Determining tent door panel angles

[Scott Jennings]

Hi everyone,

I’m about to start making a 2 person, 2-trekking pole tent, with dimensions sort of an average of the Zpacks duplex and the Gossamer Gear The Two, and with the non-zip, slightly-overlapping door flaps of the Duplex.

I’ve used Sketchup mostly successfully to design the tent and determine dimensions of the various component pieces of material. I’ve found the protractor tool in Sketchup, which works for determining angles of corners that exist on a single plane. But, I’m having trouble figuring out what the angle should be for the top corner of the door panel pieces, where the panel wraps from the plane of one door panel to the other. To be clear, I’m trying to figure out what angle to cut in the fabric.

My initial plan has 4 inch overlap at the top of the door panels. Any feedback on that?

Thank you,

Scott

 

 

[Jerry Adams]

I always lay out triangles, then I don’t have to measure any angles

Except sometimes I need to do 90 degree angles.  Carpenter square that’s a couple feet long works.  Or measure out a triangle, like one with sides measuring 3, 4, and 5.

This works as long as all tent panels are flat.

[Brook / MtGL]

Hi, Scott,

If I understood correctly, you can draw the interacting line of the two door panels (the line of the zipper in a traditional design) to be 45 degrees from the ground. 45 is the theoretically correct angle.

After finishing the 3D model, you can use some plug-in. Here I used a SketchUp plug-in called “unfold tool” to flatten all the panels, so that you can plan the cut layout accordingly.

Good luck to your project.

Brook

[Scott Jennings]

Thank you Brook. Good tip on the plug-in; sounds like just what I’m after.

Is 45 degrees the theoretical best angle for the actual tent door panels, for wind-shedding or some other purpose? Or, is is the best angle to have from the top of the trekking pole to the stake, in order to get the best compromise between downward tension on the pole and outward tension on the ridgeline? When flat-tarping, I aim for 45 deg for the line from the top of the pole to the stake for the later reason.

For this project, my current design is to have the angle on the door panels somewhere closer to 26.5 degrees, substantially steeper than 45. It looks like this is more similar to the angle on the Zapcks Duplex, while the Gossamer Gear The Two appears to have an angle closer to 45. I will have a separate line from pole top to stake, such that the doors are not responsible for pulling tension on the pole and ridgeline.

Thanks again!

Scott

[Jerry Adams]

“Or, is is the best angle to have from the top of the trekking pole to the stake, in order to get the best compromise between downward tension on the pole and outward tension on the ridgeline? ”

Yeah, for angles greater than 45 degrees, there’s progressively more tension pulling out the stake to get a specific sideways tension to keep the tent from blowing over.  Arccosine of angle.

Normally, I don’t worry about it.  Make the tent pole height as desired for headroom, and the width as desired for room for my sleeping bag.

One side of my current tent is just to store stuff so I could make it fairly narrow, but I don’t want that angle to go too far above 45 degrees.  My tent pole is 5 feet tall.  3 feet wide.  That has held up in 30 MPH winds.

[Scott Jennings]

Thanks Jerry. I wasn’t thinking of forces on the stake, but that makes sense.

FYI, if anyone else is trying to work out this problem, I realized over the weekend that it is actually very simple to solve. Since the 2 door panels are symmetrical around the axis running from the top of the trekking pole to the outer corner of the vestibule, the angles at the top of the door panels are also symmetrical. So, I can easily measure the outer-end-of-vestibule:trekking-pole:tent-corner angle using Sketchup’s protractor, then double it to figure out the true angle to cut into the door panel fabric to get the little overlapping flap right.

I’m using the free, online version of Sketchup, and could’t figure out how to get the unfold extension.

Scott

[Jerry Adams]

I use Pythagorean theorem – a^2 + b^2 = c^2 – of a right triangle

For example, if pole is 60 inches, tent is 54 inches wide, then the diagonal at the side = sqrt ( 60^2 + 54^2) = 80.72

Then the diagonal at the corner is sqrt(54^2+80.72^2) = 97.12

 

[Brad W]

i’ve never done what you are proposing, but I’ve done things sorta like it.

I can do the math…. but my suggestion is to do a mock-up.  do the math first to get an idea maybe…. but It’s really easy to calculate….then measure….then measure again….then recalculate, then measure again…. then cut it wrong.

[Jerry Adams]

many good ways to do it

Pythagorean doesn’t work for weird curved tents, like most tents sold these days(?)  Then, something like Sketchup would be really useful.

[Scott Jennings]

Thanks again for the suggestions everyone.

Yes, but no, Pythagorean theorem doesn’t work for this situation.

I’ve got the fly portion cut and sewn together, and as far as I can tell the method I mentioned above (May 21 3:41 PM) worked well.

Scott

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