Design Preview – Cargo Kite

In-progress CAD of my design.

My final project concept, as you may have gathered from the title, is a big kite! Since I wanted a large kite for potentially lifting things in the future, I went for a rigid, box design, very similar to the inventor Lawrence Hargrave’s initial designs. After roughing out the ratios of the sails’ dimensions, it turned out that the entire assembly is about 1.8m long!

A few of Hargrave’s box kites, which my kite is structured like. I also took inspiration from the non-square cross sections and long sail spacing. [1]

Of course, given its design as a truss with large flat planes attached, my mind went to modernist, Bauhaus-like design. Its sails could have been decorated any other way, leading to any number of aesthetics, but something about the minimalist, black-on-white look stuck with me.

While its design is (at least currently) quite plain, it has a number of deliberate design features. Firstly, the rounded edges of the sails; it would be drastically easier and simpler to have them be nearly square, their only curvature coming from wrapping around the spars; however, I thought it would be more geometrically interesting to have a noticable fillet, and I was inspired to design something approachable and ‘friendly’ as per Dr. Hertzberg’s discussion of Contour Bias. As such, I designed the sails before any other part to ensure that the look of the kite’s largest pieces remained as I wanted.

This led to the ribs. I struggled to think of a good-looking way of stretching the sails to be shaped as they are now. I considered a hollow quarter-circle tube, perhaps filled with spokes. I considered a simple supporting surface, probably made of some bent material. Neither of these convinced me – I was worried about the perspective to the interior of the kite, and how simple and boring these designs would be from that viewpoint. I eventually remembered one of my earlier inspirations from a previous post, the Savyolovskaya metro station, and how I found its circular beams quite attractive; I adapted this idea into the ribs you can see here.

A view looking into the mouth of the kite, showing off the little ribs.

Savylovskaya Station, my main inspiration for the ribs, and to a lesser degree, the roundedness of the design. [2]

The dimensions and spacing of the sails were carefully chosen. Making the sails cubic, or even just the same length in length and width, led to an uninteresting appearance. I had known this from early on in the sketching phase, so I considered a few options for the ratios between the sails’ dimensions. I tried simple integer ratios, and even the golden ratio, but those didn’t impress me either; instead, I settled on doing it purely by eye. The sails, as you see them now, are 800 mm wide, 420 mm tall, and 560 mm long, with a edge radius of 70 mm.

An early sketch of mine of a cubic-cell box kite.

Further in my avoidance of excessive symmetry, the separation between the sails isn’t equal to their length either. I had tried setting them up as such, and it wasn’t to my liking. They are spaced 660 mm apart, slightly more than their length.

Top view of the current design, showing off the spacing between sails.

I also added a little text to the corner of one sail; as I wrote in my last post, I distinctly remember some famous product that had its information printed in black Helvetica on a white background, on the corner of a surface, similarly to what I have here. Still, I can not remember what that was. I’m not satisfied with the look of the text as it is now. I think it needs more consideration put into the font choice, spacing, and information itself. I didn’t even have Helvetica on my computer! This is in Arial!

Detail of the text on the front sail.

This CAD assembly is definitely not ready for production – there are a number of things I need to add, swap, or improve before I get to cutting and sewing. I wanted to add visible stitches onto the sails, and perhaps I won’t add that into the CAD itself for simplicity, but I believe that big, black stitches running down the midline of one of the sail’s surfaces would do good in breaking up the large, white faces.

Further, I’m not sold on the rib design. While it looks fantastic, to me, I feel it would be generating a good amount of turbulence in flight with its sharp edges. How much, I don’t know; if this even matters for a non-performance kite, I also do not know.

The black lines on the sails, full and dotted, aren’t real; they are an artifact of Solidworks’ design space rendering. I’m sure that they would disappear if I did a proper photo of this design. I’m not sure if I will make a nice render for this design, though – I’m sure the real thing would be more impressive.

The mechanisms of spacing the long spars out from eachother, and capping their ends to stop the sails from falling off, haven’t been designed yet. As you may be able to see, the cross spars actually intersect with eachother (again, work in progress!). The joints themselves could also use a more aesthetically coherent design. Right now, they are blocky and angular, unlike the flat and gently curved everything else.

Mounting of lines or anything else hasn’t been considered yet.

The manufacturing schedule is still very approximate as a final design hasn’t been made. However, I have a pretty good idea of how each of these parts are going to be made, so I will estimate them here. The spars will be fiberglass or maybe carbon fiber, and in a stock size so that the only procedure I will have to do is cut them to length. Given 12 members in my current design, I figure that making them all should take an hour if I know what I’m doing. I don’t, though, so I’ll give it two. The ribs can be lasercut of some flat material, maybe polycarbonate or wood. There are many, I believe 88, so it’ll take a good while for the machine to cut them out. I’ll have to learn to operate and program the thing first, which I think will take two hours. The cross-spar supports would likely be 3D printed given their complex geometry. The printing itself would likely take a few hours, but that can be done autonomously; I would likely take an hour to set up the printer(s). Further prep like sanding could take another hour. Cutting and sewing the sail is simple, but I imagine that I’ll have trouble sewing since it’s been a while since I’ve sewn, so I’ll give that two hours as well. Assembly will be relatively quick, give that another hour. In total, this gives (very roughly) 8 hours of my time to make this kite. I bet I could fit that in two weeks, maybe one.

What I should be more concerned about is the shipping time; some of these materials will have to be sourced from a distance, and nothing has been ordered yet, so that may cost me 2-4 weeks, by a rough guess.

Overall, I’m happy with the design’s current status, but a good bit more work needs to be done.

Works Cited:

[1] Bayliss, Charles. Hargrave and Swain demonstrate how the man-lift was achieved. 1894. https://commons.wikimedia.org/wiki/File:Hargrave-demo.jpg.

 

[2] Golubinsky, Yury. “New Moscow Metro Station – Savyolovskaya BKL.” 02 Jan. 2019. https://urixblog.com/en/2019/01/02/savyolovskaya-bkl-metro-moscow/.