[photo]
Circoflex Hints and Tips

up Back to Circoflexi Information

ASIDE: The following is never complete, progress usally achieved by people mailing me, which gets me back into thinking about tetras, and thus adding even more information to these pages. So the more people mail me with questions, information, or their experiences, the better the page gets.

Contents

Sail Cloth
Bridle Lines
Spars
Counter Weights
Leech Line
Transport
Flying Problems


Sail Cloth

Mylar...
See the mylar page of Kite Hints and Tips
Ripstop...
Ripstop is also a good material and provided the means for creating a pocket for a removable spar. It is also great for fancy designs and applique. It is heavier and more expensive (100 times more) than mylar but much more durable and open to different construction techniques. It is however a lot heavier than mylar.

Tyvek...
Tyvek is in my thinking rather heavy for a circoflex, however I have had an email from Patrick Mann <patrick.mann@bigfoot.com> who has built a 7.5 meter circoflex with tyvek. It is also quite cheap.

Polyimide, Kapton, `Space Blanket' material...
This is basically the same as Mylar but is much more wearing (the silver will NOT rub off with wear), and is more rip-resistant. It is sold in the form of "Space Blankets", and is often (not always) gold on one side and silver on the other.
Know your material
Be sure you understand how to work with the material, be it ripstop or mylar, or something else. The more experience you have with working it the better the kite you can build. Practice on scraps before trying something different on a new kite design. See the general Kite Hints and Tips page for more detail of the above materials.

Width of the kite ring...
The width of the sail is not critical. Actually, for stability the suggested ring width is not thick enough. But for efficiency it isn't thin enough. The thickness of the ring is more for 'looks' than any particular formula.

Because of this, and the way mylar rips, I generally avoid cutting mylar for a circoflex, using the whole width of the roll (60cm or so) no matter what the size of the circoflex being built (7 meter to 12 meter).

Bridles

Bridle Point and Line Lengths...
The calculation of bridle lines is fairly straight forward. Basically it is the distance between the appropriate point on the edge of the circoflex ring to a single bridle point in front (above) the ring.

This point is always (in all plans so far) directly above (in front of) a point halfway between the centre and the 6 o'clock position. The distance of the bridle point from the plane of the ring however varies from plan to plan and the size of the circoflex. Typically it looks like this distance is about 1/4 of the rings radius. Though it does not seem to be very critical to the kites success.

Bridle Line Calculator...
The following `pseudo program' can be used to calculate the bridle lengths needed. Just code in your favourite computer language. The current settings was for a smaller mini-circoflex I was building at the time.

Curtsey of Bruno Diviacco <Bruno.Diviacco@elettra.trieste.it>.

    
    # Kite size -- figures for a specific 3 meter mini-circoflex
    c=306           # circumference (all measures in cm)
    h=25            # height of the towing point in-front of ring.
    f=3/4           # displacement of bridle point (3/4 from centre)
    ndiv=8          # number of bridle lines

    # For a normal circoflex (10 meters such as table above) use
    #  c=1000   h=30  f=1/2  ndiv=12

    PI=3.1415       # PI
    r=c/2/PI        # radius
    d=f*r
    nlen=ndiv/2+1   # number of bridle measurements needed

    for i = 0  to  nlen-1
      a=PI*(1-2*i/ndiv)                          # angle (in radians)
      len=sqr( r*r + d*d - 2*r*d*cos(a) + h*h )  # Length
      print i,len
    next i

    
For Example, the output (for Mini-Circoflex_306 the above program was set for) results in...
    
       0     88.8         # 12 O'clock
       1     82.7
       2     65.8         # 3/9 O'clock
       3     42.6
       4     27.8         # 6 O'clock
    
Here is a Perl Version, I built from the above algorithm. It will output the information, nicely formated and with `clock' numbers if the bridle position matches up. You will have to edit it to set the settings, and I haven't converted it into a web form, for you to use directly. Sorry.

Andrew Wells <AndrewWe@AdvantageGroup.co.nz> converted the above formula into an Excel Spreadsheet. Plug in the values into the yellow cells and read the bridle lengths below.

Alex Menzies <happyalex198@gmail.com> generated a online Java Script Bridle Line Calculator.

Bridle Line Table...
The following table contain the bridle lengths from the original articals, and what I used for my prototype. This was used before the above calculators were developed.
Bridle Line Lengths (cm, by clock face position)
Size(m) 12 11 , 110 , 2 9 , 3 8 , 4 7 , 5 6
7 + 169.0 164.0 150.0 127.0 99.7 73.4 61.1
7.5 * 172 167 153 133 108 75 58
7.5 * 181.5 176.2 160.7 136.8 107.6 79.8 66.8
9 216.9 210.5 191.8 162.9 127.6 93.7 77.6
10 * 240.6 233.5 212.7 180.5 141.1 103.1 85.0
12 288.6 280.0 255.1 216.4 169.1 123.4 101.7
12 290.0 281.4 256.6 218.2 171.4 126.6 105.6
12 ** 337.2 326.2 293.9 242.9 177.9 107.9 65.6
All measurments are in the metric system, bridle lengths in centimeters (NB: 2.56 cm/inch if you want to convert).
+ My prototype circoflex was this size, using 2 x 2mm fibreglass rods
* Measurements from magizine articles of original plan
** Bridle point moved down to 3/4 disance from center (see below)

In the original plan the upper 7 bridle lines and the lower 5 lines are usually attached to two separate rings. These rings are then separated by a short length of line (10-20cm) to allow for ``tow point adjustment''. I have however not found any need for this separation or adjustment. See below for the two bridle ring methods I use.

Bridle Point for Mini-Circoflexi (less than 5 meters)
While building mini-circoflexi, I tried use use the same bridle point position as for the larger circoflexi. However positioning the bridle point half way between the center and the lower edge, just seems to cause no end of problems. The main ones being

  • If I put the bridle point at about 8 cm in front of the leading edge ring as would be required for a 1/2 mark, to keep it proportional, just seemed to be too close, causing a wind gust to suddenly pull the ring into a tangled pretzel shape. A point further out did not have this problem.

  • If I just moved the bridle point outward to solve the above problem, the kite did not get enough lift, and/or the ballast weight caused the kite to tip the kite just that little too much backward.

The solution was to not only move the bridle point outward, relative to the normal sized circoflex, but move it downward as well. This meant the weight balance was still fine, and the bridle point was not `too close' to the spar ring (See the flying problems below, and bridle line calculator).

The bridle point on a 4 meter mini-circo is thus, 25cm out from the ring, and 3/4 the radial distance offset from the center point (instead of 1/2). This works well, and I have never needed to adjust it for any mini-circo between 3 and 5 meters circunference.

As a bonus the mini's fly at a much higher angle, than the larger ones! Flying at a 60 degree flying angle instead of the 40 to 45 of the `normal' sized circoflexi.

This bridle change might be usable for the larger circoflex, but I found the mini-circos easier to build, transport and just more usable, in general. As such it may be some time before I can try out this bridle on the large models. It may be that the lesser "spring", and more off center bridle may be too much for full sized rings.

Three Ring Bridle Arrangement... [photo]
To keep the bridle lines neat, I larks head the 7 upper bridle line to a small solid (no gaps) brass ring, and the 5 lower lines to second brass ring. I don't bother with a 10-20cm line between the two rings (as given in the original plan), but instead use a split ring to link the two small brass rings directly together (like a chain).

This split ring is in a vertical arrangement, which makes it very nice to clip my flying line to directly (using a fishing swivel clip or snap). This arrangement ensures than the fan-out of bridle lines is neat-n-tidy when flying, and does not tangle easily in storage.

Single Ring Bridle Arrangement...
If you only wish to use one solid (no gaps) brass ring for all the bridle lines, (as I use with my mini-circoflexi), I attach the lines around the ring, alternating from side to side. That is if I started at the top with a 12 line circo, the lines are attached around the ring in the following order...
12 o'clock, 1, 11, 2, 10, 3, 9, 4, 8, 5, 7, and lastly 6 o'clock.

This weird side to side ordering means that the ring will naturally want to sit vertically. Thus making it simple to attach a flying line to the ring between the top (12) and the bottom (6) bridle lines. All the bridle lines will also still fan out neatly from the ring, neatly.

Pigtail Bridle Attachment...
To allow a bridle line to be removable (for replacement and adjustments) I recommend the larks head and `pigtail' approach...
[photo]

Method...

First I add `pigtails' (short lengths of line with a `stopper knot' on the end) to each of the bridle points on the main (only) spar. The length of the pigtail does not matter as it will be measured when measuring the full length of the bridle line.

Then tying a loop in the end of the line coming from the roll, I larks head that to the pigtail.

I measure out the line from the main spar (including the pigtail) of the appropriate length + a small amount to take care of the line used up in a final knot and larks head (+1 cm for the line I use).

I fold the line at the measured point, and tie another over hand loop to create a loop at that end. I now cut the bridle line (melt cut with a lighter) from the rest of the roll.

I take the line off the pigtail (undoing the larks head) and thread it through the appropriate brass bridle ring. I then thread one end through the loop of the other end of the line and pull it tight to larks head it to the brass ring. The loose end is then re-larks headed back on to the same pigtail.

Repeat for all the other bridle lines.

Why...

This arrangement means that by reversing the process the bridle line is very easily removed for replacement. Or in one case swap two bridle lines I attached to the wrong places on the clock face. In fact this arrangement means you could very easily replace ALL the bridle lines to try out different bridle point heights from the leading edge plain, or other positions. Though it is tedious, but easier than untying it all.

Spars
Spar Pockets...
Be generous with mylar spar pocket!

I have had a lot of mylar circoflexi fail simply because I made the spar pocket fold along the leading edge too small. If it is too small the spar and mylar in time starts to stick to each other. Also during the folding up for transport (see below) a small spar pocket may allow the spar to contact the double sided tape closing the mylar pocket.

As such be generous! If the spar is 4mm thick ensure at least 1.5cm of material is folded over the spar to keep it free.

The problem with a mylar kite is that once the spar is sealed inside a spar pocket you can't really unseal it easily without destroying the kite, even when you are being very very carful. The smallest mishap and a rip will zip across the kite. It has happened to me twice and is not a enjoyable experience.

This is of course NOT a problem with ripstop circoflex. For other ways of adding a ripstop spar pocket to a mylar circoflex see my page on Mylar Circoflex Construction Notes. [photo]

One spar sleeve constructions was offered by Leong Ceewan <ceewan@pc.jaring.my> in the form of a Double Sleeve


Counter Weights
Ballast Weight placement...
The English plan says...
``The weight should be spread evenly over 30-35cm inside the bottom of the kite in the middle of the hours 5 to 7, some 8 to 10cm before the end seam. ''

This is a bit confusing, so I will try to explain.

Basically the weights should be spread along a line starting at the 5 o'clock mark, past the 6 o'clock point (bottom of kite) to the 7 o'clock mark on the other side. This is NOT critical, I myself have often don't apply weights over the full length of this line, just evenly to both sides of the kite along it.

The line of weights is 8-10 cm in from the trailing edge. That is it is in the `hollow' of the kite material formed by the `leech line' in the trailing edge. In this position the weights are NOT visible from the ground except possibly as a shadow through light coloured ripstop, or plastic. Not a problem with silver mylar or dark (EG: black) ripstop.

One thing that I do do is that while I spread out the weight along this 5 to 7 o'clock line, I put more weight round the 6 o'clock mark and thin out the weight toward the ends of the line. This seems to make the kite roll slightly less and you don't get a sudden boundary between the weighted sail and un-weighted sail.

Amount of weight to add...
For my 12 meter circoflex I use 13 iron washers (as used for nuts and bolts). For a 4 meter mini-circoflex I use 4 of these. You could say the weight required is about a washer per meter!

Their are big differences in the number of weights from kite to kite, and plan to plan so the above is only a guide. Basically is the kite is made of a heavy material you need a heavy weight to put more weight below the bridle point than above it. It also depends on how heavy the individual weights are, the smaller they are, the more you need, but the more you can distribute the weight around the bottom of the kite.

Weights should be at the back, not the front...
Putting the weights near the back or trailing edge of the kite (spread out as much as possible around the bottom of the ring) means they sit in the hollow made in the fabric by the leach line, helping to hide them from sight. Also at the back they help the kite to lean backward.

If placed at the front they could cause the kite to do into a forward dive from which their is no recovery.

Also I think putting more weights at the very bottom 6 o'clock mark (IE: a denser distribution of weight) will help the kite stabilise more, with the more distributed weights to either side spreads the load, and stops the kite distorting from one big lump.

For an example of this see Paul and Irma Kings email, about their experience with a very heavy first circoflex.

Pockets for weights...
Mike Jones <michaelj@wt.net> in Rec.Kites, suggests...
The way I did it was to sew the pocket for putting the coins/washers in like so..

              ______
            _______ \            Leading
       __ _/ ####### \_ ___       Edge
    -----^-------------^------     --->
                    Washer Pocket
    
Basically it's two strips of fabric sewed around the circumference at the appropriate offset from the trailing edge, overlapping each other enough so that when the length of the fabric strips is segmented every few centimetres with another seam, it makes a row of pockets where weights don't fall out of.

You can fumble them in, but they don't fall out again without much persuasion.

Leech Line
What is it...
The leech line is a line that is sewn or threaded into a pocket along the trailing edge of a kite. It is shortened by a very small amount from the rings circumference, so as to restrict the flow of wind very very very slightly. This increases the pressure on the inside of the ring a little and stops the sail flapping like a flag. It also provides a very very small amount of drag to the kite preventing it gliding forward and then into a dive.

The leech line I have found must only be minimally shorter than the real circumference of the circoflex. Just enough to `fluff' out the ring (stopping any wind ripples) and no more. Any more just produces drag and stops the kite flying as high as it should.

The smaller the circoflex the less shortening is needed. In some of the mini-circo's I have built I only use the leech line to `wrinkle' and `pucker' the sail, after that the leech line was left loose, with the ends sticking out, for future adjustments and the sail softens over time from use.

The only case I have for more leech line is for when the wind dies suddenly and the circoflex is too high. The weight of the flying line in this case may pull your kite into a forward dive. More drag is needed to stop the kite getting too high to prevent this from happening. Though it is probably more of a case of just not being a good day to fly circo's.

Making Leech line gather evenly spread
To make the gather even when building, I do the following BEFORE inserting the main spar. I tie the two ends of the leech line together too long so the ends aren't lost Then pull as much leach line (both lines) out of the kite, gathering the whole trailing edge on as small a section of leech line as possible!

This puts lots of little folds and creases into the trailing edge, making the gather the same over the whole trailing edge. In fact in my smaller mini-circos this creasing is often enough to do the job leaving the leech line just loose in the pocket.

After that spread out the sail again but I DO NOT reduce the line at all. The main spar can now be inserted (and if desired, sealed) into the leading edge of the ring.

The leech line is left like that (too long) until after or during the first flight. It is then reduced as needed, a couple of centimeters at a time, to avoid too much of the kite sail flapping at sides and top. The bottom most sail often flaps until the kite settles into normal flight, so ignore that for adjustments.

If the kite rolls to one side all the time the leech line gather is not even. Too much gather on the side toward which the kite rolls.

emiel <miel@tref.nl> suggested in the Rec.Kites newsgroup...
Sew the rear leech line at 12 o'clock to the fabric!

If you do this, you can shorten each halve of the cord independently and therefor make corrections to make it fly good.

However I also fine that the adjustments for each side can be tedious, and the knot joining the leech line ends can dissappear into the leech line pocket.

Transport

Folding into three for transport..
A circoflex will fold without twists into three. Experiment with a thick rubber-band and you will see what I mean very quickly. Of course somehow removing the spar all together is even better!

See The Mini-Circoflex Plan for one method of folding a circoflex into three.

WARNING: Be careful that you fold it the right way or you could really twist the spar, which in fibreglass can cause it to fracture and splinter.

Sail Join for Transport [diagram]
Bruno Diviacco <diviacco@elettra.trieste.it> on 2rd of December, 1998 wrote...
Sail is made in one long strip, and Velcro is used to ring-shape it; this makes spar insertion/removal really easy when open flat, and adds some balancing weight at the bottom. The trailing edge leach line ends come out at the bottom, tensioning being obtained by a spring clip which also adds some weight at the rear of the kite.

Flying Problems

Kite immediately collapses...
The kite just collapses in a heap when a wind gust hits it or gets a bit stronger, then the spar is probably not rigid enough for the close in bridle point OR the wind is too strong, or turbulent.

Remember a circoflex is a light wind sea breese kite. Medium and strong winds tend to be too much for them :-( [photo] My mini-circoflexi however while smaller can handle a medium (but steady) breeze, unlike my full sized mylar circo.

If the wind is light but you still have problems, then your spars are just not ridged enough to spread the load from the bridle lines along the sail.

My first prototype used 2mm spar in a 7 meter circoflex, far too small. This resulted in consistent pretzel shape heaps (see photo). I solved the problem by added two more 2mm spars around the kite, taped to the outside of the kite as I couldn't get in in the spar pocket!

One side always seems to collapse... [photo]
The trailing edge may be uneven. This basically improves with time and possibly more spreading of the sail along the trailing edge leech line. It maybe also be that the spar is just not ridged enough (see above).

I do see this problem on my larger working circoflexi, and pulling the edges back in position or letting the flying line go completely loose, lets the spar spring back out into a proper circle shape.

Rolls or loops to one side only...
If the kite likes to suddenly roll to the same side when a gust of wind hits it, or continually leans in a strong wind but straightens up when the line is released a bit, or wind drops slightly, then the leach line is uneven from one side to the other. This is pushing the kite over, due to increased drag on one side.

On the side to which it rolls, stretch out the leach line gather a bit, moving it round to the other side. Test, then repeat until it flies straight.

Emiel <miel@tref.nl> suggested, that you sew the rear leech line at 12 o'clock to the fabric! If you do this, you can shorten each halve of the cord independentally and therefor make corrections until the problem is fixed.

Other less likely causes of sideways flying is: uneven sail stretch or sewn seams, or even uneven bend in the leading edge spar. The better and more even the kite construction is the less likely sideways flying becomes a problem, particularly in moderate winds.

A roll to one side can also be caused by the wind being less strong on that side due to a wind shadow from tree or tent. In fact getting a circoflex up out of a strong wind shadow is very difficult.

Goes up fast, then comes down doing loops...
Generally this is cause by either very large one-side drag problems (see above), a very bad bridle point (such as a large circo bridle point on a mini-circoflex), or the wind is just too strong or too turbulent (wind is more than the circoflex can handle).

Remember a circoflex is a LIGHT wind kite. Unless you are very lucky they will not stand up to moderate to strong winds. Large circoflex wind limits is determined by the spar collapsing from wind pressure into multiple loops. But small mini-circos (less than 7 meters circumference) usually has a really springy spar due to its size.

As such a high wind limit in smaller circo's is the result of this `looping' behavour. The better the kite was made the less chance this is a problem. NOTE: I still get this problem on occasion, a couple of time it was unresolved.

Rolls back and forth to either side...
Simply not enough ballast weight has been added between the 5 to 7 o'clock marks, just inside the trailing edge. Add more (See weight notes above).

In a lighter winds you may like to remove some of this `extra ballast' to lighten the kite, it will roll more but should fly better in lighter winds.

"Nose" dives forward when wind drops...
When the wind dies the elastic stretch of the flying line and its weight pulls the kite forward and downward. The top edge then over flies and the whole kite `nose' (not that a ring has a nose!) dives.

Use a lighter, less stretchy flying line (try braided dacron, instead of springy nylon). In strong turbulent winds more ballast will also stop the top edge over-flying, but it will also make the kite heavier.

Once a circoflex has started a dive the weight of the leading edge spar will keep it in a dive, straight down to the ground. The result is sort of a slow motion ringed parachute. Rather pretty, especially if it isn't your kite!

If you are very fast, you can pull the kite line HARD, to bring the lower edge back under the top edge. Then as the kite rises, you can again let out that line again. This is one case where pulling the line on a diving kite is a good thing to do. Most other kites require the opposite behaviour to stop the dive.

It is for this reason that it is not recommended you fly the kite out over water. If it `nose' dives, the kite will probably end up on the bottom of the lake (or whatever), and if the bridle tangles with bottom junk, or a current is present, you might as well say goodbye to it.

Top collapses backward...
This is the opposite of the last on (nose dives). Now you probably have too much ballast weight for the wind conditions. As such weight is pulling the kite to far backward. Also may mean the kite spar is not springy enough, but this is not a good indicator for that problem.

Note that it is normal for the kite to lean backward slightly when flying is flying correctly.

Flies with a low flying line angle (less than 30 degrees)
The bridle point it too far out in front of the leading edge. This means you need to re-calculate and re-bridle all twelve (or however many) bridle lines.

OR more likely...
You have tightened the leech line far too much, so it is producing a lot of drag. Very common for someone's first circoflex kite. It is a lot easier to over do the leech line than not enough.

Leans so far back it collapses...
That is when you let the ring go to fly up in a good wind, the kite leans too far back in the wind. Note this is different to ``Top collapses backward'' point above, The Top is not collapsing, the whole kite just leans too far back.

The problem is that the bridle point is to close to the leading edge ring plain, so that the kite even in a good wind just leans too far back, to fly properly.

The solution is the same as the last, re-calculate and re-bridle all the bridle lines, this time moving the bridle point away from leading edge ring plain.

NOTE: Once the bridle point is roughly correct it does NOT require adjustment for different winds, thank the powers that be. The ballast however may need some change for ultra light to medium wind changes.

Oscillations...
Oscillations are tricky. Generally it means that the kite is close to the limit of the winds that it can handle.

Factors include:-

  • spar stiffness
    the more stiff a spar is, the higher the wind it can handle.

  • The amount you shortened the leech line.
    If you shortened the leech line too much the drag increases to the detriment of the kite. It needs only be enough to allow the fabric to `fluff out' and not flap, which is not very much at all.

  • The spar length relative to the sail material.
    I have found that with mylar, the material doesn't stretch much, so the spar should exactly match the material length.

    But with ripstop which stretches a little (depending on humidity) I like to add 2cm or so to the length of a spar in a mini-circoflex (4 meter circoflex), otherwise I find the material could get too loose on a damp day. That little extra also help ensure all the spars don't slip out of their ferules.


Created: 10 August 2000
Updated: 14 September 2004
Author: Anthony Thyssen, <A.Thyssen@griffith.edu.au>