bowing out.

Finally, a horizontal guy line 6″ below the peak will again resist a bowing out of the leeward side and still leave ample space below it to use the door.  On a 90″ arch, this will span 45″, attaching to the arch 60 degrees up either side.  This will also help resist bowing out on both sides under a vertical load – wind or snow.

Related: you could make a traditional tunnel tent that used a pair of trekking poles in an A-frame for the rear, windward arch.  This would cut down on head room somewhat, but would be bomber in high winds, as well as saving the weight of a pole.  The effective internal volume might be akin to a sloping tunnel – just narrower instead of lower towards the foot.

[Roger Caffin]

Could be difficult if you don’t carry trekking poles. Most Oz walkers don’t as they are pretty useless in our scrub.

Cheers

[R]

I don’t either, but I can’t remember the last time I was out and no one else had any.

If some one else carries my gear can I count that as a negative against my pack weight???

[Roger Caffin]

If some one else carries my gear can I count that as a negative against my pack weight???
Ask again when you have just climbed a 2,000 m peak. Did your pack feel any lighter? :)

Cheers

[Sam Farrington]

Rene and all,
The blue hoop tent pictured on page one of this thread by Matt is similar to some of the designs by MacPac, in that the the hoop ends come together at the ground. For a solo side-entry tent, I think this approach might be more stable than two hoops equidistant from each other at all points, as there will be less square feet of unsupported fabric, and the large cant shown in Matt’s photo will add to stability.

A tent like that would also be able to have the poles installed while on the ground, and then raised like an accordion in one motion, which is the sine qua non of tunnel tents when pitching in severe winds. I don’t think the lack of a transverse ridge pole, as shown in Franco’s photo early in this thread, would be as necessary as with parallel hoops, so the weight factor could still be kept down using just two poles, especially if the added stability of the tent allowed for less guy-lines and stakes, the stakes being the issue weight-wise.

[R]

Interesting.  Angling the hoops would also help tension the roof.  But this conflicts with a few design notions I haven’t explicitly called out.

• I want to pitch this with a minimum of 2 stakes (so, conical vestibules)
• I want to be able to use internal guy lines

The 2-stake criteria has consequences if you bring the pole tips together, since they define the sleeping area.  You’d have to make the arches wider (heavier and floppier) if you pull the tips together

The internal guy line criteria is well satisfied w/ parallel poles because the guy lines align with the plane of the side walls and don’t encroach on the internal volume.  If the plane of the arch moves in to the living space, the guy lines would also intrude on that space.

I’m pretty settled on parallel arches.

I’ve been iterating on the pole design, and I’m leaning towards something like this.  I’ll probably order a set of Easton Carbon 6.3 (8.8mm) poles from questoutfitters.com so I won’t have to wade through the full product line of 2 arrow shaft manufacturers and then ponder the ferrule situation.  I’ll model the arch on a 45″ radius.  I’ll use 8 segments, every other connector being a 145d arch (3 in total), which will put a 10d curve in each segment – more or less.  This is half of a regular octagon.

The thing I’m puzzling over at this point is how best to do the ridge seams.  I have to join the conical vestibule to the cylindrical roof.  At the same point, I need to support the pole.  I also need to add an internal element to support any of: internal guy lines; points to attach an inner tent body; side walls if I make it a single wall.  And of course it needs to be sealable.

 

[James Marco]

Actually, you could take an off the shelf WarmLight and simply add zippers to the “windows” they have. This would give you the side entrance, and removing all the front door crap and substituting a single stake there would lighten it a bit. Just a thought…

[Roger Caffin]

A problem with most 2-pole tunnels is that any snow loading on the middle is likely to crush the tent.

Cheers

[Roger Caffin]

Hi Rene

The complexity of the poles seams was one of the reasons Easton was not able to get satisfactory production from the Asian factory for my tent design. The sewing can be technical.

Cheers

[R]

Roger,

I’m not thinking of this as a winter tent, so snow loading isn’t a design priority.  While I do want to make it as strong as possible for the given materials, I’m prioritizing weight, and so opting for lighter fabrics.  If things go well, a stronger mountaineering version might follow.

I think I have a plan for the seams.  It leverages the fact that the poles only have shallow arcs to them.  I’m going to treat them as flat in the fly pattern and just let the fabric stretch to accommodate the arc.  That means that I can use a continuous piece of fabric over the length of the tent.  So four strips, each ~3′ wide, tapering at the ends, joined by lengthwise seams that sit at the elbow ferrules.  This should be stronger than vestibule panels sewn to the roof panel at the pole sleeve. If the pole was a continuous, curved arc, I’d have to cut separate vestibules with a curved edge where they join the roof.

The pole sleeve will be a simple strip folded in half (this is a simplified description) with a seam going through several layers of fabric before reaching the fly.  On the inside, the inner wall will be joined by the same seam.  This protects the fly fabric from the thread on both sides, and accomplishes everything in a single pass.

The down side to this is that it won’t look all that great, but more importantly, I’ll have to seam seal 3 surfaces which will be tedious and add more weight in sealant.  But I think the strength of the continuous fly fabric and the simplicity of construction will be worth it.

In the event I do make a winter mountaineering version, I could increase the slope of the walls slightly to improve snow shedding by putting a cat-cut in the left and right length wise seams while keeping the center seam straight.  I can also fold the center seam over a few extra times to turn it in to more of a ridge line and then support the arches with trekking poles.  I suppose I could do this on the first version as well.

[Franco Darioli]

James,
I had a look to see if anyone had done that mod but could not find one.
I would think that the main reason is that rain or snow  would fall onto the floor going in or out of it.

[R]

You could potentially arrange a vestibule off the side of the cylinder, but my main objection is that I don’t want to cut the tensioned side wall.  You can over-size the door panel slightly to eliminate tension across the zipper, but from a structural perspective, you’re still left w/ a big hole in the wall.  This reduces overall strength and introduces some bending forces on the poles which are already under compression – that’s a recipe for buckling failure.

[James Marco]

Franco, No, the snow/rain won’t come in…at least no worse than any other tent with a door under a vestibule. The panel actually covers the window. With a small stick (or two) it can be propped up for use as a vestibule and easily zipped closed.

Rene, actually, there is very little strength associated with the nylon mesh…it will stretch a LOT compared with the tent body fabric (depending on the year you got it around 1.1oz silnylon.) Mine is a bit better than 15 years old. The metalized stuff is a bit heavier I think…like 1.6oz or so. The floor and actual roof (about a 12″ wide strip down the middle with a seam across the top) support the poles very well. The front poles are pre-curved aluminum about 1/2″ (around 127mm) thick and are quite robust. Most of the strength is the increased diameter. They use a smaller pole for the short end, but the angle they place them at means most stress is on top and ends. There is enough fabric to support them in 60mph winds. I have been out in that (maybe more, I didn’t measure it. It was difficult to stand up.) A standard “D” shaped door would work fine but only measure about 3′ at the highest.
Anyway, just a thought…

[Sam Farrington]

Rene, thanks for raising the issue in your thread. I enjoy posting about tent issues as you and others have raised. Agree that a 2 peg tent is ideal. This often means cone-shaped end covers. Here is a problem I ran into that along with Roger’s posts, persuaded me to go to a min 3 peg tent.

For a fully self-supporting dome tent, like a Hubba and many others, a door on a one peg cone-shaped vestibule (end cover) can be opened without overly releasing tension on the main canopy (roof and sides). However, using one-peg cone-shaped end covers with a tunnel design, where the end covers tension and support the main canopy, unzipping a door on an end cover will release the tension on portions of the hoops supporting the main canopy, making the structure much more vulnerable to winds.

In some 2-peg tunnel designs, this was addressed by putting circular zips in one side of the cone to produce circular doors, so most of the tension on the hoops would be maintained. Maintained, but also weakened, and it can be a PITA getting in and out of a circular opening. As I understand it, this is why the door end of tunnels use two pegs, creating two partial cones-one on each side of the end cover, as on the Stephenson tents, Roger’s designs, and others. That way, full tension is maintained over all or most of the entire hoop when the door is opened.

Especially for a wider side-entry tent, that tension will also maintain the shape of the hoops, giving them and the canopy they support much greater wind resistance. This was pointed out to me by Daryl C. when he noted how the end covers maintain the shape of the canopy on his tent. Unfortunately, I lost sight of this futzing around for several years trying to perfect a single peg design for an end cover with a door. Even though the design in question was a self-supporting side-entry tent, I still eventually had to conclude that a 2-peg entry would make the structure much more stable when the door was opened, no matter how the zipper was located.

Although I’ve not yet tried to build a Macpac type design (Celeste, Polaris, Nautilus), where the 2 hoops are highly canted to join at the ground, it just seems quite apparent that the cant will greatly increase the stability of the structure. For a solo tent, where the distance between the hoops at the peaks can be limited to around 3 feet, snow loading should not be a problem either; but then again, I’ve not trekked in AU in winter and been exposed, as Roger has, to such extreme conditions. Although I could see it happening on some of the high table lands above timberline in a Colorado winter. Like the old blues man said, I’m built for comfort not for speed, so do not venture forth into such extreme conditions.

[Roger Caffin]

Sam has covered some of the problems with a single-peg end to a tunnel, but there is a another very serious problem which no-one has raised yet: one which can be fatal. Yep.

Imagine you have your tunnel staked out with a single peg at each end. Now increase the tension in the roof a bit by pulling on one peg. What will happen?

Because you now have a triangle of forces (think of the ground plan), the bottoms of the poles will start to converge inwards on each other. The curvature at the top of the arch will rise – badly, the bending stress will rise, and you may well snap the pole at the top. This can equally happen just due to the wind blowing along the axis. In practice the pole will usually snap in two places close together at the top of the arch. This too is ‘known’.

For this reason I have two pegs at each end of the tent, said pegs being almost as far apart as the width of the tent. This geometry cannot cause the poles to misbehave and snap. In addition, two anchors at each end are far more reliable than a single one. The ideological and token advantage of a single peg is of almost zero value in comparison. (Sorry, but …)

Cheers

[James Marco]

From a structural standpoint, the best overall set of compromises (between strength of the poles, tension on the fabrics, etc) seems to indicate a square sleeping area with cones on the ends and sides…basically this becomes a dome. This is rather well known. But a square for two people is rather inefficient with internal space. Normally a 80″‘x24″ space (200cm x 60cm) is allotted per person. Then we have sidewall angles to consider to avoid condensation. But, it still means a LOT of extra room in a dome with 84″x84″ sleeping space. So, most refine this as down. In practice, a rectangle of about 84″x60″. To continue the refinement process, we end up with a tunnel, a rounded body with tapered ends.

While it is possible to use two stakes, three is the absolute minimum. One on either side of the door, as was said, and one at the far end. This is, of course, the arrangement commonly used on the Stephenson’s. It doesn’t really matter which way the arrangement of the poles and fabric go. Guy lines merely reinforce the structure and are ignored, since, they can be added regardless of the actual design…internal and external.

Wind loading becomes important insofar as structural weight of the fabric/poles is ignored. From an end, the standard front entrance tunnels are far superior. But on a diagonal (assume about a 45 degree impacting wind) the lengthwise tunnel is better. A lengthwise tunnel also is better on a side wind presenting less surface area to the winds and perhaps a better overall wind profile.

After considering the extra strength, and weight, required for the added wind resistance, I don’t think I would do it. Minimum weight would best be accomplished by reducing the weight of the poles and extra fabric for the larger, blunter ends and finding a more suitable location for the tent, ie in a more sheltered area. Using a side entry on the tent is certainly possible as I mentioned with my comment on modifying a Stephenson’s. In a sheltered location, weight becomes more important than on open snow or top of a mountain. Worrying about a less than half an ounce in stakes is kind of a moot point when in a 20mph wind(and above.) ALL tents need extra staking and guy lines, anyway. Saving the fabric weight alone would easily make up for the stake weight. The extra strength of the poles (increased diameter, increased wall thickness and extra length) is just added weight that good location skills would allow you to circumvent.

[Sam Farrington]

Roger, it is good that we agree.  Even if bomber poles are used to combat your disaster scenario, tension cannot be maintained with an open door by just one peg, no matter how tautly the cone end cover(s) are crafted. Without the tension, the tunnel designs will greatly distort in high winds, as seen in the oft posted video clip of a Warmlite from A. Olivier: https://www.dailymotion.com/video/xb55bc
And high winds are what scare me about camping in those high tablelands above timberline that I mentioned. IMO, once the tent starts billowing and blowing out of shape, something is going to give, and even if it doesn’t, it will be a long and unpleasant night. I remember as a kid, waking to see that the tent of our adult chaperones was wrapped around them in the snow on the ground. Lucky for them there were no downpours to go along with the blow. Finally, the weight of bomber poles defeats the main purpose of designing a superlight tent. But if someone comes up with a workable one peg solution for the door end of the tunnel, I’m all ears.

I’m also partial to gothic arches for the hoops in a ‘lateral’ tunnel, as suggested in Rene’s OP.  IMO they will make side guyouts much more effective in limiting distortion of the arched hoops by wind. But I think that in order to provide more interior space, the angle of the elbows at the peaks will be increased to 145 degrees, as opposed to the 120 degrees originally planned.  This shoots the plan to use cut down hubs now sold by Quest or US Plastics for the elbows.  The Easton 340 elbows are awfully heavy, and the Firbraplex ones bend out of shape fairly easily.  Will come up with something.  (I know, I know – you make your own elbows)

It should be noted that widening a tunnel to allow sleeping parallel  to the door (‘side entry’) will require greater pole length, which may make the tent less stable and weaker.  If the pegs are not quite so far apart as the width of the tent (no need for a 7-8 foot wide door), the partial cones created by the vestibule walls may also help to maintain the shape or the pole arcs.  Also, the Easton carbon poles now sold by Quest calculate to be a little heavier than the Victory and Gold Tip (11.59 gpi ((grains per inch)), as opposed to 9.69 – 8.9 gpi), so may be a little stronger without much of a weight penalty for a 2 pole tent.  These look like an improvement over the Easton carbon poles formerly sold by Quest, which were 12 gpi.  That could also help to limit pole distortion.  Will have to buy some and do some tests.

James, it is good that we agree on the basic points in the first paragraph of your most recent post; but I must confess to losing you a bit on a couple of points about the diagrams.

[Roger Caffin]

I started with gothic arches and made a couple of tents that way. Then I moved on to having 3 elbows instead of 1 in order to get a bit more head&shoulder room.

(Deep in rainforest jungle, about mid-2002.)

Caution about Easton CF poles. Some of them have an aluminium core – or they used to anyhow. The Al core is a disaster: it separates from the CF after a few extreme temperature cycles (eg -10 c to +30 C) due to the differences in coeff of thermal expansion.

Quite frankly, I do not trust and would not use a Warmlite tunnel in bad weather. Yes, I did have one years ago, for the tunnel survey.

Cheers

[James Marco]

Roger, I do not use the Warmlite much. Too bad, really…it promised to be a good tent from others recommendations. But, with two people, condensation is a b!tch in wet/cold weather. In dry weather, who needs a tent? Evan an old tablecloth will work to suppress heat loss. I used it on one 6 week thru hike as a solo shelter but it was heavy…went to a tarp after that.  In 20mph winds, the Stephensons end on to the wind is VERY stable. But this stability declines as winds approach the sides. I don’t use it in the ADK’s, there are way to many eddies. At 20mph you can set up the tent easily, at 40mph, the eddies can move 90 degrees leaving your tent very vulnerable.

Sam, The overall first row is simply morphing the overall tent designs. From a dome, to an elongated dome, to a tunnel, to a lengthwise tunnel. Ignoring pole placement, of course… Well, the arrows in the lower pair of drawings indicate the resistance to wind stress. From your example (I hadn’t seen that video before) this is predicted, but there is nothing new there…just a summary.

It is rather different to think of a two stake shelter. But sure, it can be done with a circular opening in one of the ends. This allows the stress to be relieved and picked up again, before the stakes. In practice, I would guess that a tear-drop would be a  bit more efficient at transferring forces to the stake. But, that has been done and makes getting in/out (usually by crawling) a bit difficult. Not a good tradeoff, generally speaking, but at my age, any crawling is not all that easy.

“It should be noted that widening a tunnel to allow sleeping parallel  to the door (‘side entry’) will require greater pole length, which may make the tent less stable and weaker.”
Well, less strength  for sure, due to the wider span. Less stable is not true. In the drawing above, it is noted (by the arrows) the resistance to stress. Generally you can add  up the number of arrows to indicate an overall “tent stability.”  There are 6 for the  normal tunnel, and 7 for the lengthwise tunnel with the most stability at the 45 degree quadrant. This means the lengthwise tunnel is actually more stable in the winds than the average tunnel. This does not consider pole strength, nor snow loads, though. It is often possible to beef up an errant pole design with internal and external guy lines. In the stability analysis, it presents a somewhat shorter side  wall to the wind, though (about 2 feet less.) But the decreased angle at the roof means a higher snow load or water load, due to the larger diameter of the pole arch. Hence a stronger pole, and greater length is indicated.
Like a floor joist scheme in a standard house, this is exponentially decreasing with the desired clear span below. So, for an 8′ floor joist, a 2×6 at 16″oc *just* fits the bill. At an 10′ span, a 2×8 at 16″oc will just fit. At 12′ spans you need a 2×10. At 14′ spans, you want a 2×12. At 16′ spans you *can* drop back on spacing to a 12″oc. At greater than 16′ spans you want heavier timbers (3×10, 3×12 or a 16″-24″ wide board/engineered truss/joist) to do the job of stiffness but a 2×12 at 12″oc is usually used because most bedrooms do not carry extreme loads(refrigerators, kitchen cabinets, dishwashers, washers, dryers, etc) in one room. They only carry some furniture. Anyway, the same is happening with a lengthwise tunnel. The longer 7′ span requires about 140% of the strength of a more standard 5′ span, even though you have only increased the length of the pole by a couple feet (around 25%, ignoring the arc.) These are not detailed calculations by any means, just off the cuff examples.

Using a pole strength of about 150% would likely work, but this increases the weight of the pole, along the whole extra length. And, due to the weight of the pole itself, it requires more strength to hold itself up, but this is a minor consideration and is not considered. Personally, I would simply increase the diameter of the poles at that point to get to the 200% strength I would *like* to see. But that’s just me.

The gothic pole architecture works OK. It is designed to decrease up/down stress along the arc. But any sharp point in an arc will disrupt the overall strength. In a wind or asymmetric load, it becomes more unstable, more rapidly than a smoothed ellipse. It is a cross between a triangle and an arc. Additional head room can be supplied by simply lengthing the poles a bit…all joints are bad, actually. But can be used as anchor points for guylines, greatly decreasing their effect, as Roger has discovered.

[Sam Farrington]

Roger, another nice tent. It looks like a one peg vestibule on the gothic arch. In any event, as was said, the intention was to use it on a side entry tunnel with a much wider pole spread where IMO a one peg entry would reduce the tension on the canopy by an unacceptable margin. Agree that for a two person tent, the gothic arch would have to be quite high to obtain a spacious inner, and is probably not the most efficient use of space. But for a one person ‘lateral tunnel’ tent, I’m suggesting that reducing height at the sleeper’s head and feet by using a gothic arch rather than a hoop would reduce weight and increase stability, while limiting space where it is not needed.

James, thanks for elaborating a bit on your diagram.

[Roger Caffin]

Hi Sam

Back in the 60s and 70s I made two 4-man domes for summer use. Very roomy and quite light, but not what you would call ‘windproof’. Nylon fabric and (Jarvis Walker fishing rod) fiberglass poles. 7′ or 8′ square.

The one shown above was the first of my MYOG tunnels. Yes, 2-pole and single peg at the end. Quite reasonable in heavy rain-forest deep in a valley. MOST unreliable in strong wind: we spent an hour or so one night in Central Australia holding the tent up and down.

These two-poles tents led to my ‘real’ 3 & 4 pole tunnel designs, where I drew on a fair bit of field experience. But if you can guarantee zero wind, the 2-pole design is OK.

Cheers

[James Marco]

Roger, you exaggerate a bit. Most any tunnel will hold up to a 10-15mph wind. Only the wider unsupported fabric really makes the normal tunnel unstable. As you say a three or four pole design works pretty well in heavy winds. But any heavy side wind on a tunnel is a problem. Due to the short span (about 2’or ~61cm less) a lengthwise or lateral tunnel will be more stable. It picks up stability due to the extra length of the body and is closer to an ideal “tear-drop” footprint in form. This removes a large stress component where there would normally be a much longer side wall. As an example, one problem with the Stephenson’s is the slanted poles. They increase the length of unsupported fabric allowing it to pick up large stresses from the side as you must realize. You use multiple poles straight up to relieve this stress in short unsupported panels (besides being easier to engineer.) But, the lengthwise/lateral tunnel looks a lot like a dome.

The half “tear drop” shape of standard tunnels is actually quite good for wind directions along the length. A symmetric lateral tunnel with it’s ends doing essentialy nothing but gear storage (or room for a child/dog,) only serve to shape the tent into a more aerodynamic form in a *rotation* of the wind vectors. Holding that shape becomes one of guy lines…they can be used in either case, so, I ignore these. A LOT depends on staking (2 stakes is not enough) and tension on the fabric. And, actual pitching, of course. Of course, the normal tunnels you make are not effected by these forces, are they? (A joke;-)

As I said earlier, due to the extra long poles and the live loading on the flattened roof there is more stress on the longer poles (snow, ice and water) and the structural support needed is much higher on a longer span. The weight of the poles to carry that stress is roughly 200% or twice that of a normal tunnel to be safe. You end up using three pole sets on a normal tunnel with shorter, lighter poles which results in a significant weight SAVINGS, and, likely a strength increase, overall. (Ignore the weight of the extra fabric on the ends.) Doorways don’t really matter, you can put them on the side or at the front/rear. I wouldn’t do it because of the weight increase, alone.

Domes are not the worst thing out there. they are just wasteful of useable living space and weight. This is what the lateral tunnel more closely resembles than to a traditional tunnel in most stress analysis and especially in an aerodynamic analysis. You could as easily simply cross the poles as in a typical dome or variants and get similar results, weight-wise/stability wise. You really don’t get any real additional benefits from a lengthwise/lateral tunnel. Like a dome, it has too much wasted space in the odd shaped floor/vestibule area. All that extra fabric does nothing but shape the tent.

[Roger Caffin]

Roger, you exaggerate a bit. Most any tunnel will hold up to a 10-15mph wind.
OK, OK, true.
And yet, in some ways possibly not so true. Deep in the rainforest you don’t get wind. But if you are somewhere that can get a 10 – 15 mph wind, could it not on a bad day get a 30 – 40 mph wind? If the site is open to wind, anything is possible. Yeah, I’m am quibbling.

But any heavy side wind on a tunnel is a problem.
Not seen yet with my 4-pole winter tent. Granted, there is always the next night, but so far I lack fear. :)

If the wind is that high, flying debris might be a bigger problem. We have had that once too.

I should add that I strongly suspect, on a simplistic engineering analysis, that a door in the side of a tunnel tent is going to be a major structural weakness, compared to the classic door at the end of a tunnel. The whole design will be a lot weaker, especially when the door is open, and you will most likely get rain and snow onto the groundsheet. For me, this latter is an absolute no-no.

With the door at the end you can have a major working area in the vestibule for shedding wet clothing, removing snowy boots, cooking, and even for making an indoor toilet. The last may sound terrible, but in a storm of -10 C & 100 kph wind, I can assure you it is infinitely preferable to going ‘outside’. And of course, at -10 C there is no smell!

Cheers

[Sam Farrington]

‘If the site is open to wind, anything is possible. Yeah, I’m am quibbling.’
Roger, I don’t think you really are quibbling. Watching the video clip from Olivier that I posted a link for earlier, he used an anemometer frequently, and with some squinting, the readings varied quite a bit, and that is just for a short clip, not an all night blow.

‘But any heavy side wind on a tunnel is a problem.’
I think James may have been focusing on the near vertical walls of a tunnel, regardless of the number of poles. I always thought you used more poles to simplify construction, yes; but also to protect from snow loading and downdrafts, and most important, to anchor those side guys you use.

‘If the wind is that high, flying debris might be a bigger problem. We have had that once too.’ Followed later by: ‘And of course, at -10 C there is no smell!’
Yeegads! Do we have to design for flak and poop too?! Sounds like the WWI trenches.

‘I should add that I strongly suspect, on a simplistic engineering analysis, that a door in the side of a tunnel tent is going to be a major structural weakness, compared to the classic door at the end of a tunnel.’

Agree that a door in the side of a tunnel tent ‘is an absolute no-no.’ The theme of this thread at least seemed to be about leaving the sides of the tunnel intact, but shortening and widening the tunnel so that the (front) door is to the side of the sleeper(s). Again, for a solo this probably makes sense; but if I misunderstood what Rene had in mind with his thread title, a reset may be in order.

After constructing a model of my original take on a solo ‘lateral tunnel,’ with Macpac type canted poles, the solution to the elbow angle issue was evident – simply by extending the width of the short tunnel to 8.5 feet created more space above the head and foot of the sleeper. Of course this is often done by necessity on A-frame and other flat wall tents, but it took a model to get to it. It also became clear that the 3′ span between the pole apexes was not going to be a problem. Love models.

But there may be some surprises with the stability of such a wide tunnel, even with the slope of the walls created by the gothic arches. How much this will be cured by the tension from the end covers, essentially two partial cones with a door between them, may become clearer when some very light fabric is pinned over the model. If that works out OK, on to the real thing, and we may have something concrete to discuss.

Two of the heavier Quest carbon pole sections are on the way. If they have more rigidity (although weight alone does not guarantee that), that should go a long way toward a more rigid and wind resistant structure overall, without too much of a weight penalty. That the poles are made by Easton for tent applications gives hope.

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