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Public Lab Research note


  • 1

Weighted tail for high wind range kite stability

by Ecta64 |

It has taken me quite some time (and several attempts at collating everything into a research note) to perfect and learn all the eccentricities of this particular type of tail but I do feel confident in my recent experiments to post the videos below. While I focus on kite anemometers again, I do think this might be interesting to try on the mini-kite kit (https://store.publiclab.org/collections/mapping-kits/products/diy-mini-kite-kit). The patent of the weighted tail is here: __ TALA_kite_tail.pdf

There are several inconsistencies I found when trying out the real kite system based on this patent. Only one weight was used (at the bottom of the second tail section) and the streamers were only found on the bottom of both tail sections.

DSC03877_-_Copy.jpg

One more thing, in terms of tail length I found that anything shorter than 5-6 meters produced wild oscillations. Simply adding more line to make the tail 8-9 meters eliminated the oscillations. The weight required is something I'm still experimenting with. I have gotten favorable results with my 18 inch sled using only 2 6/32 nuts tied to the end of the tail. A formula is given in the patent.

tala_kite_-_Copy.jpg



kite diy-kite kite-anemometer


4 Comments

From the Patent (US421351): "The criterion for success is neither weight nor drag, taken separately, but their ratio: Weight/Drag. The value of this ratio determines the angle at which the tail streams at its point of attachment behind the kite. If θ is the angle of the kite tail below the horizontal, D is the drag of the tail, L is the lift of the tail, W is the weight of the tail, V is the wind speed, and K is a drag constant, θ=tan-1(W-L)/D. For a non-lifting tail, L=0, so that θ=tan-1W/D. Also, D=KV2 approx., so that

θ=tan-1W/KV2 (1) Knowing the value of down-trail angle, θ, necessary for right-side-up trim at the desired high speed, V, the value of the drag constant, K, is made as small as possible by using the thinnest filament, the fewest streamers, and the shortest length which will provide dynamic stability. The value of the least weight W which will accomplish the action is determined by solving equation (1). The trailing tail is made to weigh this much and no more."

I have no idea how to discover θ, I guess K could be discovered empirically, though I'm not sure, short of a wind tunnel, how to calculate its drag.


I guess you could reverse everything by basing it on the weight on the actual TALA tail weight you have (we know the angle of the tail off our photos and we could put in the wind velocity when the photo of the kite was taken and add in the weight of the TALA tail weight) though given the changes between the patent and the actual design there could be some discrepancies. I forgot to mention in the video about the ratio of weight and drag (using as little of both as possible).


I have the measurements of the two tails that came with the TALA. Since the TALA seemed to be dimensioned in inches, I measured the tail in inches.

the first tail is made with the same line that bridles the kite, and I think its original. it has no weight on it. Length: 171.5"

Tassels are tied at 9.5, 137, 147, 152, 155, 161, 164, and 171-- two tassels at the end

The second tail is made from black line and does not appear to be original. it has a weight at the end.

Length: 260.5"

2.3g (35 grain) lead split-shot sinker at 259.5"

tassels at: 78.5, 82, 84.5, 87.5, 98.5, 229, 235.5, 242, 244.5, 249, 252, 255.5, 260.5-- two tassels on the end.


This is perfect! Now between this note and my unboxing note, one can now build a exact copy of the TALA!


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