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...