Interesting effect

[Mikefule]

Flying a small diamond kite with a single point bridle today.  No bow and probably not quite enough tail.  I was also flying it on a line that was rather too heavy for the kite, and there was only barely enough wind.

The kite rocked from side to side.  This set up a standing wave in the line, which was hanging rather heavily in a catenary curve.   A standing wave is where the peaks and troughs have fixed positions.  This means that the line has several fixed points along it, with the line between these fixed points oscillating from left to right and back again.  I doubt I could have set up the perfect conditions for this deliberately!

[makatakam]

I had that happen once, a very long time ago. I remember trying to duplicate it on several occasions, and nearly had it a couple of times. A few variables have to mesh to make it possible. Fascinating how the rocking motion and the oscillations in the line seem to strengthen each other. One thing I remember is that the tail has to be just a little bit less than what the kite can possibly lift, and the rocking motion of the kite can be amplified by making the distal end of the tail heavier than the rest of it, for instance, using a rock or other object to add weight to the existing tail. I spent a whole summer trying, but never got it to work as well as the time it happened initially.

The weight of the tail, wind speed, length of the tail, weight of the line, length of the line, area of the sail, how high or low the attachment point on the bridle, and even the bow in the frame that the wind creates all have to be in exact proportion to each other. Absolutely mesmerizing when it happens.

[Mikefule]

Full marks for"distal".    You in the medical profession, or aeronautics?

I don't have any commercially produced flat kites but I have been making some simple small kites recently.  This one is a diamond with the spine and spar of equal length, crossing 25% of the way down the spine.  There is a single point bridle at the intersection.  The sail is brown paper so it is completely windproof. 

With a heavy tail and strong wind, the kite "nods vigorously" oscillating about the axis of the horizontal spar.

In a light wind, as today, it "shakes its head vigorously", oscillating about the axis of its spine.

Weird.

 

 

 

[makatakam]

The spars in that configuration = Eddy. The Eddy kite is less stable when stretced flat than the typically available commercially made diamonds, and should make it easier to replicate the action. If you bring the bridle point down a 1/4" it should increase the tendency to rock. Even 1/8" should make a difference. The bridle point is the actual intersection point of the spars as I understand it. Am I correct in this assumption? There is not a bridle made of bridle line attached to the frame?

distal = army medic

[Mikefule]

According to the patent, an Eddy has equal length spine and spar, and these cross 19% of the way down the spine.  It has a 2 leg bridle and a bow for stability, and flies with no tail.  Part of the Eddy's stability comes from having a very loose fitting sail so that, in addition to the bow, it curves back either side of the spine to give the effect of a keel.

The "standing wave" kite in question is not an Eddy.  It is a diamond.  I read that if you use equal length spine and spar and cross 25% of the way down the spine, you can bridle directly to the intersection with a single point, and this is what I did.  Rather than a bow, you use a tail.  This particular kite follows this pattern.  It is very sensitive to what tail is attached.  Because it is a paper kite, it is very stiff and flat in configuration.  If I had used plastic sheeting or cloth it may have been more flexible and therefore more stable.

Over the last few weeks, I have made an Eddy and a diamond using the same length of spars - each kite using two 18" garden canes.  The Eddy has a plastic sail and has spar pockets so it can be dismantled.  The diamond is a permanent structure with the spars taped into place.  The Eddy flies like it's pinned to the sky.  The diamond dances.  Unfortunately, it does not always dance prettily.  Sometimes it dances like a drunken uncle at a wedding.

My personal preference is for kites without tails, and I also prefer "demountable"kites as I carry a bag with about 15 kites in it.  I took early retirement a month or so ago and I have taken the opportunity to get out my old kites and give them a good airing, and I have also started to experiment with making a few.

[makatakam]

My bad. I thought an Eddy was about 25% down. I never checked the specs or built one. All the "diamond" kites I made as a kid and afterwards involved unequal spar lengths, and tended towards tall and thin. All were made with bowed cross-spars and were fairly steady in flight with no tail. They were all equipped with line bridles and the location of the bridle anchor points made a dramatic difference in flight characteristics. 

I, and my father, built mostly box kites using laminated basswood spars that we would make in the basement "shop". We built many large ones, up to about 15 feet tall that could lift a small person. The small box kites that I made as a kid were the only ones with a direct-to-frame attachment point for the line. The large ones were all bridled for load distribution.

[Mikefule]

Amazing stories to share.  Thank you.  I like box kites.  I have a square box, winged square box, a winged hex box, a Cody and a Conyne in my bag - all commercially made.  My biggest kite is an 11 foot span delta and that pulls like a train when the wind is up.  I can't imagine handling a 15 foot box kite!

Book illustrations and childhood memory say that diamond kites are normally tall and thin, I agree.  The British "standard" is probably the Bookite keel diamond.

I prefer a bridle I can tinker with (that is, make fine technical adjustments to...) but having read the 25% rule for a single point bridle, I wanted to try it.

 

[Mitch]

Re developing a standing wave with the fly line, I've seen a standing wave with one of my kites and the line leading to the drogue behind it. In fact, I've read that the tow line for a drogue should me a non-integer multiple of the length of the kite (e.g. not 2x or 3x the length) to avoid this phenomenon.  There's a great old black and white newsreel of a bridge falling down because of a standing wave amplifying the force of the wind. You know you're a master flyer when you can look at the kite and line and say, "I think that's a G sharp set up".

 

[makatakam]

15' box kite flying line = 150' of braided steel cable.

[Kansas Flier]

Kites that use the Magnus Effect, like Prism's Flip Kite, cause the line to oscillate. This might be cheating to get the effect, no?  

[makatakam]

1 hour ago, Kansas Flier said:

Kites that use the Magnus Effect, like Prism's Flip Kite, cause the line to oscillate. This might be cheating to get the effect, no?  

Whatever way you can achieve is great. The effect is fascinating to watch. If you're not familiar with it Google "standing wave". Watch the part 1 demo by James Dann. Now imagine the kite attached at 1/4 or 3/4 of a wavelength and rocking at the same tempo as the wave. Easier to imagine when you see the slo-mo. I've seen rope move like this in a wind in a circular motion like a jump rope also. Would be interesting to design a kite that can replicate it at any time.