Under-correction/over-correction

Published: 01 Dec 2009

Under-correction/over-correction.- Bintulu '09


Does under-correction merge into over-correction with no stable point between- that is , as the kite under-corrects and traverses to the side, at a certain rate of doing this the correction builds into violent figure eighting.  Could the stable point be at MUCH faster correction, rather than between under-correction and over-correction?
A test could be a square diamond shaped kite (polystyrene?), with tip drag for stabilising (small wind socks), and a sliding weight along the spine.
Snake development in Bintulu- Bali supported "The main reason why kites don't fly" principle.
The new Rays are also rotationally unstable because of angle of attack- when rear bridles are tightened even fractionally.

LAD  (lateral area  distribution) effects.

 The August '09 yellow pilot (second in new development for UKS, first with closed outer cells), especially in light winds, tended to fall to one edge or the other and the upside flare was then showing significant billowing, lifting the kite's trailing edge even higher, causing the kite to tip even further.  The downside flare was generally reverse pressured (pushed inwards) at this time also- contributing even more to the tip over tendency.
It is because this kite's flares have much more area behind the C of P than forward of it,  which, when a correction occurs,  tends to cause the kite to fall off more to one edge or the other even  to the point of collapsing and rolling under. This is a new perspective: that lateral area in this effect, doesn't only have a wind aligning function.  The previous assumption that disposing area to the rear would generally be beneficial to stability is therefore not (ever?) correct.
Perhaps long shapes have a similar effect- when lying over at one edge, if the rear body has more lift than the front has, then this will tend to exacerbate the initial lean.
It probably doesn't make much difference whether flares or keels are central or to the side- will still likely have the same effect.
This probably explains much edging behaviour- but how to identify  the difference between rearward disposition of lateral area effects and basic under-correction?- Under-correction should usually correct eventually- provided the kites doesn't progress to a dive, but lateral area edging should exhibit a stable mode hanging at the edge (unless the lower side folds under).
Implications for Slarcs; VERY likely to be a major cause of their edging behaviour.  Solutions may be:
1. To hinge the tips so that their lateral area is ineffective.
2. To wedge a lot more so that the tips are not so rearward of the c of p.
3. To taper the tips a lot.
Lateral area rearward disposition (LAD) edging seems to be maximum in very light winds- why is this?- because in stronger winds the kite is not able to move as far off line with wind direction before a strong component of line tension works to centre it again?
Yellow Pilot, Sunday 9th Aug at Bintulu (light winds); cut off entire rear sections of flares  and this stopped the LAD edging immediately. Kite swung back and forward around a centre not far from the LE, quickly recovered from any misalignment- too quickly: serious over-correction.  Would just about damp with max pull-in on b's, and reduced a lot at very low angle of attack also- but not sufficiently for useful flying.  A significant step for all that- suggests that the
amount of lateral area matters, and it's disposition matters- as expected.
For this kite; will make new flares of at least the same area as originals, but displaced forwards to test this. Average bridle length can probably return to original also-lengthening did not reduce under-correction- as should be expected if
it was a LAD effect.

The Prototype Hornbill (about 2.5m span) at Bintulu in '09 also showed a LAD effect- but opposite in cause while similar in result to the yellow Pilot.  Its neck was very long and tended to catch the wind to one side or the other- wouldn't fly central, especially in light winds.  I've previously called this "frontal area instability".
Basically, its lateral area was disposed too forward (the maxi Hornbill had a reduced neck length.)