Date: Mon, 6 Sep 1993 12:35:33 -1000 From: plepez@ulb.ac.be (Lepez Philippe) Message-Id: <9309061435.AA27234@is1e.vub.ac.be> Organization: Division of Applied Sciences, Harvard University Subject: re ascpect ratio In <1993Sep3.190436.5094@das.harvard.edu>sasaki@netop3.harvard.edu (Marty Sasaki)gives us a great explanation of the aspect ratio. Thanks Marty, I want to learn: please give me more, or give me books titles. I have found no book that can easily be applied to stunt kites. Even the book of Marck Cortrell (sp?) 'swept wing stunt kite' doesn't cover all I'd like to know. You surely have remark that I'am allways asking stupid questions about everything and asking you all to include because ;-). When you speak about plate lift 'near the ground' at low velocity, shoudn't it be interpreted as 'in the middle of the window', because high in the sky is equivalent to near the ground at the edge of the window ? If you allow me other 'stupid questions' : why does a kite turn and even worst :-) why does it slide ? Ok all of you smiling there, try to answer the questions for yourself (keeping also in mind the zero velocity case): it is not trivial, isn't it ? Thanks again Marty, even if may may seems kidding, I realy appreciate the amount of information your are giving us. Good winds. Philippe. -- 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: Tue, 7 Sep 1993 04:47:11 -1000 From: ilh@lcs.mit.edu (Lee Hetherington) Message-Id: Organization: MIT/LCS Spoken Language Systems Subject: Re: re ascpect ratio In article <1993Sep7.165330.3562@das.harvard.edu> sasaki@netop3.harvard.edu (Marty Sasaki) writes: Well, I won't go into why a kite turns, we've had that discussion here with no really satisfying result. Darn. I was hoping *I* would finally find out why a kite turns without having to ask. Could someone summarize what the net came up with? I wasn't around at the time. (This could be via email if we don't want to rehash this in public again.) At the UP Sports event, Steve Thomas did a beautiful slide from a launch. Steve popped the kite a few feet off of the ground and slid it 3/4 across the window. Very smooth and very difficult. Yes, it sounds difficult, but was it artistic? Just kidding. ;-) -- Lee Hetherington ilh@lcs.mit.edu = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 7 Sep 1993 06:53:30 -1000 From: sasaki@netop3.harvard.edu (Marty Sasaki) Message-Id: <1993Sep7.165330.3562@das.harvard.edu> Organization: Harvard University Subject: Re: re ascpect ratio In article <9309061435.AA27234@is1e.vub.ac.be>, plepez@ulb.ac.be (Lepez Philippe) writes: >Thanks Marty, I want to learn: please give me more, or give me books titles. I >have found no book that can easily be applied to stunt kites. Even the book of >Marck Cortrell (sp?) 'swept wing stunt kite' doesn't cover all I'd like to >know. You surely have remark that I'am allways asking stupid questions about >everything and asking you all to include because ;-). I don't think that there are stupid questions, although I've put my foot in my mouth enough times that I sometimes think I am capable of stupid questions. Anyway, I don't know of any text book that covers aerodynamics in a simple straightforward way. Aerodynamics is really about fluid flow which is one of the major topics in mechanical engineering. Most of the information that I have gathered comes from model airplane magazines and a few books, and from discussions with people who really understand this stuff. >When you speak about plate lift 'near the ground' at low velocity, shoudn't it >be interpreted as 'in the middle of the window', because high in the sky is >equivalent to near the ground at the edge of the window ? Yes, middle of the window is implied here. Why these conditions? Because near the ground and at low velocities removes most of the Bernoulli lift from the equation. It is also easy to figure out the angle of attack under these conditions. Remember that the angle of attack is the angle between the apparent wind and the mean camber line. The apparent wind is the vector sum of actual wind, and negative of the velocity of the kite (the wind is in the opposite direction of the forwad motion). Downwind, near the ground, the angle of attack is high, maybe 80 degrees. High in the sky, the angle of attack is lower. >If you allow me other 'stupid questions' : why does a kite turn and even worst >:-) why does it slide ? Well, I won't go into why a kite turns, we've had that discussion here with no really satisfying result. If "slide" is the same as a skate or a "helicopter" (west coast only ;-), then the answer is pretty easy... Let's start by explaining how to do a slide with a quad line. Start with the kite to the left of downwind. By adjusting the tilt of the handles, you can hover the kite. Pulling with the right hand will cause the kite to slide to the right. You can adjust the tilt of the kite by changing the angle of the handles. With a two line kite, it becomes a balancing act. You can't change the angle of the kite to keep it in one place, so you have to change the wind speed on the kite's face. If the kite starts to go down, you have to move backwards. If the kite starts to rise, you have to move forward. Okay, now you have the kite sitting still, to the left of down wind. Pull slightly on the right handle and the kite will start to slide a little to the right. If you pull too much the kite will start to turn to the right. To compensate, you can push the right back a little, and/or move forward a bit. Since pulling one handle too much will cause a two line kite to turn, people usualy start the kite moving in the direction of the slide, i.e., they get some momentum built up. At the UP Sports event, Steve Thomas did a beautiful slide from a launch. Steve popped the kite a few feet off of the ground and slid it 3/4 across the window. Very smooth and very difficult. -- 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: Tue, 7 Sep 1993 20:53:29 -1000 From: plepez@is1e.bfu.vub.ac.be (Lepez Philippe) Message-Id: <2909@rc1.vub.ac.be> Organization: Brussels Free Universities (VUB/ULB), Belgium Subject: Re: re ascpect ratio I also like to have a copy of the discution of the net (if possible). Most newtimer (does that exists ?) would probably like. Shoud'nt the answer of Marty and that discution be include in the FAQ. Good winds. Philippe. -- 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, 8 Sep 1993 07:50:34 -1000 From: lmarshal@pnfi.forestry.ca (Larry Marshall) Message-Id: Organization: Forestry Canada - Petawawa National Forestry Institute Subject: Re: ascpect ratio In <1993Sep8.165550.26206@das.harvard.edu> sasaki@netop3.harvard.edu (Marty Sasaki) writes: >trans-atmospheric, hypersonic flight conditions. So, everything that I >said about plate lift doesn't hold below around 60,000 feet, and five >times the speed of sound. Maybe long lines on that small flex-foil you mentioned? ---------- Larry Marshall lmarshal@pnfi.forestry.ca Forestry Canada (613) 589-2880 Petawawa National Forestry Institute (613) 589-2275 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 8 Sep 1993 06:55:50 -1000 From: sasaki@netop3.harvard.edu (Marty Sasaki) Message-Id: <1993Sep8.165550.26206@das.harvard.edu> Organization: Harvard University Subject: Re: re ascpect ratio Well, there is someone out in rec.kites land who knows something about aerodynamics. The good news is that I described plate lift perfectly. The bad news is that plate lift is only applicable at trans-atmospheric, hypersonic flight conditions. So, everything that I said about plate lift doesn't hold below around 60,000 feet, and five times the speed of sound. Oh well, it's back to the drawing board. I'm going to look at a few books on aerodynamics and revise my posting. I might even take a stab at answering the question about why a kite turns that satisfies me. -- 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 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =