Friday, July 26, 2013
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
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
Friday, July 12, 2013
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:
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:
Here's Makani now:
The genesis of the original
Crosswind Kite Power article is described in a talk at Stanford in 2010 at the
airborne wind energy conference:
Thursday, July 4, 2013
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.
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.
Friday, July 20, 2012
What are crosswind kites?
Kites that fly fast across the sky, usually on two to four lines, are crosswind kites. Those that fly in one place on a single line are not. Parafoils, delta stunt kites and kiteboarding kites are all flown quickly across the sky. My interest, however, is not with these crosswind kites. I would like to show you how to fly faster, more efficient kites that are shaped like airplanes.
Here is a video of an airplane kite: Control-line crosswind kite #1
Below is a kite that I built from a Guillow's model airplane kit. It is modeled on the Me 109 World War 2 German fighter plane. The structure is mostly balsa, with some spruce and a foam-filled plastic nose. It has a 2 foot (62cm) wingspan and weighs about 5 ounces (140 grams). It flies on two 100-foot (30meter) long Spectra kite lines that I made from 20-pound-test Tuffline XP fishing line. I hold a handle that is about 9 inches (23cm) wide. I fly this size of plane one-handed because I am used to that style from control-line model airplanes, a type of flying in which the plane flew in circles around the pilot. But unlike those planes, this kite requires no engine, just wind!
Below is the same plane:
Below is one of the line attachment tabs. It has three more holes that are filled with paper or paint. I clip the lines to these with fishing line connectors.
The shot below shows the paper fibers. This paper is called Unryu. This type of paper was originally made in Japan, but these days the paper sold here is made in Thailand. I buy it from Miki's Paper in Berkeley, California. Because of the long mulberry fibers in it, it is very strong and light. After covering, I brush on 3 coats of clear nitrate dope, thinned about 30%. This seals the porous paper.
Below is my latest kite, a model of a Hawker Hurricane, a British fighter that fought against the Me 109 in the Battle of Britain. This is built from a Dumas kit in the same 1/16 scale. It has a 30 inch (77cm) wingspan and is similarly lightweight. This plane uses only paper for color decoration. The military markings were printed on thin printer paper from scans of the kit decals, so they don't look overly shiny and the don't come off easily.
The paper below has white and purple fibers. I painted the frame beneath in the shade of gray that was used on the original plane, so the purple is very subtle. If you look carefully, the line tabs have the fishing line connectors on them.
Below you can see that I paint the frame before covering it with paper. This allows the structure to show through the paper to varying degrees. The structure of this Dumas kit is more complex than that of the Guillow's kit above. I enjoy building them, and they fly very well, but they do not survive hard crashes. So far, I have only lost one plane out of six to a crash.
Below is a 26 inch (66cm) wingspan kite that I made from an Radio-controlled powered foamie combat kit. It is made from EPP foam, the same foam that is used in car bumpers, so it survives crashes pretty well. The foam is covered with strapping and packing tape. After each crash, the tape must be ripped off the damaged area and retaped. This plane didn't fly at all until the fifth day of trying. The airfoil was symmetrical, so I had to add flaps to get enough lift, the tail moment was too short, and the tail was too small. Once all of these problems were solved, it flew. My wife, who usually flies a 2-line parafoil kite, tried this one and crashed it several times. It was kind of boring to fly compared with the wood planes, and I got tired of retaping it. I kept thinking of all the plastic that was being wasted with this thing. We still have it, though, and it still flies. I think that great kites could be made from these materials, but I am not very interested in doing so.
Here is a video of an airplane kite: Control-line crosswind kite #1
Below is a kite that I built from a Guillow's model airplane kit. It is modeled on the Me 109 World War 2 German fighter plane. The structure is mostly balsa, with some spruce and a foam-filled plastic nose. It has a 2 foot (62cm) wingspan and weighs about 5 ounces (140 grams). It flies on two 100-foot (30meter) long Spectra kite lines that I made from 20-pound-test Tuffline XP fishing line. I hold a handle that is about 9 inches (23cm) wide. I fly this size of plane one-handed because I am used to that style from control-line model airplanes, a type of flying in which the plane flew in circles around the pilot. But unlike those planes, this kite requires no engine, just wind!
The shot below shows the paper fibers. This paper is called Unryu. This type of paper was originally made in Japan, but these days the paper sold here is made in Thailand. I buy it from Miki's Paper in Berkeley, California. Because of the long mulberry fibers in it, it is very strong and light. After covering, I brush on 3 coats of clear nitrate dope, thinned about 30%. This seals the porous paper.
Below is my latest kite, a model of a Hawker Hurricane, a British fighter that fought against the Me 109 in the Battle of Britain. This is built from a Dumas kit in the same 1/16 scale. It has a 30 inch (77cm) wingspan and is similarly lightweight. This plane uses only paper for color decoration. The military markings were printed on thin printer paper from scans of the kit decals, so they don't look overly shiny and the don't come off easily.
The paper below has white and purple fibers. I painted the frame beneath in the shade of gray that was used on the original plane, so the purple is very subtle. If you look carefully, the line tabs have the fishing line connectors on them.
Below you can see that I paint the frame before covering it with paper. This allows the structure to show through the paper to varying degrees. The structure of this Dumas kit is more complex than that of the Guillow's kit above. I enjoy building them, and they fly very well, but they do not survive hard crashes. So far, I have only lost one plane out of six to a crash.
Below is a 26 inch (66cm) wingspan kite that I made from an Radio-controlled powered foamie combat kit. It is made from EPP foam, the same foam that is used in car bumpers, so it survives crashes pretty well. The foam is covered with strapping and packing tape. After each crash, the tape must be ripped off the damaged area and retaped. This plane didn't fly at all until the fifth day of trying. The airfoil was symmetrical, so I had to add flaps to get enough lift, the tail moment was too short, and the tail was too small. Once all of these problems were solved, it flew. My wife, who usually flies a 2-line parafoil kite, tried this one and crashed it several times. It was kind of boring to fly compared with the wood planes, and I got tired of retaping it. I kept thinking of all the plastic that was being wasted with this thing. We still have it, though, and it still flies. I think that great kites could be made from these materials, but I am not very interested in doing so.
Subscribe to:
Posts (Atom)