From: aatd1@sgies14.sdrc.com (derek hart) Subject: large tetras Message-ID: <320@heimdall.sdrc.com> Date: Fri, 8 Jan 93 16:19:00 EST Organization: SDRC Hi all - Does anyone have any good suggestions for building modular tetrahedron (triangular pyramids) box kites? I am specifically wondering about the best design (strongest/lightest) for the interface between modules. Also, what would be best unit size for a single module? I seem to remember a photo of a man hanging from a very large assembly of these kites while it was towed behind a large ship. Thanks. Derek Hart = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: sasaki@netop3.harvard.edu (Marty Sasaki) Subject: Re: large tetras Message-ID: <1993Jan11.162409.6773@das.harvard.edu> Organization: Harvard University Date: Mon, 11 Jan 93 11:24:09 EST In article <320@heimdall.sdrc.com>, aatd1@sgies14.sdrc.com (derek hart) writes: >Does anyone have any good suggestions for building modular tetrahedron >(triangular pyramids) box kites? I am specifically wondering about the >best design (strongest/lightest) for the interface between modules. Also, >what would be best unit size for a single module? One of the problems with tetras in general is that they weigh a lot for their effective wing area. In a normal tetra it takes 6 sticks for each cell. The tendancy is to use light materials in order to get a kite light enough to fly in light wind. The approach that I've seen most often is to have a large tetrahedron frame made out of fairly strong material. Smaller tetrahedrons are attached to this frame, sharing parts of the frame where possible. Someone makes a tetra that uses a rather clever system of four hollow fiberglass rods and two thin solid rods that produce a fairly strong, yet still light weight, cell. I've experimented with kites that use tensegrities as frames and found that tie-wraps (those plastic things that are often used to bundle wires together) are useful for assembling multiple sails together. You can get tie-wraps as big and as strong as you like, they are even being used in lieu of handcuffs. -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@netop3.harvard.edu Network Operations Division 26 Green Street 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: sgreene@access.digex.com (Stephan Greene) Subject: Re: large tetras Date: Sun, 10 Jan 93 13:09:33 EST Organization: Express Access Public Access UNIX, Greenbelt, Maryland USA Message-ID: <1ipootINNiio@mirror.digex.com> In article <320@heimdall.sdrc.com> aatd1@sgies14.sdrc.com (derek hart) writes: >Hi all - > >Does anyone have any good suggestions for building modular tetrahedron >(triangular pyramids) box kites? I am specifically wondering about the >best design (strongest/lightest) for the interface between modules. Also, >what would be best unit size for a single module? > >I seem to remember a photo of a man hanging from a very large assembly of >these kites while it was towed behind a large ship. > >Thanks. Derek Hart Many (over fifteen!) years ago, I purchased a tetra kite kit. The joints between "cells" were ijection modlded plastic parts with short stubs for joining the individual cells and the stringers that formed each cell. The system was inherently expandable, by joining groups of four-cell kites into a single larger kite. These joints were also rather weak, and were prone to disconnecting at inpapprpopiate momemnts (like in flight!) and breakage on the ground. I wonder if tinker-toy pieces and wood dowels would work? The tinker toy pieces are rather large, but glud could keep ebexxx everything tohxxx togetger (at the price of not being able to disassemble the monster!) Steve Greene sgreene@access.digex.com = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) Subject: Re: large tetras Message-ID: <79868@hydra.gatech.EDU> Date: Tue, 12 Jan 93 11:38:57 EST Organization: Georgia Institute of Technology Just one question; Why do you want to build a tetra? If your looking for power, there are much better alternatives. If you like the design, I would encorage you to examine the work of Bell and duplicate his work as a historical endevor (SP?). Otherwise, KITELINES had an article about an obtruse tetra a few issues ago. I friend build one and it's OK, but not fantastic. The big thing is going to be the connectors. Marty related a very valid option, the use of wire ties. They can be had at hardware stores in the electrical section. -- The Mad Hata "Hey, Mon....Tako Kichi!" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: jeffy@syrinx.umd.edu (Jeffrey C. Burka) Subject: Re: large tetras Message-ID: <17947@umd5.umd.edu> Date: Wed, 13 Jan 93 17:15:01 EST Organization: University of Maryland at College Park In article <79868@hydra.gatech.EDU> sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) writes: >Otherwise, KITELINES had an article about an obtruse tetra a few issues >ago. I friend build one and it's OK, but not fantastic. The big thing >is going to be the connectors. Marty related a very valid option, the >use of wire ties. They can be had at hardware stores in the electrical >section. I fly with Bill Kocher, the guy who wrote the article in KiteLines, and I've seen his tetra several times. I think that if you're interested in tetras, this really is the way to go. Admittedly, it loses a bit in elegance and ease in building large, complex shapes, but it still _looks_ like a tetra and it does fly in pretty low wind. Jeff -- |Jeffrey C. Burka | "Fairies are the perfect people to do this | |(suffering Bad Grammar) | sort of work. Biologically, their upper | |jeffy@syrinx.umd.edu | bodies are strong enough to wield a pickaxe...." | = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) Subject: Re: large tetras Message-ID: <80124@hydra.gatech.EDU> Date: Thu, 14 Jan 93 08:59:10 EST Organization: Georgia Institute of Technology Yeah, Jeff it does look like a tetra. But I'm trying to generate interest in historical kites. Maybe it will get off the ground one of these days as a comprehensive event. When I was a kid, I built a tetra from long drinking straws and tissue paper covering for the sail. The straws were held together by running string through them. It flew nicely in a moderate breeze but like so many other things from your child hood, it got destroyed when I tree'd it and pulled it back out. Oh well. PS: The plans were in National Geographic, circa 1967. -- The Mad Hata "Hey, Mon....Tako Kichi!" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: andrew@tug.com (Andrew Beattie) Subject: Re: large tetras Message-ID: Date: Thu, 14 Jan 93 06:56:37 EST Organization: Negligible. In article <79868@hydra.gatech.EDU> sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) writes: >Just one question; Why do you want to build a tetra? Don't dismiss them lightly. I'm no expert on this type of kite, but I understand that: 1) The big ones are very stable. When a diamond kite is within a few wingspan lengths of the ground, it becomes very unstable. This means that a big man-lifter may be unstable while still a considerable distance off the ground. A large matrix of Tetras tends to act as many small kites flying in formation, multiplying the lift without sacrificing so much stability. 2) While one single cell is heavy, in a matrix, the each cell shares all of it's sticks with adjoining cells, so the overall sail-area/weight ratio becomes quite good. Hmm... Perhaps I'll build a big tetra next... Andrew -- Andrew Beattie PO Box 109, Basingstoke, RG24 0YB, UK. Email:andrew@tug.com Phone:+44-256-464912 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: Peter Manson Subject: Re: large tetras Message-ID: <1993Jan14.144655.7179@bnr.ca> Organization: Bell-Northern Research X-Useragent: Nuntius v1.1.1d9 Date: Thu, 14 Jan 93 09:46:55 EST I built a 4-cell tetra (my first) following the Kitelines article's instructions. I found that it flies well in medium winds; say 7 - 15 km/h. If it's too windy, it rises to horizontal, the wind gets on top of it, and it drops from the sky. I haven't tried to fix this yet; but what I'd like to try is a two-point bridle to hold the tail end down just a bit (the article says to just attach the flying line to the top of the bottom edge). Will this help? Any other ideas? As for the connectors, the method in Kitelines works quite well. The four 3-stick joints within a cell are done with a piece of vinyl tubing with a hole punched across the middle. (I found these to slip out sometimes, but then I didn't paint the dowels as instructed.) The cells are joined with a connector made out of a piece of neoprene fuel hose, with four holes punched through it (the two top ones in the same direction, and the two bottom ones at right angles to the top ones). This cell-joiner is "universal": only one kind of connector is needed, even though the different cell joints join 2, 3 or 4 cells. The other nice thing about the design is that you can put together a bunch of cells, and then decide on how many to assemble "in the field". The cells can be left assembled, and stacked like chairs for transporting them -- then all that's left to do is connect the cells. I've got 6 more cells on the way, and maybe more after that! Cheers. Peter = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: robertw@cv.hp.com (Robert B. Williams) Subject: Re: large tetras Message-ID: <1993Jan14.210053.21557@hpcvusn.cv.hp.com> Date: Thu, 14 Jan 93 16:00:53 EST Distribution: na Organization: Hewlett-Packard Company, Corvallis, Oregon USA I don't know much about tetra's, but I got a toy for Xmas (flexi-frame, or something like that, not related to Flexi-Foil!) that has connectors made of soft rubber tubing. Half the tubes have a hole punched through the middle, in which you insert the other half of the tubes, making a 4 way connector. You then insert tinkertoy like sticks in the tubes to make a fleixible dodacahedran or something. I'd guess surgical tubing of the appropriate diameter would work for any kite stick. It will definitely stick to painted spars. Something like this: V hole in which to insert the other tube Half the tubes __________________________________ O ---------------------------------- The other half __________________________________ ---------------------------------- Joined: | | | | | | | | | | ________________________________ O -------------------------------- | | | | | | | | | | If you're having trouble getting the tube through the hole, take a short stick, put the unholed tube on the end and use it to thread through the hole. I suppose you could make a second hole to make n-way connectors. -- Robert Williams robertw@hp-pcd.cv.hp.com 503-750-2818 HP in Corvallis Oregon = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Subject: Re: large tetras Message-ID: <1993Jan14.194237.15535@stsci.edu> From: yen@stsci.edu (Felix Yen) Date: Thu, 14 Jan 93 14:42:37 EST Distribution: na Organization: Space Telescope Science Institute The Mad Hata (sc5@prism.gatech.EDU) writes: > Yeah, Jeff it does look like a tetra. But I'm trying to generate interest > in historical kites. Maybe it will get off the ground one of these days as > a comprehensive event. > > When I was a kid, I built a tetra from long drinking straws and tissue > paper covering for the sail. The straws were held together by running > string through them. It flew nicely in a moderate breeze but like so > many other things from your child hood, it got destroyed when I tree'd > it and pulled it back out. Oh well. > > PS: The plans were in National Geographic, circa 1967. You might be interested to hear that the Smithsonian Institute marketed a children's science kit last year that featured Alexander Graham Bell and included a small tetra. Instead of tissue paper, some variety of plastic. Instead of drinking straws, plastic rods. The joints are made by tying together the centers of three lengths of plastic tubing with plastic wire ties (the ones mentioned earlier by TMH and Marty Sasaki) thus producing a six-way connector. It appears to be a clever design, but the weather has prevented me from attempting a launch so far. Felix yen@stsci.edu = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = From: sc5@prism.gatech.EDU (CSEPLO,STEPHEN P) Subject: Re: large tetras Message-ID: <80273@hydra.gatech.EDU> Date: Fri, 15 Jan 93 08:53:29 EST Distribution: na Organization: Georgia Institute of Technology In article <1993Jan14.194237.15535@stsci.edu> yen@stsci.edu (Felix Yen) writes: (edited) >The joints are made >by tying together the centers of three lengths of plastic tubing with >plastic wire ties (the ones mentioned earlier by TMH and Marty Sasaki) >thus producing a six-way connector. It appears to be a clever design, >but the weather has prevented me from attempting a launch so far. That does sound clever. Thanks for mentioning it. -- The Mad Hata "Hey, Mon....Tako Kichi!" = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =