Sled Kite Stability - Vents and Leading Edge


(Terry)

Q:

I've built several sled kites over the years, but have never tried the V shaped leading edge or vents. Are they useful enough to warrant their inclusion? I see you have them in some but not all of your sleds.

I'm in the process of collecting materials for a 4' sled and will be using some rectangular model airplane spars from a hobby shop and a Tyvek like material that I got free from a lumber yard. They use it to cover lumber while transporting it on trucks.

TIA for any info.

A:

Good to see another Sled kite enthusiast in action! I'm surprised more people don't make their own since they are so quick to make and convenient to fly. I guess the main downside is that many designs are prone to collapse in rough air.

The V-shaped leading edge is supposed to reduce the tendency for the middle section to begin curling under at negative angles of attack. For example, when a patch of turbulence comes along when the kite is at a high line angle. This seems to be a good idea, and my Simple Sled with this feature is particularly resistant to collapse. Despite this kite being just a bog-standard 2-stick design with no other fancy features.

A 3-spar design like the 8-foot Multi-Dowel Sled has no need for a V-cutout since that 3rd spar is propping up the leading edge. I have noticed tiny curl-unders happening on either side though, from time to time. But these are so minor that they have not caused any problems at all so far.

I'm not so sure about vents! In theory they provide extra drag near the trailing edge which can only be good for stability. However, a well-proportioned Sled is already extremely directionally stable in flight. I've kept the cut-outs on the Dowel Sled mainly because some feedback indicated that kids loved the look of it!

That lumber yard material sounds promising. I've had a heck of a time trying to get hold of Tyvek at the right size/quantity/price here in Oz.

One thing I would recommend with Sleds is to experiment with making the trailing edge shorter than the leading edge. This really helps to hold the sail open in difficult conditions. Not only that, but the kite will pop open much more willingly after a collapse. If you are into KAP it could save your camera!

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Aug 03, 2013
Thanx For The Info.
by: Terry

Thanks for the info Tim, I appreciate it.

I'm of the same opinion on vents. I haven't seen much improvement with them. Some references indicate that they are important, but they haven't proven to be so in my experience.

I'll try the leading edge V and the shorter trailing edge on my new 4 footer.

Yesterday I created a simple spreadsheet for designing Sleds of various sizes, and thought I'd share it with you and your readers. All that's needed is to input the length of dowels you wish to use, and the spreadsheet does the rest. It's here http://www.wa0itp.com/sledprop.xls

Thank you again and happy flying.

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