Date: Wed, 4 May 1994 17:05:17 -1000 From: mgraves@leadingedg.win.net (Michael Graves) Message-Id: <388@leadingedg.win.net> Subject: Cross connected upper spreader In article , David Lord (lord@eskimo.com) writes: ><356@leadingedg.win.net> > > >A better solution to sewing a patch on the sail is to sew the patch then >cut a hole in the patch so a small vinyl connector can be attached. The >connector has a hole punched at right angles to the axis of the vinyl >tube for the spine. Another hole at right angles to the spine hole and >the tube axis is punched for the upper spreader. The displacement >between the two punched holes is 1/2 to 3/4 inch. This will >significantly improve the frames ability to withstand the bridle loads. >I use this technique on all the kites I build and it results in either a >significantly higher wind range or allows using a smaller spar size. If >you look at the loads created by the bridle you can see that the >triangle formed by the upper spreader attach point to the leading edge >and the center "T" connection is not very well reacted by any structural >member. A diagonal brace would be stronger but a big weight penalty. > Dave Lord Ok Dave, I'm going to bite! If this is supposed to work so well why does it work so poorly on the Lite Flite Radial? A couple of years ago I bought a radial, and thought the cross connected upper spreader would've been a large improvement. I've broken many upper spreaders just trying to get the slip bridle working. The entire kite is framed in 5.5mm RBJ carbon, but the upper spread breaks very easily. The breaks are always just off centre. Michael Graves = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 5 May 1994 23:55:05 -1000 From: salanne@convex.csc.FI (Simo Salanne) Message-Id: <2qd45p$l03@pobox.csc.fi> Organization: Centre for Scintific Computing Subject: Re: Cross connected upper spreader In <388@leadingedg.win.net> mgraves@leadingedg.win.net (Michael Graves) writes: >Ok Dave, I'm going to bite! If this is supposed to work so well why >does it work so poorly on the Lite Flite Radial? >A couple of years ago I bought a radial, and thought the >cross connected upper spreader would've been a large improvement. >I've broken many upper spreaders just trying to get the slip bridle >working. The entire kite is framed in 5.5mm RBJ carbon, but the >upper spread breaks very easily. The breaks are always just off >centre. Upper spreader/spine connection takes pretty heavy loads. I have broken 3 times stiffer sticks (compared to 5.5 RBJ) there. ... and RBJ is propably the poorest carbon spar I have ever seen:-( Simo -- Simo.Salanne@csc.fi STACK Finland = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sat, 7 May 1994 22:58:19 -1000 From: lord@eskimo.com (David Lord) Message-Id: Organization: Eskimo North (206) For-Ever Subject: Re: Cross connected upper spreader <388@leadingedg.win.net> I am not familiar with the radial liteflite so I can't comment. However on most every delta shaped stunt kite I have seen the upper spreader is the least stressed member of the kite frame. This especially true of the low aspect designs that are more the norm. A typical kite will use the same spar for all elements of the frame. Some people use a heavier spine than the rest of the frame. I don't think this is necessary unless actual flying experience shows breakage. Anyway look at the configuration. The upper spreader is the shortest of all the elements and the sail area where it is located is also smaller. Integrating the spine and the upper spreader helps both elements resist breakage. I have built many kites and have broken only one upper spreader and that was the result of both lower spreaders breaking first thus dumping the whole load onto the upper spreader. This connection should be with a vinyl so that the slight rotation around this connection does not result in a concentrated stress. There may be specific kite designs that overstress the upper spreader, but I have never met one yet. On your radial was the connection soft like one would get with a vinyl or did it have a stiffer connection more similar to the lower "T" connection one finds on many commercial kites. If you do even a rudimentry loads analysis on a delta stunt kite I think you will come to the same conclusion. Also it is very instructive to build a large delta stunter and observe the frame in flight. It will fly slower so it is easier to see the deflections in the spars and while the percentage deflection will be the same in a well designed larger kite, the absolute values will be larger and easier to see. The difference of connecting the upper spreader to the spine can readily be seen in the deflections of the leading edge in turns. All my experience as well as the analysis I have done confirms for me that this connection is very beneficial. Dave Lord = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =