Date: Mon, 1 Jan 1996 08:47:20 -1000 From: Matthew Hurrell Message-Id: <115284509wnr@hurrell.demon.co.uk> Subject: Cross bridle design theory Designing foils bridles is definitely a black art. Here are some of my ideas on cross bridle design. Short bridles. Short bridles cause less drag. The kite flies faster and pulls harder. However if you make them too short the kite starts scrunching up in tight turns, and can collapse unexpectedly. This is extremely annoying. I found this out when I put a cross bridle on my 3m^2 Sputnik. I scaled down the measurements for a 3.6m Peel bridle. However what works for a Peel may not work for a Sputnik. Even when I enlarged the bridle, it was still too small. In the end I went back to an arch bridle. Which is fine for this little kite. Long bridles. Long bridles cause less of a crushing load on the cells in the kite. This will enable the kite to inflate more easily, it should also enable the kite to keep a better shape when in a stall. However they cause more drag etc. Turn rate. To make a kite turn more tightly you need to get it to lean more on one side than the other. If the tow points are close together no matter how much you pull on one line the kite will not turn any tighter. The crossed bridle lines in the middle will restrict the amount the kite leans on side. I made my sputnik turn more tightly by shortening the lines at the edges of the kite and lengthening the lines in the middle. In straight flight the lines in the middle are slack, but in a turn they go taught (they should do, but not on mine yet). In effect you have two bridles one for straight flight and one for turning. e.g. In a tight right turn the left bridle is redundant Turning circle size This is restricted by three things. The kites wing span, the wider the kite the more room it needs to manoeuvre. The bridle tow points (see above). And finally the length of you arms. Basically even a small kite turning around a point a metre from its wing tip will turn in less room than a large kite turning on its wing tip. In my limited experience of buggying I've found that half the game is being able position the kite effectively, a manoeuvrable kite lets you do this more easily. Finally I repeat, these are just my own thoughts. Id like to hear everyone elses ideas on the subject. -- Matt ___________________________________ Cheshire = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 1 Jan 1996 16:25:44 -1000 From: Steve Bateman Message-Id: <4ca538$6ga@hole.sdsu.edu> Organization: San Diego State University Subject: Re: Cross bridle design theory Matthew Hurrell wrote: > > Designing foils bridles is definitely a black art. Here are some of my ideas > on cross bridle design. If I'm correct, most of the people interested in this are rebridling sputniks. I would be interested in the reasons for this (what's wrong with the arch bridle?). Thanks Steve Bateman bateman@mail.sdsu.edu Flying along. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 1 Jan 1996 21:05:51 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Cross bridle design theory Matt@hurrell.demon.co.uk writes: >Basically even a small kite turning around a point a metre from its wing tip >will turn in less room than a large kite turning on its wing tip. Here, we have a choice. You can either configure the cross-bridle so that on maximum turn, the kite retains it's shape and will turn tightly, without collapse (a fool-proof setting) OR we can go past this point and choose that with 100pull on one line the wing-tip is liable to collapse. I need to double check this in the field, but I think that it was this feature that I was using to turn big kites (like 10m^2 and 15m^2) *inside* the wing-tip. Andrew -- http://www.kfs.org/kites as returned to life! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 2 Jan 1996 10:22:38 -1000 From: miel@knoware.nl (Emiel Stroeve) Message-Id: <4cc3u6$5o4@news.euro.net> Organization: Euronet Internet Subject: Re: Cross bridle design theory Steve Bateman wrote: >Matthew Hurrell wrote: >> >> Designing foils bridles is definitely a black art. Here are some of my ideas >> on cross bridle design. >If I'm correct, most of the people interested in this are >rebridling sputniks. I would be interested in the reasons >for this (what's wrong with the arch bridle?). >Thanks Hi Steve, There's nothing wrong with an arch bridle (at least if you use the disc one). A crossbridle however has two main advantages over an arch bridle: 1. steering is more direct, the tow points are direct connected to the foil so a pull on a tow point will direct result in a turn. With an arch bridle you first have to stretch an angle; 2. the foil is kept in shape better, especially during turns. one disadvantage is the increase of drag due to more bridle lines. check out my homepage for more details. see you, emiel Emiel Stroeve The Netherlands miel@knoware.nl --------------------------------------------------------------------------- <<< *** http://www.euronet.nl/users/mielse/index.html *** >>> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 2 Jan 1996 10:08:36 -1000 From: Matthew Hurrell Message-Id: <90135634wnr@hurrell.demon.co.uk> Subject: Re: Cross bridle design theory In article: andrew@tug.com (Andrew Beattie) writes: > > Matt@hurrell.demon.co.uk writes: > >Basically even a small kite turning around a point a metre from its wing > >tip will turn in less room than a large kite turning on its wing tip. > > Here, we have a choice. You can either configure the cross-bridle so that > on maximum turn, the kite retains it's shape and will turn tightly, > without collapse (a fool-proof setting) OR we can go past this point and > choose that with 100pull on one line the wing-tip is liable to collapse. > > I need to double check this in the field, but I think that it was this > feature that I was using to turn big kites (like 10m^2 and 15m^2) *inside* > the wing-tip. Presumably the tow points were far apart and relatively close to the kite producing a more arched kite? Incidently after plotting Peel bridles into a CAD package I found that the 3.6m Peel is flatter than a 5.1 Peel. I asume this is because turn rate is not as important on a small kite as a large one. The 3.6m is setup for power rather than turn rate. >From this I deduce that the larger the kite the more arched it is to keep up a decent turn rate. By the way, what do you use the 15m^2 kite for? Breaking the sound barrier in your buggy!! -- Matt ___________________________________ Cheshire = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 2 Jan 1996 11:04:31 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Cross bridle design theory Steve Bateman writes: >If I'm correct, most of the people interested in this are >rebridling sputniks. I would be interested in the reasons >for this (what's wrong with the arch bridle?). The Catenary (Sputnik) bridle has one definate, clear advantage over a cross-bridle. Fewer lines give less drag. Let's get out an envelope and do some calculations: Cross bridle: 52 primary bridle lines. Average length 1m 26 secondary bridle lines. Average length 2m Total: 104m Catenary bridle. 52 primary bridle lines. Average length 1m 13 secondary bridle lines. Average length 2m 1 tertiary bridle line. Length 3m Total: 81m So you've got 23m (70') less line-drag. Not to be sniffed at. For smaller canopies, the difference in handling and steering performance are less marked, but for my taste, I much prefer the way that a *good* cross-bridle performs. It's a personal preference sort of thing, but in order to explain, I'll exagerate. Imagine a flying a small wind-bow as a 2-line kite. It bends too much towards you - the tips arn't helping much and they are inclined to fold in. Steering involves making the bend in the middle of the wind-bow move to one side and hoping. This is tha Catenary bridle. The Cross-bridle supports the entire canopy more fully and holds the kite flatter. This is, of course *grossly* unfair. I'm trying to explain a farily subtle difference, ok? Cat bridles are, in fact rather rather good. Andrew -- http://www.kfs.org/kites as returned to life! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 2 Jan 1996 21:15:48 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Cross bridle design theory Matt@hurrell.demon.co.uk writes: >Presumably the tow points were far apart and relatively close to the kite >producing a more arched kite? I guess so. >Incidently after plotting Peel bridles into a CAD package I found that the >3.6m Peel is flatter than a 5.1 Peel. I asume this is because turn rate is >not as important on a small kite as a large one. The 3.6m is setup for power >rather than turn rate. Probably down to the fact that you need longer arms for 5m than 3m, so you can use a different set of compromises. >By the way, what do you use the 15m^2 kite for? Breaking the sound barrier >in your buggy!! *grin* No. Smaller kites are faster. The big stuff is to let me give tandem rides when other people are flying 360's Andrew -- http://www.kfs.org/kites as returned to life! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =