Date: Mon, 30 Jan 1995 21:46:19 -1000 From: lord@eskimo.com (David Lord) Message-Id: Organization: Eskimo North (206) For-Ever Subject: 1.5 wrap spars Andrew I apoligize for not reading what you said more carefully. Your method does end up with a wall thickness that is equal to any other standard construction spar. The problem though is that a spiral wrap is not as stiff longitudinally as linear wrap. It is much more resistant to torque than a linear wrap. I have designed some graphite golf shafts and one puts the fibers straight down the shaft to increase stiffness and at 45 degrees to reduce torque. For the 45 degree wraps they contribute to stiffness .707 times as much as the longitudinal fibers at the same diameter. So a spiral construction kite spar would be less stiff for a given weight and woul resist torque much better. But since resisting torque is not particularly an advantage in kite spars it is not a good construction practice. Dave Lord = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 1 Feb 1995 10:52:06 -1000 From: ac078@detroit.freenet.org (Ken Nealey) Message-Id: <3gos9m$3r9@detroit.freenet.org> Organization: Greater Detroit Free-Net, Detroit, MI Subject: Re: 1.5 wrap spars In a previous article, lord@eskimo.com (David Lord) says: Stuff deleted... > >But since resisting torque is not particularly an advantage in kite >spars... > Here is my take on this. In straight forward flight, this may well be true. In turns (especially linear turns - a.k.a. snap turns,) ground work and power stunts a number of other things are going on at the same time. As leading edge connector fittings continue to evolve, we will see the effects of torsional loads on the kite frame better. That is right, that vinyl tubing you are using to hold your kite frame together is masking a large portion of the torsional loads. By way of illustration, but not by way of limitation, lets look at a couple examples. Lets assume - delta swept wing kite with a cambered (curved) leading edge and the frame is connected with a semi-rigid molded vinyl plug in connector(s). Said connector fits the leading edge spar and spreader properly. A simple linear turn will induce a front to rear (or rear to front) snap motion on the lower section of the leading edge spar (from the lower spreader connector - to the wing tip.) Since the leading edge is already cambered, a rotating oscillation occurs on this portion of the leading edge spar. The front to back snap motion, by way of the leading edge connector induces a torsional moment on the lower spreader (we have not even considered the effects resulting from the "spine" of the spars.) Aggressive ground work is also a very good example. Just look at the loads and stress on the frameworks resulting from over center wing- stands, spikes, over center spikes, over center wing wave, etc. Still skeptical? Try this - take a full size ultra-light kite with a linear graphite frame (e.g. Beman L14, etc.) Install a set of Power-Tite connector fittings (this fitting holds the leading edge spar as well as it does the spreader regardless of the aspect ratio.) Watch what happens to your kite from all angles (especially the side and rear) while someone puts it through some of the newer power stunts. Stiff spars and loose vinyl tubing connectors tend to mask what is really going on. I hope this helps to demonstrate why it is important to consider what is going on out there from a three dimensional perspective. In part, the life expectancy of a spar will depend on its ability to handle torsional moments. Ken Nealey ac078@detroit.freenet.org = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 2 Feb 1995 10:44:14 -1000 From: sasaki@netope.harvard.edu (Marty Sasaki) Message-Id: <3grg6u$op8@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: 1.5 wrap spars In article <3gos9m$3r9@detroit.freenet.org>, ac078@detroit.freenet.org (Ken Nealey) writes: |>By way of illustration, but not by way of limitation, lets look |>at a couple examples. Lets assume - delta swept wing kite with |>a cambered (curved) leading edge and the frame is connected with |>a semi-rigid molded vinyl plug in connector(s). Once again, in aerodynaics camber has little to do with a curved leading edge. Take a cross section of an airfoil parallel to the centerline (the spine in a kite, the body in an airplane) and draw a line between the furthest foward location and the most rearward location. Assuming a single surface airfoil (the typical stunt kite), the fabric falls along the "mean camber line". The distance between the mean camber line and the first line mentioned above is the "camber" of the airfoil. It is usually expressed as a percentage of the wing chord. Sorry to harp on this. I find the article that I quoted above very informative in general... -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@harvard.edu Network Services Division 90 Melrose Street 617-496-4320 10 Ware Street Arlington, MA 02174 Cambridge, MA 02138-4002 phone/fax: 617-646-1925 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sat, 4 Feb 1995 15:39:43 -1000 From: ac078@detroit.freenet.org (Ken Nealey) Message-Id: <3h1a8v$rst@detroit.freenet.org> Organization: Greater Detroit Free-Net, Detroit, MI Subject: Re: 1.5 wrap spars Marty, It was not my intent to imply or suggest that a cambered (curved) leading edge = a cambered sail. I felt that the concept would be easier to visualize if same was described with reference to a cambered (curved) leading edge. I really do not think you are harping about this matter. Since several manufacturers wrongfully imply that their curved leading edge = a cambered sail. I sort of knew that you would jump on this. Really, as I was writing I was telling myself to be careful... How is Marty going to percieve what I am saying? Ken Nealey ac078@detroit.freenet.org = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =