Commentaries on Single Line Kite Stability

Commentaries on Single Line Kite Stability

1. Delta style wingtip drag-When flying at apex, with low angles of attack (when pendulum effect is least), there is no lift from tips, just drag- this is a progressive stabilising effect.  I tried this on a prototype ray (building in twist to the wingtips so as to reduce their angle of attack relative to the centre sections)- but the wing tips luffed and folded, required strong steady wind to hold them back.  Will next try reflexing tips rather than reducing their A of A- some dihedral as well?

2. For kites on short lines- and all kites to the extent that they initially traverse laterally around some point on the line nearer than their tether point- flat is not zero dihedral, a small amount of nominal anhedral is the zero point.

3. Von Karman effects- test with smoke- but Shark as compared to (new) fish shows expected effect- fish has continuous fins on upper edge, doesn't "von karman", Shark doesn't have continuous fins on upper edge, does "von karman".  Another test is that effect should diminish/disappear as wind becomes very strong and turbulent- because the flow is then always detached somewhere before the trailing edge.

4. Long kites almost require a different theory?- is their some effect analogous to the increase in the lift on the faster side being greater than the loss of lift on the slower side that applies to after-body's?- do they get some deleterious apparent wind effect by their swaying from side to side? 

5. Also for long kites- the heads may be de-coupled from the body (allowed some independent freedom to pivot laterally) in some cases to reduce undercorrection.

6 How to deal with Dragon kites?- are they single kites or trains of kites?

7. Aerodynamic effects - eg, Rokaku stability, masking effect of protruding underbody when rays are misaligned.

8.  Line length: There is a corrective force on kites that are out of alignment with the wind equal to line tension x sine of the angle of the line to the wind direction- measured laterally (vertical projection?).  The shorter the line length is relative to the kite's size the larger this will be for a given lateral displacement.  A tendency to overcorrection will be exacerbated by short line flying, a tendency to undercorrection will be mitigated.  Kites that undercorrect extremely can be flown off their bridles from an arch line.

9. Very small kites: Air is sticky at very small dimensions- (eg boundary layer effects, insects).  For kites smaller than a few millimetres this becomes significant.  Explain Reynolds number also

10. Scaling: For framed kites, area increases with the dimension, Load increases with the square of dimension, but weight increases with the cube- so kites get heavier in proportion to their aero forces they can withstand as they are made bigger.  Soft kites are also subject to this but as fabric is more than strong enough up to a at least a few hundred square metres, scale effect doesn't kick in for soft kites until then. Except that enclosed and entrained air mass increases with the cube of dimension- acts to resist correction- so larger soft kites tend to be more inclined to under-correct than small scale versions of the same design- role of super ripstop.

11 Volkers comment on von Karman- angle of attack decreases with increasing wind, reduces von karman-ing.

12.  Some kites recover SO fast that dynamic effects don't build up- A diamond with a heavy tail for eg that sits there oscillating 15degrees either way about 5 times a second.   Probably there is some critical recovery rate-faster and slower doesn't cause dynamic runaways.