SSSL Boomers

SSSL Development from Chongqing, from 4 April'14

Reprise:

SSSL 3 was reasonably promising but none of the attempts from then until SSSL13 were very hopeful (some did fly OK in smooth mid range wind).  SSSL4 to SSSL12 were all pure sleds of one form or another (no central keel).

Some observations so far:

1. Using a lower leading edge seem to enable lower A of A without LE collapse- but SSSL19 green?

2. It appears that pure sleds become too wide at rear, tapering in LE then causes collapse.

3. Or, is the unsupported LE the problem- consider Robert vW's.

4. Supporting the LE in centre span (tried on some of the sleds) causes luffing at higher apparent winds.

5. For SSSL13 to SSSL19, left/ right tuning is very responsive to "c" sides.

6. Not having taper-in at the LE (in plan view), seems to be critical to prevent tip collapse.

7. LE collapse always occurs at tips first- so far- even for SSSL's with extra centre panel camber near LE.

8. Later SSSL series are least stally when central keel bridles are at low A of A- but the keel then flaps.

9. Reducing the keel A of A causes the rear part to narrow- offsetting the A of A effect.

10. SSSL16 (shallow central keel) was clearly less stable than any of the series with deep keels.

11. There doesn't seem to be any stability disadvantage in the central keel being shallower towards the LE.

12. SSSL19's lack of a lower LE (it has the arch section pieces) doesn't appear to have reduced LE stability.

13.Has SSSL 19's centre panel forward camber helped extend the lower end range?- appears to have so far.

14.Tails don't seem to help light wind stability at all- but maybe would in conjunction with reduced A of A.

15.Up to SSSL 19, recovery from dives is very slow- a function of Cof P being very close to C of G?

16. What causes light wind /low line angle tip-overs?- is it fundamentally C of P falling below the C of G?

17. 4th April Chongqing, SSSL19 (purple) eventually flew reasonably in light conditions; down after 9sq.m Pilot. 

18. Low pull and line angle though;- would SSSL 18 (different keel camber) have been better?   

After Chonquing

20 was cloned from 19, no significant changes (was it light weight fabric?), given to Orlando in Uiseong Korea (April'14?) to see what he can make of them.

 21(green) had minor changes from 19, but no lower leading edge. 

Quite a bit of testing, but has not yet (October '14) flown as well as 19, which does have a lower leading edge- for now this has to be assumed to be significant.

At Uchinada  (May '14) 19 flew well as a pilot above a Ray +- was really excellent, steady, better angle than any of the pilots and much more pull relative to its size- pretty much the same as a 9sq.m Airbanners.

This is hopefully a harbinger of what may be possible from the SSSL approach but at Uchinada there was a soft steady sea breeze- just enough to keep above 19's stall point, not so much as to cause LE collapse on that bridle setting- (above about 30km/hr).  When the wind dropped, the 9sq.m Airbanners and 19 came down at about the same time- though I strongly suspect that the 9sq.m has a generally lower light wind threshold than 19- because the SSSl's weak point currently is their inability to recover from a stall.

After this sequence of events, tried a 3 cell with higher aspect ratio- 22 (red),

22 also went to 3 bridles per cell- 12 total  (earlier series are all 4/cell, 12 total) tested at Wakanui  in Sept, initially with chronic outside LE collapse.  Sewing in a pleat to choke A side flares by 50mm was a substantial cure for this.

Taiwan (Sept '14). 22: Appeared to be much more stable off the launch than lower AR SSSLs- goes straight every time, not as loopy at high angles of attack as the lower AR versions, but also had an edging type behavior- would not stay at the appex for long, would always evntually fly off to one side or the other and crash- maybe a bit less inclined to do this in stronger wind than light.  22 also appears to have a creasing problem on the outer cells especially at B, from point bridle loads- a consequence of  having just 3/side- but maybe also because B flare is too small (B outers are out about 75mm further than A and C).  Just before Taiwan, sewed out pleats beside the outer flares to reduce overall camber.  Unfortunately I accidentally made one of these adjacent to the centre cell instead, so consequently 22 did not get a good test in Taiwan. After unpicking both these pleats it didn't seem to fly as well- suggesting that less camber is indeed the right direction.  It did still fly in mid range winds, still inclined to edging though.  Took 21 (no lower leading edge) to Taiwan also- wouldn't fly very well, I expect not nearly as well as 19 would have there, even after some bridle changing.

19 was in Mongolia with Craig and Gavin as a pilot while I was in Taiwan - did they use it?

After Taiwan, re-cut the outer panels on 22 to make the tip choke more accurate- and sewed pleats in the outer cells adjacent to the centre flares to generally reduce camber.  Wakanui test looked promising- definitely holds its form well now, quite resistant to tip collapse, but still edges.   

Shenzhen October '14, very light wind

19 (purple) wouldn't stay up- stalled and collapsed, neither would  22 (red) for any length of time- would appex then eventually dive off to one side or the other with a serious crease at B outer.  At a school demo, we could tow launch and run 19 around- definitely more inclined to ground loops than 22 is on launching, but does stay in the middle while flying

Weifang , Nov 2 '14

1. Is 22's edging behaviour an aspect ratio effect (super stability) or is it just point bridle load at B outer?- make B outer flares larger and re-test at Xiamen.

2. Choking the tip panels by 50mm over 250mm (approx 1m chord) definely reduces wingtip collapse.

3. Tapering off the lower leading edge to the flares at the tips and in the centre seems to have worked well- doesn't seem to reduce the effectiveness, provides access for sewing on the bridle without a lot of stuffing around.

4. It's tempting to try an Arc style SS- flat choked centre panel, 2 long flares per side (so that  A of A can be changed, but I'm anticipating that if such a kite stalled it would not easily re-inflate- would hand clap like ram air arcs only maybe worse because of having no structure to initialise the opening.

5. Flat multi cell fully bridled SS's after the style of Michel's 4 line SS traction kites seem to be able to fly at lower A of A's without stalling or collapsing than the Skin style.  Maybe the significant measure of A of A is a line from the stagnation point at the LE through to the trailing edge- and using bent down TE's as the Skin and current SSSL's both do may not allow a lower A of A - but just moves the overall C of P rearward, puting it closer to the C of G and maybe exacerbating instability approaching the stall. 

6. The current inability of SSSL's to recover from stalls may be just that when they fall backwards, one side rear collapses preferentially causing the kite to tip to that side even to 90degrees or more- from which re-inflation and recovery is impossible in the very light conditions that there must have been to cause the stall in the first place. Could also be just that the cambered down TE tips them over backwards.

7. But is there any soluton to this except just reducing the stall speed?  What if the outer rear flares were made with reverse choke?- though this would also cause them to push in when flying normally- but maybe there's enough pressure back there to resist this, at least so as this wouldn't cause collapse. Or what if the SSSL could be caused to drift back with reducing A of A (that is, glide back) rather than at increasing A of A as now (which is a caused by a combination of long bridles and TE camber?)

8.  Try a flat, hour glass shaped, AR 0.75  (19's AR seems to be too low for best stability and recovery, but 22's is too high?), multi cell 5 bridle/cell SSSL with no TE pull down and a 10% (+/-) lower leading edge.

Say 7 cells (8 sets of bridles spanwise), Flares 60degrees included angle or even a bit more tapered?

9.Flare choke could be applied by adjustable cords between the rear edges of the outer A flares- and this might also have a useful feedback function in stability- choking the side with the least bridle load on it (bridle tension decreases on the LE bridle as that tip begins to collapse)  his could also work for the rear flares reverse choke- would this cause the rear to narrow or collapse?.

10. Another approach might be to make in the form of a laterally symmetrical trapezium,  narrow LE, with a row of flares down each side, all angled so as to pull outwards- maybe the front flares could have more choke than the rearward.  This shortens the leading edge a lot and maybe would work with bridles only to the side flares- try 4/side to start with- and overlapping.

11. Another approach; try making from a single sheet with folded over LE like the centre section of a NASA, bridled to each tie, 4 (?) side flares all bridlesd and many centre bridles directly to the skin- sew on cording for attachment points.

Weifang, November 3 '14;

Made; 23 green: 7 cell, parallel sides, with matching convex LE, concave TE to maintain equal chord,  1.2m span (nominal), 1.3m chord, 4 bridles/cell, 32 bridle total, about 5% lower leading edge with 6mm x 2 of pleat per cell to match bridle camber.  All cells spanwise are to have equal bridle lengths in 3 cascading sets.  Concern is whether LE tips will hold form without choke- but the outer cell sweepback is around 45 degrees, so this will be a test of how much sweepback contributes to tip stability in the absence of choke.

It has no camber at all as cut- completely flat skin LE to TE.

First pull up test at workshop door, appeared to fly OK on first (guessed) bridle dimensions, which are very forward. No noticeable tip or LE collapsing.  

Weifang, Nov 4 '14:

Made 24 yellow: 7 cells spanwise, semi circular shape (curved leading edge) 24 cascaded bridles (spanwise rows of 4, 4, 6, 8), approx 5% lower LE, but this tapers to no leading edge in each outer cell (LE in this cell is very swept back.  approx 1.3 m span, 1.3m chord, perhaps AR 1.2.   There is around 5 degrees choke in every cell. As for 23, no camber at all as cut- but 2x6mm pleats in the centre 5 cells to accommodate arch.

The thinking behind this design is that if sweepback does prove beneficial, this is the type of shape that will be used.  Their difficulty is that the rib to panel connections at the high sweepback sections are difficult to shape right so as not to wrinkle- and difficult to sew( the more the sweepback the trickier this is).  Maybe making the LE of individual spanwise strips like for the 19 would make this easier- maybe only necessary for the outer more swept back cells.

24 was also bridled very far forward for first pull up test outside factory door.  Appears to fly, no LE or tip collapse apparent, but has major wrinkling the 3rd rib LE each side caused at least in part by having paired 3A and 3B bridles; should have used only spanwise pairing..

Xiamen 2014-11-07

Strongish wind off the sea- 30km/hr.

23 green;:leading edge smooth and completely solid (seems fairly forward bridled too).

Trailing edge (actually the rear 25% of the kite)  loose and flapping-and pulling in the 4th row even to stalling didn't stop this- why?- not enough (or even negative) chordwise camber which will need to be corrected by letting B's and C's out, not by shortening D's?

 Flying off the bridles, seemed to be a bit volatile.

Quite a bit of pull- but I'd say nothing near as much as 19 would have had in this wind- but very much doubt that  19 would have flown- or that its LE would have stayed solid.- check this.

24 yellow: LE solid but notchy, and sides need an arch pleat- very loose.

TE is solid too- doesn't flap at all like 23-  the skin does seem more cambered  than 23.

Flying off the bridles was towards superstability- or is it ROI (roll over instability)- and noticeably right wing (bridlings on 23 and 24 are still the fairly random first guesses from Weifang.     

Directions; Need to test now in very light winds- check if stall collapses are a problem. With these designs also.

Generally 23 and 24 are a breakthrough.  Still to be determined: Best- or at least functional-combination of :  lower LE, LE being deeeper, having ribs closer together, and less camber?  There doesn't now seem to be much doubt that SSSLs will be successful kites.

The next 'pilot" version could be some combination of 23 and 24 maybe- 23 with higher AR or 24 with slightly lower AR and the LE panels shaped better. 24 has the virtue of only 24 bridles (32 for 23). Could try releasing the D bridles on 23- and if it flies OK (will need to shorten A's a bit to compensate for C of P shift) then try cutting the rear ¼ off.  This increaseas the AR, and reduces  bridles to 24.

And make a new test kite in the shape of a Ray's wing; could standardise on shallow ribs , making bias cut strips, slight scalloping, bridles at about half the current spacing and say 4 or so different depths, which could then be used for the different chords required on show kite wings.  The primary bridle set could be in chordwise sets , all the same length (perhaps the LE bridles should be singles).  Strips like this would probably have a better appearance than the current triangular flares. There might be some possibility of just using close spaced bridles, no ribs at all- like NASA 'spines'.

Xiamen 7 Nov '14.

Very light to no wind.

23 does seem like it will fly without the rear quarter- all D flares. With D's released rear was still not very solid. LE and shoulders are very solid though- better than 24 whaich has excellent centre but creased and collapsing shoulders.  Did play around with 24 extensively- flattening off to see how far forward it can go.  It's a lot, especially when D's are released until just short of getting a crease towards the front of the D flares. If the LE is pulled down too far it dives off to one side or the other irretrievably sometimes- presumably because one shoulder or the other is collapsng more (has this appearance).  With the flattest profile it will accept without creases (perhaps 50mm to 100mm camber chordwise and at the most forward bridling it will fly without too much narrowing of the LE spanwise or indenting. It's just volatile unstable in the lightest wind it will fly in but steadies up if there's 10% more.  With a V tail, was quite reliable.  It would fly in wind as light as the latest 9sq.m Airbanners but only when continually pumped.

Tried taking a duct tape 2 x 15mm arching pleat from the shoulders- did improve appearance but didn't by itself reduce preferential shoulder creasing. It recovers well from lulls- drops back, sometimes turns quite a bit sideways, but then zooms off to the side and  comes back up in a long curve.  I did briefly try 19 in the same conditions- 24 is noticeably easier to launch, is more forward bridled for the same or better LE stability, and recovers much better from lulls.  24 does still exhibit the same volatile behaviour which steady's down as it gets to a higher angle- and in more wind- but it has it to a lesser extent.

Tested 21 with the larger B outer flares- still wouldn't stay central- always dived off to one side soon after getting to appex.  More and more likley that this is ROI from too much camber towards the rear.  Didn't try different bridles though.

Next prototype: a 22  with higher aspect ratio and maybe only 3 flares/cell (they need to be slightly larger than for 23 anyway to reduce its volatility.  Should the TE be concave or convex?

Xiamen 9th Nov '14:

Light onshore wind building to  35km/hr by 5pm.

Tested 23 in light wind mode;did narrow LE a lot and was inclined to edge terminally because of shoulder collapse, but seemed quite close to being flyable.

Ashburton from 13 Nov '14

Tried a 4 bridle per cell 7 cell developed from 23, did fly quite acceptably in a gusty northwest, but also seems to have a hang-up mode when it sits at lowish angle stalled.  In light winds it tends to edge quite badly.

24(orange, 3 x 8), developed from this was not improved in the edging- what's causing this?, but does seem to be able to accept quite forward bridling without LE or shoulder collapse.  it's interesting that even without chordwise choke, the LE shoulders do stay well inflated

25 (purple 3 x 6) had a lot of flying and development but is plagued by this edging problem- when it gets perturbed by more than about 20 degrees it inexorably dives off to one side or the other and crashes.  Tried many things, but nothing seemed to make much difference.

26,(yellow, 3 x 6) same basic patterns but small changes to the shoulders and some camber in the ribs.  A lot of testing with this in mainly gusty winds, no useful improvement.

27 (red, 3 x 4) reduced spanwise to 3 cells (12 bridles total).  Did fly for periods in gusty easterly, especially after adding another bridle set between A and B. Very sensitive to tuning and with the dreaded non-recovery when flying sideways

28 Orange, developed version of 27, with 4 bridles/cell (16 total) small changes to bridle points and with a larger lower leading edge-  not significantly better - is quite volatile so;

29, purple, same as 28 but with a 300mm wide cemtre panel (28 is 225mm) many hours of testing with this in gusty easterlies.  Initially it wasn't nearly as reliable as 28 but reducing the LE return by 30mm- 25mm helped somewhat, as did cutting away the central ribs between bridles to reduce pocketing.  A theory now is that the edging is caused in part by transverse flow.  When the kite is lying on it's side towards the edge of the wind, it functions as an airfoil with the rear outside upper edge generating more lift than the front outside upper edge- which causes the rear to tip up and the kite to slide/dive off to that side.  If the dive gets steep enough, the kite will loop and recover, but on a short line and in the tree, wind shadow it more usually crashes to one side or the other.  Shortening C on one side is an excellent and sensitive tuning system- but this kite is extremely sensitive to tune- if it is set to not deviate more than a degree or 2 either way it will stay up for periods, but more usually hangs off a bit then gets into a death dive.

Tried cutting 2/75mm dia vents in each rib near the LE for cross venting- did this reduce edging? - didn't make it worse anyway, but top skin now has more bumps.  

Tried cutting away the rear outside bridle triangles to reduce area at the rear relative to the front and in this form 29 does still fly about as well as before this- but is suffering from poorly supported rear area- develops creases, makes flapping noises and hangs low- or crashes.

Summary: it now seems likely that cutting away the front flares from 25 on, which did improve the shoulders a lot (in the absence of choke) but had the initially unrecognised consequence of shifting the lateral area rearward which seems to be causing the edging/tipping. A solution may be to return to using larger area front flares in the centre ribs only (and go back to 3 bridles per cell in the centre?) while continuing with using the cutaway front flare at the shoulders and 4 bridles/per.  It may be that once this edging is solved, a return to 7 cells might be possible (and helpful if volatility is a problem for the lower aspect ratio versions). 

25 Nov '14 Ashburton; made 30 green 4 x 4:

Reduced lower leading edge to what 29 had been modified to above, but didn't add cross venting.

Added flares back to the centre A's and reduced centre B, C and D flares to 100mm shorter than for 29 and earlier prototypes - to move the lateral area C of P forward as much as possible, and to reduce the flopping of the centre ribs which may have been contributing to edging. 

Added flares to outer B's and reduced outer C's and D's by 25mm also to move lateral C of P forward (see in red above).  Kept outer A's cut away so as to not have shoulder collapse.

First test (gusty easterly behind the trees) looks promising- definitely recovers now, much less tendency to edge, maybe a little volatile- so make bigger or higher AR?   Recovers well from stalling- probably the best yet.

Quite a tidy smooth kite and appears to be able to retain inflation at low A of A.  Need to test and tune in smooth wind and try very light wind.

Up to 2 December '14

Extensive testing of 30 in easterly at 105 and at beach- can't get it to stay up reliably, even with a lot of bridle adjustment.  It's OK for a while but as soon as it tips to one side more than about 60 degrees it dives over to the ground, doesn't recover.  Is good in light winds, doesn't have the tendency to tip over whenever it drifts backwards and tip over that 19 has.

Despair!

Took  19, 24, 25, 26, 30 to the beach and tuned/tested them- 20+ km/hr north easterly (not from the sea).

The only one of these that looks promising is 24 (yellow, 24 bridle plus 2 extra) made in Weifang, quite high aspect ratio, every cell is choked a bit very curved leading edge.  This kite did look promising at Xiamen but was very distorted at the LE of the outer ribs. 29 Nov, after the beach, added a fabric wedge to eliminate the distortion and added an extra bridle on the LE between the outer rib nose and the rear outer flares.  After some more bridle adjusting, this kite has become an excellent flier- was as good as any of the pilots and lifters at the 30 Nov Ashburton Domain flying day - when the wind moved from south to east (every minute), was quite strong (difficult to hand hold a 12sq.m Lifter) and VERY gusty.  In current mode, 24 is very flat in the profiles- almost reflexive.  It is exceptionally stable, not quick recovering but doen't tip over so doesn't ever need to recover.  Pulling in B on an outer rib (there's A B and C on this rib) works for tuning - 5 -10mm has a big effect in strong winds.  In the strongest conditions the trailing edge tramps- but it continues to fly.  In even stronger this will probably cause super stability- was just starting to at about 40 or 45 km/hr. 

See discussion and photos in December Newsletter.

On 2 Dec, made a development of 24; single panel with scalloped ribs (4, 4, 3), slightly lower (10%?)  AR, slightly shorter lower LE and it's made from a separate curved piece, not an extension of every panel as 24 was. A bridles come straight from the LE lower edge, do not overlap 20mm as for 24. 

In initial testing it was fairly cambered and zoomed around a lot- would loop, but more inclined to dive to the left and crash.  After letting off TE about 25mm, pulling in B's and C's about 20mm and letting A's out 20mm, started to look and fly somewhat like 24- though isn't yet as flat in the TE  and appears proportionally narrower at the TE.  This kite will be a bit wider than 24 on account of not having chordwise panels with seams, so maybe AR is closer to 24 than I intended.

 27 Dec '14: Why does 32 (green, 4 Dec '14) collapse while 24 (yellow, 4 Nov) doesn't?

1. 24 has chordwise choke, 32 doesn't have.

2. 32 is larger than 24 (10%?)- fabric stiffness effect

3. 24 has compound triangular sewn on flares, 32's are one piece scalloped.

4. 24 has marginally greater leading-edge tuck.

5. 24 is flatter in profile- test by de-cambering 32

6. Is it to do with progressive collapse?- 24 collapses in such a way as to remain flying, 32 folds to one side.

7.  Bridle overall length?  No, checked this by trying much longer and much shorter on 32.

8.  Fabric type?- 24 is lighter, softer- so how could this be?

Wakanui, 27th Dec '14 Strongish NW: 24 stayed inflated, flew marginally, LE crumpled back a bit but not destructively, TE panel tramped.  32 not much behind- but LE would eventually crumple enough on one side to cause a dive -off.  No TE panel tramping (bridling?) and much more noticeable creases at 2nd and 3rd bridles.  Became noticeably compressed chordwise compared to 24. Tried with cambered ribs and without, same bridling, no significant difference- maybe a little less inclined to collapse chordwise with the rib camber removed.

For 33 , try same as 32, same chord and ribs and bridles but 10% less span; by theory that there is a spanwise as well as chordwise max bridle spacing.

Built 33 (Orange) on 28th, flew 29th at Wakanui and 105, strong gusty easterly. 

Definitely the best SSSL yet- flew well immediately with initial bridling (all the same length), not even checked for symmetry. Much less lateral wrinkling than 32 or 24 .  LE stays inflated better too.

There is no other explanation for this improvement than that spanwise bridle spacing matter- narrower cells , closer spaced ribs hold better shape.  There is likely to be a formula for this- perhaps some product of spanwise and chordwise spacing is approx. constant - though deeper flares do appear to help as well.

30th Dec '14, built SSSL 34 (Red), quite strongly right wing, didn't fly anything like as reliably as 33- but had let out centre B's by 15mm to eliminate crease at B- which it did. 

1 Jan '15, re-sewed one side's ribs (except one nearest centreline) to get lateral symmetry, restored bridles to original- all same length.  Now flies as well as 32, and slightly left if anything.  Does compress chordwise and LE bends under a bit in strong winds but recovers exceptionally well and remained flying when 12 sq.m Airbanners Blue was crashing every 30 minutes or so - and 34 was on half the line length- strong easterly.

1Jan '15, began templates for larger version; scaled x 1.5 chordwise, x1.4 spanwise- all flare depths scaled 1.5x

2nd Jan '15.  This one, SSSL 35(yellow) is the best yet- flying reliably (came down twice in 3 hours, each time because an unsettled bridle had stretched out 20mm- (used soft Dyneema not hard finish)  on a short line in a strongish easterly/southerly- trees are thrashing a bit.  Has a LOT of pull- not really possible for me to hang on to it on 2mm line.   There is a serious crease at C bridles centre, none at A or B or D- but trailing edge flaps loudly in strong wind, compression collapse.  This seems to be having effect of moving the C of P of the functioning (forward) part of the kite rearward which ensures that the LE stays inflated.  Definitely an effect worth keeping if it's doing what I think it's doing- working like a reverse spring bridle. 

SSSL 35 has 26/ 3m long bridles, weighs 360gm without line (45gm acrylic coated fabric).

Built SSSL 36 (green), same as 35 but centre ribs shorter by 150mm, 2nd ribs by 120mm, outer ribs by 80mm- 2.5sq.m effective lifting area.

SSSL 36 flies OK- quite right wing, more creases on right rear, does tramp trailing edge but not as much as 35- does it fly as well in stronger wind?

SSSL 36 compared to 9sq.m Airbanners (latest model) Pilot:

Light gusty intermittent easterly at 105 AF Rd, 4th Jan '15

36 has more pull on average, holds a higher angle, doesn't wander off to the sides as much (quicker recovery from perturbations), seems as reliable or more reliable for same height, but presumably won't have the upper end.  Light end seems equivalent but this needs testing in smooth unobstructed gradually dying wind.

7pm same day, More north easterly now, 30km/hr?:- Trunks on main pines are moving noticeably.  35 came fairly straight as bridles settled in- some tendency to SS in strongest gusts, either way.  Angle same or only marginally better than the 9 Pilot in this wind, pull around the same for both-  20kg to 25kg.  Pilot is much less stable (but 70 m out as compared to 80m for 36), collapses, inverts and usually recovers.

Lots of TE tramping on 36, but the LE holds form very well in the strongest gusts- strongly suspect that this is because of C of P shift deriving from TE panels disengaging from lift? Much less centre panel creasing than for 35.

All the bridles the same length exactly still seems to be better across the wind range than any other variant- even just 15mm +/- on a few bridles.

6th Jan '15.  Built 37 (Purple) shortened as for 36 green but with more even spacing of bridles, especially on outer ribs (35 has big gap from B to C)  Flies exceptionally well with reduced TE tramping in strong winds (still a lot though) after 8 or 10 hours heavy wind flying, quite noticeable wear marks in TE panels.

Tuning: was initially left, then caught in a big tree, damaged pulling out, After repair, strongly right.  Tried very many things over 5 hours+ continually.  Pulling in left side 3/B and 2/B,C  and letting out right side mirrors did almost correct the lean but in stronger winds it re-appeared.  Max 30kg pull (gusty easterly).

Tried releasing left TE bridles - but didn't work at all.

Then tried letting out left LE on shoulder and 3A- works immediately and precisely, no other bridle asymmetries required.

TE Tramping:

Is it a necessary A of a modifier that allows the kite to hold LE inflation at higher wind speeds, as per above, or is it just inadequate TE support.

If the latter, fixes could be:

1. Shorten TE a little to create some hook- works for sports kites

2. Shorten TE of ribs so as to do the same.

3. Move rear bridles rearward by 50mm or so.

9 Jan '15 Tried 2. By sewing 2 x 12mm pleats in rib and tip TE's of 37 purple.  Quite strong easterly, 20kg + pull, does seem to be flapping a bit less - and does seem to now fly at a higher angle in this wind (or is the reason that it's now flying straight?)

38 red; as for 37 but with rear bridles (ribs and tips) moved rearward by 85mm (other bridles spaced appropriately). Flying 38, strongish N E; initially strongly left wing, after making bridles symmetrical is straight- but responds very well to tuning ONLY with shoulder bridles- +20mm on left shoulder was enough to cause strong left, when corrected, kite is central.

TE tramping a LOT less severe than earlier versions, probably better than modified 37 above.  Because 37 modification did reduce tramping and doesn't appear to increase instability, suggests could do this to 38 in addition to moving rear bridles rearward- which didn't seem to cause any additional creasing anywhere either.

10 Jan '15 Built SSSL 39 (gold 30gm). - Very minor template tidying from 38.

Flies straight off but strong right (lightish easterly) Still to the right after shoulder bridles made the same- and still a little right with LH shoulder 15mm longer.

Doesn't appear to be any less inclined to hold LE shape than heavier fabrics, and no more (perhaps less?) creases in the main skin.  This bridle line is very stretchy- even after each bridle has been individually tensioned to 2 or 3 kg, there is still a lot of settling to come.  Weight is 250gm complete.

In stronger winds, terminally right wing- had to lengthen LH shoulder and 3A 20mm, shorten 3B 20mm, lengthen 2B and 3B 20mm to get almost straight- is this stretchier lighter fabric inherently more likely to distort asymmetrically?

There are now 5 of the larger 26 bridle SSSLs in good flyable condition, each one significantly different in some respect- maybe best to get some hours at events on these before too much more development- need to check light end for eg.  Is tempting to try hooking the TE on 38 or 39 though either by way of TE tightening or rib pleats.

Is also now possible to establish some formulas for bridle spacings and lengths?

11 Jan '15 SSSL40 orange: Increased spanwise length of lower leading edge by 45mm per side- previous did look to be too tight causing unnecessary looseness in upper LE.  Also reduced cutaway at LE of tips- now back to 90 degrees.  39 shows quite a notch at the shoulder bridles, but their spacing seems appropriate- have increased the width of the LE at this point by 20mm. Also tried cutting LE pieces on the straight not bias.

Cutting out- 30minutes to 45minutes?  All sewing took just less than 2 hours.  Bridling, total, including pre-stretching; 45minutes.

Light Norwest, slight drizzle, flies really well straight off- LE does seem better and shoulders aren't as notchy, but there is a bit of a flare out in LE of tip flare. Quite right wing in stronger gusts- but haven't checked bridle symmetry yet.

Seems to be flying at a bit higher A of A than previous- quite a bit stiffer and a little slower to respond to line pull in the light - is this because the leading edge is now 90mm longer, increasing forward area, so moving C of P rearward?  Tried shortening all LE bridles by 15mm and it does now feel more like 35-39.

No noticeable tendency to nose collapse yet- nor to instability- and this will have increased camber so decreased wrinkling in forward area, which was noticeable for 39. Need to check this in stronger and lighter winds.  Does now (15mm shortening of all A's) behave in no wind more like 34-39, that is, lower leading edge does fold in a bit during acceleration. Cut away LE of tip flares- a lot less flare out now, changed template to this.

15th Jan '15 SSSL41 pink; Made all new rib templates with difference between rear and front flare depths all ribs, now 50mm (was 40mm)- to shorten front bridles matching SSSL40.

Light gusty easterly; does fly OK but appears to be significantly SS caused by quite noticeable creases at B and C (less) during gusts: noticeable chordwise compression.

Let out all B's by 20mm, chordwise compression much less now flies much better, reasonably determined right wing though- as is 39 and 40. 

Tried shortening all bridles by 720mm to increase camber (after restoring all B's back to original length) Almost as good as with full length bridles, B's lengthened, but crease at B again- so let out B's by 20mm again and it's probably now flying best- does seem more volatile, less inclined to stall in gusts.

After some more testing of this version- need to try it in strong wind, 40 also- and if the increased camber hasn't caused instability of some type, should try pleating ribs to match camber again, see if this can now help. Damaged in a tree, repaired; restored bridles to 3.1m, not worse, maybe better.

16th January, 42 green: had to lengthen centre A's by 15mm to reduce LE collapse, but then flew well at Nelson - a bit right - and earlier kites, back to 34, noticeably flew as well or better in the quite strong gusty onshore winds there - with some exceptions.  39 gold 30gm soft fabric was a stand-out- very straight and seemed to get better as the wind became stronger. There seems to be a limit to the efficacy of tuning by lengthening/shortening shoulder bridles- possibly the resultant A of A changes overlap with LE inflation in their light wind/strong wind effects- whatever, neither shoulder bridle tuning, nor outer rib B (camber changing) are always sufficient.  Shortening the rear outer rib bridle on the right to pull the kite right does always work though- unlike for parafoils.  I presume this is because the SSSL's are always at high A of A.  This shortening is just like steering a 4 line kite- but does seem to have slightly opposite effect in light winds sometimes- why could this be?- doesn't fit any theory I can think of.     

19 January '15; 42 orange (After Nelson); 3.0m bridles; cambered centre and 2nd ribs 40mm by a vee between B's and C's, also added 15mm to A's centre to reduce nose collapse.  Light to strongish gusty easterly at 105.  Spanwise creasing is noticeably less than for earlier prototypes.  This one's pretty good. "Natural" camber for 3m bridles is 60mm for 1.2m between A and D so  40mm shouldn't create any more camber than the bridles are requiring, but should decrease rib flutter- which it has.  Noticeably less flutter in rear panels, and sometimes flies at a very high angle.  Do they now have a greater tendency to "roll-over" instability (a consequence of progressive attached flow over the cambered top surface as A of A decreases)?  Not sure about this yet, but later prototypes do seem to have an apparently increasing problem with sensitivity to tuning- they can dive off unrecoverably to one side or the other in gusts. 

Shortening D outer on the preferred side by 15mm +/- does seem to be effective tuning in stronger winds.

One possible solution to "roll-over" could be a flap strip on the upper surface at around 1/4 chord.  Another idea worth trying could be to make the rear 25% of the skin in flag type porous fabric; would be heavier to reduce super stability, porous to improve stability in stronger winds, and more resistant to flapping fatigue.  

To January 31 '15; Goa-Pune-Dubai.  35, 39, 42, 43: All performed well.  In very light winds they are definitely a match for standard pilots- and they hold their pull right down to when they are about to fall out of the sky, unlike ram air pilots.  They pump so easily it's possible to keep them up in almost nothing by active flying- also unlike ram air pilots. In very light conditions, 42 and 43 have a noticeable tendency to figure eight automatically (basically an effect that is a function of size and aspect ratio, everything else being unchanged). This is very likely to be improving their light end by generating apparent wind speed.  39 did this a bit less- why?   Less rear camber? When they do get pointed down though (very rarely), they can only be recovered by releasing line in classic rokakau technique.  This would be desirable if they were meant for fighting with but isn't good for pilot style kites- they do need to fly in upward curves not straight lines. Earlier versions did this; how to get this back without losing anything else?

Currently, to fly in strong winds, tuning needs to be very precise- and they don't seem to stay the same from one day to the next.  The marker instability is to hang increasingly off to one side or the other, and very occasionally this will progress into a slow inexorable dive.  Maybe this isn't classic super stability, but rather an effect by which the LE on one side of the other gets progressively pushed in as the kite leans (caused by the apparent wind not hitting the LE squarely in this case) creating ever more asymmetric drag, which increases the lean. Perhaps try cross venting (again) to equalise LE pressure- this should have an opposite and restorative effect by firming up the downside LE relative to the upside LE.  Maybe taking the shoulder bridles through a pulley would do this too.