Saturday, June 1, 2013

Kite sewing videos

Here are three short narrated videos on kite sewing techniques. It is much easier to pick up the details by watching someone do it rather than reading about it. You can watch these larger on YouTube or Full screen by clicking on the icons bottom right of each video.

Just for demo purposes I'm working on the top triangles of a 1.7m rokkaku but the techniques can be used on all kites.

Here is a page listing all my KAP related videos.

Panel layout, cutting and sewing a flat fell seam

Reinforcing patches for corners, spine, bridle points and spar crossing points.

Spar pockets and loops

Friday, May 24, 2013

1.7m yellow rokkaku - 20 sq ft

This scaled-down rokkaku is designed for KAP, fitting in between the 9ft Levitation Delta and the 28 sq ft 2.0m white rokkaku.

Like the 2.0m kite the size ratio is 5:4:3. This means 5 units high, 4 units wide and 3 units between the cross spars. The top and bottom triangles are 1 unit high and the bridle points are 1 unit out from the spine. For this kite 1 unit equals 34cm making it 170cm high, 136cm wide and 102cm between the spars.

Woven cloth has least stretch along the WARP fibres (down the length of the roll). The WEFT fibres (across the roll) may not be as straight or as strong, and the BIAS (at an angle to the fibres) gives the most stretch. Cut out your panels so that the WARP fibres are parallel to the outer edges of the kite. This is the reason 5 or 6 panels are used for the rokkaku.

Ripstop nylon from Emma Kites is 155cm wide which is wide enough to cut out the rectangular panel (forming main body) in a single piece with the warp threads aligned correctly. The top and bottom of the kite still need to be made from 4 right angled triangles.

I bought a 5m pre cut length for US$21 (free postage) and used less than half.  I did notice that the WEFT fibres run in quite a pronounced curve across the roll, maybe that is why it was so cheap. However the kite still flies perfectly.

Spars are 82.6cm Skyshark Camo P4X tubes from Kites and fun things. US$3.50 each with US$42 postage. To spread the freight cost I bought 20 of them with carbon fibre rod ferrules (3.75" x 0.24") and vinyl end caps (0.281"). That will be enough for another 3 kites or lots of breakages.

I did the seams a little differently this time for a neater finish. Virginia tells me the correct term is flat fell seam. Two panels are sewn together front to front along the marked sewing line (20mm in from the edge) then the panels are opened out and the 20mm seam folded over to the left or right. About 12mm of the underneath seam is trimmed off, then the top seam edge is folded over and under the trimmed edge then sewn down close to the folded edge. This gives a neat finish with no raw edges.
For the first time ever I also used the correct thread colour top and bottom for the entire kite.

I'll do some instructional videos on the sewing details soon. Stay tuned.

The patches, webbing pockets and velcro loops are all the same as the 2m white rokkaku as are the folded hem edge and bridle.

Here is an A4 size plan for the 1.7m kite. Feel free to download it for your own use.

Timelaspe of cutting out and sewing the 1.7m rokkaku. 4hrs in 80seconds

Here's the first flight in Bft 2

Here's a test flight in Bft 4+

Tuesday, April 30, 2013

WWKW 2013

World Wide Kite Aerial Photography Week is on at the moment. 26th April to 5th May.

The idea is for KAPers from all around the globe to shoot as much as possible this week and share the results on the WWKW Flickr Group.

We are encouraged to share all sorts of photos related to the KAP sessions, even non flying ones when the wind doesn't play ball.

Many KAPers make this an opportunity to push the limits, try something different.

I decided to try shooting just water, trying to capture the colours, textures and moods created by wind.

Friday, March 29, 2013

Rapid Bay South Australia

Rapid Bay jetty on the Fleurieu Peninsula South Australia is the best dive spot to find Leafy Seadragons. These bizarre fish are related to seahorses and are only found in South Australia, nowhere else in the world.

We planned a 4 day trip to dive flat out and photograph seadragons but the weather had other ideas. The trip became a KAP trip due to strong winds ruining the diving.
A new jetty has been built to allow access to the crumbling old jetty where the seadragons live. Depth up to 10m but 6m mostly.

Second Valley jetty 10min up the road from Rapid Bay. We stayed in a holiday rental house here with a very short steep driveway. Had to be pulled out by 4WD after getting bogged in deep dust. Very embarrassing but the neighbour said it happens regularly.

Cape Jervis where the Kangaroo Island ferry docks.

Leafy Seadragon - we did get in for one dive and found 3 leafies making the trip worthwhile.

4 min video of our one dive

Tuesday, February 26, 2013

Rokkaku pushed to the limit

Continuing on with rokkaku testing, here's a video in Bft 5 or up to 20kn. That's beyond the recommended wind range for this kite but I just had to see how it would behave.

Line pull was averaging 20lb and peaked at 25lb, which is unpleasant.

The Skyshark P4x spars flexed alarmingly but survived.

Sunday, February 24, 2013

Rokkaku bridle and bow adjustments

Here are two videos showing the tuning adjustments used on a rokkaku kite.

If either of these adjustments are a long way off the kite will either pull like a donkey and not fly high, or swing around wildly from side to side, or fly forward then drop back repeatedly.

But within a small range of adjustment you can choose how high it flies or how hard it pulls.

Angle of attack or bridle height adjustment.

Spar bow adjustment

Friday, February 22, 2013

Making a 2m Rokkaku - bow tension and flight

Part 4 of 4

Spar bow lines
A rokkaku is a flat kite which means it has no inherent stability. Some bend in the spars is required. Adjustable tensioning lines bend the spars like an archer's bow.

In the sewing instructions I mentioned how to create an end loop in the pockets for the bow lines. This photo shows how the end loop works.

The lines are about 2.2m long, tied at one pocket, looped through the other pocket then back to a sliding clip.

I made the sliding clip from UPVC plastic which can be heated and bent into shape. A 30mm x 15mm piece is drilled with two holes, rounded off and heat bent with a slight curve.

The clip slides along the line and holds the bow under tension.

The amount of bow can be adjusted to change the flight characteristics of the kite.
More bow gives less pull, more stability and a lower line angle, better for stronger winds.
Less bow gives more pull and a higher line angle but will reduce stability. If the kite is wiggling side to side you need more bow.

Some folks say you must have more bow in the bottom spar than the top, others say they can be the same. Mine seems to fly well either way.

I tend to set up with 6 to 8" of bow in the bottom and a little less in the top.

Angle of attack
The final small loop in the bridle is used to adjust the flight angle. The prussic (prusik) hitch, or double larkshead hitch holds it in place under tension but can be loosened and moved under no tension.

With the loop at the centre point of the bridle the kite will pull like crazy and sit on the ground. Moving the loop up a long way, say 12", will make the kite go up a bit but tip over towards you.

This ideal bridle position is somewhere between these two extremes. Try placing the loop about 8" above centre and see how it flies.

If the kite flies but with not much pull and is luffing or tipping over at the top move it a bit lower.

If the kite is pulling hard and not rising far move the loop a little higher.

When it is in the correct spot the kite will climb up high and sit there with moderate pull on the line. You can now dictate exactly how much line pull you have by moving the loop up or down in small amounts. If you need more pull for lifting an SLR move it down a bit, and if you want less pull for easier flying move it up a bit.

The rest is up to you, go fly the kite and have fun.
I'll make a video showing different bridle positions and the resulting flight characteristics soon, maybe different spar bowing too.

Thursday, February 21, 2013

Making a 2m Rokkaku - Spars and bridle

Part 3 of 4

Carbon tube spars
Wrapped carbon tubes seem to be the spar of choice for many Rokkaku flyers, they are certainly the lightest and quite stiff but a little expensive locally.

Kites and fun things have a great range of SkyShark tubes way cheaper than I can find in Australia. The P4X camo are US$3.50 each, an absolute bargain even with $42 shipping. I ordered 12 spars plus internal solid carbon ferrules and vinyl caps to fit.

The P4X spars are 0.297"OD, 0.244"ID, 32.5" length, or in modern units 7.5mm OD, 6.2mm ID, 82.6cm length. It's pretty much impossible to find full length spars so joining is essential. Most of the wrapped carbon tubes are made as arrow shafts, hence the standard 32.5" length.

It's best to avoid joins where spar and spine cross and at bridle attachment points so some nutting out is required to determine what lengths to cut.

The cross spars are roughly 160cm requiring a 3 piece design. 2 x 3/4 lengths with a 1/2 length in the middle. That left 4 x 1/4 cutoffs.

The spine is 200cm requiring a 4 piece design. To reuse some of the cutoffs  I used 2 x (1+1/4) lengths. The 1+1/4 being permanently glued with an internal ferrule so it's actually a 2 piece spine.

Ferrules are glued in using epoxy.

The next job is to carefully fit them to the kite, trimming the ends evenly until they are the right length. Take it slowly, you don't want to cut them too short. Then you can pop the vinyl caps on to cover the ragged ends.

The final task is to make up the bridle. It consists of top and bottom Vs (black in the photo) joined by another V (red) with a short loop at it's apex (green).

For the top and bottom Vs take 3.6m of 200lb dacron line (making a 1.8m V), pass the ends through the kite bridle points and tie to the spars using a larks head hitch. Carefully find the centre of the V and tie a small loop. The line for the third V is about 2m long (making a 1m V) and is tied between the top and bottom bridle loops using a bowline knot.

The final short loop is made from about 30cm of line and attached by a prussic hitch to allow angle of flight adjustments. This hitch grips under tension but can be moved under no tension.

Initial placement should be about 8" higher than the middle. You might need to slide it higher or lower to tune the flight angle.

Here is my first flight of this wonderful kite.

and another compared to the Skydogs Pirate Rok

Next post will cover spar bow lines and kite angle of attack.

Making a 2m Rokkaku - Sewing

Part 2 of 4
Ripstop is very light and slippery which makes accurate sewing a little tricky. I pinned the panels together to sew the seams. Other kite makers use tape, glue or melting tools but pins worked for me.

Common sewing stitches used are straight and zigzag. Straight stitch has less stretch and is good for seams.  Adjust the stitch length to about 8 stitches per inch. It's essential to practice first on scrap cloth to ensure the tension is correct. Consult your manual or ask an expert to adjust the tension. I used zigzag on the corner patches because that seems to be what the experts do.

Panel seams
Pin the panels together face to face and sew along the 15mm seam line pulling the pins out before you run over them. Open out the panels, fold the seam over, and sew it down flat. The raw edges will be exposed but coated ripstop won't fray. For a really professional finish you can fold the top edge under before sewing down. Might try that next time.

Corner reinforcing patches
Corner reinforcing patches are cut like pieces of pie from a 150mm diameter circle of stiffer cloth. Once the panels are sewn together position the circle over the top corner, mark the angle and cut out the wedge. For the side corners you only need to fold the remaining part of the circle in half and cut along the fold.

Once all the panels are sewn together you can sew on the corner patches but first fold and make a crease all the way around the kite along the hem line. Now position the corner patches a few mm in from the hem line with pins and just sew around the curved edge.

Now for my favourite bit, the double folded hem. I like this bit because it's easier than seams and it finishes off the kite, apart from a few more patches. Fold the fabric edge over to the crease then fold again to form a 10mm hem. Sew down using straight stitch all the way around the kite. You can fold as you go.

Side and top spar pockets are made from 100mm lengths of 25mm wide webbing with 35mm folded over folded over to form the pocket. When sewing down the side pockets you can form an end loop for the bridle lines by sewing across 10mm back from the fold.

The bottom spine pocket needs to be adjustable to tension the spine. Velcro and webbing are used to form a pocket and adjustable flap.

Bridle holes and spar crossing points and ties
Four 40mm square patches are sewn on 400mm out from the centre of the kite and in line with the upper and lower spars, and another in the centre of the spine. Beware, the centre of the kite is on the folded edge rather than the middle of the centre seam. 

To make holes for the bridle to pass through I melted holes in the patch using a heated piece of coat hanger wire. Other kite makers fit brass grommets as well.

At the spine and spar crossing points I used a 80mm x 40mm patch. Onto the patch goes an 80mm piece of webbing which has velcro pieces sewn on to hold the cross spar. A 15mm stitching gap is left in the middle of the webbing for the spine to slide through. That way the spine always sits between the spar and the cloth.

Velcro is sewn on to the centre spine patch to hold the spine.

Here is a video of the process which will help make sense of these instructions.

Next post will cover spars and bridle

Tuesday, February 19, 2013

Making a 2m Rokkaku - Preparation

Part 1 of 4 
I have made kites all my life, but nothing as big or serious as this one, and have a fair bit of sewing experience. Between high school and uni I spent some time as a sailmaker's assistant and made my own sailboard sails. Wife Virginia encouraged me to use her precious Pfaff Tiptronic 2030 so I was almost set to go.

Great advice given by expert sewers is "new project, new needle". Respected kite maker  Gary Engvall recommends that a size 90 universal point needle is right for ripstop. So I bought a packet of size 90 universal points and 2 rolls of Gutermann polyester thread.

A Rokkaku kite is very simple being basically a flat hexagon with patches and pockets added and there are plenty of plans and How-to websites available.

I closely examined Rokkaku photos on Flickr. especially those by Cris Benton, Blue Kite Team, KAPPIX and Jones Airfoils and read through Gary Engvall's instructions many times.

I decided on a 5:4:3 size ratio and 2m high design. This means that the height is 200cm, width 160cm and main body 120cm high. This is a good size for a wide wind range similar to the Skydogs and Premier Rokkaku kites. It should have roughly twice the line pull of a ITW Levitation Delta making it perfect for lifting an SLR in Bft 3 and 4 and lighter rigs in almost any wind.

Now for sourcing the materials. Ripstop nylon varies greatly. Don't go to a normal material shop and buy their cheap ripstop, it's heavy, stretchy and only good for shower curtains, kite bags and tails.
For kites you need the stiff crackly stuff used for spinnakers. The most common weight seems to be 3/4oz. I used Emma Kites $6.00 ripstop. Although it's very light weight it worked really well. Might try ITW, Kitebuilder or a local sailmaker's spinnaker cloth next time.

You also need some stiffer reinforcing cloth for corner patches and other stress points. I had some cordura for my kite but dacron sailcloth is more often used. 1" wide webbing is also needed for corner pockets and spar loops.

Here is an A4 sized gif of my kite plan. Feel free to download and print it. Red seam allowances are not to scale.

It's important to cut out the panels with the long edges aligned along the warp or down the length of the piece of cloth. That way the finished kite will hold its shape better with less ugly stretch wrinkles. The warp has less stretch than the weft.

I made a template for the triangle panel which made marking out
much quicker.

Mark out the finished size of the panels on your ripstop in clear lines (to sew along later) then add the seam and hem allowances (for cutting out)

Next post will discuss sewing together the panels and adding reinforcing patches