macboy - 9-11-2009 at 02:37 PM
Forgive me - I've just had eye surgery and am not allowed to touch my kites for a couple weeks so I've been living through all of you the past while.
(The poor SA is taunting me everytime I walk by "the bag that I haven't even opened yet")
Anyway, here comes the ramble - just thinking out loud. I've been thinking for a long time about the Arc autozenith and the how and why of it all and
as near as I've come is the following - am I right or is there even more to it?
So my thought is that the reason they autozenith is because of the arc shape. When the kite drifts off to the edge of the window (say towards 3/9
o'clock) the arc shape maintains a surface that stays parallel to the ground and therefore carries the kite back up. The natural resting place where
all the upward forces from the sides of the kite are equal is up at the top.
The only place this theory of mine falls flat is that if the kite's profile is an airfoil shape (which they are as far as I know) then the lower
wingtip - the one nearest the ground - would be generating lift in a downward direction. But then again, maybe the upward facing / downward facing
ratio is always on the upward facing advantage so despite the downward lift, there would always be just enough MORE upward lift to keep returning the
kite to the zenith.
Actually - that could be it - the wing tips are smaller by square meter so there would always be more lift in the upward direction despite the
downward - or more accurately - lateral pull being created by the wingtips.
I think this has been discussed before but if it has I didn't absorb it for whatever reason....if I'm right here then I think I've just got it sorted
- just needed to put it in blurry black & white in front of me ; )
flyjump - 9-11-2009 at 03:10 PM
Also the arcs displace a large surface area compared to others, they are "puffy". That combined with the shape is what I think causes it to happen.
For instance, the scorpion is notorious for being really twitchy, it has the thinnest profile of all the arcs. Others such as venoms or synergy are
way stable because they have thicker profiles.
krumly - 9-11-2009 at 04:18 PM
Macboy -
Read from Peter Lynn himself regarding kite stability. Go to his newsletters starting Jan 2009 and look through them up until Sept. 2009:
http://peterlynnkites.co.nz/news/0901news.htm
Or go to this site and the artcilcles are posted in a slightly different format:
http://www.peterlynnhimself.com/Technical_Kite_Papers.php
I've wondered how much of Arc's pitch stability - that they tend not to overfly the apex - is due to slightly reflexewd foil sections. I know the
amount of that reflex has changed over the years and by model. It may also be one reason the kites are generally not light wind machines - reflexed
foils generally have lower lift coefficients than positively cambered foils.
krumly