Date: Tue, 7 Mar 1995 09:10:30 -1000 From: sasaki@netope.harvard.edu (Marty Sasaki) Message-Id: <3jib36$i29@netope.harvard.edu> Organization: Harvard University Subject: Efficiency I started this a while back with the discussion about "induced" camber. At the time, someone asked what I meant about efficiency. I didn't respond right away because I wanted to come up with something relatively complete. Well, I never had the time, so I figured that before I forgot about this entirely, I would write down a few things. Before a kite can become airborne the air moving around the kite must generate enough lift to overcome the force of gravity and the drag on the kite. Faster moving air creates more lift, which results in a faster moving kite. All else being equal, a lighter kite will fly in lighter wind because there isn't as much weight "holding" the kite down. The approach taken with many ultra-light and indoor kites is to reduce the weight of the kite by going to lighter weight materials and using special construction techniques to use less material. Reducing the weight, usually reduces the stiffness and the strength of the kite. Ultra-light stunt kites are sometimes very fragile as a result of this. Let's suppose that rather than reducing the weight, we change the design of the kite so that it is more efficient. For a given wind speed, more lift will be generated than before. If this new kite weighs the same as the old kite, it will fly in lighter wind than the old kite. We could also use different materials to make the kite stronger since the added lift will be able to move a heavier kite. Non-foil stunt kites are very inefficient. The single surface airfoil, with very little camber (induced or otherwise), and a sharp leading edge, is one of the least efficient ways of building a wing. So, what can be done to increase efficiency? Dave Lord has done some experimentation with putting real camber into the kite sail by using appropriately shaped battens. He reports greatly increased pull in moderate wind (more lift!). Bob Childs has created a kite with double surfaces in parts of the wing. The thicker airfoil section will increase lift. The Wangdoodle has great low wind performance. Look at a board sail boat some time. The sail has real induced camber, with battens to hold the sail's shape. High performance hang gliders use rigid wings, with double surfaced, high tech airfoils. Some high performance sail boats (in classes that allow their use) have strangely shaped masts. These are designed to create a blunt nose (which increases efficiency) and a thicker airfoil near the mast. What am I doing about this? I'm experimenting with leading edges to duplicate the masts mentioned above. I'm playing with styrofoam to try to create lightweight double surface airfoils. Problems? Lightweight construction is difficult so far. Prototypes have been heavy. Control is "weird". A standard stunt kite is flopping all over the place. The shape of the wing is constantly changing. This has a large amount of "self compensation" built in. When the force gets too high on the winglets of the Katana-2, it just pushes back, decreasing the force on it. More rigid wings don't self adjust as well, at least I haven't figured out how to do this. Although my success has been minimal, it has been fun playing around. If I have a breakthrough, I'll post to rec.kites... Marty -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@harvard.edu Network Services Division 90 Melrose Street 617-496-4320 10 Ware Street Arlington, MA 02174 Cambridge, MA 02138-4002 phone/fax: 617-646-1925 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 7 Mar 1995 12:43:07 -1000 From: Bruno.Brottier@icare.fdn.org Message-Id: <1995Mar7.224307.8232@icare.fdn.org> Organization: Individual - Levallois, France. Subject: Re: Efficiency In article <3jib36$i29@netope.harvard.edu> sasaki@netope.harvard.edu (Marty Sasaki) writes: > Marty There is a french guy, so called Long Duong who builds such kites for many years. He builds this kites with two induced cambers per half wing, with very special auto-adjusting stand-offs. They are heavy because of extra carbon matter, and they fly in low wind. But at this time, the kites are too radical to perform real tricks, and even if the turn radius is important, there is some oversteer because of inertia. Speed is very important, and they are usually used as tracking kites, or for having strong emotions. Kites are pieces of cake, very good work. If you come to french kite festival, you could met him. If you want his address, to share experience/feelings, I can bring it to you. Cheers Bruno --------------------------- Bruno Brottier 37 rue Chaptal 92300 LEVALLOIS PERRET - FRANCE E-mail: Bruno.Brottier@icare.fdn.org -- [NeXTmail] --------------------------- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 7 Mar 1995 19:33:36 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Efficiency In article <3jib36$i29@netope.harvard.edu> sasaki@harvard.edu writes: >I'm playing with styrofoam to try to create lightweight double surface >airfoils. Hmmm... Could you use heat-seal techniques to create a custom polythene tube that you could inflate within a pocket under the leading edge? Andrew -- New to rec.kites? START HERE! | To: www@kfs.org send an email message like this>>| Subject: service /-\ () >< () |\/| () >< () /-\ | http://www.kfs.org/kites/welcome/index.html = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 9 Mar 1995 10:18:02 -1000 From: higginson@pfc.mit.edu (Wavey Davey) Message-Id: Organization: MIT Plasma Fusion Center Subject: Re: Efficiency > > Could you use heat-seal techniques to create a custom polythene tube that > you could inflate within a pocket under the leading edge? > > Andrew You could call it 'The Pump' - although Reebok may not be too happy... :-) -- Dave Higginson higginson@pfc.mit.edu = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 9 Mar 1995 02:34:52 -1000 From: andrewh@holly.harvard.edu (Andrew Hawken) Message-Id: <3jmslc$44@epsilon.qmw.ac.uk> Organization: Queen Mary & Westfield College, London, UK Subject: Re: Efficiency Andrew Beattie (andrew@tug.com) wrote: : Hmmm... : Could you use heat-seal techniques to create a custom polythene tube that : you could inflate within a pocket under the leading edge? I did some thinking on those lines, but actually considering a push bike inner tube for a le. Weight of rubber aside, getting it stiff enough meant quite a lot of air, and that has more mass than the styrofoam solution. A lot more. BUt of course, it is collapsable. Andy -- ____________________________Andrew Hawken______________________________ "However many ways there may be of being alive, it is certain that there are vastly more ways of being dead" R Dawkins. Home : 0895 420110 QMW : 071 975 5542 AIIT : 0494 677045 Email : A.Hawken@QMW.AC.UK = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 10 Mar 1995 04:35:11 -1000 From: jburka@Glue.umd.edu (Jeffrey C. Burka) Message-Id: <3jpo2v$1a8@geog20.umd.edu> Organization: Project Glue, University of Maryland, College Park Subject: Re: Efficiency In article <3jmslc$44@epsilon.qmw.ac.uk>, Andrew Hawken wrote: >Andrew Beattie (andrew@tug.com) wrote: >: Hmmm... > >: Could you use heat-seal techniques to create a custom polythene tube that >: you could inflate within a pocket under the leading edge? >I did some thinking on those lines, but actually considering >a push bike inner tube for a le. Weight of rubber aside, getting >it stiff enough meant quite a lot of air, and that has more >mass than the styrofoam solution. A lot more. BUt of course, >it is collapsable. Actually, I had taken what Andrew B. said to be an inflatable pocket in addition to a spar or perhaps a flat batten...something to increase the diameter or change the shape of the leading edge. As for inflatable "spars", they have been used successfully by Bill Tyrell in some of his monster kites -- a 50' eddy and a 50' rok. They were some sort of vinyl, and they were not terribly stiff, but they did add some structure to the kites. The kites *did* use a lot more bridle lines than is traditional to help them hold their intended shape, but it was the flex of the spars and the length of the various bridles that created the bow to the kites. My guess is that you'd want to avoid something stretchy like an innertube in order to try to get some stiffness at a low enough pressure. Jeff -- |Jeffrey C. Burka | Pithy, insightful quote to be inserted | | | when one occurs to me. *If* one occurs | |jeffy@glue.umd.edu | to me. | = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =