How to build a Chevron

The plans for the Chevron are not available, but none the less, it may be educational to document how they are built, because much of the technique applies to most soft kites.

The components:


Organising the skin components

First, unroll the dark sheets onto the floor. These will be the dark portion of the Chevron graphic. Note that the shape is not rectangular, but rather skewed because of the Chevron shape. Identify the leading edge by the kink in the shape (the Chevron is not diamond shaped - it has a rectangular centre section - the 4 middle cells are identical). The longest straight edge will form the join between dark and light fabric.

Note that the lare sheets are in fact 2 identical pairs. 2 of the sheets are slightly smaller and have bridle positions marked. They are smaller to allow for the leading edge gauze. The 2 wider sheets have no bridle positions marked as they are for the upper skin.

As they come off the roll, you should have an upper sheet, a lower sheet, then an upper sheet and a lower sheet again. Lay them on top of each other in this order.

Now take the triangular yellow sheets and stack them next to the dark sheets. Note that one of the edges of the triangle also has a dog-leg. This is will form the trailing edge. The long straight edge of the triangle will join with the dark sheet. All the triangular sheets have an identical shape, but note that two of them have bridle positions marked on the rib and two do not. Again, the ones marked with the rib positions are for the lower skin.

Lay out the yellow triangles next to the dark sheets, so that the long edge of the pile of triangles is next to the long edge of the pile of rectangles. Ensure that you follow the same "upper/lower/upper/lower" pattern as before.

Sewing the skin

Before you start sewing, you will want to practice using the very fat DIN-40 thread on Icarex fabric. Not only is it difficult to get the right tension in the first place, but the thread is so heavy that when you've sewn one stitch correctly, the tension on the *next* stitch is likely to pull the previous stitch!. I strongly reccommend a Pfaff with a walking foot, because the extra foot *clamps* the previous stitch, neatly avoiding this problem.

Now you're ready to start sewing the skin. Grasp a pair of sheets by the long edges and lift up and take them to the machine, and sew the long edge. Great care must be taken to ensure that the rib marks on the sheets will align when you finish. Note that the rib-lines are at an angle to the edge. This means that when you sew, the rib-lines must coincide at the sew-line, not the edge! Aligning this is fiddly. You may find it easier to use some sticky tape (I like 3M "Magic" tape for this purpose) to hold the seam in position while you get it under the machine's foot.

Note that the join should be sewn from the middle of the kite to the tip.

As you sew, ensure that the alignment is maintained. I strongly reccommend a Pfaff walking foot machine for this purpose.

Do an upper skin and a lower skin in this way. For the next two pairs, pick up the fabric such that the seam goes on the *other* side

You should now have 4 sheets of fabric. Upper left, upper right, lower left and lower right.

Next we'll sew on the gauze.

This is done as follows:

                                  ....gauze.........:....... |

(where ":" is the stitch)
Then the seam is folded out and stitched again.

inside                                    /-----:--:-/
                                          | ....:..:.........gauze.......
                                             new^  ^existing
Care must be taken to ensure that you end up with the correct portion inside!

The gauze is sewn first to the dark leading edge of the lower skin (remember - identify the lower skin by it's smaller size and the bridle marks). Start as usual in the middle of the kite and sew to the tips. Note that when you first start to sew, the dog-leg in the gauze will point *away* from the kink in the leading edge, be will be ok when the seam is folded out.

When the gauze is fixed to the lower skins, it is next fixed to the upper skin, before the left and right halves are brought together. This makes life easier where all the seams must come together in the middle.

Take extra care to ensure that you sew each seam the right way round, so that the inside of the seam is on the inside of the kite...

With the gauze sewn to both upper and lower skins, we now have only two sheets - the left and the right. Start sewing at the gauze, sewing the top and bottom seam separately. You will see how consistantly you've sewn everything else by how well everything lines up on this seam. Sewing from the middle outwards means that any mis-alignment will be at the trailing edge where we will later trim it off.

When sewing across the red/yellow seam in the skin, fold the red/yellow seam towards the leading edge, so that the light colour overlaps the dark colour, giving a cleaner appearance from the outside (if the dark colour overlaps the light colour, then the dark seam allowance will be visible when the kite is complete)

Skin reinforcing

Next, we reinforce the bridle positions.

Cut 33 2" squares of rip-stop repair tape, plus 6 1.5"x2" rectangles. Then trim the corners off the squares to make octagons (this helps to reduce any tandancy for the corners to lift) The octagons go on each bridle point on the skin, except for at the leading-edge/gauze seam. (the seam offers it's own reinforcement, and it's difficult enough to bridle through the seam without adding ripstop repair tape...)

When sticking over the centre seam, fold the seam to the left.

The rectangles are for the tips. Only trim 2 corners off and but them to the edge of the fabric.

Note that you've just distributed one gross of sticky little triangles about the floor. Pick them up or you'll never hear the end of it from your wife/mother.

Attatching ribs

Now, we'll prepare the ribs. There are 13 different rib sizes, from "1" at the tip to "13" at the middle. There are 2 each of sizes 1 through 12, and 5 of size 13. Arrange the ribs into 2 stacks of sizes 1 through 12. Take care to ensure that the ribs are all the same way up - the bottom is flatter than the top. If the ribs are unnumbered, then number them at the nose, ensuring that you will be able to tell which way up the rib is later. The ribs are flatter on the bottom than on the top - when you've stacked the ribs into 2 piles, look at the pile to check that the ribs look neat - that you havn't got one of them upside down.

We sew the ribs onto the bottom skin first. We start by sewing the nose of the rib to the seam where the gauze is joined to the upper skin, then continue across the gauze to meet the rib-line on the lower skin. It is very important when sewing the rib to the lower skin to ensure that you have the body of the rib on the *right* of the sew-line and the seam-allowance on the left. It might not look significant now, but later when you sew on the top skin, you'll curse if you get it wrong... When aligning the rib, align with the line on the skin, not the line which has been rolled round the gauze (which may be several milimeters out of alignment). When sewing, take care to ensure that you are following the rib-line accurately, because the seam and the line will be visible, and everyone will see if you mess up. Also, take care to maintain a constant seam allowance. Any difference here will be invisible to any judge, but will affect the performance of the kite...

Note that there is no line across the gauze for you to follow. You are expected to be able to do that bit without assistance.

Note also that the end-ribs are sewn differently from the rest - you'll need to turn everything around to ensure that the seam allowance ends up on the inside.

When sewing the rib across the red/yellow seam in the skin, fold the seam towards the leading edge, so that the dark seam allowance isn't visible through the light colour from outside.

If you make an error while sewing the ribs, place a patch of rip-stop repair tape on the inside of the skin before punching *another* line of sew-holes.

When you've sewn all the ribs to the bottom skin *stop*. You need to reinforce the ribs to take the bridle before you carry on! It's ever so inconvenient to do this later...

Rib Reinforcing

On each bridled rib, you will sew a re-inforcing line. This line is a zig-zag of polyester line which will distribute the point load from the bridle through the depth of the rib. The polyester is deliberately over-spec because in the case of failure, we want the bridle to break before the internal, sewn line, so that repair is quick and easy to do in the field, rather than difficult to do in the workshop.

To sew the polyester line quickly and accurately, you want a groove in the foot of your machine. On newer machines, this is easily done with a file. On my older Pfaff 1211, I needed to use a grinding wheel in order to make any impression on the hard metal!

First, just try sewing thread through the line, then practice on scrap fabric. Note that you want to apply the minimum amount of tension to the line in front of the foot, because if you sew under tension, the fabric will bunch up as soon as it is released.

The zig-zag line is not marked on the rib. The only critical point is that there must be a corner at each of the bridle points marked on the skin. Simply build a zig-zag so that accomplishes this (the opposite corners are going to be mid-way between the bridle marks).

It is a matter of skill and pride to get each of the corners of the zig-zag to finish in the same spot, relative to the position of the skin. When the kite is flying, it will be flying off the re-inforcing, not the rib, so this is important.

Note that the reinforcing is done after the rib is attatched to the lower skin. This means that:

Take special care when reinforcing the tip-ribs. Your sewing will be in view!

When the reinforcing lines are done, go round the whole kite and tidy up the spare threads from all the seams, together with any excess reinforcing line.

Sewing ribs to top skin

Now, we are ready to sew the ribs onto the top skin. To find which end to start, fold the top skin over as it will be when completed and lay the kite on the floor, leading edge away from you, with the lower skin on resting on the floor, the ribs in the middle and the topskin on top. The rib to do first is the tip-rib to your left.

You'll have to turn everything inside out to do that particular rib, but it's important to start at the correct end.

As you continue down the kite from that rib, you'll notice that the completed canopy builds up on your left, and the only thing that you need to pass under the arm of the sewing machine is the upper skin.

If, when originally attatching the rib to the *bottom* skin, you had left the seam allowance at the right hand side, then the completed canopy would now be assembled to your right and would have to pass under the arm of the sewing machine for every rib. This is very inconvenient.

If you had started sewing the upper skin from the wrong end, then you come to do the second rib, you need to be *inside* the cell. This is inconvenient.

If you finish sewing the ribs and then you notice that you've forgotten to add the reinforcing line, then you'll find that adding this now is also somewhat inconvenient.

Folk wisdom says that in order to sew the last rib, you need to roll the entire kite into the last cell. You won't manage this. Instead, just manipulate the fabric so that you can *begin* sewing the last rib. Sew a few inches, then feed in some more fabric so that you can sew a little more. When you finish the seam you'll find that you have only a few cells near the wingtip stuffed inside the last cell. Just pull them back out again.

Closing the trailing edge

Having completed all the ribs, the last sewing task is to close up the trailing edge. Lay out the kite on the floor. Starting from the middle of the kite smooth out the fabric (both top and bottom), checking that the rib-lines are alligned. Take a hot-knife and trim the excess fabric from the trailing edge. Trim off as little as possible. Make sure that knife is nice and hot, so that the fabric is not only cut, but also welded together. When you reach the wingtip, curve the edge free-hand to meet the end of the tip-rib. Do this to both sides of the canopy.

Now sew a roll-seam down the trailing edge. I start a little way from the tip, so that I can start at a nice straight section, sew the rest of the trailing edge, then come back to the tip that I missed afterwards.

The roll-seam is where you fold the (double thickness of) fabric over twice before sewing down the roll. With 6 thicknesses of fabric to sew through (more where you cross seams) and fat thread, it proves to be be a regular occurrance that you will break a needle while back-tacking at the end of this seam ie: you break a needle on the very last stitch on the kite.

After trimming any excess threads from the completed canopy, you might think that we're nearly done. Alas, no we're only about half way - there's a lot of bridling still ahead of us...

Bridle Overview

The primary bridle is the section of the bridle which is attatched to the skin of the kite (or rather the reinforcing on the rib). Each set of 4 primary bridle lines converge at a single point - the primary tow-point.

13 of the ribs on the canopy are bridled. Each rib has two completely separate primary bridles, one tuned for maximum power, the other tuned for minimum power.

Each primary bridle appears to consist of 4 lines, named A, B, C and D, from the leading edge, but infact, the lines are loops. A & B are a loop, C & D are a loop.

At the primary tow-point, the primary bridle joins to the secondary bridle. The secondary bridle is very simple - it's just a single length of line. The purpose of this is to extend the tow-point further from the canopy for the purpose of steering, without increasing the length (and thus drag) of the 4 primary bridle lines more than necessary.

The cross-bridle attatches to the bottom of the Secondary bridle. At first glance, each secondary bridle has a line to the left kite-line and one to the right. In fact, several of the outer cross-bridles are omitted (there is no line from the right wingtip to the left kiteline), and the bulk of the cross-bridle is woven from a single line.

Because there are two separate primary bridles, there are two separate secondary bridles and two separate crossbridles.

Bridle construction

There are two main knots used in the construction of the cross-bridle. the figure-eight:
            |    \
            |      \        |
            |       X       |
            |        \      |
                       \    |
This knot is considerably stronger than the overhand knot. It is a lot easier to undo too.

The exact position of the knot is usually critical. In order to tye it accurately, mark the spectra with a magic marker (the mark may be 6mm wide, but you can still position the mark within 1mm). When the ink dries, the it will produce a slightly stiff portion in the soft Spectra. When you tie the knot, tie it loosely with the mark at position 'X'. As you tighten the knot, the stiffer portion will be disinclined to move from the centre. With practice (and believe me, you'll get plenty), you'll be able to tie the knot quickly, with spot-on precision.

The other knot is known as the bridle knot:

    |   |   |
    \-----\ |
        | | |
      /-|-/ |
      | |   |
That looks a little complex. Let me explain:

First you pass the line over the bar, then end twice round the standing part, then poke the end between the knot and the bar. There is a stopper-knot at the end.

As you tighten the knot, it slips until it stops against the stopper-knot. thus the exact position of the knot can be adjusted by moving the stopper-knot and re-tying.

The bridle jig for the primary bridle is a long zig-zag line. Near each corner of the zig-zag, there is a cross-mark. Fix a smooth nail (I reccommend a plated pin) at each corner of the zig-zag. Tie some 80lb spectra to the pin at the end of the zig-zag and wind it round each pin in turn, till you can tie off on the last pin.

Next, go round the jig with a magic marker (red for the low-power bridle jig and green for the high-power), and mark the Spectra where it passes round each pin, and also where it passes every cross-mark.

To avoid confusion, don't cut yet - cut each line only as you are ready to attatch it to the kite.

The first, shortest line is the A-line for the tip, the next is the B-line for the tip, followed by the tip C-line, tip D-line, then the A-line for the 3rd rib (the 2nd rib isn't bridled), the 3rd B-line etc...

Cut the A-line and B-line from the jig without cutting them from each other (the A-line and B-line are a loop, not individual lines). Now use the bridle-tool to attatch the A-line to the 'A' bridle position on the tip rib.

The bridle tool is a sewing machine needle, threaded with a loop of 80lb Spectra, with a handle. Poke the needle through the skin, over the bridle reinforcement sewn in the rib and back out the skin. Now, take the A-line and poke it into the loop of Spectra. Pulling the bridle tool back out will pull the bridle-line back through the skin and rib. Next, tie a fig-8 knot, centred on the mark near the end of the line, and tie a bridle-knot to secure the A-line. Leave the B-line loose - we can come back to it later.

The next pair on the rig is the c/d pair. Cut it off and attatch it at the C bridle point on the tip. Continue in this fashion to do the rest of that side of the wing.

Having completed one side, we re-load the jig and do the opposite wing. Finaly, you do an extra set of lines for the middle bridle and attatch them.

We now have all the primary bridle-lines attatched for *one* of the bridles (either high power or low power, whichever you chose to do first. We now need to bring out the other bridle-jig and repeat the process for that bridle.

In fact, I lied. I don't do one jig at a time. I do both jigs together, pulling both bridle lines through the skin simultaneously. It was just easier to explain it singly...

Now that we have all of the bridles attatched to the skin, (even if only by one end), we can move away from the bridle-jig to a more comfortable chair to finish off the primary bridle. Each a/b bridle line needs a loop tied at around it's mid-point. There are three marks in the line near this point - one at the middle of the loop (where you fold the line) and two where the knot shall be tied. Use the stiffness of the line at the two knots to tie a figure-8 knot in the doubled line at exactly the right spot. Do this to all the lines.

Next, join the B end of the a/b pairs to the skin. You can pull both the high-power and the low power lines through the same hole, but tie the knots individually, not together. Before tying, ensure that no other lines are tangled round this particular bridle, and check that the lines arn't twisted round each other.

When you've attatched all the primary bridles at both ends and have tied the loops at all of their mid-points, wh're rerady to start of the secondary bridle.

Secondary bridle

The secondary bridle is very simple - it is just an extension to the primary bridle to bring the attatchment point further from the canopy, but using 1 line rather than 4.

The jig for the secondary bridle is similar to the primary, except that each bridle is cut individually, rather than being joined as a pair. On the other hand, the jig includes two of each size, rather than one, so that you can prepare the whole canopy in one session. Note that you will use exactly the same jig for both high-power and low-power bridles (except that you'll mark one in red and the other green...). The secondary bridle is built from 150lb Spectra.

The knot used to join the secondary bridle to the primary bridle is exactly the same as the bridle-knot on the skin. It's just easier because you have a loop to pass the line through, rather than having to poke it through the skin. Each secondary bridle line must go through a loop in and a/b line and a loop in a c/d line. Take care when assembling to ensure that the bridles arn't twisted.

Cross Bridle

The third section of the bridle is the cross-bridle. Again, we have two complete cross-bridles, each constructed from 80lb Spectra. The cross-bridle jig has an unusual lay-out. Down each edge, are a series of points which which will later be brought together to become the main tow-points. Across one end, in an almost random-looking arrangement are the points where the cross-bridle will tie to the secondary bridle. Find the middle point of the points at this end and mark it "15". This is the middle of the crossbridle. The pattern is symetical about this point. Mark the points wither side "13", the next ones "11", and so on down to "3" (The tip-bridles "1" are infact identical to "3").

Locate a plated nail at each of the corners of the cross-bridle jig.

Take a roll of 80lb Spectra and tie it off at one of the points marked "5". The first pin you want to wind round is the pin on the *same* side of the bridle as the "5" pin that you started with. Now continue to follow the pattern, weaving a cats cradle that follows the lines on the jig. Take care, especially near the middle, because some of the nearly parallel lines are closely adjacent. Stop when you finaly reach the opposite pin "5".

Check the jig carefuly to make sure that you got it right, then go round with a magic marker and mark the bridle round the back of each pin. Remember to mark one cross-bridle bridle red and the other green.

Now take some 450lb Spectra and measure 8 arm-spans of it. The actual length is unimportant, but you must now cut it exactly in 4 - Fold it in half to find the middle, cut, then fold in half and cut again. You'll use 2 pieces per cross-bridle. Locate the main tow-point pins in a straghit line down one edge of the cross-bridle. Remove each one in turn, tie a fig-8 knot in the doubled line to make a small loop and without disturbing the jig more than necessary, lace them all together with a length of the 450lb Spectra. When you have finished one side, tie the 450lb Spectra to it'sself to form a loop (don't tie too tightly - you'll be undoing this later...)

When you have the main tow-points sorted, place a block of wood or a fat book across the middle of jig to stop things moving too much. To attatch the crossbridle to the secondary, start at the mid-point of the canopy, select the primary and secondary bridle-set who's colour matches that of the cross-bridle and ensure that it is not entwined with it's partner bridle in the opposite colour. Since this is rib 15, take the cross-bridle at the pin marked 15, make a small loop with a fig-8 knot in this doubled line And attatch the secondary bridle here. Work methodically through the bridle, attatching the cross-bridle to the secondary in this manner, taking care not to disturb and tangle up the cross-bridle before you have attatched it.

When you have attatched one cross-bridle, turn the canopy round, and lay the bridle so that it is *away* from the jig, then build and connect the second cross-bridle to the remaining primary/secondary sets.

Note that you can lay a completed kite on it's back, and pull one cross-bridle top one side and the other cross-bridle to the other side, without any part of one being twisted round the other.

We are still short by 8 tip-bridles. These are individual lines, all the same length. The length is the distance on the jig from point "3" to the earest main tow-point. Make 8 lines marked at that distance, but ensure that they are over-size, because you need to make a loop at each end, with the middle of the loop set at the mark. Remember of course, that half these lines are marked red and the other half are green.

Attatch each bridle to an appropriate tip (or next-to-tip) bridle, and thread it onto the nearest main tow-loop.

The kite is now ready to fly in a minimum configureation. To fly with the kite set to "mid power", simply larks head onto both high-power and low-power bridles at the same time. To increase the power (as you would want to do in light wind, tie an aditional knot in the high-power tow-loops, a couple of inches above the existing one, and larkshead to that instead. To decrease the power, perform the same operation on the low-power tow-loops instead.

That's enough for now. Later, I'll write about:

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