The Amazing Circofoil : 18 Steps (with Pictures)

Somewhere in the early 00's I designed a circular kite that had no internal or external support like rods or spars. Why? Well, just because it did not exist yet. Inspiration came from the well known CircoFlex. I've built it with a kitedesign software called SurfPlan. Now years later I decided to provide the plans for this kite for everyone to enjoy. Therefore I needed to build a similar kite, at first without the use of a computer program. Posted the kite to the instrucables community, even receiving a price. The story does not end here. Getting to know the kite has led to some changes which can be seen on the following pages. It is now only available in 1 size only but progress is in the making. I would love to invite other kite builders to bring this design to the next level. As a matter of fact, the next level is comming to live as we speak. I hope you'll enjoy it as much as I do. Go check it out.

Images 1 and 9 courtesy of Waalcko Elema

Images 2 and 3 courtesy of EveKites

Images 4,5,6,7,8 of DxFoster

Step 1: Update Page: Bridle and Trailing Edge (20-08-2016) + Video

Since the introduction earlier this year I had a lot of nice comments of people who like to make this kite. There where three things I needed to change on this kite.

1. Sloppy trailing edge

2. Better flying angle

3. Resistance to collapse

With these updates I've tackled at least point 1 and point 3 and in some extend point 2.Cleaning up this instructable is something to be done in the future. For now it is priority to provide the necessary changes if you are planning to make this kite. See video

The file and drawing plan of the trailing egde (TE) profile has two options. Option 1 is for when you want/need to include the profile when you have not started construction of the kite. Option 2 is for when you have build the kite and want to replace the TE hem with the TE profile. The difference is in the seam allowance. Option 1 includes the seam allowance for attaching it straight onto the panels of the kite. Option 2 is for making a ribbon like feature to close the TE. (see pictures and next page) Construction details on Option 1 is now available also.

Summary of this update:

The trailing edge of the kite is no longer closed by a hem but this is done by the trailing edge profile, Therefore some steps are different. The bridle has changed, therefore the bridle loops need to be only on the inside, that is the inner skin, of the kite. See next pages on how to install the TE profile when you have build this kite prior to this update or when you are building this kite from the start.

1 Sloppy trailing edge:

The pressure on the trailing edge is significantly lower than on the leading edge. The leading edge is the nose area creates most of the lift that makes this kite fly. The pressure inside the kite is more or less the same. (yes more or less, continue reading please). The difference in pressure on this part makes the nose area stretch and therefore the trailing edge to bulge out even more. With ram-airfoils you can never eliminate this bulge .However this bulge creates an interesting effect. Funnel effect! The circumference of the trailing edge appears to be less than the leading edge. Not very undesirable but not pretty too. The area in the trailing edge folds inwards and make creases in the fabric. So in short, the bulge can be reduced but not eliminated. The bulging creates a desirable funnel effect.

The funnel effect is what I was after, but the bulge needed to be controlled. The solution is provided with this update : Trailing edge profile. The circumference of the trailing edge needs to be smaller by a small percentage. I reckoned it needed to be around 6-7% smaller. The trailing edge profile does just this. A piece of fabric sewn to the inner and outer skin of the trailing edge shaped like an oval. The curve of the oval matches the existing length of the cel at the trailing edge.

You can download it at this page as a full size PDF file or as a plan so that you can manually create it with a compass and ruler.(don't have a compass? A strip of cardboard with two holes [/-/-o-/-/-/-/-/-/-/-o-/-/] at the right distance will do just fine

I had to make my adjustment to the trailing edge by first removing the complete hem I made earlier. Therefore I made the trailing edge profiles in the shape of a ribbon. To make things easier, I used double sided sticky tape because it was a finicky job to complete.(see pictures)

2. Better flying angle.

The lower half of the kite creates lift in an opposite direction. It makes the shape of the kite circular but it creates a lot of drag. Also the majority of this drag is in front of the center of pressure. Not ideal. In other words, it does not have an effective Lift to Drag Ratio. More drag slows a kite down, for example the ability to fly at all. Looking at the angle of the flying line I managed to reach a 60-70 degree angle. But only with the help of extra bridles on the lower halve of the kite which has lead to undesirable flying characteristics. (luffing, collapsing, excessive flying window seeking). A line angle of around 45 degrees was satisfactory for me. This kite will not be a high flyer but it doesn't need to be either. If you are interested, have a look at the articles named "more reasons why single line kites often don't fly" at Peter Lynn's website www.peterlynnhimself.com. That guy is just fantastic.

3. Resistance to collapse

It's a foil kite! Duh! Ram-air foils don't have internal or external support but air pressure airflow and bridle. This needs to be balanced. This balancing act is between the towpoint, center of pressure, center of weight and center of lift. Somewhere here is the sweet spot! It only took me 10 attemps to find this sweet spot and it was right under my nose. The aha-moment combined with the ignored KISS-message (Keep it simple Stupid!) eventually led me to a new and far more simple reliable bridle.

In my attempts I've seen that the support of the lower half of the kite was the trickiest. In fact, the kite supports its shape just by itself. But a certain angle towards the wind is what it needs to get airborne. The kite pivots at a certain point. It is bridled just under this point so that the kite leans back a bit and continues doing so if the wind flow drops or changes. (makes the nose go up so that the kite knows it direction where it needs to go)

Pressure (tension actually) on the lower half is divided and transferred onto the upper halve of the bridle via an extra line, called the recovery line. In tests pushing and pulling the flying line I have not managed to make the kite collapse. The lower half of the kite does need some time to pop back in position and therefore the kite looses altitude. But it does not collapse. The new bridle can be seen on this page and on the bridle page in this instructable.

Other thoughs:

Ah yes. Failures galore. In an attempt to make the bridle really contribute to the system and improve aesthetics I came up with the circoFLAKE add-on bridle. A facet like kite attached to the front replacing the bridle. Since I was convinced about the sweet spot where to anchor the bridle of the kite I made the CircoFLAKE bridle. It turned out to be the CircoFAIL. Except for the added weight (failure 1) a complete new point of pressure was created.(failure 2)Therefore the pivotpoint needed to move down under the kite itself. (failure 3) Making a spar to cope with the compressive forces was admitting defeat (failure 4). However it proved that it could be done.(flew bad though) So the story is not over yet. But other ideas have taken over my head. Just a thought, If a rotor kite (single skin) can stay open, and a circoflex has a minimum supported leading edge: How hard would it be to make a single skin CircoFoil? What's next?

Teprofiles.pdf
Download

Step 2: Update Page (2) Trailing Edge Profile

This step is for those who already made the kite and are changing the Trailing Egde hem for the Trailing Edge Profile. (TE profile)

If you are making this kite form the start you can skip this step. Although seeing the photos of a paper model might illustrate the process and outcome.

First step is to print or make the trailing edge profile with the drawing or PDF file on the previous page. Take care of the right dimensions. Lately I found out that the printer settings can change the outcome by more as 10%. Don't know why. Check the box in the printer setting that says: use dimensions embeded in Pdf file. If it fails; go use a ruler and compass.

1. Make a ribbon out of the profile by connecting them, either with double sided sticky tape or continues connecting by drawing. The seam allowance should be 1cm.

2. Remove the current TE hem. You should have the 1cm seam allowance on these panels to use for the seam allowance for the TE profile. Tidy things up, leave no loose threads.

3. Install the ribbon like TE profile on the outerskin in such a way that the seam will be on the inside of the kite. I used double sided sticky tape for this step. You can go without but it will be much harder. It's all up to your nimble finger work here. Forcing a flat surface onto a curve. Creases should be spread evenly. Sew your way around. Watch out you only sew it to the seam allowance of the upper skin! Mistakes are made easily, so check and take your time. (Seam allowance shown pink in the model)

4. Fold the TE profile ribbon back, leaving the seam on the inside. Since you are using double sided sticky tape (I hope) you can add an extra strip along the seam edge to paste it to the upperkin. This will create a smoothed surface and an airtight seal.

5. Now attach the TE profile ribbon to the seam allowance of the inner skin. Also, double sided sticky tape is your friend in this step. Sew your way around in a 1cm seam. This will close the TE permanently. Again, beware you are only sewing on the seam allowance! This is particularly tricky around the area where the profile meets the seams of the panels towards the trailing edge.

6. You have 1cm left, this is enough to make a single hem by folding it double and finishing it off with a zig-zag stitch. Yes, I keep repeating myself, take care you only sew on this edge. You are done. Nice work.

Teprofiles.pdf
Download

Step 3: Update Page (3) Trailing Edge Profile

This page shows you a way on how to install the trailing egde profile (TE profile) while constructing the kite. Pictures are not from the actual kite, but are from a simple model representing the kite and the steps you take to install the TE profile.

In short, you combine the inner and outer skin panels on the leading egde and then sew the TE on the trailing egde. All seams on the same side. Combine the panels to create seams onto where you sew the profile ribs. Continue untill the last cell but leaving one side of the TE profle open. Connect the beginning and end of the kite and sew on last prolie. Pull inside out and close of TE profile with seam. Also read the note please.

Steps:

Picture 1: make the trailing edge edge profile, use the template on the first update page that says result 1 . Sort out all the panels.
Picture 2: sew leading edges of inner skin and outer skin panels together with a single seam (display side to display side)
Picture 3 ,4 and 5: place the trailing edge profile (TE profile) on the trailing edge of the innerskin and then the outer skin. All seams should be on the same side to that the display side has no visible seams.
Picture 6: when all TE profiles are connected to the panels you have formed one element of three pieces of fabric. To start building cells you silde them over each other in such a way that the display sides face each other.
Picture 7: showing the seam to sew on the profile (symmetrical ribs)
Picture 8: sewing the profile onto the seam starting from the tail area of the profile.
Picture 9: profile sewn onto the seam.
Picture 10: making the seam for the final profile to complete the cell and closing the kite. Important note: this TE profile is only sewn on the trailing edge on ONE side. In the following steps you need to pull he kite inside out to have all seams on the inside.
Picture 11: closing the circle by connecting the first cell with the last cell. First making the seam where the last profile is sewn on.
Picture 12: showing the seam for installing last profile
Picture 13: sewing last profile. Be careful to only sew on the seam edge. By sewing the edges together, the kite will gradually be turned inside this last cell.
Picture 14 and 15: pulling the kite out of this last cell reveals the kite with the seams on the inside. One side of the TE profile seam is left exposed.
Picture 16: close the TE profile on the outside by making a single or double seam. Or use nylon bias tape. Also see the note below to read a better alternative.

Note: the last combination of panels you add to the kite is the last cell. This is the cell that needs to stay open at the trailing edge so that you can pull the kite inside out to have the seam on the inside. This panel and TE profile needs a bit more seam allowance to close properly. A nicer way to do this is to have the last panel you are installing to be a panel that has an air intake. That means when you are finished connecting all pieces and want to close this Final TE profile, you can pull this cell through the air intake and start your last seam also on the inside.(not shown in the pictures)

Step 4: Intro (2)

This kite is a great project for those who allready have some experience with building kites or at least having some feeling with a sewing machine.
Once you know the way around, this kites is quite straight foward. Just a lot of repetition of steps. So if you are a true beginner it is advised to start something less complex (unless you love to challenge yourself). If you have some experience just go for it.

You should definitly have these skills:

- being accurate
- being patient
- basic sewing machine skills (after this project you are a pro ;-)

You should definitly have this:

- at least €50 euro's for the fabric, yarn, small materials
- sewing machine and appropriate working space (floor area + working table)
- the absense of cats

Video instructions.

The instructable covers all the steps to complete the kite. However a little technical understanding and spatial awareness is required for finishing this project. I included a video to support this instructable.

See video:

00:00 - 00:40 Introduction. Finished project
00:40 - 01:30 Combining the different panels on its leading edge
01:30 - 03:41 Adding panels to the kite + bridle loops
03:41 - 04:05 Bridle loops and continuing the kite
04:05 - 04:21 Air inlets ( valves)
04:21 - 05:06 Finishing the kite, last cell and trailing edge hem
05:06 - 06:32 Bridle: figure 8 knot
06:32 - 06:48 Lark's head knot
06:48 - 07:39 Bridle loop knot
07:39 - 09:02 Connecting bridle lines. End.

Steps in this instructable:

Step 1 Introduction
Step 2 Kite Lingo And Kite Plans
Step 3 Cutting Out The Panels
Step 4 Gather Your Tools And Materials
Step 5 Sewing The Panels (1)
Step 6 Making Bridle Loops
Step 7 Sewing The Panels (2)
Step 8 Sewing The Profiles
Step 9 The Air Intake
Step 10 Making The Cells: Sewing Panels And Profiles
Step 11 Closing The Last Cell
Step 12 Closing The Trailing Edge
Step 13 Tying The Bridle

Step 5: Kite Lingo and Kite Plans

Okay, let's get started. First it is good to know some of the anatomy of the kite.
This particular kite is a single line closed cell ram-air foil kite. Yes really.

In other words: it has several air pockets, made of leightweight fabric, that are filled by the wind through some air intakes (holes) therefore presurising its body an maintaining a shape that makes it fly.

Some more lingo:

Leading edge: that will be the front of the kite facing the wind direction.
Trailing edge: that will he the rear of the kite where the flow of wind leaves the kites.
Skins: the surface area can be devided in two parts. Usually it is the part that's up (back of the wind) and the part that's down(facing the wind).
In this case we are a talking about a circular kite. Therefore I will refer to the outer skin (big circle) and inner skin (smaller circle)
Cells: air chambers, compartments, pockets of air. There are 24 of them in this design. Cells are made of 1/24th part outer skin, 1/24th part innerskin and two profiles.
Panels: The cells are made of pieces of fabric. These parts I call panels. Together they form the outer and inner skin of the kite.
Profiles: Piece of fabric to give the cells its aerodynamic shape and the volume. Sewn lengthwise on the inside of the kite between the inner and outer skin. Front is called nose, back is called tail.
Bridle: pieces of string attached to the cells towards the flying line, helping the kite to maintain its shape and angle towards the wind.
Rip-stop nylon: leightweight fabric (around 40 grams a square meter) for making kites and sails made of synthetic material with reinforced yarn in a cross-hatch pattern making it lightweight but less prone to tears.

The plans or templates,

Below for you to download are the files you need to make this kite. Choose between templates in parts or one piece. They are all in a .pdf format

Outerskin panel, slightly convex lines ( curving outwards)
Innerskin panel, slightly concave lines ( curving inwards)
Profile, symmetrical along its length. ( outline above and below are the same)

Preparing the templates:

The plans need to be printed and made into templates to transfer the design onto the fabric.
Once printed you need to combine the pages. Just to be clear, the outerskin template need to be used 24 times, the innerskin template needs to be used 24 times and the profile template needs to be used 24 times. 3 templates for 72 pieces of fabric in total! The prints have an actual size ruler in centimeters included so you need to check it for acuracy.

Aligning the markings and making the template:

The template is used to trace the outline and some specific marking onto the fabric with some kind of marker. I used a soft 3b pencil for this. In this step I asume you cut your panels with scissors.
The profile is printed on two halves. Two sheets of A4 paper. I used sticky tape to attach it to a window and aligned the markings to make it fit.(see picture)
Because you have to use this template 24 times its best to make it somewhat durable. Thin cardboard works fine. Actually I made it giving it just some layers of packaging tape along the surface. Works fine.
When you don't want to use scissors you can go for a stanley knive or even a soldering iron to trace the outlines of the panels. It speaks for itself that your template needs to be way more durable. I suggest you paste it onto 4mm MDF or some thin plywood.

Step 6: Cutting Out the Panels

Once more, you need 24 outerskin panels, 24 innerskin panels and 24 profiles. I took little effort in reinforcing my templates so tracing the outlines was more work. I used what I had lying around to weigh it down. I used a sharp but soft pencil (3b drawing pencil) so you need to sharpen it a lot. The outline already includes the allowance for the seams (1cm)
Important note on rip-stop nylon: place your panels aligned with the crosshatch pattern of the fabric so that the vertical lines and horizontal lines are perpendicular to the central lines of the panel your making. Check how you get the best fit on the fabric.

Make sure you remember to put the markings on the right place:

Mark where the bridle needs to be attached. ( later you need to sew a bridle loop to that spot)
Mark what panel it is. Specially when you use a colour scheme on the kite. To help you from getting confused ( Yes, I also have sewn panels up side down more than once) put the markings of the panel numbers on the Leading Edge of the kite. So for example: inner skin panel 4 is written like i-4 on the leading edge of that panel. Only the markings closest to the leading edge is used for the bridle loops!

Marking and cutting the profiles:
The profiles are symmetrical so the top and lower curve of the profile are the same. You do need to mark the place for the cross vents. The plan shows you more places you could add markings. More markings will help you aligning the profiles when you sew them in.

Cross vents: the air inside the kite needs to travel from cell to cell as fast as possible. Therefore holes are cut at certain place to allow this to happen. In the the plan you find the place and size for these holes. Actually you can add more holes across the central line of the profile. I suggest you don't cut holes near the "nose" (front) of the profile or directly above a bridle point. Anywhere else is fine.
To create these holes you need to mark them on the profile. I made a wooden template with holes of the correct diameter so I could use a soldering iron to cut them out. Otherwise scissors will work but it is more tedious.

Step 7: Gather Your Tools and Materials

Ripstop nylon: You need about 4 running meters for the project

The kite is made of a lightweight ripstop nylon. This material is used for spinnaker sails, parachutes, hangliders, tents, hot air balloons paragliders and kites. For its strenght is really lightweight. Specialised shops for kites usually have this in stock but you could buy it online too.
The best you could purchase is Chikara. (Toray) Hands down. Others options are: Chitex (good and affordable), Elltex, Paratex, Carrington, Mirai and Icarex (polyesther)
Make sure it is airtight, lightweight, has excellent strength and has been coated on both sides. Preferably the coating is PU (polyurethane) based and not silicon based.( Sticky tape does not adhere to silicon) The weight should be between 31 grams and 60 grams per square meter. One running meter is usually around 1.5 square meter. Prices vary from €5 till €20 euro. Browse around to find the best deal. Sailmakers might even provide you with a good deal.
Sources:
http://www.dutchflyingobjects-shop.nl
http://www.vliegeruit.com

Bridle lines: I prefer using dyneema ( braid) for the bridle for its strength and low stretch. Polyesther can be used to. Nylon has far to much stretch.
If there is no shop that sells this to you then you could have a look at braided fishing line. Diameters ranging from 0.40 to 0.80, with a test strength of roughly 40-60 pound are correct.

Sewing machine, household versions are just fine.
A4 printer if you own one.
Sewing yarn: Go for quality here, polyesther only. You can choose for a thicker thread if your machine doesn't have troubles with that. Using a thicker thread fills up the holes from the needle much better. Brands you can use are Gütermann, Goldmann. Serafil. It is a no-brainer if you can find and use Serafil. You need at least 250 meters for this project.
Sewing needles: rip-stop nylon is very thin and slippery. Using stretch needle have proven to deal with this problem. Go for sizes between 60 and 80.

Soldering iron. Not essential, but very handy
Scissors. Two pair: one for cardboard and paper, one used only for cutting fabric.
Pencil: soft type, 3 b, pencilsharpner
Waterproof marker
Measuring tape, ( paper version from Ikea or DIY stores)

Sticky tape: packaging tape for the templates.
Double sided sticky tissue tape: optional but highly recommended! Sometimes very hard to come by. Specially the 5mm wide version. Can be expensive too. Used by kitebuilders all around the globe so you need to search for it. The Dutch discount store Action sells them for scrapbook appliances in a 10 mm version and is dirt cheap but good!
Wooden plank, 1meter plus in length.
Clothespins
Cardboard

Step 8: Sewing the Panels (1)

Check your sewing machine first! In this instructable you will find little information on how to sew in general. Things you need to check before you start is the tension on the threads and pressure of the foot. Sew some leftover pieces of rip-stop nylon together. 13 layers of rip-stop nylon should not be a problem for your machine. Sewing a profile onto the bridle loops requires this. Also in contrast, just two layers should not give you problems.

IMPORANT UPDATE!
Not shown in the pictures yet is the inclusion of the TRAILING EDGE PROFILE. (See UPDATE PAGE) The trailing edge profile needs to be sewn on the, what else, trailing edge. Make sure the seam is then also on the inside of the kite. Further construction is somewhat the same except for closing the trailing edge and turning the kite inside out, (finishing last cell)

First step in sewing: combine the leading edges of the inner skin panels to the leading edges of the outer skin panels. Have your panels stacked in order.

Important construction note: Sewing the two panels together on the leading edge creates a seam that should eventually be on the inside of the kite. This method of construction is used throughout the kite. With all panels, the seam needs to be on the inside of the kite. Once you joined the inner and outer panels on its leading edge you create seams on the chords (length) of the kite. Onto this seam your profiles need to be sewn. To have the seams on the inside you need to place the fronts of the panels together. Let's call it display side to display side

The leading edge of the panels are marked with either an O or an I. So place the O on the I. (See picture) Check your needle position.(see picture) The bulk of the kite should be on the leftside of the machine. While sewing I always align the edge of the fabric with the right side of sewing machines' foot (see picture) . Placing the needle position to the right makes a seam of 1cm wide. Set the length of the stiches between 3 and 4 mm. Start sewing, attaching the thread, and secure it by going back and forth. Tie-off by doing the same. Needless to say, there is a special button on your machine to do this..

Step 9: Making Bridle Loops

The kite shape is supported by a bridle. The bridle also makes the kite fly in the right angle towards the wind. Forces created by the wind on the kites' surface is spread out on the bridle lines. Therefore you need a connection point on the kite for the bridle lines: bridle loops. I made these with a leftover piece of rip-stop nylon. I cut 5cm squares and fold them in a V shape. The bridle loops are placed and sewn between the two layers of skin at the marked area.( see next page) Every cell/ panel on the inside of the kite needs a bridle loop.

Step 10: Sewing the Panels (2)

As said, you create your cells by adding panels one at a time. The seam you create by placing the panels front to front creates the edge or seam where you also sew on the profiles. Picture 1 shows 4 panels (2x outer skin,2x inner skin) sewn together showing the seam where the profile needs to be sewn on. Also it shows the bridle loops between the layers of skin. Notice the typical shape of the skins, hollow for inner skin, outward curved for the outer skin. ( note: in this version I added an extra bridle loop on the outer skin)
Second picture shows you the display side of the kite with the seams inside.

Joining the panels:

Take the two panels you want to join. Make sure the inner skin faces the inner skin and the outer skin faces the outer skin. Display side to display side. Start sewing on the trailing edge of the outer skin. Attach and tie-off properly. Remember the needle position for the 1cm wide seam.

Placing the bridle loops: The bridle loop is placed on the marked place. It is advised to stop sewing at this point, lifting the pressure foot but leaving the needle in the fabric. Now Go back and forth over this point because it deals with a lot of tension from the bridle. All inner skin panels need a bridle loop at the point closest to it's leading edge.

Sewing can get a bit tedious over several cells. Concentration fades at this point so I speak out of experience when I say that you might forget to place the bridle loop. Check your panels before continuing. It will be much harder to change anything when you closed the cell with the profiles.

Step 11: Sewing the Profiles

It should be clear at this point that the profiles are sewn on the seam on the inside of the kite made by combining the outer and innerskin panels. You'll soon find out that attaching the profiles to the skins is a challenging job. The easiest trick for inexperienced kite makers is to use double sided tissue tape to stick it onto its place first. (See picture)

Problems you could encounter is that the glue from the tape accumulated around the needle(hole) making irregular stiches or even making the thread snap. A possible solution is that you soak the thread in some sewing machine oil.

In my case i didn't use the tape. The trick is all in your fingers to pinch and manipulate the profiles outline to the outline of the seam. Take your time for this step because the stronger the curve, the more difficult it gets.

Start sewing the tail of the profile first on the outer skin. Important: The trailing edge has a 1 cm seam allowance, therefore you start sewing the profile 1cm from the trailing edge. Work towards the middle of the profile at the nose. The needle position needs to be in the middle (7mm) from the right edge. (See picture)
Check your work after the first profile. Then continue building the cells by adding an extra panel to start a new seam.

My tips are:

Pauze a lot,
Lift the pressure foot, leave the needle in the fabric when you want to straighten or tidy up the piles of fabric on your table.
Make short controled lines of stiches. Only stich 1cm at a time when you reach the steeply curved profiles' nose.
Check between the stops if you are only stitching the profile at the seam. ( it happened to me more than once, luckily not on this kite )
Once you reach the center of the nose of the profile: flip the kite having the trailing edge faced towards you. (The profile has a bit of a sharp nose so you can actually see when you have reached this point.
Check your markings to see if the profile still aligns with the skins.
Mistakes made in the nose area of the profiles are far worse than in the tail area.
You can cheat just a little ,when you realize in advance that your missing a few millimeters in the tail area, by stretching the fabric just a little bit over a larger distance. It is a just cheat,.
Don't give up! I promised myself to never make a foilkite again after my first attempt. Boy, I was wrong.
Be carefull with the use of scissors or sharp objects wile working with the kite. Yes. Experience.
Do trim off the remaining threads. It could find its way in the lower bobbin mechanism.

Step 12: The Air Intake: Valves

Before you are getting to busy adding panels, please read this first. The kite needs to fill itself with air to maintain its shape. This is done by the air intake. Air intakes on foil kites are usually open. But it in this case I chose to make a closed valve construction. In a sense it is just a hole in the innerskin covered by a kind of wind sock. When air wants to escape, the sock blocks the entrance and closing the entrance. 4 of them are added ( cells 11,12,13,14)
Okay, from all the steps in making this kite, this might be the most fidley. Use the double sided tissue tape for this.Take your time.

Steps picture 1

1 Mark and cut a circle 55 mm in diameter in the 4 innerskin panels closest to the top/ middle of the kite. Circle starts 1 cm from the edge, right in the middle.
2 and 3 Make a square as a template for the wind sock. The basis of the square is made out of A4 paper. It includes a 1cm seam but for some reason make it a wee bit bigger.
4 Sew the sides
5 Use tape on the outside of the edge of the sock. Notice the seam is now on the inside of the sock.

Steps picture 2

1 and 2 Put the sock with the tape on the outside. You might need to stretch the circle a bit to make it fit.
3 Start sewing. Turn the sock constantly after making 4 stiches. Make sure you don't wrinkle the inner skin fabric. A fold, crease or wrinkle in the sock itself is no problem. Needle position to the right (5mm)
4 There is just a small area to work on. Make sure you sew close to the tape and not on the tape.
5 The seam should be on the inside of the kite.
6 and 7 Turn inside out and straighten out. Well done.

Step 13: Making the Cells: Sewing Panels and Profiles

I prefer to build my kite cell by cell. Starting at the bottom of the ring and ending there too. In this proces it is easy to forget the bridle loops but I like to see the kite progress cell by cell and to break the pattern by alternating between adding profiles and panels.The other method is by first sewing al the panels together. The speed of working between pasting cells first with double sided tissue tape or sewing it straight away is trivial. For beginners it is advised to use the tape. Check every cell, profile and panel for mistakes before you continue with the next.

Alternative construction method: the tape can be used to construct the entire kite before sewing on the profiles. The tissue tape adheres really well to rip-stop nylon with a PU coating.Get yourself 10mm wide tape and remove the seam allowance on the right side of the panels and the leading edge on one of the panels. Align the tape neatly around the edges of the panels to stick them together. First all the outerskin panels, second the lower skin panels. Then combine the skins. Stich everything together when you add the profiles on the inside of the kite. Bridle loop are a bit more diffilcult too because they need to be strengthened on the inide and on the outside as well. This method makes a really smooth kite and is almost completely airtight. Difficult to do though.

Step 14: Closing the Last Cell

24 cells, 24 profiles. The last profile connects the beginning and end to complete the circle. First connect the outer skin and inner skin by starting to sew on the trailing edge of the outerskin. This procedure might be a bit confusing because the kite will partially end up inside the cell while you are sewing! Remember the bridle loops in this chaotic process. Don't pull the kite inside out yet but continue with sewing the profile on the newly created seam. Passing the thick package on the left side of the machine is a bit a handful to cope with. But pulling the kite inside out at last to reveal the ring is very rewarding though.

The trailing edge is already closed when you have sewn the trailing edge profile onto every cell. This creates a problem when you want to close the last cell since there is no opening anymore The solution is to leave the last cell open to the very last moment. This means that the last cell should not have a trailing edge profile just yet!

First close the cell as in the steps described. The last cell is therefore left open with no trailing edge profile at this point. Now sew in the trailing edge profile on one side only (for example the upper skin) The seam should be on the inside of the kite. You are now left with one side open which can be closed by sewing it on the outside only. You have 10mm seam allowance here so the nicest thing is to fold the seam to the inside of the kite and making a line of stiches just on the very edge of this seam.

Step 15: Tying the Bridle (updated 20-08-2016)

The bridle is a system of lines connected to the kite's surface towards the flying line with the main function being to hold the kites shape and change or hold the kite in a certain angle towards the wind. In the case of the circofoil

I found out that the bridle is constantly working with and against the kite. It only took no more than 10 attempt to get it right. The bridle presented here is simple but effective. It has a lot of advantages over the other bridle system but the main reason I chose for this bridle is its ability to recover from collapsing and maintaining an inflated shape, making it go in a nose-up position and continuing flight. Every cell is bridled on the INNERSKIN of the kite. (completely different from the first bridle I published.)

Tying the bridles.

All bridle lines should be made as accurate as possible. Use the bridle board for this.(see picture)
The bridle board is just a piece of wood with a measuring tape ( free paper ikea version?) secured to it. Put a nail at 0 cm and and nail 100 cm. Place the loop of the bridle line at the 100cm mark and then back if you want to measure lines above 100 cm. I mark it with a permanent marker and cut it with scissors.
Practice tying your knots. (Figure 8 knot, lark's head, bridle knot) In the video it is explained how to tie them.

Instead of making knots you can also choose to lock splice the bridles. I made a video demonstrating the idea. You can view it here .You need a soft braided hollow bridle line to do this and a piece of iron wire or preferably steel wire.

Bridles can be confusing so have a plan ready. The bridle plan has different colours of lines. This bridle is pretty straight forward. It has 4 bundles of primary bridle lines (blue and green) leading to 4 single secondary lines which are then connected to a loop that forms the tow point of the kite. The secondary bridle (red) is one continues line so that you can change the angle of attack (shorter upper line, low flying kite, longer upper line, high flying kite ).

The bundles are also connected with an extra line.(orange) I call this the recovery line. When the wind drops, this line straightens out and tensions the upper bridle. (which is conveniently placed at the pivot point of the kite)

For the sake of experiment I used (don't hit me, I know what I said about nylon lines for bridles) the cheapest nylon I could find. (It is not even braided, it is twined) The kite flew astonishingly well. But the sake of durability go at least for braided polyester with a 20 pound breaking strain for the primary bridles and slightly thicker dyneema for the secondary bridle.

Start every bridle line by making a loop. Also I add an extra 2 cm for the knot and tag end while measuring and marking the bridle line.
If you measured one line then it is easy to copy this for the other side too. Start with the lines that needs to be tied to the middle of the inner skin and work your way down. I immediatly tie every pair of bridle lines to the kite so that it won't confuse me.
Just start at the top in the middle of the kite and work your way down.

Now you need to pair the lines to form groups. This is done with the red lines. The red lines itself are combined with a Lark's head knot to a small loop to form a tow point. That is the point where you add the flying line. Use the bridle line knot from the video to combine the lines to the bridle loops and the bridle lines to each other. Don't forget to tie the orange recovery line. The best way of installing this is not connecting it to the big bundle of loops but to tie it to the knot that holds these bundle of loops.

Flying it for the first time:

Very exciting. The air chambers need to fill with air properly. You can help the process of filling by swaying the kite yourself a few times. I have succesfilly hand launched this kite but it helps to tie the line to a ground anchor with at least 20 meters of line out ito get this kite in the air. The pull is quite light so a 40 kg flying line is more than enough. I found out that the kite can be responsive to wind changes so a thicker line helps keeping it in the air a lot. Nylon lines are fine for this. You can change the flying angle by changing the towpoint on the kite. Towpoint down is high angle ( kite catches more wind) towpoint up is lower angle ( kite catches less wind). Make small adjustments. The way it is set now it that it is flying at a low angle. Moving the point down makes the kite go higher.

I am pretty sure (did not test it yet) that you can fly the kite with two lines or even four lines. Will try it out if someone does not beat me to it (open invitation). Enjoy!

Thank you for checking out this instructable. If you have questions or you are liking my project, please feel free to leave a comment. I also would like to THANK YOU for your vote in the "make it fly" contest! I won one of the 10 second prices!

Step 16: Circofoil Built by Others (Instructable Member DxFoster)

Had a nice wind today, flew the kite for a couple hours (just got tooo hot to fly). Found that with the strong wind, the kite filled up with air really nice but had a tendency to go from side to side. It would go over on its side, fly almost to the edge of the window, come down, roll a bit and then start heading to the other side. The kite would self launch so wasn't too worried. The wind got a bit stronger and now the kite would come down and have a harder time getting back up. I decided to add a weight to the bottom bridle point (like a circoflex) and this made a huge difference. I used a drifting sinker and attached it with a clip to the bridle point. This stopped the real wide side to side motion. It would still want to go to the side but the weight caused the kite to straighten out. If the wind died and the kite came down, the weight kept the top up and when the wind picked up the kite was back in the air.

I flew the kite with my circoflex and the circoflex was just a real pain to fly while the circofoil (with the weight) kept flying and was a pleasure to fly.

Here's the circofoil and circoflex. (picture 1)

The circofoil in high wind. Really inflates well. I can blow it up with an battery air mattress pump.(picture 2)

The bridle lines were from the first kite so had knots. On the next circofoil will do the lock splice.(picture 3)

TE under high wind.(picture 4)

I followed a different procedure when I sewed the kite together. First, I sewed the air vents using tabs. (Picture 5)
I reinforced the opening by sewing on a 75 mm round piece and then hot cutting the 55 mm open. (Picture 6)

Next I cut the fabric to size. I stitched a line in 1 cm at the bottom, sewed the edges together and then made tabs at the bottom by making a cut to the stitch line every 12 mm. I made a wood plug the ID of the fabric cylinder, folded the tabs up and inserted the plug so that the folded tabs were 1/4" from the end of the plug. I placed double sided tape around the inside opening of the inner skin and then inserted the plug into the fabric opening (I had a 1/4" piece of plywood below the fabric with a larger hole in it). I took each tab, pulled it tight to the edge and pressed the tab in place. Then went to the sewing machine and stitched 2 runs around the tabs. (Picture 5)

Next sewed all the Inner and outer panels edge to edge (did half and half and then sewed the halves together). This way I could use the light table and hot tack the panels. I made a one piece TE and laid it out so the break would be in the center of the curve. This made it easier to sew the TE together after all the profiles were sewn on. I tried sewing on the TE with out tape and finally gave up. I had never used tape on a seam so this was a new experience. Was a bit tough at first but once I got going tape was the only way to go. One edge sewn on. (Picture 7)

Both edges sewn on.(Picture 8)

Time to sew on the rib profiles. I used the light table to locate the profile and then hot tack one edge (up to the start of the curve). The alignment notches I had hot cut made it nice and easy to line up the ribs. (Picture 9)

Over half the rib profiles sewn on.
Because I had sewn the seam of the Inner and outer panels flat when attaching the TE, I had to make a cut half way thru the seam (where the TE crossed). The cut allowed the seam to fold up so I could sew on the rib profiles. (Picture 10)

I sewed the ends of the TE together, sewed one edge of the seam shut and pulled the last rib thru so it was on the inside. Then pulled the seam thru an air vent and sewed it shut. I tried using the sewing machine and realized there was no way to get the seam line straight enough so that the feed dogs would pull the fabric thru. Decided it would be easier to hand stitch the seam line. I stitched over one stitch, back a stitch and then over the original stitch hole to form another stitch- then back one stitch and over. This seemed to lock the stitching and really held the edge in place. Was a lot easier than using the machine as I was able to get into the corners and lock all the seam allowance points together.

For the next circofoil:
1. Going to hot cut locating notches in the inner and outer panels (just like I did on the ribs). Won't have to worry about locating marks.

2. Make the air intakes larger- was a real son of gun sewing the final seam

3. Plan on hand stitching the last seam line. Want to pre "stitch" holes in the the seam lines in the TE and Inner and outer panels (stitch with needle only). Then use the holes when hand stitching the final seam.

4. Use the lock splice to make the bridles

5. Put in one bridle loop at the center point of the TE. When storing the kite can take the "pig tailed" end of the bridle line and attach that end to the loop to stop tangles in the bridle.

6. Put in one bridle loop at the very bottom on the outer panel to attach a weight. Or sew in Gross Grain Ribbon to tie on a weight. Not sure if this would work- creates a place for the kite to get caught on something. May be better to attach to the inside bridle point.

7. If possible, cut a V in the top "nose" of the rib profile so it will be easier to sew. Would have to experiment with this. Sewing the rib profile close to the end will give the necessary curve.

I gave the kite the real test- how it flies in very high wind. My wind indicator flag pole at the river had the flag flying straight out, there were white caps on the river and the weather station was calling out for small craft warnings. All in all, the conditions were such that I couldn't fly 98% of my kites. The few that I could fly, well I wouldn't put them in the air, it was just too gusty. Decided to give the circofoil a chance to prove itself. I walked out 50 lb line, attached the kite to the line and let go- up it went. Seems the stronger the wind the better it flies. It did the side to side thing so I increased the weight of the sinker hanging on the bottom bridle point. That helped a bit, but the wind was soooo strong that it still went to the side. Now the kite would recover and go back up, it didn't come to the ground and roll around. I was on the field when a gust came up, I had to hang on to my hat and it was hard to walk- the kite just went higher in the air. This is truly a high wind kite.

DxFoster, Buffalo USA

Step 17: Closing the Trailing Edge (not Necessary With Update of TE Profile)

Congratulations when you reached this part. I really hope the instructions where of any help to you. Last thing except for the bridles is to close the trailing edge. To do this I made strip of nylon sewn once on the trailing edge, folded over the edge and sewn twice to complete the hem. Make a strip of rip-stop nylon measuring around 4cm wide and 350 cm long to create the hem. Combine several strips when you don't have that much material left.
(See picture)

1 Place the strip along the trailing edge like in the picture. Fold a tag end over once to make a neat finish.
2 and 3 Continue sewing untill you reach the beginning where you doubled the tag end. Cut off the excess material.
4 Flip the kite over to cover around the edge and fold the strip 1cm inwards
5 Align the fold with the line of stiches you created in the first step. To hold it in place I used clothes pegs. Pins are not suited for this sort of work.
6 Finished!! Sway it around in your room to fill it up for the first time. Or, use a hair dryer or a fan.