Upscaling a Delta kite

by Dave Combs
(New Lebanon, OH, USA)

Q:

Greetings, Tim! I have a love-love relationship with the wind: If there isn't much of it, I launch model rockets. If there is, then I fly my rip-stop delta kite that I've had for a number of years.

I'd like to do some kite photography/cinematography, because I'd like to see what a REAL bird's eye view is like. I'm used to upscaling rockets; you multiply the dimensions by a scaling factor to determine what parts you'll need and what dimensions to make them. So, I want to see if this can be transferred to kites.

I'm interested in building a delta kite with a 10' tip-to-tip wingspan, based on upscaling my delta kite. I'm considering Tyvek for material for its good strength to weight ratio. One of my concerns of course is how to attach a keel to the kite (i.e. what can be used to glue Tyvek to itself). Also, I need to decide on what to use for the spars; whether wood would be sufficient, or if I need to consider woven carbon tubing to get a good bending resistance vs. weight ratio. But for now, I first need to know if the dimensions of my delta kite can be simply upscaled or if there are other factors to consider.

Thanks again for the input; I plan on buying the Delta kite book download as it may help with this project.


A:

"I have a love-love relationship with the wind:"

Haha - ditto: except in my case I try to match the kite with the prevailing conditions. The Dowel Delta or Dowel Rokkaku for the zero-wind and thermals scenario right through to the Fresh Wind Box for 40kph sub-gales.

"I'd like to do some kite photography/cinematography"

I'm about to start doing this myself very soon, with a large dowel and plastic Rokkaku. Keep an eye out for the flight reports...

"I'm interested in building a delta kite with a 10' tip-to-tip wingspan, based on upscaling my delta kite."

As long as your current Delta is not less than about 4 feet in span, you should be able to scale up to 10 feet without changing anything. Your spar diameters (not circumference!) need to go up by the same factor as everything else. And Tyvek is a great sail material.

One area in which my Dowel Delta book would definitely be a help is the method for constructing and attaching the keel. Tyvek can be taped since it is paper-like and adheres well. The strain is actually taken by lines that are run along the surface of the keel on both sides. Hence the taping is not structural - it just keeps the base of the keel neatly against the center-line on the underside of the sail. For a big 10 footer, you'll probably want to use packing tape rather than sticky tape! This is what I do on the big (8 feet tall) 2-Dowel Sled.

So, one approach might be to scale up the MBK Dowel Delta using dowel / tyvek / packing tape to prove the concept. Then, substituting lighter and stiffer spars should make the kite even better for KAP (Kite Aerial Photography).

Feel free to share your big Delta experiences via this site. See the 'YOUR stories' link over there on the left. Plenty of people would admire your efforts, particularly in the first few days when it would be the latest thing on the site blog page as well.

Comments for Upscaling a Delta kite

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Nov 15, 2012
Keel-less Deltas Etc
by: Tim Parish

Yes Tony, good point about not really needing a keel. Must admit it cling to them mainly for the looks! I've observed they don't make a lot of difference at low line angles. They must give a little more directional stability at high line angles, but even so I've seen plenty of fine-flying keel-less Deltas at the Kite festival...

Re spar sizes - if diameter is doubled, that makes the area (hence strength) go up by the square, hence stays in snych with sail area, which also squares if all dimensions are doubled. A = Pi x (D/2)squared.

Re your most recent contact - will update the home page to make the reference to vitamin D more accurate. Thanks for that!

Nov 14, 2012
Delta Expansions
by: Tony Sangster

Dave - I would suggest NOT using a keel at all - that makes construction simpler. Attach a bridle at points where the usual keel would start and finish with reinforcement of the material and perhaps binding on the central spar to stop slippage. And better to use stronger line than you need say 200 lb breaking strain and the central spar needs to be strong enough and fibreglass is stronger than most wood (except maybe well- constructed bamboo).

What diameter spar is not something I can answer categorically but would suggest square of the factor you are increasing by (e.g. 4 foot to 10 foot = 2.5 increase so at least 4 times diameter spar).

In order to keep things more stable without a keel consider extending the trailing edge of the Delta. Up to say 10 to 20 cm - the flapping adds drag and stability. Alternatively there are commercial deltas without keels.

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