Building Box Kites

Two Unconventional Approaches

Perhaps you haven't thought about it much, but building box kites successfully does not necessarily mean using 2 sets of cross-sticks to tension the sail! That time-honored technique is very good design for a couple of reasons...

Unconventional approaches for building box kites.

It is relatively simple. Also, it minimizes the total weight of the kite, for any given combination of spar and sail material. Light kites are good kites, for any proven configuration.

Actually, I have managed to go one step further with my 1-Skewer Box design... There is only one pair of cross-sticks, with a strategically placed internal tensioning line keeping the kite rigid. There it is in the close-up in-flight photo...

But if you really want your box kite to be a little different, why not try one of the 2 methods outlined below. It so happens that both of these approaches will result in a slightly heavier kite for its size, than a traditional approach would generate.

However, what does that matter in ... 'box kite weather'? That is, a nice stiff breeze! You will still end up with a perfectly air-worthy kite for those windier days. Or maybe for when a good solid trade wind is coming off the ocean.

I would recommend a slightly larger gap between the upper and lower cells of the kite, than the distance from the leading edge to the trailing edge of each sail panel. This is for the sake of stability.

Try this Stake Line Winder from Amazon if you need some flying line. The 30 pound rated Dacron is good for a wide variety of small to medium sized kites. Anything with a span of 2 meters (7 feet) or more would be safer on heavier line.




Building Box Kites Unbraced

Unbraced with cross-sticks perhaps, but still rigid. A visitor to this site submitted this idea, with photos, and has proven the concept in stiff winds. Thanks Jack!

Note that, unlike my MBK designs, this idea works best with square section dowel rather than round.

The photo on the left down there shows the kite frame, around which the upper and lower cells are wrapped. This contrasts with the more conventional approach of attaching the spars to the sail material first, closing the cells then applying tension by inserting cross-sticks. Both approaches work well for those who prefer them!

Notice the 4 short sticks near each end of the frame, and how they are secured with small, accurately-cut wood blocks. The photo on the right gives a close-up view of such a block. Obviously, you need a wood-working aid such as a table-saw to do this quickly and accurately. But if you can organize that, it's a solid approach to building box kites.

The complete box kite frame, using corner blocks to give rigidity.
A close up of the corner blocks used in a cross-piece-less box kite.

A couple of further points...

As with building box kites the conventional way, the short pieces should be positioned to the center of the cells, along the main spars. (Yes, I know my Moderate Wind Dowel design has its cross-sticks near the trailing edges. In lighter winds, you can get away with that.)

Apparently a press-fit can work, if everything is cut accurately enough. I would prefer to glue all those joins though, since the kite will be flying in strong wind. The frame will be under considerable stress.





Building Box Kites With Slab Panels

You have to choose slabs with reasonable lightness and strength of course.

I explored this idea some years ago, using bamboo skewers for spars. Small slabs of packing foam can be glued together to form the upper and lower cells, before gluing the skewers into the inside corners. At this size, the kite was rather inefficient and heavy. But it flew!

Bamboo skewers are used for spars and foam slabs for sail panels in this small kite.

The nice thing about thick slabs of foam is that they lend themselves to shaping. I carved the edges of the slabs to create a crude airfoil section, like a plane's wing.

This gave it more lifting force and I'm sure it contributed to the successful flight in the gusty fresh wind down at the park. Actually, it was more like gale force near the end of the flying session!

There's the kite, over there in the photo...

The foam slabs were so solid that the skewer tips didn't need to go all the way to the nose and tail of the kite. Ordinary woodworking glue was used to secure the bamboo to the foam. The foam slabs were just butt-joined to each other and secured with the same wood glue. The dimensions arranged so the whole thing was square, and hence could fly on one edge like a traditional box design.

Foam slabs would lend themselves to building box kites with rectangular cells rather than square. You would then need to fly the kite 'flat' rather than on one edge. This would require a 4-point bridle instead of 2 or 1.

OK, I hear you say 'we don't often get gale force winds around here.' Not to worry - just build something bigger and look around for foam slabs that are relatively thin compared to their other dimensions. Use wood dowel for the spars.

For the best chance of success, I would go for dowel and slabs that appear a bit thin or weak for the job. If anything breaks in flight, just try again and move up to stronger materials where required. Otherwise, it's just too easy to build something that won't fly in anything but a gale or category 5 storm, due to sheer weight ;-)

In the case of foam slabs breaking, that would mean trimming down the dimensions a little to achieve greater stiffness. Leaving the thickness the same of course.

As for busted dowels, just buy the next size up that is available, and try again.

Worried about the 'airfoil shaping' idea for the foam slabs? It's not strictly necessary, but it would still be helpful to at least round off the leading and trailing edges of both cells. This will definitely cut down the drag forces a little and hence help the kite to be more efficient.




And how about building box kites with balsa wood panels?

In theory, balsa wood could be used in a similar way to the foam slabs idea. Do you have any aeromodelling skills? Have a go at making a little balsa box kite, it should work fine. Particularly if you carve a bit of an airfoil section into the sails! More than just decreasing drag, this would also increase the lifting force of the sails.

Try this using thick slabs of the lightest balsa, to get some rigidity. Perhaps try a harder grade of balsa for the main spars. This way, they can be thinner and hence have lower drag to increase the efficiency of the kite.

Balsa wood would be ideal for building box kites in tiny sizes. Ones that would use ordinary sewing thread for flying line, perhaps! Also, these days it's easy to get hold of polyester sewing thread in supermarkets. That's similar to Dacron, the single-line kite flier's favorite.





Some Simple Bridle Ideas

Regarding the towing point, this should be located on one spar, about midway along the upper cell. A simple 2-celled box kite of almost any size seems to only require this single attachment point in order to fly stable. Perhaps with the aid of a tail, in the case of very small box kites.

Some experimentation will be required to get your box kite trimmed for best performance. Hence you can choose to attach a bridle loop between the nose and another point at least half-way along the same spar. Then attach the flying line to this loop with a sliding knot. Start with the knot almost level with the leading edge of the upper cell, and shift it back in small steps until the kite gets best height.





Why not try some of these ideas for building box kites. Don't let those windy days go to waste!

Try this Stake Line Winder from Amazon if you need some flying line. As mentioned earlier, this product is a good compromise for many small to medium sized single-line kites.

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