Peter Lynn ARCHIVE
Up to mid '10: For both the 12m's and 8m's, change to a much more reflexive section and use adjustment by overlapping the flare between B and C for steering/tuning
For the 12m's, reduce leading edge heights by 30mm and test- then take more out until satisfactorily balanced between overcorrection and undercorrection.
For 8's and 12's, try increasing the flare dimensions for more lateral area, then camber the profile more to get back to undercorrection/overcorrection balance- should give a smaller kite with more pull, - no loss of light end/.
For a new direction; try the mid section of an arc (closed LE) with flares similar to the current Pilots- or a simple triangle. This should provide excellent stability with bridling only to the tips, and water launching.
To assist launching off the water, the leading edge of the inflated section could be wider than the TE- so when lying on the water it's pointing slightly up. The flares would offset this so that the when-flying shape is still approx parallel.
A more extreme version of this kite might be good for altitude attempts also.
Remember that bridle stretch is inimical to single line stability except B versus A and C.
Xiamen '10 and future directions
The 4 bridle 12m's up to end Oct '10 still tend to hang left or right in light winds and have not yet been stable in very strong winds- OK up to 50km/hr or so though, and the best one so far, when tested against the Airbanners 8m beside the kite factory in a strong gusty southerly, did crash a bit more often than the 8m- which also edged then tipped over and crashed quite often also. This new 12m (extended to 13m by adding 10% width to each cell) does have more pull proportional to area though
Tried angling the outer cells back a 250mm and the next inward by 60mm- making both the kite's leading edge convex and the trailing edge concave. This made it hang off to one side even more in light winds- visibly caused by disposition of lateral area. The flare's lateral area c of p was further forward than for the 8m style- but is the problem that they have more actual amount of lateral area (in proportion to lifting area) towards the rear. Could try cutting away the trailing edge of each flare. When the width was increased, each rib leading edge was reduced in height by 100mm or more by sewing in pleats- amount adjusted to retain adequate stability. Flying angle was generally better than the 8m style.
Adam (ex John Waters re-rigged sky diving 'foil from 1987 was stable single line- and had side flares only, and only in the front 25% chordwise. Perhaps this could be a new starting point.
At Weifang, had a new 8m style pilot made with large cross venting holes at about half chord in every internal rib (no gauze), sand holes in each cell TE, centre leading edge bridle to the top skin and the flares increased in height 50mm at B, decreased 50mm at C.
Testing this at Xiamen in light wind (first day), could let off B outers by 150mm or so to create more camber for light wind flying- did help noticeably, but when caught at one side or the other, would occasionally luff that side cell and tip over. Putting the bridles back to the original marks (standard 8m) but letting B middle off by 100mm or more retains excellent light wind performance, appears to improve the flying angle and was rock steady up to the maximum wind that day (20km/hr). Need to test in strong wind.
The vent holes do appear to cause the kite to camber more in light conditions.
The top skin centre bridle does seem to allow launching, flying and recovery with less inflation- but needs much more testing to be sure of this and that it doesn't cause other problems.
'11/10sq.m development plus
Single line kites with wide wind ranges all seem to have some dynamic anti-hunting system;
*Delta's use flattening off wing tips (less lift more drag as apparent wind increases).
*Rokaku's increase the camber of the mid section subject to more apparent wind while flattening the camber of the opposite side.
*Fighter kites use the same wing tip flattening as deltas.
*Genkis do also
*Flow forms use rearward centre of pressure migration to reduce the angle of attack of the faster side- coupled with a vee'd middle section to reduce torsional rigidity.
*'11 style Pilots use flare induced camber in the outside cells to generate angle of attack reducing response to higher apparent wind- like Flow Forms (?)- and does the 8m series use the same mechanism?
* Eddy's use perimeter tension to flatten the slower side while adding leading edge reflex in the slower.
* And there was the dramatic effect of pulleying earlier versions of the '11/10 sq.m.- which worked only at low angles of attack, exacerbated hunting at low line angles in strong wind.
Jalbert (and Hagaman) style 'foils don't have any such mechanism so are either bridled so far back as to surge in light winds (apexing then stalling back), or luff (non reflexive profile), or hunt (reflexive profiles that prevent the angle of attack reducing in stronger apparent winds to shed lift). When they have sufficient lateral area or other features to to resist the onset of hunting, they are characterised by almost square law pull increase with apparent wind- though this doesn't seem to be necessary, such kites could still employ angle of attack reduction. Parasleds damp hunting by wide spaced frontal drag, don't seem to have any dynamic anti-hunting system- how close to square law is their pull increase with wind speed?
What other dynamic anti-hunting systems could be employed for soft kites?
One would be to allow pressure egress only in the central area- then when one wing speeds up relative to the other, dynamic external pressure on the faster side would exceed the internal pressure and cause drag inducing nose flattening.
G1/10 sq.m hunting, inverting, questions and changes to try:
1. Aspect ratio- did the small (80mm in 3200mm) reduction between P1 And G1 contribute to G1's greater inclination to hunt?
2. Rib depth/chord ratio- did the small (30mm in 600mm) reduction between P1 And G1 contribute to G1's greater inclination to hunt?
3. Position of max rib depth-did moving this rearward 75mm (?) contribute to G1's greater inclination to hunt?
4. Flare tip position. Is the positioning of the flare tip (G1 initially was 90mm (?) rearward of P1 and PM is 50mm (?) rearward of final G1 (similar to P1) as critical as it seems? (More rearward appears to promote hunting.)
5. Is the flare's depth critically significant except wrt bridle point.
6. What is the ideal narrowing towards the flare- to retain area and tautness while still applying camber to the outer cell TE's?
7. How much flare induced camber is optimum- and where should this curvature be?
8. Does having the 3 centre ribs cambered rather than reflexive promote inverting- as it appeared to do on the 6th Jan at AFR (gusty east)?
9. What's the best position for B bridle? - at 1m?- as appeared to be better than at 600mm for P1 when this was tried or has that now changed?- for G1, shortening B does seem to push the hunting threshold to higher wind, while on at least some versions of P1 and B1 it exacerbated it.
10. Is the upper skin position for A bridle always better? - what exact effect does it it have on hunting, length staying constant?
11.Is it possible that adding curve to the TE panels PM and G1) exacerbated hunting by improving lift/drag?
12. Presumably the spanwise camber (set by the difference in length between flare bridles and A,B) effects the ratio of load taken by the flares wrt the centre- so should have a noticeable effect on hunting-shortening A,B would be expected to reduce hunting by 4 above.
13. Could try lengthening all bridles- generally this seems to reduce hunting for kites of all types.
14. Try cutting away the front corner of the flares closest to the LE, replace with a cord- moves flare C of P rearward and allows more airflow to underside of canopy, especially when leaning.
15. If torsional stiffness reduces the effect of C of P dynamic anti-hunting in parafoils, higher aspect ratio should help this- or splitting the centre cell.
16. Try higher aspect ratio to get more hunting damping by frontal area drag- then optimise this by using cords in the centre of each leading edge cell?
Flying at Ahmedabad 9th Jan '11
Mid range very turbulent wind at first:
G1/10; flew OK but wandered side to side quite a bit. Pulled in B; then hunted and looped
Then tried P1/10; inverted every 5min or so
Then tried Airbanners 8m; it inverted and fell every 5min or so also.
Other peoples Pilots were having same problem- all kites were.
Then tried Airbanner 8m out 100m plus (no recovery area); was sort of OK, but dived onto a high-rise roof once and then miraculously re-launched.
Later in day wind seemed to steady a bit; tried R1/22, flew well on quite short line, lifted Ray and 2 mid Tigers.
10th Jan '11
Gusty wind; P1/10 flew for a while at 50m but when tipped dove straight down- and couldn't be risked flying on longer line. G/10 tended to hunt a bit in moderate wind but was reliable. Twice it went into terminal looping. R1/22 flew very well on 30m later in the day (smoother wind).
11 Jan'11
R1/22 flew exceptionally well in light wind- held up when all other pilots were down. An outer cells lower skin tends to buckle inwards eventually causing that side to collapse tipping the kite over when the wind is too light. This will be because the inward component of the flare bridle load exceeds the ability of the outer cells to resist this compressively. The effectis only significant in light winds; because the kite's angle of attack is then such that all the flare bridle tension is along their leading edges.
Possible fixes are:
1. Make the bridles longer.
2.Increase the depth of the outer cells at their leading edges.
3. Bridle all ribs at the leading edge.
4. Taper the cells- wider at the front- so that the flares hold themselves out.
5. Or just arrange for the front part of each flare to deflect outward.
6. Close the outer cells at their leading edges- completely or just half of?- and perhaps valve their inflation from the inner cells. This also generates a form of dynamic anti-healing.
12 Jan '11, Kutch salt flat (at Dhordo).
Very light wind in morning, a few periods of say 20km/hr. Added 0.5m to all bridles on P1/22m stayed up all day, on one occasion it did loose inflation until one side collapsed, looped and recovered. G1/10 also flew well but did once hunt into a series of loops (but one rear camber tie was off- and would have been in Ahmedabad as well). Flare pull in from 11 Jan above is probably not a problem that needs solving- only happens when there isn't enough wind to fly- but that it doesn't recover from collapses in the way that the 8m does is concerning. Closing outer cells might make collapses so rare as to make the recovery unnecessary anyway. P1/22 seems to be if anything too steady- but need to try it in strong wind before adding volatility.
13 Jan '11 Mandvi Beach, Kutch.
Very smooth wind, very light during morning, in afternoon R1/22 and BT Ray could just lift me. G1/10 steady all day, no collapses, slight hunting- not sure whether this would steady in stronger winds or accentuate. Lent to Rolf Z with line for him to use and take patterns from- will return at Berck. P1/10 very steady, also flew well in the light wind. Had right lean, not sure whether this was getting worse as wind became stronger or not. Tried correcting with 40mm shortening of internal LH adjuster. Seemed straighter but not enough subsequent flying to be sure. Lent to Bagus and Eli, to be returned when R1/22 gets to them, (sold for US $400 cash paid, no line). R1/22 very steady- too steady? - but did recover once from tip over. Leans left, didn't try any corrections. Line angle is excellent in light wind, drops back to 45 degrees in mid range then climbs again as wind increases further. No sign of corner folding. Looks very smooth and wrinkle free also.
14 Jan, Ahmedabad; conclusions so far, directions.
1. 10 sq.m series can be very steady- but what is the significant small difference between P1/10, B1/10 and PM/10, G1/10? Is it aspect ratio? R1/22 could be excessively steady because of entrapped air mass- but it is slightly higher AR than G1/10, similar to P1/10. Need to test this by making another 10 with AR restored to P1/10 equiv.
2. They aren't very good at recovering from collapses- not like 8m series- but they probably don't collapse as often either.
3. R1/22 loss of L/D in mid range could be addressed by pulleying A-B (pulley closer to kite than flare bridle knot to reduce tangling), but P1/10 and G1/10 don't seem to show the same effect.- presumably something to do with where the camber is and the way this initiates de-power.
From Pasir Gudang, February 16th '2011-02-21
Very difficult conditions for all pilot kites; A purple 8 bridle 12m was basically unusable, Simon's sun/moon 8m was OK but not very good in lulls- too waisted. Yellow 10m very steady, slow recovering, and relatively often (perhaps 20 times in 3 days) it inverted, crashed. B was already short enough to limit light wind flying. Quite right wing initially; 30mm adjustment on left pulled it strongly left, then progressively as this was removed, it continued left- stretch from tree extraction?- 20mm made significant difference. After ongoing adjustment, eventually it hung left in light conditions, was relatively straight, tending right in stronger, Did loop wildly once or twice- but the Rays and crocodile were also looping at that time- because of swirling winds, not too much wind. Never exhibited hunting/looping as far as I could tell. Was still, on average, as reliable as 8 bridle pilots (crumping up and falling to the ground was not unusual). Sold to Indonesia for US $200, paid , cash. 22m Blue was better than the Yellow 10- did let off B to second position, which improved light wind flying a lot. Was steady in all winds, no hunting/looping ever- even when other kites were all misbehaving- amazingly steady. Hung right in stronger winds- even with max. left adjustment, but manageable. Inverted maybe 10 times but recovered almost every time- albeit then flying straight down to the ground some of these times. Excellent kite!
Need to make 10m 4 bridle more resistant to inverting- but best to wait and see how production 10's and 13m's perform first? A solution might be more reflex in outside profiles- especially at nose. It's noticeable that the under-side collapses and folds under when these kites are caught at the edge- can do duct tape testing of this direction.
