Date: Wed, 2 Jun 1993 17:16:44 -1000 From: plepez@ulb.ac.be (Lepez Philippe) Message-Id: <9306021916.AA14063@is1e.vub.ac.be> Organization: Division of Applied Sciences, Harvard University Subject: Spar stifness Hi all, The posting of Simo Salane on spars was very interesting and it gives me an idea I would like to submit to the group : why not use tapered spars on our delta kites. I think mainly on the leading edge : have a light (and less stiff) spars near the nose and the wing tip and a stronger (and heavier) in the middle. Any comment welcome. Good winds. -- Philippe Lepez (CP 125), | | Good kite Universite Libre de Bruxelles, | Email: plepez@ulb.ac.be | + Good wind 50 av. Roosevelt, | Phone: 32.2.6503553 | ---------------- 1050 Bruxelles, Belgique. | Fax : 32.2.6503323 | = A lot of fun ! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 2 Jun 1993 10:18:14 -1000 From: sasaki@das.harvard.edu (Marty Sasaki) Message-Id: <1993Jun2.201814.27683@das.harvard.edu> Organization: Harvard University Subject: Re: Spar stifness In article <9306021916.AA14063@is1e.vub.ac.be>, plepez@ulb.ac.be (Lepez Philippe) writes: >The posting of Simo Salane on spars was very interesting and it gives me an >idea I would like to submit to the group : why not use tapered spars on our >delta kites. I think mainly on the leading edge : have a light (and less stiff) >spars near the nose and the wing tip and a stronger (and heavier) in the middle. There are several USA manufacturers that are experimenting with tapered spars and some are actually using them in production kites. >From a structural point of view they make a lot of sense. From a manufacturing point of view they can be a real headache. Imagine a dealer having to stock replacement parts for a slew of kites each with slightly different frames. This is part of the reason that many stunt kites use spars that are 32.5 inches long, and the range of stiffnesses isn't very high. Until the volume of kite sales increases to the point where it is reasonable to stock all sorts of tapered and non-tapered spars, you probably won't see this type of technology used except in very high end kites. -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@noc.harvard.edu Network Services Division 26 Green Street 617-496-4320 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 2 Jun 1993 13:02:28 -1000 From: Darrin.Skinner@ebay.sun.com (Darrin Skinner) Message-Id: <9306022302.AA19307@stuntkite.EBay.Sun.COM> Organization: Division of Applied Sciences, Harvard University Subject: Re: Spar stifness Lepez Philippe (plepez@ulb.ac.be) writes: -] Hi all, -] -] The posting of Simo Salane on spars was very interesting and it gives me an -] idea I would like to submit to the group : why not use tapered spars on our -] delta kites. I think mainly on the leading edge : have a light (and less stiff) -] spars near the nose and the wing tip and a stronger (and heavier) in the middle. -] -] Any comment welcome. -] -] Good winds. -] -] Vince Brobrosky has been doing something simular to this with his kites (stinger 1000 and 750, and Pro Air Warrior and Chief) for quite some time. He uses a two piece leading edge with a lighter spar toward the nose of the kite. I know from personal experience that this works well. I would think that a less stiff spar at the wing tip would cause a great deal of shudder along the trailing edge. As such, the kite would tend to flap its wings. Might be an interesting idea for a novelty kite (might try it myself on something I have in mind -- big secret), but for performance I can't see it working. Also, tip stands could get real intersting with a soft wing tip! Oh, you were talking about a delta "stunt" kite... right? I made that assumption in my response. Darrin Darrin = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 3 Jun 1993 05:16:29 -1000 From: jeffy@syrinx.umd.edu (Jeffrey C. Burka) Message-Id: <1ul4kd$q4f@hecate.umd.edu> Organization: University of Maryland at College Park Subject: Re: Spar stifness In article <9306022302.AA19307@stuntkite.EBay.Sun.COM> Darrin.Skinner@ebay.sun.com (Darrin Skinner) writes: >I would think that a less stiff spar at the wing tip would cause a great >deal of shudder along the trailing edge. As such, the kite would tend to >flap its wings. Might be an interesting idea for a novelty kite (might >try it myself on something I have in mind -- big secret), but for performance >I can't see it working. Also, tip stands could get real intersting with a >soft wing tip! A couple of comments: First off, the new WindSport Composites rods are tapered. They're widest where they're ferruled. Spine, bottom spreaders, and leading edges are tapered. Upper spreader is a small-diameter pultruded stick. I've seen Jordan Air Pros and MEFMs (the super-ultralight version of Big Easy's EFM) flown with WindSport, and even in winds of 15mph or more, I've seen no suddering at the wingtips. I've heard from Ray Bordelon of Big Easy that the MEFM with WindSport (and 1/2 oz Icarex sail) can handle winds of 30mph. On Monday, I was flying a Skynasaur/Skyward Trixter, as well as my own custom 3/4 Tracer. The Trixter (and Tracker) are slightly larger than 3/4 scale. However, the Trixter has no dart keel. Both my kite and the Trixter are framed in AFC .2100. My kite was flying beautifully, with no shudder whatsoever (as far as I can tell, the shudder kicks in around 20mph, and I break a bottom spreader at about 25 (I really need to give it a bigger ferrule on the t-fitting!)). The Trixter was having *serious* problems with wingtip shuddering in winds that I really didn't consider to be that strong. The kite is rated 3-20, and I have a tough time believing that. Part of the answer might be to use a cut-out wingtip such as the one on the new I.Q. from Trilogy. On the other hand, I'm starting to see more enlarged wingtips ("winglets", etc.) such as on the Spectra Sports Reactor and Edge and Marty's Katana II. Marty: I know you've got a bracing line running from the internal corner of the winglet to the--um...t-fitting, isn't it?--despite the fact that the second "stand-off" holds that corner back. Does this help with shudder in the wingtip or just in that corner of the winglet? Jeff -- |Jeffrey C. Burka | "When I look in the mirror, I see a little clearer/ | |SAFH Lite [tm] | I am what I am and you are you too./ Do you like | |jeffy@syrinx.umd.edu | what you see? Do you like yourself?" --N. Cherry | = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 3 Jun 1993 07:33:43 -1000 From: sasaki@das.harvard.edu (Marty Sasaki) Message-Id: <1993Jun3.173343.7605@das.harvard.edu> Organization: Harvard University Subject: Re: Spar stifness In article <1ul4kd$q4f@hecate.umd.edu>, jeffy@syrinx.umd.edu (Jeffrey C. Burka) writes: >Part of the answer might be to use a cut-out wingtip such as the one on >the new I.Q. from Trilogy. On the other hand, I'm starting to see more ^^^^^^^ Should be Legend... >enlarged wingtips ("winglets", etc.) such as on the Spectra Sports Reactor >and Edge and Marty's Katana II. Marty: I know you've got a bracing >line running from the internal corner of the winglet to the--um...t-fitting, >isn't it?--despite the fact that the second "stand-off" holds that corner >back. Does this help with shudder in the wingtip or just in that corner >of the winglet? Well, the line runs from the corner of the winglet to the spreader where the inside standoff is attached. The line is there to keep the winglet from moving backwards. The theory behind these things is that they give you a little more area on the wing tips and little more drag. This helps forward flight stability. Most kites that have these don't brace them. The feeling here is that by not bracing, this can bend back and dump more air which helps in landings and stalls. The winglet on the K-2 is larger than most and letting it flap back actually destabilizes the K-2. The line does make assembly more difficult, but the kite flys much better with the line than without it. -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@noc.harvard.edu Network Services Division 26 Green Street 617-496-4320 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =