Light and Frost(L&F) obtained a used Flysurf Sonic 2 13 meter kite. The owner stated the kite began folding up in abrupt stall. The kite lines had been tuned but the problem still persisted. This paper will deal with the tuning performed on the line system. L&F has no knowledge on the kites performance, flight characteristics or durability respect other kites of similar design, and we have no issue with Flysurf Products having used them for over 20 years.
Upon receipt of the kite, the outer cloth surface was inspected visually and an internal cursory inspection for obvious damage was done on the internal straps. Nothing was found.
The lines had only very small 1 to 2 cm larks head extensions on only a few of the leading and trailing edge lines (i.e. the "a" and "br" lines on the line plan) . No adjustments were seen on the "b" and "c" hard points or on any branch lines except possibly BR-Main.
This kite as mentioned above was folding up abruptly. Ram-air kites loose their flight performance thru three(3) main factors. The lines shrink, the internal straps stretch, or the kites monocoque structure(ie skin of kite) become porous, reducing the ram air induced internal pressure. Internal strap problems are usually a manufacturing defect in that a thinner skin is used, but the designer does not add stronger internal straps to offset the stretching of the kite length due to thinner skin. This problem is generally rare. Porous skin is not addressed in this paper. There is off course internal damage, but that is case by case and can usually be seen when the kite surface becomes deformed when airborne or inflated. The most likely problem with a Ram-air kite loosing flight performance are the lines.
Restoring the Flight Performance by Adjusting Line Lengths To Factory Settings
Download the Line plan from the manufacturer showing the factory lengths of all lines on the kite. Flysurf has a substantial library available.
Perform a line audit by measuring the existing line length and then compare it to the factory length. Add larks head extensions to each line returning the kite to factory settings.
L&F have done many line audits on ram air kites from several manufacturers, not just Flysurf. L&F has never found a single case of a line stretching. Lines have always been seen to shrink on every kite from Psycho I to Speed III and some other manufacturers that underwent this line audit process. Exceptions here are the two(2) steering lines and two(2) center lines. These lines were never measured against factory lengths. The lines were just balanced by adding larks head kite line extensions to the shorter lines.
Line Shrinkage - Not an Urban Myth
Some say the line shrinkage is caused by fine sand and dried salt absorbed within the lines themselves expanding the line diameter thus shortening the line length. However L&F think there is something else also going on. For example two(2) 7 meter Psycho II kites used maybe three(3) times total and kept in air-conditioned rooms out of the sun in their storage bag were later test flown after a few years. Neither kite would fly, and all the lines had shrunk.
We have seen comments that line shrinkage can be ignored as it is equal across all lines. This is false. Shorter lines have smaller shrinkage while longer lines have greater shrinkage. In general we have found that trailing edge lines have a much higher shrinkage rate then other lines but this is not always the case.
L&F prefer to add larks head line extensions rather then stretch the lines, as stretching is a temporary measure. There seems to be a limit to the shrinkage that can occur. When our Psycho One, Speed I 17 meter and Speed II 15 and 19 meter kites began to become difficult to fly years ago, line audits were conducted. These kites were restored to factory setting with larks head extensions and of course a mixer test conducted when applicable and the kites have flown fine after that with no further problems till present. Note these Psycho One kites are two decades old. Only one(1) line audit was ever performed and the kites were flown within the last weeks just fine.
Adding Larks head Extensions
Tools Required
1. Tape Measure - Suggest a sewing cloth tape measure be used over a metal one.
2. Dacron 100 lb test fishing line for the thin lines
3. Medium line for the thicker lines
4. Kite line for the longer thick lines
5. Knife or Box Cutter
6. Notebook with Factory length and data on the kite
7. Pen or Pencil
8. Lighter
9. Tweezers used to separate larks heads on the kite.
You can use a larks head extension in most cases to extend the length
Making a larks head extension
Measure the difference to adjust then double it and add 7cm for the knot for thin lines and 8-10 cm for thicker lines. Hence on a thin line, if you want to extend the line 5cm then:
5cm X 2 = 10cm + 7cm = 17cm
Fold the line in half and tie the two ends together with an 8 knot or overhand knot at the end so from the knot to the other folded end is 5cm in length. Then burn the ends with a lighter to seal the line ends to prevent fraying
If you have a helper this process can go very quickly. One person measures the line and installs the extensions and the other person keeps track of the larks head lengths required, cuts the lines and makes the larks heads.
Start with a line audit by adding larks head extensions to only the lines attached directly to the hard points of the kite. On the sonic line plan the hard points would be labeled a,b,c and br. The exception is if you are doing a kite where the kite lines are attached directly to the hard point. In that case you have to work up thru the branch lines.
On the Sonic the line shrinkage was small on those lines attached to kite hard points. However the b and c lines were very difficult to remove from the small hard point larks heads installed by the factory. A difficulty in removing the line from the hardpoint larks head attachment almost always indicates that the line is under higher tension. We suspected that the longer branch lines were going to have larger amounts of line shrinkage and this proved to be true.
This line audit of lines attached directly to the hard points can be done in a very small space by rolling up the kite from tip to tip(i.e. do not fold and roll) and then slowly unroll and expose a row of a,b,c,br, then measure and correct the lengths and then continue toward to the next a,b,c, br hard point column working toward the kite center rolling the tip up and unrolling toward the center.
Once the lines attached to the kite have been returned to factory settings, the branch lines must be audited. The kite was taken outdoors, the lines spread out and the branch lines restored. Suggest you only take one line off at a time when possible, especially on short lines. If you take two(2) lines off on the same branch and become confused as to which is which, the shrinkage can make determining the lines by measuring the length impossible on the short lines near the tip. When doing branch lines do one side of the kite completely and then the other so you always have an example of how the lines are arranged on your kite.
Finally a mixer test is performed
Initial Conclusions
Long thin high aspect ratio kites are probably more sensitive to line shrinkage then lower aspect models and will tend to stall more abruptly then a lower aspect kite. Lower aspect kites tend to become sluggish and require more wind to function as lines shrink.
The longer A1-A6,B1-B6,C1-C6,BR1-BR6 and all the I lines i.e. AI thru BRIII showed extensive line shrinkage. Racers looking for that extra edge should carefully monitor the line lengths especially in these lines.
The kite was taken out for its initial test flight. The kite flew up from dead downwind quite easily in 3-4 knots of wind but the tip area on the right side a12 thru a9 was deformed and the kite tended to tip stall and fold during turns. It was expected the lines were either installed incorrectly, or not extended properly as the left side flew perfectly. An inspection was conducted on all right side lines for hard point stations 12,11,10 and 9 lines. Sure enough during installation one set of lines c10,C9, and C5 were installed improperly. The next day the kite was again air tested and the kite flew just fine. 30 minutes of flight time was conducted to set all the larks head knots in place.
As the kite was put down a hydrofoil racer flying a large ram-air kite came in. During conversation it was pointed out to him that the lines on these ram-airs tended to shrink over time and suggested he walk over and look at the amount of kite line shrinkage on the Sonic lying 30 meters away from him. He said "how can that be!?!" indicating that was impossible then abruptly turned and walked away?
The data on the Sonic showing you line shrinkage is provided as a text attachment due to the length of the document.