Ever heard of a Winged Tetrahedral Kite

by Craig Ensey
(The Willamette Valley, Oregon, USA)


Q:

Hi, I'm quite interested in learning about "tetras". I mean tetrahedral kites, not the tropical fish. Over in the Willamette Valley, where I live, we rarely see winds that top 10mph. I can always go to the coast if I want to fly in a STRONG offshore wind, but that's quite a ways away. So, my question: "Is it possible to combine a high aspect ratio Delta with a four celled Tetrahedron?"

At first it seemed like a no brainer, but then I took into account the different angles that these two kites fly at. I'm referring to "Angle of Attack" as they say in the airplane world. Deltas fly at a very high angle and Tetras fly at a lower angle according to the research I've done. Will the two different angles counteract, or meet in the middle, or will it be a problem? The "Delta Conyne" works good and is similar to my idea.

I'm hoping this will work, 'cause I like the look of a big tetra "nailed to the sky." I just don't have the wind to fly one.

I've done a little mock up of the frame I'm thinking of building for it. It's just a regular delta with a four celled tetra hooked on the bottom. Please excuse the mess of hot glue and skewers.

Thanks for your advice.

A:

I'll address a number of your points in turn...

"Is it possible to combine a high aspect ratio Delta with a four celled Tetrahedron?"

I'm pretty sure this would work, since as you have observed, a Triangular Box kite is often combined with a Delta wing to form a Delta Conyne - a great stable lifting kite. Here are two kite types with very different operating angles on their own!

"Angle of Attack"

You have this term a little confused with line angle :-) In aeronautical terms, the angle of attack of a wing is the angle it makes with the airflow approaching it. A kite sitting at a low line angle usually has a rather high angle of attack to the airflow. Kites which tend to 'ride on top' like Deltas and Genkis have rather low angles of attack to the airflow, while maintaining a very steep flying line angle. (My apologies if I mis-read you, and you don't actually have the 2 concepts confused. Anyway...)

"I just don't have the wind to fly one."

Weeeeeeell... That depends entirely on the 'wing loading' of the kite! In other words, the ratio of total weight to total (effective) sail area. A high wing loading requires plenty of wind to get the kite flying, but if you manage to get the weight right down - any design will fly in light winds.

Hence, rather than fiddle around with a Delta wing, I think the 'ultra lightweight' path might be simpler to follow for a first attempt. However, I would suggest doing a little further research to find a design that uses more than 4 cells. For the sake of stability! Although work-intensive, one straight-forward way is to simply connect four 4-cell tetras together to make one big 16 cell design.

Here are my tips for a very light-weight tetrahedral kite:


  1. Thin 12" bamboo skewers for spars. (The ones in the photo look very thick)

  2. Try to be accurate and sparing with the glue - the weight adds up.

  3. Find the thinnest possible plastic for sail panels.

  4. Attach each fold-over tab with just 3 or 4 squares of clear sticky tape, rather than running the tape the full length of each tab.


Do all that, and watch your tetrahedral kite float way up in the first thermal that comes through!

Looking forward to hearing how it all goes...

Comments for Ever heard of a Winged Tetrahedral Kite

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Dec 18, 2011
Tetra-delta
by: Tony Sangster

What an interesting subject and discussion!

Firstly I would think the tetrahedral structure needs airflow through it to help maintain stability so enclosing the top entirely with a delta wing might compromise that stability.

Delta wings on the side sound OK but that leaves a lot of the delta sparring as weight and not contributing to sail area. An extension of the outer tetrahedral spars with perhaps a fitting to flatten out the 'leading delta edges' from 60 degrees to a lesser dihedral may work to produce sparring for delta wing on the edges.

For the tetrahedral cells I wonder (an armchair exercise at present) if, as an alternative to sparring for larger individual cell sizes, a circle of bent fibreglass, joined with a small ferrule and placed with suitable tubing where the proposed halfway spars were proposed, would provide the strength to hold the three diverging spars apart. The bending of the fibreglass means the size (diameter) and therefore weight can be reduced. Eye protection is, of course, a major consideration!

Dec 16, 2011
Tetralite
by: Tim Parish

I have come across this method online, although I have never actually used it. Probably a good choice that also has the advantage of less chance of damage to the structure if / when it has a few knocks out on the flying field. There would be a chance of fixing it on the spot, if it did happen.

(Take a small repair kit with you when you fly - I'm never without my tape and scissors, except ..ahem.. when the tape runs out like it did the other day...)

12 cells sounds like a nice compromise between construction time and stability in the air :-) Give it a go, I reckon..

Regarding weight saving, you could try half-length spars for each one that does not hold any sail material. This complicates things a little since they have to be shifted half-way down the V formed by the other 2 spars it connects to. Weight saving is significant at 1/12 (8.3%) of total spar weight.

Erm... Maybe not quite 8.3%, since a little extra tubing might be required!

Alternatively, a rigid fitting can allow you to do away with the 6th spar of the tetrahedron altogether. But this takes you away from the Tetralite method.

Your choice! Have fun...

Dec 16, 2011
Re: winged tetrahedron
by: Craig E

You're right about angle of attack vs. line angle. I think I was trying to convey the line angle concept by using the wrong terminology. It doesn't surprise me 'cause I'm not the best communicator. Something didn't seem quite right, I just couldn't get my finger on it.

While I'm at it - What is your opinion of the "Tetralite" construction method? It seems pretty similar to your suggestion of bamboo skewers but they use tubing to connect the pieces. They are very thorough, however they don't make mention of the regular 16 cell tetra (Sierpinsky Tetra) in their plans They suggest at least 12 cells for stability.

Also, is it possible to use string in place of the inner frame pieces to save weight? I would have to use longer / thicker dowel for the outer frame so It might not make much of a difference.


Thanks, Craig

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