Good Bye Spreader Bars (and plug for the new D4 Portaledge)

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anita514

Gym climber
Great White North
Feb 15, 2017 - 06:30pm PT
Will it be available in hot pink?
healyje

Trad climber
Portland, Oregon
Feb 15, 2017 - 06:32pm PT
..and with a 'pussy fly'? Want to be able to make a statement with it if it's going to hanging out there for everyone to see.
couchmaster

climber
Feb 16, 2017 - 09:39am PT

Have this fella do the product set up video, the man clearly has skill for it. Look how ridiculously easy he makes this one appear. It's enough to make ya hate him for how easy it should be. Like a Carney with the skillz to take yer money cause he can whack the balls every time and you can never do it. Spoiler alert, the 1st 30 seconds are music.

[Click to View YouTube Video]
matty

Trad climber
under the sea
Feb 16, 2017 - 10:28am PT
^^^ way easier standing on ground with unused ledge resting on table
Mungeclimber

Trad climber
Nothing creative to say
Feb 16, 2017 - 10:45am PT
My ratio of 1:3 times getting my Fish ledge to fold up easily is getting better. Lack of time on wall is a clear factor this year.



Deuce, it wouldn't be right if you hadn't have spent time in the Valley working on it. Great story/stories! Keep em coming!


This is a proper Supertopo thread.

deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 16, 2017 - 11:17am PT
Sorry, was called off yesterday to do some payback for my paragliding pilot friends--did a all-day retrieval for two local pilots going for the Tassie distance records. One of them was brought down by Wedge Tail Eagle attacks, the other made only 40 km or so--big challenge because legal airspace is very low in the midlands where the land passes are also high, so narrow gap to break through for bigger distances.

The next part of the story needs to include some technical engineering info, so i have been pondering how to explain clearly. I made this video last year in response to the Aluminum/steel 'debate' to help explain how flex/rigidity compares with tube geometry as well as material aspects, It doesn't cover the 'why' so I will work on a simpler explanation, as it plays into how spreader bars are unnecessary and really a design 'kludge' based on lack of proper engineering design.

[Click to View YouTube Video]
Plaidman

Trad climber
West Slope of Powell Butte, Portland, Oregon, USA
Feb 16, 2017 - 03:55pm PT
Thx John for posting the history and the path of development of your new Portaledge.

Plaid
deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 16, 2017 - 04:07pm PT
No worries, Plaid. It was nice meeting you last fall, have enjoyed reading of your adventures as well!
Gunkie

Trad climber
Valles Marineris
Feb 16, 2017 - 04:54pm PT
I'm sure many frame variations have been analyzed, but to keep weight down, has double butted tubing ever been considered? How about triangular cross section tubing? At some point various costs (time, money, opportunity) outweigh performance benefits. Just curious.
deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 16, 2017 - 07:33pm PT
Love all the ideas popping up. As I posted on the Wired Bliss thread somewhere in here, I think there's some potential for better online group collaboration sites, to enhance idea sharing--still experimenting with sites like this one: https://500px.com/JohnDeuceyMiddendorf/galleries/monkey-paw Sketches and visuals are essential in my opinion to share ideas properly, so they can be more clearly discussed and refined.

Back to the main story:

So here's the rub: One thing Metolius did was to respond to folks wanting a more comfortable big wall camping experience (I suppose I could say in the 90's survival was more the overarching parameter!), and so they made their ledge bigger than the then best-selling A5 Alpine Double, to 45" wide and 84" long. Of course, making it bigger affects the engineering, but they did so without redesigning the frame--they simply used the same 1.125"OD 0.058" 6061-T6 Aluminum tubing of the A5 Alpine Double, which size, as mentioned before, was optimised for that tubing to be 43" by 75".

Guess what? No surprises here, frame flex became an issue. If you think about a simply supported beam (which is what a portaledge tube really is), if you extend the distance from the support to the load, an 'elastic' beam will flex more (in engineering terms, materials are elastic until they permanently deform, then they are plastic!). In fact, the relationship of load to bending is dependent on the third power of the distance between support and load. Here's a simple case with the mathematic formula:


So for the long tubes, we can use that formula (I'll explain the other variables later) to get a rough idea of the relative additional flex an 84" air side tube will have over a 75" air side portaledge tube by finding the ratio of 84 to the third power divided by 75 to the third power, which turns out to be 1.4.

What this means is that for a given load and beam configuration, an 84" long air-side tube will flex 40% more than a 75" long air-side tube.

(ok, it is more complicated than how I am describing it, as the beam in question has a distributed load supported on both ends which is a slightly different formula, etc, but the analysis gives a good general idea of what is happening--the "third-power" relationship of deflection to length in beam loading is the key here).

To make matters worse, they came up with what I consider a whacky open corner concept to ease assembly. Now, I came up with the portaledge block corner design back in 1986 (now seen on all BD, Metolius, and Runout ledges) to ensure a rigid corner connection. Rigid corners were the first big breakthough in portaledges--starting with the Fieldware/Fish single ledge in 1985--ledges before that time all had soft or hinged corners which frankly only work when the ledge is set up on a nice flat wall--put the ledge in a corner or some other bad loading situation, and a ledge without rigid corners turns into a trapezoid. Rigid corners are essential for a good sturdy ledge.

Below are some pictures of open corners--I think it is easy to see that the whole frame becomes less rigid and flexes more with an open corner.



So with a more flexy ledge, Metolius re-introduced the spreader bar.

(not finished with this part, but gotta go pick up boy from school--tell me if I am getting too technical).
Also want to discuss a super simple way to ease assembly without having to resort to open corners.

nathanael

climber
CA
Feb 16, 2017 - 08:23pm PT
Not too technical! Thanks for sharing, reading with great interest and awaiting more updates.
deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 16, 2017 - 09:24pm PT
Ok, back.

Metolius did not invent the spreader bar. Charlie Row had built a homemade single portaledge out of 7/8" thin wall tubing back in the 70's, and because the tubing was under designed, which he knew, he added a spreader bar to keep the ledge open in the middle.

Now, I have never used a ledge with a spreader bar, but I hear that they can be hard to set up, have to be placed fully square or they spontaneously spring loose (good review here: http://www.fishproducts.com/miscpages/portaledge_review.pdf ), and that they can dig into your back when you're sleeping (PTPPete told me that)--doesn't sound like fun.

What we are after here is rigidity, less flex, or, in engineering terms, less deflection for a given load. People often think "strength" when talking about portaledge tubing. Of course strength is important, but almost more important is rigidity. Similar to the reasons why steel frames flex more than aluminium for a given weight as shown by FEA in the video above, so does titanium. We had a titanium ledge on Great Trango--the first of its kind--and though a pound or so lighter, and stronger too (in terms of its ultimate failure strength), but because of its smaller diameter (7/8") and thinner wall (0.028"), it flexed more than the equivalent weight aluminium frame. Titanium was ideal, however, for the 3kg super light custom single ledge I made for Catherine Destivelle for her historic solo first ascent on the Dru (pictures at the end of this article: http://www.bigwalls.net/climb/mechadv/index.html ). Her ledge, with fly, packed into a tiny (for a portaledge) 24" x 4" bag, so a main advantage of the titanium for her ledge was its smaller packed size, as the tubes were less than 7/8" O.D., and the flex wasn't as big an issue because I made a super small custom ledge and lightweight fly for her (from memory, I think 72" x 25").

More on titanium: In the 90's the Soviet Union was collapsing, and the market was flooded with cheap titanium, presumably raided from once government and military stocks. I had a line on the stuff from a Russian climber, and once made a super heavy 1" (maybe 3mm wall thickness) titanium portaledge. It was adequately rigid and unbelievably strong--I think we once got 10 guys jumping on it without failure--but way too heavy for taking up a wall. It was the perfect car-camping portaledge, though, and spent many happy nights, often with girlfriends with whom I was exploring the southwest, while hanging from a nearby tree for the night.


But besides that one-off and way overdesigned titanium ledge, even the next-strongest A5 ledge back in the day (and we made a lot of variations of one-, two-, three-, and even four-person portaledges) did not do well when tied to a tree-- a lot of flex--the point load from a tree is one of the worst case loading situations, one that would rarely be found in real-world big wall applications. And I doubt that the BDs and Metolius, with under-designed tubing for its size, even with the kludge spreader bar, do well in terms of flex when set up in a tree (it seems to me that the point load would compromise the integrity of the spreader bar causing it to pop out if put against a tree?).

But my new D4 design does incredibly well when set up in a tree--I recently had about 7 people in it (ok, some were kids) with almost no flex, and no spreader bar. How? For this I need to introduce another engineering concept--the Second Moment of Area, aka Area Moment of Inertia (not to be confused with the Mass Moment of Inertia), or we can use the Elastic Section Modulus. These are properties based purely on the geometry of the tubing, and can help us figure out relative strengths and flex of tubing under load.


More tomorrow on Section Modulus and the secrets of eliminating the spreader bar (y'all can probably guess where I am heading, now ;)
Moof

Big Wall climber
Orygun
Feb 17, 2017 - 08:35am PT
Trouble I havehad with my home made projects is that to keep bed sag low enough side to side it is necessary to make the bed tight, resulting in difficult assembly. Really small window to hit while winging it on a home project. Spreader bar helps with all that, but then you have to use a stupid spreader bar. Looking forward to the details.
deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 18, 2017 - 01:25am PT
Ok, after thinking a bit, I will try to explain this using the Section Modulus, as I would like to include a discussion of both strength and flex. (Note: Engineers think a bit differently, strength is thought of in terms of stress, and flex (deflection) is never simply called flex, of course ;)

Strength uses the Section Modulus (we'll call it 'S'), and flex uses the Second Moment of Area/Inertia (I). Again, these are purely based on the geometry, and they are related by the outside diameter (OD) of the tubing, where I=S*OD/2.

Never mind that. Think about a piece of 2x4 wood--if you were building a cantilever, which way would you put the wood? It would be stronger and less flexy if you put the wood upright, or course, rather than on its side. That's what the section modulus formula is all about--the more material away from the center in the direction of load, the better, for both strength and flex.

Here's the formula for Section Modulus of a tube (again, note how it only relates to geometry, not actual material properties).


When you are designing the best tubing for a portaledge, there's a lot of engineering things to think about: bending, deflection, buckling (a problem if you make the tubes too thin), size and weight, to name a few. We'll focus on the comparative aspects of strength and flex here.


For strength, we can simply create a "Strength Index" = S * Y, where Y equals the Yield strength. Bigger numbers are better.

For flex, we use the formula above to create an "Flex Index" = (L*L*L)/(E*S*OD), where E is the Elastic Modulus (Young's), S is the Section Modulus, and OD is the outside diameter. Smaller numbers are better. Note that actual material properties are now coming into play.

I use this site for my material data: http://www.matweb.com/search/PropertySearch.aspx

Here's a table of some properties we will use for the next part:

Next up: Section Modulus, Strength Index, and Flex Index charts...

deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 18, 2017 - 08:48am PT
Have I lost everyone? Seems like the thread isn't getting much response lately.
Rock!...oopsie.

Trad climber
the pitch above you
Feb 18, 2017 - 08:55am PT
Have I lost everyone? Seems like the thread isn't getting much response lately.

confirmed lurker standing by... carry on please!
WBraun

climber
Feb 18, 2017 - 09:07am PT
keep em coming John.

It's interesting stuff and people read your stuff instead of all that daily cesspool politard garbage .......
stevep

Boulder climber
Salt Lake, UT
Feb 18, 2017 - 09:11am PT
At this point, I'm not too likely to ever be using one, but this is interesting from a historical and engineering standpoint. I see similar materials science discussions in bicycle manufacturing.
Would using carbon fiber tubes be worth it? Or too much risk of impact damage on the wall?
Leftwich

climber
Feb 18, 2017 - 09:14am PT
I'm waiting on pins and needles. This is the best thing going on the internet right now.
deuce4

climber
Hobart, Australia
Topic Author's Reply - Feb 18, 2017 - 09:33am PT
Ok, cool!

In case anyone was wondering, I live in Tasmania, so I'm not up at 1a.m. as my last post per supertopo time suggests, but I do get up early, right now it's 4:30 a.m.

I stopped last night because I wanted to add Carbon Fibre to my list of ledge materials and have been looking for the best engineering data. I once made a ledge from Carbon Fibre with my old A5 portaledge design. But it didn't seem to work well because with block corners, there is a large point load at the joint (where the end tube connects in the A5/BD/Metolius block corners is only 0.8" deep). This is okay for a relatively ductile material like aluminum (which you can also easily double butt with a riveted insert), but for the very stiff and thin carbon/resin tubes, the shallow joint is not kind to the tubing. My new D4 design is actually well set up for a carbon fibre version, and i am building a prototype now, but it's very expensive, even with materials from China. I think Luke at Runout has also made some carbon ledges with the A5 design. More on the carbon fibre friendly designs later, but for now, let's add carbon fibre to our Strength Index and Flex Index list.

Stand by, looks like this site has some decent data :
https://www.rockwestcomposites.com/round-tubing/round-carbon-fiber-tubing/high-modulus-carbon-tubing

Hard to find good general data on carbon tubing as it is a carbon/resin composite, and there are so many variables, the way the layers get laid up, etc.
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