Article: 20510 of rec.kites Newsgroups: rec.kites Path: tug!andrew From: andrew@tug.com (Andrew Beattie) Subject: New traction kite: The Chevron Organization: /usr/lib/news/organisation Date: Wed, 3 Jan 1996 22:35:01 GMT Message-ID: I've posted enough about the kites that I'm making that I think it's about time to introduce the whole thing. The Chevron. It's getting different enough from other people's kites that I think that it deserves a name of it's own. There's little that's truly *new* about it, it's more my combination what I like in other kites. The easiest way to sum it up is to say that it's a Sputnik with a cross-bridle, but let me go through it in detail: The profile. This is taken from a Sputnik 4 (and I checked with Nop that it's OK to sell stuff based on his profile). The Sputnik is a little fast for my taste. It accellerates too quickly, going from "no-pull" to "too much pull" at a rate that's beyond my ability to persuade the buggy to keep up. I've fattened up the profile a little in order to provide a higher coefficient of lift at the bottom end to make the power a little more gradual. This will cost me a little in absolute top speed, but then I'd rather drive a rally car than a dragster... It'll also cost me a little in lift/drag, but since my starting point is a better lift/drag than a Peel, I can afford to loose a little. The ribs. Rather than build a 36-rib canopy as Nop prefers, I've gone for a 24-rib design. This has the same number of bridles, but it's bridled on every second rib rather than every 3rd rib. There are several reasons for this: - It results in increased internal pressure within the cells, making the kite more rigid. - It makes the effective profile a little fatter (which I desire) - It reduces the weight of the canopy (which makes it more able to support it's own weight in a near-tip-stand at the edge of the window) The bridle connections. Rib re-enforcing is 150lb polyester, so that if the bridle-rib connection should be over-strained, it should break the 80lb Spectra bridle, which is easy to repair in the field, rather than the sewn re-enforcing which would be a nasty job in the workshop. The bridle points are re-enforced with rip-stop repair tape on the inside. I always use white tape, because it shows the least. The re-enforcing is not stitched (I don't want extra holes here!), but the corners are cut off the square to make it an octagon, to help avoid peeling. The Gauze. In gauze, I'm looking for the best combination of thin, light, flexible and large-holed that I can find. The stuff I've got is from Vlieger Op and does the job as required, but I'm still looking for a source for my ideal gauze. I make the gauze slightly deeper than on the Sputnik to increase the inflation rate and help the internal pressure. This may cost me a fraction off the lift-to-drag, but it's a price I'm willing to pay. Taper. The kite tapers at the tips in exactly the same way as the Sputnik. Primary bridle. The measurements are based strongly on the primary bridle for the Sputnik, but I bring 4 lines (or 2 loops) to one point rather than 4 lines to either end of a short v-line as Nop does (this is mostly a matter of taste). The tips are tuned back a bit from the "program" setting (Nop confirms that he does this on his Sputniks too...). The tip bridles sets are lengthened to the same as the rest of the primary bridle to provide a consistant interface to the cross-bridle. The primary bridle is constructed from 80lb Spectra, which is more than sufficient (ignoring several real-world considerations, the 52 primary bridles should thoretically be good for a combined strain of 4160lb). The primary bridle is over-rated in this way in order to have the freedom to tie it without sleeving and to better resist killer-tree damage and abnormal loads due to bridle tangles. (I'm sure that 40lb line would fly fine, but the stuff is so fine and fly-away that you'd be forever catching it and breaking it on things. Each kite is individualy tuned. Cross bridle. This is based on experience with Peter Lynn's cross bridles (and again, I have seeked and obtained permission), but all the measurements are mine. The bridle is again built of 80lb Spectra. Experience shows again that this is sufficient to support extreem over-strain. Note however that the cross-bridle is the weakest link in the bridle - damaged lines should be repaired or replaced promptly, as over-strain on a damaged bridle could lead to complete failure - you snap one line, which causes the next line to be over-loaded, causing that one to fail... Although it is a little disturbing to see your entire cross-bridle snap and your canopy float away, it is a simple and quick job to build and attatch a new one. Unlike the Peel cross-bridle, which is built from (approx) one single line, woven into a cat's cradle, the Chevron's cross-bridle is constructed from individual lines. Each one is over-size to allow room for adjustment (and I'll Email you adjustments as I develop them). Having individual lines means that if you get the bridle into a nasty tangle, you can take the easy way out: - ensure that the lines to one side are marked for later identification - untie the line attatchment loops - disentangle by simply pulling the lines out of the mess - re-group marked and unmarked sides together - re-tie the line attatchment loops Do *not* try this on a Peel cross-bridle - the accepted wisdom is that if the Peel line attatchment loops have been untied in order to attempt this type of fix, then the mess will be so bad that it's best to cut the cross-bridle off and build another one. Line attatchment. The cross-bridles join together at two line attatchment loops. On a Peel, these loops are a few inches long. On the Chevron, these loops are *much* longer (A 10' or so length of 450lb Spectra, folded double). This is in order to avoid getting the cross-bridle tangled in the line-knot. Fabric. No compromise. The canopy is built from hot-cut 32g (1/2oz) Icarex to allow maximum performance in minimum wind. Thread. The thread used is 40 DIN Nylon. This is much thicker than domestic thread. I have to buy it direct from the manufacturer, who has it listed as suitable for constructing training shoes and matresses :-) The large diameter of this thread means that it is less inclined to cut the fabric (under stress, it's the fabric that fails, not the thread), It is also considerably more elastic than regular thread, allowing another element of "give" to help avoid bursting the fabric. I sew at the maximum stitch length available to minimise the number of "tear down the perforations" holes in the fabric. In the event of an under-tension problem while sewing (and when you're sewing silk with boat anchor, you're thinking about tension all the time...), I'll usually carefuly retension the stitches and tie off the excess rather than unpick and re-sew to create another row of holes) Graphic. The "slice" on the Sputnik and the "wave" on the Peel are not just for decoration - they serve the purpose of dividing the skin into pieces narrow enough to fit into the available width of fabric. The design that I use is in the shape of a Chevron pointing forwards: ::::::::::::::://////\\\\\\::::::::::::::: ::::::::::::::://////::::::::::\\\\\\::::::::::::::: :::::::::://////::::::::::::::::::::\\\\\\:::::::::: ::::://////::::::::::::::::::::::::::::::\\\\\\::::: /::::::::::::::::::::::::::::::::::::::::\ (kinda difficult to draw in ASCII...) Whilst the design is dramatic and striking, there is also a practical purpose behind it: Once in Berkeley, I came out of a spin on the buggy, glanced at the Peel I was flying and thought it was going safely upwards when it was, in fact, just starting a power dive. Unaware of what was going on, I failed to release the kite and suffered a face-plant on the grass as a consequence. The large "It's going this way!" arrow might help me avoid this confusion again... Postscript: I found out today that I won't be getting a free ride to El Mirage from my employer. I have 4 Chevrons, If I can sell (*) a couple of them (commitment now, cash in the desert) *before* I leave then I'll still be able to attend. (*) Yeah. Sell. This is an advert. I'm still discussing rec.kites.marketplace. I think I've earned a break... The kites are: 7.1m^2. White (semi-transparant) 1/2oz Icarex. Bold black Chevron graphic. 2 available: US$ 450 7.1m^2. As above but with black ribs. (Nice effect but a pain to sew the black ribs. I ain't doing another one!) 1 only: US$ 500 12m^2+ (I must work out the exact size...) Dayglo orange with fine double- chevron graphic. 1 only: US$ 750 Andrew -- Must sell to get to El Mirage: Chevrons: (cross-bridled Sputnik derivative) 7.1m^2 white + black Chevron graphic, Spectra cross bridle. 1/2oz Icarex US$450 7.1m^2 as above with black ribs (white is transparant) US$500 12m^2+ Orange + black double-chevron (buggy when others must walk!) US$750