Kites built in Summer, 2013

Here are 3 foam & carbon kites that I built in July, 2013.  They all have EPP foam-cored wings.  The two nearest ones have 3-foot wingspans, and the far yellow one has a 2-foot span.  The far one is covered with strapping & packing tape over the foam and carbon spars, while the 3-foot span ones have Japanese paper covering the foam and spars.  The front body pods are of similar construction to the wings, and the tail booms are carbon tubes.  The tails are coroplast sheet.  The wings rubber-band on to the bodies. They hold up much better to high-speed crashing than the balsa and paper planes do, and they go very fast.  The red one is the fastest because it has the smoothest finish on the wing, due to 2 layers of paper over the foam, a very thick wrinkly paper base that has been clear doped and sanded, and a second, thinner layer with the coloring you see.  The blue one only has one layer of medium-thick, somewhat wrinkly Japanese washi paper, so the finish is a little rough.  The yellow one is finished in mylar packing tape, so it's pretty ugly, but quite strong.

Crosswind Kite videos

Here's a video of my 4-foot wingspan, airplane-shaped kite in 5-10 knots of wind at a beach near Half Moon Bay, California in July, 2013:


4-foot wingspan airplane kite video

Four other videos date from summer 2012.  The kites are smaller 2 to 3-foot wingspan ones built from modified model airplane kits.  Here's the first video:

2012 crosswind kite video #1

Genesis of crosswind kite ideas

I worked on a project with my dad about 30 years ago to develop airplane-shaped kites as a means of power generation. 

Over a period of several years in the late 1970's to early 1980's, my dad and I built and tested a variety of kites. These included 2-foot wingspan kites that we flew by hand on 2 lines, as well as 6-foot wingspan kites that I flew on one line using radio control.  As a result of that flight-testing and much computer time on a very early home computer, in 1980 my dad wrote an article called “Crosswind Kite Power” that was published in the Journal of Energy:

http://homes.esat.kuleuven.be/~highwind/wp-content/uploads/2011/07/Loyd1980.pdf

The publication of this technical article got the attention of editors at Smithsonian magazine, who ran an article about new uses for kites.  My dad and I were interviewed and a photo of me flying a 30-inch wingspan two-line airplane-shaped kite was included in the article.  This was published in June, 1982. 

Funding for wind energy research was not available, so power generation using kites had to wait until a company called Makani Power read my dad's Journal of Energy article and has continued to pursue research in large-scale power generation using kites.  Here is Saul Griffith, then leader of Makani, in a 2009 TED talk:

http://www.ted.com/talks/saul_griffith_on_kites_as_the_future_of_renewable_energ...

Here's Makani now:

http://www.makanipower.com/

The genesis of the original Crosswind Kite Power article is described in a talk at Stanford in 2010 at the airborne wind energy conference:

http://awec2010.com/public/presentations/loyd_miles.pdf

2013 crosswind kites

Well, a year has passed, and my focus has shifted to making kites that can survive crashes.  I've built 4 wings out of EPP foam, one of 2-foot wingspan, two of 3-foot and one of 4-foot.  I've found that the 2 foot span works well in 15-25 knots of wind, the 3 footers in 10-20 knots and the 4-footer in 5-10 knots.

I've also been trying different construction techniques.  I started with spray glue, strapping tape and packaging tape over the EPP foam cores, since this is the established approach for RC combat or slope planes.  But the result is incredibly ugly, with wrinkles all over the wing because the tape doesn't stick well to the foam, despite the use of 3M #77 spray glue.  I then tried contact cement and some of the Japanese paper that I'd used on my wooden-framed planes.  The result varied beautiful, but somewhat heavy, to a little wrinkly and pretty light.  On the 4-foot, light-wind wing, I tried clear mylar plastic film attached with contact cement directly to the foam.