Observations and Questions 2022

 1.  First law of single line kites: The C of G must be below the C of P.  This creates a correcting moment that points the kite upwards.  Certain.

 2. "Blink" stability is useful for some styles of single skin single line kites.

 3.  For SSSLs, chordwise buckling is more of a problem than spanwise buckling: space chordwise bridles closer.

 4.  Chordwise buckling is a major cause of hanging off, falling off and diving over (the 3 nasties).

 5.  Bridle supported leading edges are generally more buckle resistant than forms with lower leading edges- or at least more likely to recover from buckling. 

 6.  Deeper leading edges provide wider wind ranges but lower L/D?

 7.  Bungy and pulley from the main bridles provide effective automatic leading-edge control for wider wind ranges on every style of SSSL they've been tried on so far

 8.  Aeolian bridles are probably useful wind range extenders and stabilsers for SSSLs with substantial tails (Octopus and Serpent for example) but probably negative for others because of C of P movement.

 9. Aeolian bridles on bungies can provide useful leading edge bridle control for tailed SSSLs (see 8).

 10. Fabric stiffness is a significant factor in buckling onset when there are insufficient bridles or other supports.

 11. Weaving instability is a function of the difference in apparent wind speed squared from one side of the kite to the other for higher aspect ratio kites, of some sort of higher energy state for narrower kites?

 12. Higher aspect ratio can be used to reduce weaving instability- presumably because wing tip vortex drag then has more damping moment.

 13. Why are 30m Serpents weaving unstable from below 30km/hr, 60m ones aren't to >50km/hr?  An especially burning question seeing as kites are generally scalable- < 0.2sq.m to > 1000sq.m. for Flags

 14. Chordwise camber radius needs to be less than bridle lengths or buckling and fabric flutter will occur at higher wind speeds (as fabric stiffness becomes inadequate).

 15. Hooked TE's reduce buckling, assist form, but pull C of P to rear, reducing the correcting moment.  Hooked TE SSSLs generally therefore tend to hanging off, falling off and diving over in stronger winds.

 16. Lateral (spanwise) choke can assist LE pressurisation without the same penalties as hooked TE's.

 17. Lateral area interaction with C of Mass and horizontal line angle determines pattern of recovery. For example, excess rear lateral area causes diving over- SSSL 101 when it had rear keels only.

 18. Lateral area steadies kites but slows recovery when any rotational displacement occurs (Slarcs and 1Skins for example)

 19.  Dispose lateral area around rotation centre.  Too much forward will cause hanging off, too much to the rear causes extreme diving over (which seems to lessen with increasing wind).

 20. For easy launching from ground, lateral area needs to be as far forward as possible within 19s constraints.

 21. Tails are self-supporting drag devices.  For smooth tails, their drag is a function of weight (hence the use of heavier fabric for tails where possible).

 22.  Tail weight increases a kite's correcting moment (see 1) but to a lesser extent than weight that is part of the kite.  Tails generally pull up on a kite's TE but their attachment point is still below the kite's C of P.

 23.  Because heavier tails of the same area fly at higher A of A, they probably shift the kite's effective C of G rearward to a greater extent than a tail of the same weight but greater area.

 24. Wide tails or Y attachments slow recovery- which can reduce weaving (but see 28) and will increase any tendency to falling off, hanging off or diving over

 25.  Allowing a kite's head some rotational independence, so that it can correct without pulling the entire tail into line can be a critical factor in dynamic stability.

 26. Long tails cause falling off which will become diving over if there's insufficient time and space for recovery- when the effect is then similar to a shorter tail becoming snagged on something.

 27. To get a wide tail to fly flat, make it's edges a few percent shorter than its centre.  Taper helps also.

 28.Twin tails behave similarly to single tails with Y attachments and to wider tails- generally reduce weaving but increase likelihood of the "three nasties" (falling off, hanging off and diving over).

 29.  Adding tails sometimes increases weaving.  Observed for Serpent heads and for Singer (ribbon tail increases weaving instability in mid to strong winds). Heavier tail made mauve 30m Serpent weave more.

 30. On at least one occasion (SSP 2), one long tail was less weaving unstable than the same tail doubled - was this because it has more drag when full length?

 31. Toed in leading edges (curved LEs for example) are more collapse resistant and recover better from collapses. 

 32.  Toed in LEs appear to be more inclined to weaving instability.  Toed out leading edges are more likely subject to the 3 nasties. Is this because drag further from rotational centre slows recovery by more?

 33.  Concave cells (pocketing) especially if overlapped, (SSSL Rays) can resist spanwise and chordwise buckling even in the absence of camber-  can be contrived by cording pull-in effect.

 34. Pocketing may also decrease buckling by increasing drag- applying chordwise pull.

 35. All successful wide wind range SSSLs so far have open trailing edges (which require more bridles).

 36. Leading edge take-down lines are useful safety features for larger SSSLs.

 37. Anhedral did not capture more pressure in kite's centre line for Ray 4, but does for Sled forms. Why?

 38.  For SSSLs without keels that are subject to transverse flow during any of the 3 nasties, recovery is a function of lateral C of P migration.  Rays especially.

 39.  To what extent are AR, lateral area and Tail drag/ attachment interchangeable?

 40. What effect does total bridle length (as a function of span, chord) have on stability? Laterally, long bridles seem to cause slow recovery - double snake diving over.  Chordwise, probably exacerbate stalling

 41 By 2 line kite steering practice, linking wingtip bridles via a pulley should be self-correcting for WI. Trials of this on Ray 6 were unsuccessful.  Shortening bridles laterally should have a similar but milder effect.

 42. Is dramatic effect of front centre bridles on Ray 5 significant wrt 1Skin diving over, other stronger wind WU- maybe even Serpents?  How to reconcile this with SSP 11 and SSP 15 difference?

 43. Ray 5 nose flap dramatically reduced nose push-in for Ray 5- but didn't seem to work for early SS Octopus and Serpent.  Why?

 44.  Ray 5 nose flap may work not just because it effectively lifts the LE depth at the nose (similar effect to letting bridles out?) but because the flap then provides a lower leading edge and pressure captured in the nose then resists compression?