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.
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).
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.
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 iFor 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'clockHere 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 <email@example.com> generated a online Java Script Bridle Line Calculator.
|Bridle Line Lengths (cm, by clock face position)|
|Size(m)||12||11 , 1||10 , 2||9 , 3||8 , 4||7 , 5||6|
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.
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.
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.
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.
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.
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.
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.
``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.
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.
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.
______ _______ \ Leading __ _/ ####### \_ ___ Edge -----^-------------^------ ---> Washer Pocket
You can fumble them in, but they don't fall out again without much persuasion.
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.
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.
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.
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.
Remember a circoflex is a light wind sea breese kite. Medium and strong winds tend to be too much for them :-( 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!
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.
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 <firstname.lastname@example.org> 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.
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.
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.
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.
Note that it is normal for the kite to lean backward slightly when flying is flying correctly.
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.
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.
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.