Storm-proofing the Side Panel on a lightweight A Frame Design

I am biased – you know that.

None of the above ideas gets rid of the long unsupported fabric span. Until you put more poles in (and in the right places and shapes), you will not win. (imho)

Cheers

Hi Roger – thanks for replying! Gives me the opportunity to thank you personally for all the outstanding info you’ve shared over the years.

I realise that you’re a partisan for the tunnel, but I’m a bit bemused that you reject and A-frame project as a losing proposition out of hand. Here’s my thinking – I’m happy to be corrected.

Your 2-pole solo has a similar weight to my tapered A frame, but also a similar unsupported panel size. Your 3  pole design has a somewhat smaller panel size than the A frame, but would be a bit heavier. And you openly concede that it may require a double central pole in serious weather, adding more weight again. (And they look like an intimidating build for someone without your skills and access to tools!)

For me, the key difference is that the tunnel designs use flexible 7050 poles of around 10.25mm poles compared to the far stronger 18/16/14mm sections of my 7050 trekking poles. So if I understand you, you’re implying that I should substitute strong poles for something much weaker in the name of performance. I simply can’t see how this makes sense. The only advantage would be that the tunnel panel shape might shed the wind a bit better, but can that really compensate for inherently weaker support?

I think it boils down to two design approaches – strong and rigid poles vs lighter but weaker bendy poles.

Rigid pole A-Frames are surely a proven design?

It seems to me that rigid A-frames have served us well in the hills since at least the time of the Victorian Whymper tent. Here they are on the North Col of Everest:

As I understand it, the basic idea is to provide a rigid and stable structure at each end and to stretch the panels between them. The tent doesn’t flex much under load. In my experience, it’s a design that works very well.

In the 60s and 70s Scotland we were pretty much all using the Vango Force Ten A-frame and it’s well named. They’re bomber in wind and snow – quiet and totally reliable. I’m nostalgic for the performance, but not for the weight!

Then Ultimate produced The Tent (which morphed into the Phoenix Phortress), and proved that you could get similar stability without a heavy ridge pole. Again, they were bomber. I’ve already quoted Chris Townsend’s view that the Phortress was the most stable tent of all the hundreds he’s reviewed. So why do you believe that it’s an inherently flawed design?

And there are at least 2 other rigid-pole designs that have stood the test of time – the pyramid, with only a single point of support, and the Stephenson WarmLite with its unique rigid bent poles.

Then came the bendy poles, and pole failure became a regular event

Then in the early 80s the small diameter bendy pole came in and we all abandoned our trusty A-Frames. I think that this was partly because the new designs offered more living space, and partly because we didn’t have to lug around heavy rigid poles any more. (And partly, to be honest, because we wanted to look cool. My innovative WinterGear Sapphire used to attract crowds at campsites!)

But the new poles are much, much weaker. Obviously with a full geodesic you get a bomber tent, but that’s not practical for a lightweight solo. With anything else you’ve got to somehow support the wimpy poles with guying, and rely on flexing to take up the rest of the strain. But pegs can fail, or the wind can hit from a vulnerable direction. So pole breakage has become common, while it was unknown in the ’70s.

Then along came trekking poles and the A-frame became practical again

In the last decade or so most of us began carrying poles that could be used as an effectively unbendable, unbreakable shelter support with no additional weight. The A frame made sense again, and a long list of specialist makers began to offer them. A lot of customers seem happy to trade off a little space for simplicity, reliability and stability.

But none of the current offerings use a sleeved A-frame front and back, which in my experience contributes greatly to stability, and there are other features I feel could be improved. My idea is to replicate the best designs of the ’70s when the A-frame reached the peak of its development, but in much lighter modern materials. I’ve specced this out at around 800 grams for a well-vented single skin, including guys but excluding pegs. The options I’m asking about here are intended to tweak an already successful geometry. Another idea I’m playing with is supporting the ridge with tape in the seam. This is technique used by balloon makers and seems to work well.

But how does the A-frame compare to the other lightweight solo options?

For a lightweight solo 3.5 season tent the practical flexi-pole designs are the single transverse hoop, the Bibler-style crossed pole, and the tunnel. I once foolishly bought a transverse hoop and hated it – it’s a fiddly, flappy, vulnerable design with poor clearance over your face and feet. The Bibler is tiny and unlivable with a solo floorplan. So the tunnel is the only workable alternative to rigid A-frames and mids.

Your lightweight gothic arch is a brilliant variation on the tunnel, and I gave it a serious look. It’s a robust and liveable design and it clearly works for you. But it still leaves me with the question: for thru-hiking why carry a set of weak bendy-poles when I’m already carrying something much stronger?

With bendy poles the peg placements waste a lot of their strength simply to keep the support from flexing. And when the poles flex the panels lose their optimal wind-shedding shape. I’ve seen so many bendy-pole designs knocked flat in big winds. Even if they survive, you can’t be sure that the poles aren’t weakened and failure-prone.

I’m aware of the success of black-label Hillebergs in the Arctic, but they start at 5 times the weight we’re discussing here, and bomber peg placements on flat snow are a whole different game compared to sketchy placements in the hills. So it’s not really comparable.

A rigid pole puts much less stress on the pegs and simply sits there in the wind. It’s less damage prone, and the panels keep their wind-shedding properties. The TrailStar is a great example of this – it’s wind performance is awesome and the pole takes a lot of the strain. With the A-frame geometry, the poles take even more of the strain from the guys. And the TrailStar demonstrates that  small triangular panels with a rigid support at the top really do the business.

So that’s how I got here. This is a tent that going to get a lot of use, and if I get caught in a big storm somewhere remote there will be a lot riding on its performance. So if I’m on the wrong track I’m more than willing to listen. What, specifically, do you think is misguided in my thinking?

Hi Geoff

First of all, you might like to read When Things Go Wrong as it will help explain where I am coming from, followed by our series on Tunnel Tents at https://backpackinglight.com/tunnel_tents_part1/ . (URL to 1st part – there are many parts in the series.)

There are several key points to be made. The first is that the thin flexible poles you are talking about are not all that flexible in a tunnel. They are 7.5 mm OD carbon fibre in my tents, and 7075 T9 of a similar size in other tunnels, and field testing shows they do not flop over when used correctly. A key point here is that the poles in a pop-up and other designs are very long, and they are bendy. The poles in a tunnel are much shorter, and are therefore stiffer. Field testing confirms that. Yes, people talk about double-poles, but i have never used them.

The next point is the length of the fabric span. I have made tunnels with 2, 3 & 4 poles, and the differences are profound. When a long fabric span (2 poles) bellies in under the wind it can put significant sideways forces on the poles. The far shorter fabric spans (especially 4-pole) are just not the same.

As you note, putting high tension along either an A-frame or a tunnel is essential for stability. Allied to that is the need to make sure the windward end does not move. Once the tent starts to move, disaster follows. Long fabric spans inevitably let the tent move. Yes, this does mean that the two stakes at the windward end are crucial, and the two stakes at the lee end are also very important. But the side guys are not as critical – my 4-pole survived with only 2 guys out of 8 holding. (The other Spectra guys broke by fretting over sharp titanium edges on the snow pegs.) I don’t think I have ever had a peg pull out.

Now, my ‘2-pole solo’ – does not exist afaik. I did make a 3-pole solo for Ryan Jordan, and he uses it in severe winter conditions. My 2-pole 2-man tent was discontinued many years ago: the fabric span was too long for safety.

With bendy poles the peg placements waste a lot of their strength simply to keep the support from flexing.
That is not how I see things. The whole point of the side-guy pegs is to brace the poles against the wind. I do not call that ‘wasting’. Ah – the poles are what creates the interior space, rather than the side guys.

And when the poles flex the panels lose their optimal wind-shedding shape. I’ve seen so many bendy-pole designs knocked flat in big winds. 
Oh, I totally agree. But I suspect those bendy-pole tents you are thinking of have far longer poles than a tunnel does. A good tunnel does NOT bend like that – maybe that is the definition of ‘good’?

As for the Stephensons Warmlite – I have tested one of those and was NOT impressed. And it required a HUGE lengthwise tension to stay up.

I dare say there are plenty of other UL possibilities, and they will work quite well in the lowlands and in fine weather. So give them a go, and let us know how they perform – with photos please!

Cheers

The way to storm proof an A frame?

Turn it into a pyramid : )

One pole is better – if it’s twice as big as each of the two poles it’ll weigh the same, but it will be stronger – the strength of the pole is related to the square of the diameter

AS one who has been through heavy weather in an MSR twin peaks (brother from another mother to the Betamid you have a photo of) I can say that if your stake placements are rock solid and you have good trekking or ski poles that thing can handle big weather. But if you play with the shape much you will go downhill quick. Here’s why: that shape is essentially two pyramids conjoined and slightly spread to get an irregular hexagon floor plan. the angles are really good in the sense of roof slope, minimizing size of panel in relation to the overall size, and avoiding what I call flat side syndrome. Alter those anlges and you lose capability. Steeper sheds snow betterm but makes it taler and that hurts you in the wind. Lower does better in the wind but won’t shed snow and leaves very littlr room inside.

Your sketched shelter looks to me like it is narrower and steeper, and the proportion of ridge to overall length is larger. I think this will not do as well, because you have lengthened the ridge and thus enlarged the panels on the sides (unless you have shrunk the thing, and if you have then you must be thinking a-frame poles and that would be a different story, because a shrunk version without A-frame poles would not leave you enough room on either side of the poles) . Now if you are thinking A-frame poles I wouldn’t do it. Whay? becasue the key to making the Betamid or its cousins work is being able toe jack up the poles to get fierce tension on the thing. Staked down solid and pushed up tight, I can get my Twin peaks drum tight and if you can’t get it drum tight then forget it.

One last thing – I use my Twin Peaks in the snow, so I put snow flaps on it and bury them to seal the edge. Also critical in my opinion – without them, wind gets under the edge and causes big trouble – not to mention bringing in lots of white cold stuff.

Yeah, pity about the ‘white cold stuff’.
Cheers

Thanks for the input folks!

Roger, the one person solo design I was referring to was from your old bushwalkingnsw site. It’s a design that would give more space than a tapered A frame at a similar weight, but which might be more flappy. The space isn’t a high priority for me, so for my particular requirements I didn’t see a need for the additional complexity.

I’ll happily concede that a 4-pole tunnel with 7.5mm poles and your arch design would give a very stable and liveable tent, but at quite a cost in weight compared to a simpler tarp-tent with trekking pole support.

As you have written yourself, with modern materials a solo tent isn’t very weight efficient compared to a 2-person design, and the savings with a smaller floor-plan are pretty modest. When you have to carry the whole shelter yourself rather than split it between two people weight becomes a higher priority. I’ve given myself a max weight budget of 650-800 grams, and I can’t see how a 3-4 pole solo tunnel would be doable. Please correct me if I’m wrong.

I dare say there are plenty of other UL possibilities, and they will work quite well in the lowlands and in fine weather. So give them a go…

You’re hopefully just teasing here? We can agree that your tunnel is a great design for exposed camping, but I can’t  buy into the idea that it’s the only bad weather design. Mids and A-frames  have proven their value too, I would humbly submit. Lightweight design is all about making the right tradeoffs, and while I love what you’ve done with your tunnel you haven’t persuaded me that it’s the best approach for my specific requirements.

Jerry, I’m well aware that mids are great performers in the wind – I love my TrailStar when there are no bugs and the huge footprint isn’t an issue. But in the final analysis the mid doesn’t really work well for solo use. With small footprint designs you have fabric close to your face and feet which gets old pretty quickly, especially when there’s condensation. The central pole is a pain and doesn’t play well with bug nests. And you often have a door with a drip-line right above your bag so you’re entombed when it’s raining (eg in the MLD Solomid). The solo A-frame solves all of of these problems – small footprint, space above your head and feet, easy bug protection and potential for a sheltered vestibule you can keep open in anything short of apocalyptic weather.

Paul – thanks for the heads up on the Twin Peaks – it’s one that I’d overlooked. Actually, once you allow for the taper in my solo design the dimensions (and therefore the wall angles and panel sizes) are quite similar.  I think the projection used by the CAD software is a bit misleading.

You make a very thought-provoking point about the need to get tension by jacking up the poles – it’s the same with my TrailStar which also uses triangular panels. I do plan on using an A-frame, which might make this tricky as you point out, unless I can think of a smart solution. You’re inclining me towards the Phortress approach.

In a review here on BPL Kevin Grove makes a similar point:

The stability of the Twin Peaks shelter is highly dependent upon the pitching terrain. The shelter is very stable and bomber when pitched in snow, dirt, or grass. The Twin Peaks deflected very little in high wind conditions with a taut pitch in snow. The taut pitch keeps the sidewalls solid and unaffected by wind gusts. The stability is compromised when the terrain makes it impossible to achieve a taut pitch.

I suspect that the design with triangular panels would be the best performer with an optimal pitch, but that the Phortress design might be more forgiving in sub-optimal conditions. Decisions, decisions…

Thanks again for input – much appreciated!

Hi Geoff

Good Lord – I wonder who I made that one for? Must have been a long time ago. I don’t (won’t) make 2-pole tunnels any more. The fabric span is just too much.

The FAQ at the BNSW web site – sadly neglected I am afraid. Not enough hours in the day. One day …

Yes, my blue 3-pole 2-man tent is heavier, but only at 1260 g for tent + poles – for TWO people. When you consider the total weight of two 1-man tarps, it does not seem so heavy. And we find it quite roomy enough.

I have tried A-frames and I have tried pop-ups, and have always returned to the tunnel design. My 3-pole summer and 4-pole winter tents have looked after us in some pretty violent weather, in Australia and across Europe, so there I rest. But remember that I am always talking about a 2-man tent for my wife and myself, not a 1-man tent.

Cheers

Roger

For two people your design makes perfect sense – for exposed camping 630g per head is a good weight for that level of stability and space. And for two people, the more vertical walls of the tunnel add a lot to liveability. It’s also about the same weight as the WarmLite for something that looks a lot more liveable and easier to pitch well. But 1260g is more than I need to be carrying as an increasingly decrepit solo walker, I think.

The big drawback of the A-frame for two is obviously the lack of headroom Workable, in my experience, but hardly ideal. For a solo user, though, the height is in just the right place and my design gives me just enough room to sit, cook and pack. I know from a decade of experience with the classic A-frames that it should be stable if I execute it well, and it’s a much less intimidating build. So while I very much appreciate your input, for my particular use I think I’ll be sticking with the A-frame.

I think I’ll knock up a quick prototype with cheap parachute nylon off eBay and set it up on Dartmoor in a gale or two. I’ll post the results in a few weeks. I’d like to iron out the bugs before committing to expensive RSBTR materials.

Hi Geoff

I agree: it is the design for a solo shelter which is difficult. 2-man works easily; 3 and 4-man tunnels is harder but they too are possible.

a quick prototype with cheap parachute nylon off eBay 
You do realise the serious hazard you are stepping into here? MYOG addiction! :)

Cheers

I think that sometime folk put too much credit on the shape of a shelter and too little on the strength of the poles holding it up.

For example the Phoenix Phortress (a 5kg, 2 person  tent ) had 19mm poles (0.75″)

Now I am pretty sure that many modern shelters of just about any shape will hold up better with poles like that.

The same for those Whimper / Mummery tents of MT Everest fame.

Yeah, big poles … The OnePlanet Antarctic Pyramid (very much for real) uses 50 mm (2″) aluminium poles, and 6 mm guy ropes. I don’t think the Antarctic guys carry it on their backs.

Cheers

Roger , I have posted the same comment several times but apparently many seem to think that simply replicating the shape and ignoring the pole size will lead to the same results.

Hi Franko

I think that sometime folk put too much credit on the shape of a shelter and too little on the strength of the poles holding it up.

I agree. As I’ve rambled on at length above, I feel that the poles are the weak point of many modern designs. That’s precisely why I’m keen to make use of my trekking poles for the main support in my project. The sections are 18/16/14mm of 7050 aircraft-grade aluminium. For a small tent, this makes them essentially rock-solid and unbreakable, and because I’m carrying them anyway there’s no weight penalty.

But because they are straight, there’s a restricted choice of geometries. If you don’t want a mid your main option is an A-frame…

Somehow, the following seemed appropriate, or something:

‘Success consists of going from failure to failure without loss of enthusiasm.’
Winston Churchill
‘Insanity: doing the same thing over and over again and expecting different results.’
Albert Einstein

Geoff – I don’t carry trekking poles, so that does not work for me. But it may work for others. Tarp-Tents started that way. Photos of field test results are definitely desired, please.

Cheers

Roger: yes – I’ll feed back my experiences. Need to do a few small projects first though, to revive my long-dormant sewing skills. Been reading your series here on tunnels – fascinating. I hadn’t realised just how far that your design is ahead of most of the commercial offerings. You make a convincing case for the advantages of tunnels over geos for winter use.

Back on topic – I just came across this on YouTube: https://www.youtube.com/watch?v=Ji0JNewsN4c

It’s a Shangri-La 2 in a measured 60kph (40mph) side-wind. On the windward side the triangular panels are behaving quite well, considering that there’s no guying at all. Pretty much how the TrailStar behaves – the panels flex in the wind but don’t flap. On the leeward side they are a bit flappy, but the tent is completely open so this probably wouldn’t be an issue when battened down.

It’s a central pole design, so there’s no direct support for the side panels at the front and read. With sleeved poles at each end the side panels would be deflecting less, I think.

Geoff,
another A frame design you could look at is the way Bob Saunders did it :

weight 9 pounds 15 ounces : )

That is the typical problem with nostalgia , once you look at details it does not stand up anymore.

With tents it usually is about the weight but my point was about designs and it can be replicated with lighter materials although I still believe that most of the strength had simply to do with the pole size.

Nostalgia ain’t what it used to be …

Stronger poles => more lengthwise tension => less movement.  ++
Side guy rope flaps => more wind resistance.  + (But far more internal space in bad weather.)
I am less sure about the top sleeve for wind resistance, but I am sure it helped against snow loading.

To my mind, the need for serious lengthwise tension makes it similar in a way to the Warmlight, but the Warmlight design can still flatten badly under a side wind. And if the end stakes weaken, move or fail … you are dead. OK, that last bit applies to quite a few designs anyhow.

Cheers

Thanks Franco

I did know about the Sanders – I’m of the generation where we actually lugged these things about! Ah, but we were real men back then :-) Apart from the snow sleeve it’s very similar to Ultimate’s The Tent, which was much more widely used, I think. I guess that when a design works you don’t muck about with it. The snow sleeve thingy never caught on, probably because the Ultimate and the Phoenix performed pretty well without it.

Sure, they were heavy. But we all seem to agree that it’s the poles that are the key to an A-frame – and if you carry trekking poles you get 2 bomber poles for free. The Phortress specs are online and by modern standards the fabrics were heroically over-engineered, so there’s great scope for weight saving without much loss of performance.

I’ve been corresponding with a very experienced freelance designer of lightweight tents who has access to the labs and repair departments of many of the big brands. He is confident that with good design and reinforcement a 20D sil/PU poly is plenty strong enough for a small 3.5 season mountain tent. Roger’s tunnels also use lightweight fabric, and even the big Hilleberg black labels are only using 40D. So adapting proven old design ideas to lighter materials seems like a relatively safe way to go.

Yes, Roger, the A-frame does rely a bit more than a 3-pole tunnel on good staking front and back (though I doubt there’s all that much in it). But in all the years I used ridge tents in Scotland and the Alps that was never a practical issue – storm performance was great, particularly compared to most bendy pole designs. Note the sloped poles in the Phortress to reduce side-panel size and increase leverage, and the use of a long bad-weather guy at each end. The tapered panels are small and low, and compared to a tunnel there’s a bit less fabric, the walls slope more, and the porches have a lower profile. So it’s not open and shut. My personal take is that the benefit of tunnel as a 2-person shape is liveability more than performance. But for a 1-man thru-hiking tent the A-frame plenty liveable enough for my needs.

I’ve specced my solo tapered A-frame at around 820g including guys, and that includes sit-up space, a tough 40d groundsheet, zipped bug and draught doors at both ends with versatile porches for sheltered through-ventilation,  and DAC A poles at the foot end for stability. Even at that weight I’ll be disappointed if it doesn’t work almost as well as the Phortress in the wind. Cut back on the luxuries and skimp on the groundsheet and you could bring it in at under 650g.

PS  for anyone that doesn’t know it, this site is a treasure-trove of outdoor gear history: http://www.outdoorinov8.com/compass/ It’s not all nostalgia – lots of interesting ideas to mine as well!

I have used old Australian A frames with side walls. Franco will know the brand. We used a single pole at the end and good corner guys. There was no vestibule, but the flat end doors did attach around the pole securely. Performance was medium. I do not doubt that A-frame poles would have strengthened them. It was the fabric which ‘failed’ – Japara, and it leaked in a storm. Modern 40D sylnylon fabric would certainly survive; 20D silnylon should too, if suitably reinforced at the key points. Some care would be needed at the key seams and corners to get the strength needed.

For a 1-man tent with a tapered windward end – hum. It might handle the wind, if pitched tightly. I suspect snow loading would flatten it – I have some photos of that happening to other similar designs.

Have you considered making provision at the middle of the ridge line and the middle of the side guy flaps for an extra middle external A-frame, for use in snow? A few grams extra wt.

Cheers

When Roger used his Aussie made tent ,cameras had not yet been invented so no photos of that one.

But here is a photo  one set up up  decades later :

several versions were made but all somewhat similar to that including one similar to the Whelen tent.

That’s the light-weight Golden Tan version. Mine was stock green. Boy Scout days.

And I did not have a camera in those days, although (a bit later) Sue had a small ?Leica? or similar. She still has it, but no film.

Cheers