Article 27526 of rec.kites: Newsgroups: rec.kites Path: tug!andrew From: andrew@tug.com (Andrew Beattie) Subject: Re: Soft kite tuning Organization: /usr/lib/news/organisation Date: Fri, 12 Jul 1996 11:03:29 GMT Message-ID: References: <9607100941.aa03230@tug.com> I screwed up this posting. This is a re-post with corrected ascii graphics. Don Eckleston (http://www.kfs.org/kites/festivals/fano95/done.jpg) asked me this weekend to spend some time explaining how to tune bridles, but I never got a chance to talk to him, so I'll post a few notes here. I don't consider myself much of an expert on this matter, but even if I havn't learned to walk myself, I can still help others learn how to crawl... If we start completely from scratch, I suppose we have a rib that looks something like an airfoil and we need to put a bridle on it. Here's one that we can work with: /~~~~~~~~~~----------__________ | ~~~~~~~~~~----------__________ | \ \_____________________________________________________________/ 4 bridles are usually enough for a regular foil, so we need to postion them. Use your own judgement to place them. The bulk of the lift is from the front, so we bear this in mind as we place the bridles: /~~~~~~~~~~----------__________ | ~~~~~~~~~~----------__________ | \ \_____________________________________________________________/ ^ ^ ^ ^ Next, draw a centre-line down the rib. On a Sputnik-4, this is obvious, because the rib is symetrical. On a different rib, you'll have to pick a line that looks about right. Measure the length of this line. This is the chord of the foil. Now calculate a position 17% of the distance down this line, starting from the nose. Draw a perpendicular line from this, with lenghth = chord, and use this as your tow-point. Hmm... maybe a diagram would help. /~~~~~~~~~~----------__________ | ~~~~~~~~~~----------__________ |<--17------><---83------------------------------------------->\ \___________^_________________________________________________/ ^ ^ | ^ ^ A B | C D | | | | 100 | | | | | | v X Now, either calculate or measure the distances X-A, X-B, X-C and X-D and use them as your starting bridle. My experience is that this bridle will always launch and fly. It might not provide sufficient power, it might overfly, it might collapse, it might not fill well, but it should get you into the air. From here on in, it should be a case of identifying problems and adjusting for them. Having designed and built your *own* primary bridle, you have an important psycological advantage for learning to tune, because you *know* that there is no magic in it, everything was arbritary, it was all guesswork, so if you see something that looks wrong, it probably *is* wrong, and if you are likeley to have the courage of your convictions when it comes to correcting it. Problems and cures. The foil always inflates from the rear towards the front. Look for slow inflation problems - typically the section between A & B will take a little while to fill out, and the kite will take longer to get going. This can be cured by pullng down 'A'. In an extreem case, I've seen the section between B & C be slow to inflate, cured in a similar manner, by shortening B. If the kite is too slow, pull down A If it *is* going fast enough, but isn't pulling enough, shorten C or D or both. If it overflies too much, lengthen A (or maybe pull back C & D) If it doesn't turn tightly enough, make sure that the *primaries* are right before looking at the steering bridle. If it's not flying right, it won't steer right. Look for uneven stresses on the bridle points. To untie a bridle knot, you want a sewing machine needle held in a pin-vice. Work the knot, to ease it away from the skin, then ease the needle between the knot and the skin. Push the needle through, untill the shank of the needle is pushed through (take care to ensure that the needle has not caught any of the spectra and use the flat of the needle's shank towards the skin to help avoid damage). This should make a hole just big enough to enable you to push the stopper-knot through. I use fig-8 knots for stopper knots, they are slightly bigger and don't pull quite so tight, so they are marginaly easier to untie. Andrew -- Remember to drink champange for no reason at all. - James White