Date: 21 Feb 93 21:28:01 GMT From: jkn@ohm.york.ac.uk (John Nicoll) Message-ID: <1993Feb21.212801.14375@ohm.york.ac.uk> Organization: Electronics Department, University of York, UK Subject: porosity of seams / Flexi performance Hello all, Here's the story... my friend dave & I have built two 10foot Flexifoil clones, after I built a 6foot one a few months ago. We built most of them together, and in theory they should behave identically - but they don't. I'm trying to figure out why... Actually, I lied - they're not quite identical. The two diferences, apart from `normal manufacturing tolerances', are: 1) Dave made his too long (wide) by 6cm or so. In order to use the standard flexi spar, He has made a couple of extension couplers (steel & aluminium) between the centre CF spar and the outer GF spars. His couplers are together longer than 6cm, and so the ends of the spar stick a bit out beyond the end of the kite. His spar is also heavier than normal. 2) We (accidentally) changed the pattern of the ripstop, which has a sort of wide arrow on one side, and is solid ripstop on the other: mine RRRRRRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGGGGGGRRRRRRRRRRRRRRRRRRRR top RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR bot His GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG top RRRRRRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGGGGGGRRRRRRRRRRRRRRRRRRRR bot (R = red, G = green - bear with me ;-) The difference in flight is that dave's spar seems to bend more, and more uniformly, than mine - this I could understand, especially because the couplings have some slack. However, his is also (grr!) faster and more manouvreable than mine, by a noticable degree. (~30?) The obvious thing to do would be to try his `extended' spar in my flexi: however he had to cut slots in his tunnel to get the (larger) couplers in, and I'm reluctant to do this. The other thought I had is that if the seams are porous, than the fact that mine is on the top and his on the bottom might make a difference. I used lapped double seams (I think that's what they're called!) I ask for thoughts and comments on the above. Anyone with multiple flexis - how does performance compare? Might the weight and/or bend of the spar make all that much difference? Is there another aspect I haven't thought of ?? regards john nicoll -- john nicoll (jkn@ohm.york.ac.uk) Department of Electronics University of York Heslington YORK YO1 5DD U.K Tel +44 (904) 433221 Fax +44 (904) 432335 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: 22 Feb 93 18:43:27 GMT From: andrew@tug.com (Andrew Beattie) Message-ID: Organization: Negligible. Subject: Re: porosity of seams / Flexi performance In article <1993Feb21.212801.14375@ohm.york.ac.uk> jkn@ohm.york.ac.uk (John Nicoll) writes: >Hello all, > Here's the story... my friend dave & I have built two >10foot Flexifoil clones, after I built a 6foot one a few months >ago. We built most of them together, and in theory they should >behave identically - but they don't. I'm trying to figure out why... > >Actually, I lied - they're not quite identical. The two diferences, >apart from `normal manufacturing tolerances', are: Don't be too surprised. Peter Lynn reports [grief! it must sound like I talk to him every day - I don't - I just study carefuly what he does say and write] that he can take a batch of (supposedly identical) Peels straight from the production line, hand them to a bunch buggy racers, swap the kites around and find that the same *kite* keeps winning. This means that the minor differences in the kites was outweighing the differences in skill of the racers! If this is what happens with production soft kites, I'm not surprised at your findings. Andrew -- andrew@tug.com = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 25 Feb 1993 20:25:54 GMT From: sasaki@netop3.harvard.edu (Marty Sasaki) Message-ID: <1993Feb25.202554.15395@das.harvard.edu> Organization: Harvard University Subject: Re: porosity of seams / Flexi performance In article <1993Feb21.212801.14375@ohm.york.ac.uk>, jkn@ohm.york.ac.uk (John Nicoll) writes: >I ask for thoughts and comments on the above. Anyone with multiple >flexis - how does performance compare? Might the weight and/or bend >of the spar make all that much difference? Is there another aspect I >haven't thought of ?? I attended a tuning seminar given by Ray Merry, one half of the flexifoil team. Basically, there is only one way to tune a flexi, and that is to increase or decrease the tension on the sail by changing the the bridle points. I don't remember exactly, so the following could be reversed... When the sail is pulled too tight, the outside cells are closed when the spar is curved. This reduces the lift from that section of the kite and lowers overall speed. I did do some experimenting, and tightening and loosening the sail did affect the speed of the kite noticably. The flexibility of the spar also has an effect on the kite. The taper also changes things. I have three 4 foot flexi's. Two fly almost identically. The third has a stiffer rod and doesn't fly as fast as the other two. I didn't notice this until I tried to stack the three kites... -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@noc.harvard.edu Network Operations Division 26 Green Street 617-496-4320 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =