From: Steve Lawrie Subject: Re: Plans for Gekko Date: 1998/10/30 Message-ID: <3639814F.4C97@cs.ru.ac.za> Cache-Post-Path: tortoise.ru.ac.za!unknown@cssc.cs.ru.ac.za Content-Transfer-Encoding: 7bit References: <362F4B61.4541@cs.ru.ac.za> <19981023233902.29496.00000124@ngol08.aol.com> <3634563B.383C@cs.ru.ac.za> <719b3h$p0e1@mailnews.uk03.bull.co.uk> To: Philip Le Riche Content-Type: text/plain; charset=us-ascii Organization: Rhodes University, Grahamstown X-Cache: nntpcache 2.3.3b4 (see http://www.nntpcache.org/) Mime-Version: 1.0 Newsgroups: rec.kites Philip Le Riche wrote: > > I'd like to get into my own designs too but couldn't face spending weeks > and quite a lot of cash on a 30' monster that turned out to be good for > nothing but putting the dirty washing in. Can anyone give a few insights > into the design process? Batten down the hatches, its coming over. Assuming you know more-or-less *what* you want to make, this is an idea of the *how* part. How to make a big inflatable the Lawrie Way =========================================== or With saxophone, jack-knife and igloo across the Sahara ====================================================== Firstly, make a couple good drawings. Side-views, top views, bottom views, front views. Have a good idea of what kind of cross-section you want in the kite, both from left to right, and top to bottom. You need to have reasonably good 3D-visualisation skills.... Work out how you are going to achieve the desired cross-sections, and what internal ribbing/bracing you are going to need. Remember that for large kites you can probably get away with no ribs: instead sew reinforcing lines (say 2mm nylon/dacron/spectra depending on your budget) onto the outside of opposite skins of the kite, and then tie internal bracing lines from one side to the other (Peter Lynn Super-Ripstop technique). Remember at all times that the kite is going to try and occupy the biggest volume it can distort to - straight lines become curves very quickly. Stress points (such as bridle attachments) should be identified, and appropriate re-inforcing mechanisms developed. Bridling points can be tied directly onto re-inforcing lines, preferably where two reinforcing lines cross since this helps distribute the load evenly from the bridles onto the skin. Work out how you are going to generate lift from the kite (i.e. what the angle of attack is going to be), and how you are going to keep it stable. In general, long designs (e.g. octopus) are more stable than short wide ones - the longer the better - more drag, more stable. E.g. the trilobites fly better when they have long tails on them too. Once you've worked out what angle you think its going to fly at, you can then start worrying about inflation points. Any surface that are perpendicular to the wind flow are good candidates for these - replace a section of ripstop with gauze. Then allow for the fact that you got the angle of attack wrong, so the hole needs to be bigger than you though :-) Make a place for a zip in the side. Three reasons for this: (1) easy access to the inside of the kite to adjust the internal bracings after its been sewn closed. (2) If the zip can be opened by pulling the zipper from the front of the kite towards the back, this allows you to tie a "kill" line onto the zip which can be used to deflate the whole thing when its in the air and you can't get enough weight onto the flying line to bring it down cos the wind is now at 30 km/h. (3) It looks really cool when you bring the kite down and clamber around inside it in front of a crowd of newbie spectators :-) Try and work out how you are going to put it together. In general, I try to break it down into to lots of small pieces that can be sewn together, then the resulting slightly less small pieces are sewn together, then resulting medium size pieces are sewn together, then the large ones, and then then ones that just wont go through the arm of the machine. After this, you take those four or five pieces and sew them together using a hammer to bash them underneath the arm of the machine. At about this point someone advises you that you should have spent more time in the design phase trying to work out *exactly* how you're going to put it all together so that you never put any large pieces together underneath the the machine arm. Which is true; don't just assume that you'll be able to sew it all together - work out *exactly* how you're going to do it. Go through several iterations of this entire designing process. Work out how each of the design decisions will affect each of the others. Each generation, the drawings should get more and more specific, and eventually will include all the exact measurements, shapes of pieces, how the ripstop will be cut to make these pieces. You should now be able to work out how much ripstop & spectra you need. At this point it is customary to have a row with the wife/girlfriend/life-partner over how much this thing is going to cost :-) (My octopus = about 140m of ripstop....) Have a serious think about *where* you are going to lay out the ripstop when you do the cutting. Do you have access to a 20m long hall with a clean floor where you can actually cut the tentacles out? Finally, go through a huge bout of self-doubt. Do you really want to do this? What if it doesn't fly? Then say "to hell with it" and buy the ripstop. Make the bag first. This allows you to keep the pieces more or less under control, and prevent their tendencies to provoke the dog into chewing them or the cat into clawing them. Spend the next 6 months living the life of a castaway in a sea of ripstop, with a crazed, wild-eyed "gonna finish this kite if it kills me" expression on your face. Talk about nothing else to your friends, and visitors; drink more coffee than you should; become an internationally recognised expert at predicting when the bobbin is going to run out; and gain a reputation around the town for having lost it in spades. After these 6 months are up, you can stop making the kite for a few months to earn some $$$ to buy all the pieces you didn't think of, and then spend another 6 months living like a hermit in a sea of ripstop.... After all this, you need to bridle the thing. Find a large balcony or something to hang it over, where you can physically reach all parts of the kite, as well as the intended towing point. Tie the bridle lines in place and cut them to length, leaving enough (guess) room for adjustments. The bridle should be easy to adjust, so that you can fiddle with it for hours if you want to. When the kite is finished, announce the fact to your wife/girlfriend/life-partner. They will respond by either not believing you and laughing hysterically, or by cracking open the champagne, or by introducing you to their new half. When it comes to flying the kite for the first time, there are two possibilities. Either it will fly straight out the bag, or it wont. The chances of it flying is inversely proportional to the number of people who are around to witness the event. Seriously, though, if you've done the design right, it shouldn't take too much bridle-fudging to get it to fly well. Lastly, sit back and enjoy the admiration of friends & strangers alike, who will all ask you where you bought it. have fun Steve -- Steve Lawrie Dept of Computer Science, Rhodes University, Grahamstown SOUTH AFRICA Views expressed here might not be those of the University