Fresh Kite-Making And Kite-Flying News
Whether variety is really the spice of kiting might be debatable - but in any case, I certainly pulled out a variety of kites this month! Here's a quick summary...
- 2-Dowel Genki (2.4m 8ft span. Quite a number of outings, climbing up the learning curve, repairing and modifying.)
- Dowel Box (Fresh Wind Version, 1.2m 4ft in length. Performed nicely in gusty fresh winds)
- Skewer Tetrahedral (No amount of tail would make it fly well in fresh winds! It could be a different story with more accurate construction though.)
- 1-Skewer Box (Tiny 30cm 1ft long box. Persisted until I got a really good flight to write up, video and all - filling a gap in the website.)
Well, maybe the variety was mainly in size, since 3 of the 4 kites were cellulars.
'Making Skewer Kites' is now available. See the ad immediately below the Dowel Kites book on most pages of the MBK site, as you might have noticed by now. It's actually quite a bit bigger than the Dowel book, since both the 1 and 2 Skewer Series kites are included. Same price though - $19
'Kite Bridles and Flying Lines' is something of a hot topic with new kite fliers, judging by the questions that have been left on the site. There's a fair amount of material on the MBK site on these topics already, besides those questions and answers. Hence it has all been collated and organized into this handy single printable book. As usual, there is a detailed and clickable Table of Contents.
It might be a while before the Genki book is ready - a couple of long high flights are required first. The book will aim to give builders a good experience with the kite, by presenting a well-tested design and avoiding a number of pitfalls.
"Every new kite is an adventure!"
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Table of Contents
- Visitor Contribution Of The Month
- Flight Report Of The Month
- MBK Kite Making News
- The KAP Kite Project
Visitor Contribution Of The Month
It was a toss-up between a successful new kite and an interesting line winder idea. We'll go with the latter, since it could have applications for so many kite fliers! Check out this new style of line winder. The detail is probably not quite sufficient to reproduce it for yourself just yet, but the concepts are there. In any case, it sounds like the prototype needs a bit of refinement.
Flight Report Of The Month
Here's the short-format report on an enjoyable outing with the Dowel Box kite, fresh wind version. This kite was a response to having the original Dowel Box getting damaged in fresh winds. In the fresh wind version, the cross-pieces are in the conventional locations which keeps the kite more rigid. Also, the sail area is reduced, although the kite's length remains the same. The reduced cell size also means the cross-pieces are shorter, more rigid and less prone to fail. Finally, just to make sure the cross-pieces don't flex, they are tied to each other at the crossing-points with shoe-lace! It's going to be some time before I manage to break this one in strong wind I think :-)
By the way, note the appearance of a new toy which will be getting a mention from time to time in future flight reports!
Here's the report:
(titled "Flight Report - Fresh Wind Box Kite Makes Some Noise")
"Although the winds outside were gusting to very fresh speeds, it was still a good time to take out the Dowel Box Kite (Fresh wind version). Nothing else except perhaps the 1 and 2 Skewer box kites would cope today.
Down at the reserve, as expected, the winds were not quite as wild but good fresh gusts were certainly powering through from time to time. The Box kite only took a few moments to rig, and soon it was flying in moderate winds while the wind meter whirred away silently on a nearby grassy rise.
Thanks to the wind direction, blowing almost directly across the reserve, I wasn't game to let out much more than 30 meters (100 feet) of line. On this length, the kite would occasionally sink all the way to the grass, despite the fresh gust strength at other times.
The Dowel Box kite went through its entire box of tricks... floating high in rising air, fluttering furiously in the strongest gusts, hunting left and right when hit with gusts down low, and sometimes just sitting contentedly and smoothly at a 45 degree angle when the wind was ideal.
At one point I hooked on my newest toy ;-) , a set of spring scales, to test the pull on the line. Surprisingly, most of the time it hardly moved the pointer. During a strong gust, it popped up to maybe 3 kg (7 pounds) or so, on the 50 kg scale. However, I bought the scales to measure the line tension when flying the biggest MBK kites. For example, the 2-Dowel Sled and Genki!
After packing up, I checked the wind meter. Average wind speed was 5.9 kph, with a maximum recorded gust of 18.2 kph - but this was quite close to the ground."
Here's the sale page for the "Making Dowel Kites" book, which contains instructions for this hardy kite. I'm sorry, just haven't got around to putting out a book for just this kite on its own. OK, it's been penciled in for December...
MBK Kite-Making News
That image is still up there because I haven't had many opportunities to photograph the Genki in flight. It's had a lot of short flights, but nothing much where I could whip out the camera before the kite needed some urgent attention!
The 2-Dowel Genki is a good-looking kite that is somewhat over-engineered (ok 'heavy' ;-) in its current version. It seems stable enough to fly high and long, just as soon as I get to take it out in a reasonably smooth moderate breeze. Preferably in bright sunshine so the photos and video look as good as possible.
Now, how did I get this kite stable? Predictably and unfortunately, it turned out the kite was significantly nose-heavy. Why, oh why didn't I bother to do The Drop Test before the initial flights?
So simple - just drop a kite, practically any kite, face-down to the floor. If the nose drops and it glides forward, the kite is very likely to be unstable in flight. No amount of bridle adjustment or tail fiddling will do any good. The center of gravity must be behind the so-called center of pressure, for the tail end of the kite to behave like a pendulum. Pointing at the ground most of the time.
A Thought Experiment
I was determined to fully explain to myself why this standard design template taken from a (presumably) proven example on the Web ended up nose-heavy and unstable.
- Imagine that the spars weigh nothing at all, so all the weight is just sail plastic and edging tape. This places the center of gravity at just a little more than 50% along the center-line of the sail, measured from the leading edge end. This because the leading edge is 'raked back' somewhat more than the trailing edge is 'raked forward'.
- Now, imagine that all the spars except the horizontal spar weigh a typical amount. This should make very little difference to the center of gravity because the vertical spars run all the way from front to back and hence balance in the middle. The battens don't go all the way to the leading edge, so this will shift the balance point further back, but not by much.
- Finally, imagine what happens when we add the horizontal spar. Even if it doesn't have the extra weight of a dowel drum and short reinforcers that the real one has... The center of gravity moves forward. Quite a bit, because it is situated well forward of the 50% point on the center-line.
See the picture - as you increase spar weight from 'nothing' to 'heavy', the center of gravity shifts from a fraction behind 50% to perhaps only 30-35% or so. At the same time, directional stability goes from 'perfectly stable' to 'marginally stable' to 'quite unstable'.
So, to fix this kite, I simply added a couple of dowels side-by-side across the trailing edge, as a tail-weight. It worked. But, another way to shift the center of gravity back would be to remake the entire kite in lighter dowel! Another alternative again - make a much bigger kite using the same dowel width. And that's where I am going with the 3-Dowel Genki, sometime next year.
When you think about it, all this would also apply to the humble Diamond kite. It makes me recall the little 1-Skewer Barndoor kite, which stubbornly refused to fly stable until I bent a lot of dihedral into its horizontal spar and added plenty of tail. At this sail size, the width of bamboo BBQ skewers can make quite a difference. Some batches are thicker than others. With 3 skewers instead of 2 (as for a Diamond), and perhaps thick ones at that, this corresponds to the 'heavy spars' scenario described in the Genki thought experiment.
The old kiting adage 'The lighter the better' is certainly true! Rotational inertia is a real effect that does affect kites, but center of gravity is even more important to stability it seems.
The KAP Kite Project
This has stalled for the time being, but I have decided to keep this section in place. That's because something along these lines is going to happen sooner or later. Possibly involving that camera over there.
To visit The KAP Kite Project page to see exactly where things are at, you will need the password 'mbkkapkites'. Without the quotes of course. If you use the FireFox browser, it's an easy matter to just let it remember the password for the page.
I have added 2 photos and 2 videos of the 2-Dowel Sled. Take a look! (Added in May 2011, and no updates since)
November 2011 update:
It's looking like the 2-Dowel Kites might step in to become the vehicles for these ideas! As soon as I can justify spending $100 on the RC Plane Camera up there, it will go straight onto the center spar of the 2-Dowel Sled, or possibly the Genki - on a good day!
A set of spring-scales has been obtained to measure line tension, up to 50kg. These have already been used with the Fresh Wind Dowel Box kite. The stage is set for some interesting new pages which will document the flights of the biggest MBK kites. Imagery from the kite, wind speed data at height and max line tension for every outing. Well that's the dream!
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Issued on Tuesday, Nov 29th 2011 Issue #0052
My Best Kite
12 Muscatel Cct, Old Reynella, S.A. 5161, Australia
New! Comments Plenty of fun kite info, photos and videos - there's definitely too much here for only one visit! Feel free to leave your impressions of this site or just this page, below...