Date: Wed, 8 Mar 1995 03:55:54 -1000 From: lver@ksu.ksu.edu (Lloyd Paul Verhage) Message-Id: <3jkd1a$s0h@fox.ksu.ksu.edu> Organization: Kansas State University Subject: Stunt Kite Design Question I have a question about kite design. When designing model rockets, or airplanes, stability depends on the relative positions of the center of gravity (CG) and the center of pressure (CP). The CP is the "idealized" center of all areodynamic forces and CG is the "idealized" center of mass (weight) and is the point the rocket or plane will rotate about. The most stable model rockets have the CP behind the CG. That way an areo forces cause the rocket to pivot back to a nose up attitude. The further back the CP from the CG, the more stable the rocket (there are limits though). If the CP is above the CG, the rocket will flip over (very unstable). In modern high performance jets, they place the CG and CP very close together. This allows the jet to spin in a snap, but makes it difficult to control, hence computer controls. Now on to kites (did you ever think I'd get there?). I suppose in the radical designs, the CG and CP are very close together. In beginners designed stunt kites, I imagine the CP and CG are further apart. Further, if the CP is in front of the CG, then the kite will be unstable. Is this in fact used to design stunt kites? Does anyone take this into consideration when building stunt kites? Thanks = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 8 Mar 1995 07:43:56 -1000 From: mgraves@leadingedg.win.net (Michael Graves) Message-Id: <1707@leadingedg.win.net> Subject: Re: Stunt Kite Design Question In article <3jkd1a$s0h@fox.ksu.ksu.edu>, Lloyd Paul Verhage (lver@ksu.ksu.edu) writes: [snip] > >Now on to kites (did you ever think I'd get there?). I suppose in the >radical designs, the CG and CP are very close together. In beginners >designed stunt kites, I imagine the CP and CG are further apart. >Further, if the CP is in front of the CG, then the kite will be unstable. > >Is this in fact used to design stunt kites? >Does anyone take this into consideration when building stunt kites? I use center of pressure on each half of the kite to initially determine bridle dimensions on a new design. The optimal tow point usually falls within 2" (in any direction) of CP. Just quickly considering some of the kites I've made, they most often have CP located close to CG. Mark Cottrell's book "Swept wing delta stunt kites" has a brief section considering this issue. Michael Graves = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 8 Mar 1995 08:51:28 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3jkubg$kqs@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3jkd1a$s0h@fox.ksu.ksu.edu>, lver@ksu.ksu.edu (Lloyd Paul Verhage) writes: |>When designing model rockets, or airplanes, stability depends on the |>relative positions of the center of gravity (CG) and the center of |>pressure (CP). The CP is the "idealized" center of all areodynamic |>forces and CG is the "idealized" center of mass (weight) and is the |>point the rocket or plane will rotate about. With kites it is a bit different. Because they are attached to a flying line, or lines, the CG alone isn't sufficient to figure out where a kite will rotate and how it will fly. The center of pressure is also very difficult to calculate since it is a function of the lift and drag, which are functions of the real wind, and the velocity of the kite. As a kite, especially a stunt kite moves through the window, the angle of attack is constantly changing. The changing angle of attack directly affects the lift. I suspect that the CP is constantly moving while a kite is in motion. |>Now on to kites (did you ever think I'd get there?). I suppose in the |>radical designs, the CG and CP are very close together. In beginners |>designed stunt kites, I imagine the CP and CG are further apart. |>Further, if the CP is in front of the CG, then the kite will be unstable. Moving the center of gravity upward does make a kite more stable, especially in really light wind where gravity is a large portion of the force on a kite. |>Is this in fact used to design stunt kites? |>Does anyone take this into consideration when building stunt kites? When I frame a kite with a tapered spine, I put the larger diameter (heavier) part of the spine closer to the nose of the kite. My kites generally fly better (more control) when they have some nose weight. In fact, the Katana flies better in really light air with a top spreader than without one, mostly due to the weight, and the placement of the center of gravity. I think that most kite design is done by "seat of the pants" or SWAG (Scientific Wild-Ass Guessing) engineering. Even those who use computer modeling and such can be seen "tweaking" their designs to get them to perform properly. -- 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, 8 Mar 1995 11:27:39 -1000 From: bwg001@carina.unm.edu (Brian W. Gordon) Message-Id: <3jl7gb$3l2@lynx.unm.edu> Organization: University of New Mexico, Albuquerque Subject: Re: Stunt Kite Design Question Lloyd Paul Verhage (lver@ksu.ksu.edu) wrote: : I have a question about kite design. : When designing model rockets, or airplanes, stability depends on the : relative positions of the center of gravity (CG) and the center of : pressure (CP). The CP is the "idealized" center of all areodynamic : forces and CG is the "idealized" center of mass (weight) and is the : point the rocket or plane will rotate about. : The most stable model rockets have the CP behind the CG. That way an : areo forces cause the rocket to pivot back to a nose up attitude. : The further back the CP from the CG, the more stable the rocket (there : are limits though). If the CP is above the CG, the rocket will flip : over (very unstable). : In modern high performance jets, they place the CG and CP very close : together. This allows the jet to spin in a snap, but makes it : difficult to control, hence computer controls. : Now on to kites (did you ever think I'd get there?). I suppose in the : radical designs, the CG and CP are very close together. In beginners : designed stunt kites, I imagine the CP and CG are further apart. : Further, if the CP is in front of the CG, then the kite will be unstable. : Is this in fact used to design stunt kites? : Does anyone take this into consideration when building stunt kites? : Thanks This may or may not be in line with what you are talking about, but... I recently built a prototype kite based on the Air Force's X-29 experimental aircraft. Like the jet, the kite had FORWARD swept wings with a smaller delta shape configuration towards the rear. Picture a large"v" with a smaller upsidedown "v" placed under the large "v". Anyhoo, as you can imagine the kite's CP was well in front of its CG and hence was EXTREMELY unstable. After about an hour of messing with bridle I gave up. I think the longest flight before a crash was 15 seconds. The bridle was configured for two-line flight, but I think 4-line would only be slightly better. Needless to say I tossed the whole heap of Tyvek and Rammin dowels into the dumpster on the way back to the car. I have not given up on this concept entirely. I just don't have the time, money and effort to put into this sortof thing just to see if it will work. The key to making most kites stable or unstable lies in the bridling (some kites are just inherently unstable, see above). I once heard you can fly a Mac Truck if you bridle it right. Hmmm. I wonder of the same exact laws you spoke of (CP, CG) apply to a tethered object like a kite as they do a free flying object like a rocket or plane. Keith Kidder = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 10 Mar 1995 15:23:43 -1000 From: johnsen@eskimo.com (Brian Johnsen) Message-Id: Organization: Tethered Airfoil R&D Pty. Ltd.(C)(R)(TM) CD CASS Subject: Re: Stunt Kite Design Question In article <1707@leadingedg.win.net>, Michael Graves wrote: >In article <3jkd1a$s0h@fox.ksu.ksu.edu>, >Lloyd Paul Verhage (lver@ksu.ksu.edu) writes: >[snip] ditto >>Now on to kites (did you ever think I'd get there?). I suppose in the >>radical designs, the CG and CP are very close together. In beginners >>designed stunt kites, I imagine the CP and CG are further apart. >>Further, if the CP is in front of the CG, then the kite will be unstable. >> >>Is this in fact used to design stunt kites? >>Does anyone take this into consideration when building stunt kites? Flying my single line stunt kites (fighters), when I give a tug on the line the trailing edge folds up and unloads moving the CP forward in a predictable and controllable fashion resulting in a nice straight trajectory. Giving the line slack moves the CP to the back resulting in the kite going all wobbly again. It's a very important part of the design. -- "Mike Lowery is the Nephew Of My Child", Warns Annoyed Troll -- Brian Johnsen johnsen@eskimo.com Seattle, Washington USA = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 13 Mar 1995 06:36:33 -1000 From: plepez@ulb.ac.be (Philippe Lepez) Message-Id: <3k1sah$r3o@rc1.vub.ac.be> Organization: Free University of Brussels Subject: Re: Stunt Kite Design Question In article <1707@leadingedg.win.net>, mgraves@leadingedg.win.net (Michael Graves) says: >I use center of pressure on each half of the kite to initially >determine bridle dimensions on a new design. The optimal tow point >usually falls within 2" (in any direction) of CP. Michael, Can you explain how you measure the CP location ? Good winds. Philippe. -- Philippe Lepez (CP 125), | | Good kite Universite Libre de Bruxelles, | Email: plepez@ulb.ac.be |+ Good wind 50 av. Roosevelt, | Phone: 32.2.6503553 |---------------- 1050 Bruxelles, Belgique. | Fax : 32.2.6503323 |= A lot of fun ! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 13 Mar 1995 06:39:48 -1000 From: plepez@ulb.ac.be (Philippe Lepez) Message-Id: <3k1sgk$r3o@rc1.vub.ac.be> Organization: Free University of Brussels Subject: Re: Stunt Kite Design Question In article <3jkubg$kqs@netope.harvard.edu>, sasaki@netopd.harvard.edu (Marty Sasaki) says: >Moving the center of gravity upward does make a kite more stable, >especially in really light wind where gravity is a large portion of >the force on a kite. Marty, I'm not sure in case of kite of what stability means. Once I build a kite that was kite similar to an MEFM with a lower aspect ratio. In low wind it has a tendency to flop on its back, tail first. The obvious solution was to move the CG forward. I had nothing at hand but coins and tape. So I taped coins to the top spreader. The kite didn't show this problem anymore : you probably would have say it has a better stability. But, the general behavior has completely changed. It has become much more touchy. I was unable to slide it anymore : much less control and the kite would rotate and drop a wing or another. The oversteer was terrible. I would say that stability was worst ! Finally, I removed the coins. Maybe should I have re-tuned the bridle. Now, if someone can give some insight on this experiment and how to obtain the best of both situation, I would appreciate it. Good winds. Philippe. -- Philippe Lepez (CP 125), | | Good kite Universite Libre de Bruxelles, | Email: plepez@ulb.ac.be |+ Good wind 50 av. Roosevelt, | Phone: 32.2.6503553 |---------------- 1050 Bruxelles, Belgique. | Fax : 32.2.6503323 |= A lot of fun ! = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 14 Mar 1995 07:02:25 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3k4i71$l6@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3k46c4$bf2@cbs.ksu.ksu.edu>, lver@ksu.ksu.edu (Lloyd Paul Verhage) writes: |>plepez@ulb.ac.be (Philippe Lepez) writes: |>>Can you explain how you measure the CP location ? |> |>Correct me if I'm wrong, but...... |>I would make a paper cutout of the kite and find the cut-out's |>center of gravity. That's not a bad approximation when the kite is at rest. The exact calculation can get pretty complicated. The center of pressure is a function of the lift and the drag over a surface. Both lift and drag are vector quantities (they have a direction as well as a magnitude) and both vary over the surface. For a wing in motion, more lift is generated (for a given area) towards the leading edge of a wing than towards the trailing edge. The center of pressure is therefore further forward on a wing than the center of gravity of a cutout. -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@noc.harvard.edu Network Services Division 26 Green Street 617-496-4320 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 14 Mar 1995 03:40:20 -1000 From: lver@ksu.ksu.edu (Lloyd Paul Verhage) Message-Id: <3k46c4$bf2@cbs.ksu.ksu.edu> Organization: Kansas State University Subject: Re: Stunt Kite Design Question plepez@ulb.ac.be (Philippe Lepez) writes: >In article <1707@leadingedg.win.net>, mgraves@leadingedg.win.net (Michael Graves) says: >>I use center of pressure on each half of the kite to initially >>determine bridle dimensions on a new design. The optimal tow point >>usually falls within 2" (in any direction) of CP. >Michael, >Can you explain how you measure the CP location ? Correct me if I'm wrong, but...... I would make a paper cutout of the kite and find the cut-out's center of gravity. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 14 Mar 1995 07:02:25 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3k4i71$l6@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3k46c4$bf2@cbs.ksu.ksu.edu>, lver@ksu.ksu.edu (Lloyd Paul Verhage) writes: |>plepez@ulb.ac.be (Philippe Lepez) writes: |>>Can you explain how you measure the CP location ? |> |>Correct me if I'm wrong, but...... |>I would make a paper cutout of the kite and find the cut-out's |>center of gravity. That's not a bad approximation when the kite is at rest. The exact calculation can get pretty complicated. The center of pressure is a function of the lift and the drag over a surface. Both lift and drag are vector quantities (they have a direction as well as a magnitude) and both vary over the surface. For a wing in motion, more lift is generated (for a given area) towards the leading edge of a wing than towards the trailing edge. The center of pressure is therefore further forward on a wing than the center of gravity of a cutout. -- 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, 14 Mar 1995 14:19:14 -1000 From: mgraves@leadingedg.win.net (Michael Graves) Message-Id: <1717@leadingedg.win.net> Subject: Re: Stunt Kite Design Question In article <3k4i71$l6@netope.harvard.edu>, Marty Sasaki (sasaki@netopd.harvard.edu) writes: > >In article <3k46c4$bf2@cbs.ksu.ksu.edu>, lver@ksu.ksu.edu (Lloyd Paul Verhage) writes: >|>plepez@ulb.ac.be (Philippe Lepez) writes: >|>>Can you explain how you measure the CP location ? >|> >|>Correct me if I'm wrong, but...... >|>I would make a paper cutout of the kite and find the cut-out's >|>center of gravity. > >That's not a bad approximation when the kite is at rest. The exact >calculation can get pretty complicated. The center of pressure is a >function of the lift and the drag over a surface. Both lift and drag >are vector quantities (they have a direction as well as a magnitude) >and both vary over the surface. I've never been asked to describe my method before, so I had to think about it for a while. It's not the most scientific. I find the distribution of sail area by bisecting each of the three angles that forms each half of the kite. This yields a decent static center of pressure, and a reasonable spot to center the tow point for sake of experimentation. Recently I have been trying to compensate for the fact that more lift is gained along the leading edge. Just as an experiment I shifted that static CP by an amount defined loosly by the relationship between the linear amount of trailing edge/leading edge. Like I said, not founded in the best science. It has, however, helped me to do this experiment. I am yet sure of the resulting bridle. Michael Graves = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 15 Mar 1995 14:15:46 -1000 From: Matthew Ward Message-Id: Organization: Embry-Riddle Aeronautical University, Daytona Beach, FL USA Subject: Re: Stunt Kite Design Question Someone was asking about whether the stability of a kite depended on the location of the cg relative to the center of pressure. I am certainly no expert, but I am an aerospace engineering student, and I've been flying kites for a few years. I thought I'd mention that the bridles are what always makes the difference between a stable and radical kite. So I think that it matters more where the tow points on the bridles are relative to the center of pressure. My thought is that the only difference the cg position and the distribution of mass make is in its turning ability. Pleasant breezes, Matthew Ward = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 16 Mar 1995 08:17:41 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3k9vc5$lkv@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article , Matthew Ward writes: |>I am certainly no expert, but I am an aerospace engineering student, and |>I've been flying kites for a few years. This makes you as much an expert about these things as anyone... |> I thought I'd mention |>that the bridles are what always makes the difference between a stable |>and radical kite. So I think that it matters more where the tow points on |>the bridles are relative to the center of pressure. My thought is that |>the only difference the cg position and the distribution of mass make is |>in its turning ability. In heavier winds I believe that center of gravity isn't that important. In light winds it can be very important. This is because the other forces are no longer dominate over gravity. I agree that bridle position is one of the most important considerations in stunt kites. Not only does the bridle change the angle of incidence of a kite, but it also changes the shape of a kite... -- Marty Sasaki Harvard University Sasaki Kite Fabrications sasaki@noc.harvard.edu Network Services Division 26 Green Street 617-496-4320 10 Ware Street Jamaica Plain, MA 02130 Cambridge, MA 02138-4002 phone/fax: 617-522-8546 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 17 Mar 1995 01:01:28 -1000 From: andrewh@hal.harvard.edu (Andrew Hawken) Message-Id: <3kbq68$pj6@epsilon.qmw.ac.uk> Organization: Queen Mary & Westfield College, London, UK Subject: Re: Stunt Kite Design Question Marty Sasaki (sasaki@netopd.harvard.edu) wrote: : I agree that bridle position is one of the most important : considerations in stunt kites. Not only does the bridle change the : angle of incidence of a kite, but it also changes the shape of a : kite... I have been playing the the bridle on my Katana recently, trying to drop the tow point towards the tail, and I find that once the kite is in a stall, that it is very nose heavy, and it is difficult to keep the stall stable. I guess that this is one place where the gravity does overcome the other forces. Andy -- ____________________________Andrew Hawken______________________________ "However many ways there may be of being alive, it is certain that there are vastly more ways of being dead" R Dawkins. Home : 0895 420110 QMW : 071 975 5542 AIIT : 0494 677045 Email : A.Hawken@QMW.AC.UK = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 19 Mar 1995 08:29:15 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3kht5r$sat@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question The following reply builds off of our last response. Your aerodynamic center (AC) for each half of your stunt kite sail is the where you first locate your bridle location. For each half of your sail, the AC will be "X" distance from the center spine and "Y" distance below the nose. Your bridle point directly over the AC "X" distance and about 1 to 3 degrees above the "Y" direction. The "Y" location of your bridle point (BP) depends directly on the center of gravity, static margin and the sail washout angle. This location is used as a reference point. For percision, we move the BP 1 to 2 degrees out for our Talons. This is done by shortening the outhaul. For ballet, we move the BP 3 to 4 degress out for our Talons. Sincerely yours, Douglas K. Stout Falcon Aero Designs "Designing for the Future" 12-A Mayne Avenue Stanhope New Jersey 07874 (201) 347-4173 DStoutFAD@AOL = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 19 Mar 1995 08:13:56 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3khs94$s4r@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question As with all flying platforms, the Center of Pressure (CP) moves with a change in the angle of attack. The angle of attack depends on the sail washout angle, and the center of gravity. The theoretical location for the CP is always assumed to be at the 1/4 chord location of the entire projected view of the flying platform. With stunt kites, the center of gravity (CG) is below this location, which is why kites stay out at the end of the lines. To determine where your CG should be located you must do the following: 1. Calculate the panel aerodynamic center (PAC) for each unique vertical geometric shape, called panels, of the stunt kite sail. The PAC will be "Y" distance below the nose and "X" distance from the root chord of the panel. 2. Use the panel aerodynamic centers to calculate the overall aerodynamic center (AC) for the stunt kite sail. The AC will be "Y' distance below the nose of the sail and "X" distance from the center spine for each half of the sail. 3. Measure the CG from below the Nose of the sail. Fully assemble the stunt kite and balance it on the center spine, horizontal to the ground. 4. Calculate the Static Margin (SM) for the stunt kite. Good team and percision stunt kites have SMs ranging from 42 to 48 percent. Good ballet stunt kites have SMs ranging from 48 to 49.9 percent. If the SM is greater than 50 percent, the stunt kite will remain in a stall. The various models of our Talon, for different wind conditions, were designed for team, precision, and ballet and all have the same SM of 48.5 percent. You can also adjust our CG by rotating the center spine and placing the joiner low for ballet or high for percision, if your design allows. We do this on our Talon-MF. This can change the CG about 1/4 inches or change the SM 1.0 percent, which you will notice when flying. As you fly your stunt kite from straight flight into a stall, the CP moves foward from the 1/4 chord, until it stalls and the aerodynamic lift on the back of the sail is broken, which causes the CP to move quickly back to the 50 percent of the chord. The lower the SM percentage, or the closer the CG is to the nose, the more quickly the stunt kite will recover from the stall. Stunt kites with SM less than 40 percent also will have much smaller wind windows. Stunt kites, such as our Talon with 4 standoffs which provide washout angle for the tip panels, insure that the tips never stall so that control is present when the center of the sail has lost aerodynamic lift. I hope this answers your questions. We have been using aerodynamics as the basis for our stunt kite designs since 1990. If you need any additional help, call be at (201) 347-4173 in the USA or sent a message to the address provided below. Sincerely yours, Douglas K. Stout Falcon Aero Designs "Designing for the Future" DStoutFAD@AOL 12-A Mayne Avenue Stanhope, New Jersey 07874 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 19 Mar 1995 08:39:36 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3khtp8$sgm@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question In light wind conditions, when we enter a stall, the horizontal center of gravity and the amount of washout angle at the tips dictate stability. The horizontal center of gravity is were the stunt kite would balance, if cut in half and measured from the center spine to the tip. In almost all stunt kites, the hoizontal center of gravity is outside the aerodynamic center (AC), further from the center spine than the AC. This means the mass of the stunt kite will cause instability in a stall if the tip panels are also in a stall. In our Falcon, the standoffs were located at the horizontal center of gravity, outside the AC, but the tip panels had zero washout angle, thus oversteer and no stability in a stall. The zero washout angle is because our designs use a cambered leading edge and leach line to maintain silence. This does not allow the panels outside the standoffs to billow and washout while flying. In our Talon, we located the inner standoffs at the AC and the outer standoffs provide 10 degress of washout angle. The tip panels almost never stall under most flying conditions, thus providing great stability in a stall, and speed control under all wind conditions. Sincerely yours, Douglas K. Stout Falcon Aero Designs "Designing for the Future" 12-A Mayne Avenue Stanhope, New Jersey 07874 (201) 347-4173 DStoutFAD@AOL = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 21 Mar 1995 10:02:56 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3knbdg$5t0@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3khs94$s4r@newsbf02.news.aol.com>, dstoutfad@aol.com (DStoutFAD) writes: |>As with all flying platforms, the Center of Pressure (CP) moves with a |>change in the angle of attack. The angle of attack depends on the sail |>washout angle, and the center of gravity. The angle of attack also depends on the velocity of the kite (this contributes to the apparent wind velocity). The shape of the kite also changes the angle of attack. The CP is also dependent on the shape of the sail, especially the profile. The shape changes with wind pressure, further complicating matters. ...lots of interesting calculations deleted... After all of the calculations are done, you still have to take your kite out and test fly it. Static calculations put you in the right ball park, but there is no substitute for experimentation and fine tuning. |>As you fly your stunt kite from straight flight into a stall, the CP moves |>foward from the 1/4 chord, until it stalls and the aerodynamic lift on the |>back of the sail is broken, which causes the CP to move quickly back to |>the 50 percent of the chord. The lower the SM percentage, or the closer |>the CG is to the nose, the more quickly the stunt kite will recover from |>the stall. Stunt kites with SM less than 40 percent also will have much |>smaller wind windows. Doug, what exactly do you mean by stall here? Most aerodynamic texts talk about the stall angle as the point where lift drops dramatically. Stunt kites operate at angles of attack both above and below the stall angle. In an airplane, as the angle of attack increases, the CP moves forward which causes the nose of the plane to rise, which increases the angle of attack, etc. Just after the stall angle, the lift drops dramatically, and the nose of the plane drops. There is usually a decrease in the forward speed as the nose rises, which also decreases lift. With a kite, the bridles keep the kite's nose from rising. If the kite is rising from the ground, it's path will actually cause a decrease in the angle of attack. During a snap stall or a similar move, the forward speed of the kite is suddenly decreased, which causes a sudden increase in the angle of attack. The resulting angle of attack is very high, well behold the stall angle, and the lift drops dramatically. In both cases there is really no recovery phase... !> Stunt kites, such as our Talon with 4 standoffs |>which provide washout angle for the tip panels, insure that the tips never |>stall so that control is present when the center of the sail has lost |>aerodynamic lift. Well, the tips stall later than center panels, which is a good thing, especially in tight turns... Kites with winglets, like the Katana-2 and the Freestyle Reactor (to name two) have slightly different characteristics. Increased wind pressure on the winglets cause them to bend backward which increases the washout, delaying tip stalling. You can also snap these kites in a way to cause the winglets to snap forward, which increases the angle of attack and actually encourages stalling conditions. Snap stalls with these kites can be really sharp and stability in the stall is good. Keep up the good work Doug... -- 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, 21 Mar 1995 09:02:23 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3kn7rv$o8j@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3kbq68$pj6@epsilon.qmw.ac.uk>, andrewh@hal (Andrew Hawken) writes: |>I have been playing the the bridle on my Katana recently, trying to |>drop the tow point towards the tail, and I find that once the kite is |>in a stall, that it is very nose heavy, and it is difficult to keep the |>stall stable. I guess that this is one place where the gravity does |>overcome the other forces. I'm not sure what you mean by nose heavy. Does this mean that it falls away or towards the flyer? Does this mean that the nose drops to one side or the other? When a kite, any kite, not just the Katana, is stalled, the angle of attack is very high and the lift is correspondingly low. Small forces can easily upset the equilibrium of a kite that is stalled. Also, remember that the Katana is meant to be somewhat radical. It is the ability to respond to small changes that makes kites like the Katana fun to fly... -- 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: Mon, 20 Mar 1995 18:20:47 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Stunt Kite Design Question dstoutfad@aol.com (DStoutFAD) writes: >4. Calculate the Static Margin (SM) for the stunt kite. Good team and >percision stunt kites have SMs ranging from 42 to 48 percent. Hmmm... I'm trying hard to follow this, but you didn't say what the SM is or how to calculate it... Andrew -- New to rec.kites? START HERE! > To: www@kfs.org send an email message like this: > Subject: service > http://www.kfs.org/kites/welcome/index.html The proposal to split rec.kites is just a bad joke = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 22 Mar 1995 17:34:52 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3kqq8s$ssh@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question You calculate the Static Margin for your design. The Static Margin is distance between the Aerodynamic Center for the Sail and the Center of Gravity, divided by the mean chord for the sail. You wish to obtain a Static Margin within the ranges I have previously stated. When we design a stunt kite using our Geokite(c) program, we input all the specifications of the design, along with the mass of each component. We adjust the design, which moves the calculated Center of Gravity until we obtain the desired Static Margin. With a completed design, you can add weight to the nose or tail of the center spine to adjust the Center of Gravity and achieve the desired Static Margin. Sincerely yours, Douglas K. Stout "Designing for the Future" 12A Mayne Avenue Stanhope, New Jersey 07874 (201) 347-4173 DStoutFAD@AOL.COM = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 22 Mar 1995 18:47:31 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3kquh3$13q@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question When an airplane stalls, the Center of Pressure moves forward, then rapidly back to the 50 percent of the mean aerodynamic chord. Airplanes recover because the Center of Gravity is usually located between 25 and 35 percent of the mean aerodynamic chord, with an airplane containing a horizontal tail surface. The distance between the Center of Gravity and the 50 percent location allows for rapid recovery from the stall. Static Margins for this type of airplane are ususally 10 to 20 percent. This is what we used in my Control Line Percision Aerobatic Stunt Ships called "Apparition" and "Apparition II". A flying wing must have the Center of Gravity infront of the 1/4 Chord location for flight. Canards are even more fun to establish the correct Center of Gravity. We designed a Control Line Canard called "ISIS", which flew great, with the Center of Gravity About 20 percent in front of the main lifting surface. Most stunt kites have the Center of Gravity below the 1/4 Chord location, which allows dramatic changes in the angle of attack to the direction of the prevailing winds, without the design droping its nose and trying to recover like an airplane. I have some old delta designs which had a high Center of Gravity, and when you stalled the design overhead, it would drop the nose and try to recovery like a conventional airplane. We extended the center spine below the sail to lower the Center of Gravity, and the undesired recovery problem went completely away. The wind window also increased. That is why good stunt kite designs have a low Center of Gravity, just above the 50 percent location of the mean chord. As previously stated, when you leach a sail to gain more aerodynamic efficiency, the outer panels can not billow and provide natural washout. Washout is defined as a twist in the chord of the airfoil which allows the panel which has been washed out to fly at a lower angle of attach that the rest of the sail. Most aircraft washout the tip panels 2 to 3 degrees to insure that the tips of the aircraft will remain flying and provide control during landings, when the aircraft is flying very close to it stall speed. When a stall occurrs in an aircraft with washout, the stall starts at the center of the wing and then moves gradually out toward the tips, thus maintaining lift over the surfaces that contain the ailerons, allowing the pilot to maintain control, as long the tips don't stall. On stunt kites, we impose a much greater change in the angle of attach, which means the natural washout angle of the tip for an unleached sail or the mechanically place washout angle in a leached sail must be much greater. We have been experimenting with washout on our designs for over 3 years and have found that on leached designs, an angle of 10 to 15 degrees is about the right range. In fact, we install longer (1/4 inch) outer standoffs to fly in winds greater than 15 miles per hour. This provides more stability, but also induces more profile drag, which provides additional speed control. Dave Lord and I have experimented with wider tips and have found that under turbulent conditions, tracking suffers. We found that additional standoffs, used to generate the washout of the tips, provide the same effect as the wider tips, but work in clean and turbulent air. In closing, the detailed aerodynamic calculations or modeling that we conducted to design our Talon allowed this design, including bridle lengths, to be constructed and flown in competition during the 1994 contest season, right from the output of our computer modeling program. The prototype was not changed in any way and was used for production. We attribute this success and the same success of our recent design, the Talon-2M, to the extensive modeling capabilites contained in our Geokite(c) Program. This program was developed and has been extensively improved for over 10 years. Calibrating the program during the development of the Falcon in 1990 and 1991 was a lot of work, but the work is now done of this generation of the computer model. We take the output of Geokite(c) and draft up full size engineering plans in AutoCAD. This ensures that the modeled design is provided within specifications for sewing. If you wish to also evaluated true airfoils, let me know. We also have a PC based airfoil section wind tunnel computer model developed by Dr. Eppler and refined through the use of a wind tunnel by Mike Selig at Princeton University. It handes Reynold Numbers from laminar flow ( 50,000) to turbulent flow (500,000). The program was design around the transitional zone, which causes a lot of fun in model sailplanes. When we used to design Radio Controlled Sailplanes, we would first develop an airfoil which was tested using the wind tunnel program. Then we would design the aircraft using the pre-program to Geokite(c) called Geosail(c). Finially, we would run a performance program to generate Lift to Drag ratios for the airframe, over a range of angles of attack. Since we do not use true airfoils, we don't run the first program, and since it is much quicker to construct a stunt kite than a 10 foot sailplane, we don't see the need to run the performance program. The flying field is a much better wind tunnel. I hope you enjoy the above. It is rare when I get a change to relate this type of information to others. I hope my spelling and grammar wasn't too bad. Sincerely yours, Douglas K. Stout "Designing for the Future" 12A Mayne Avenue Stanhope, New Jersey 07874 (201) 347-4173 DStoutFAD@AOL.COM = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 23 Mar 1995 08:55:11 -1000 From: lord@eskimo.com (David Lord) Message-Id: Organization: Eskimo North (206) For-Ever Subject: Re: Stunt Kite Design Question In article <3kquh3$13q@newsbf02.news.aol.com> dstoutfad@aol.com (DStoutFAD) writes: >From: dstoutfad@aol.com (DStoutFAD) >Subject: Re: Stunt Kite Design Question >Date: 22 Mar 1995 23:47:31 -0500 >Dave Lord and I have experimented with wider tips and have found that >under turbulent conditions, tracking suffers. We found that additional >standoffs, used to generate the washout of the tips, provide the same >effect as the wider tips, but work in clean and turbulent air. Doug I agree with what you say except I think that if you design the correct size winglets to go with the proper spring constant (leach line tension) then you can achieve the same results you get with fixed twist. And you would get the added benefit of a wider wind window. It might be pretty tough to model this in the computer program. C.G. is most important in the lightest of winds and kites designed for these winds have been a design struggle to keep them as light as possible so adding ballast to trim C.G. is usually avoided like the plague. So one must resort to changes in spreader positioning and sail area and aspect ratio to move the C.G. The Banshee kite designed by Skip Parks was the only design I ever saw that had a forward C.G. Its structure consisted of a bowed leading edge and a short spine and nothing else, no lower or upper spreader. There were some wing battens but they had little effect on C.G. I thought the Banshee handled pretty good in light wind. Dave Lord lord@eskimo.com http://www.eskimo.com/~lord check it out = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 26 Mar 1995 20:00:08 -1000 From: navarrol@netcom.com (Larry Navarro) Message-Id: Organization: NETCOM On-line Communication Services (408 261-4700 guest) Subject: Re: Stunt Kite Design Question I had a chance to fly a Talon this weekend for a short while and do agree that the kite does have a very steady stall. The pushed back wing tips seem to do their job. It was similar in stall performance to the Reactor, which we were flying that day. The Reactor has winglets to steady it in a stall. The advantage to the Talon was that it would perform the radical stunts like axles and coin tosses way easier than the Reactors do. One thing I did notice about the Talon is that pulling a hard turn to initate a spin will cause the kite to actually slow down and plow slowly through the turn, as if it was floating through it. The adjustable outhauls were set to the second to longest position, and I don't know what effect this would have on the spin characteristics. The kite also has the upper spreader attached to the spine through a vinyl T connector, similar in design to many of the Prism kites. I'm also wondering what advantage this gives to the kite. Larry Navarro = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 27 Mar 1995 07:57:52 -1000 From: lord@eskimo.com (David Lord) Message-Id: Organization: Eskimo North (206) For-Ever Subject: Re: Stunt Kite Design Question In article navarrol@netcom.com (Larry Navarro) writes: >From: navarrol@netcom.com (Larry Navarro) >Subject: Re: Stunt Kite Design Question >Date: Mon, 27 Mar 1995 06:00:08 GMT >I had a chance to fly a Talon this weekend for a short while >and do agree that the kite does have a very steady stall. The >pushed back wing tips seem to do their job. It was similar >in stall performance to the Reactor, which we were flying that >day. The Reactor has winglets to steady it in a stall. The >advantage to the Talon was that it would perform the radical >stunts like axles and coin tosses way easier than the Reactors >do. One thing I did notice about the Talon is that pulling >a hard turn to initate a spin will cause the kite to actually >slow down and plow slowly through the turn, as if it was floating >through it. The adjustable outhauls were set to the second >to longest position, and I don't know what effect this would >have on the spin characteristics. The kite also has the >upper spreader attached to the spine through a vinyl T >connector, similar in design to many of the Prism kites. >I'm also wondering what advantage this gives to the kite. >Larry Navarro Larry Back in the November 91 issue of the AKA magazine Kiting I wrote an article for the "Art and Science section called "Optomizing Delta Stunt KIte Frames. Contained in the article is an analysis of the loads on the frame and ways to strengthen the frame against these loads. One of the techniques was to tie the upper spreader to the spine. The Prism people told me that after they read the article and tried connecting the upper spreader to the spine it increased the upper wind range on the Prism Radian by 10 mph. Dave Lord check out my web site http://www.eskimo.com/~lord = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 27 Mar 1995 13:26:38 -1000 From: mgraves@leadingedg.win.net (Michael Graves) Message-Id: <1759@leadingedg.win.net> Subject: Re: Stunt Kite Design Question In article , Larry Navarro (navarrol@netcom.com) writes: > >have on the spin characteristics. The kite also has the >upper spreader attached to the spine through a vinyl T >connector, similar in design to many of the Prism kites. >I'm also wondering what advantage this gives to the kite. While Doug will likely respond in detail, my impression of the T on the upper spreader is that it increases overall frame stiffness. Just for sake of curiousity, what rod do the Talon use for the upper spreader. The only kite I've flown with an upper T was the Lite Flite Radial, which broke its upper spreader very frequently. Michael Graves = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 30 Mar 1995 09:23:28 -1000 From: navarrol@netcom.com (Larry Navarro) Message-Id: Organization: NETCOM On-line Communication Services (408 261-4700 guest) Subject: Re: Stunt Kite Design Question In article <1759@leadingedg.win.net>, Michael Graves wrote: > >Just for sake of curiousity, what rod do the Talon use for the >upper spreader. The only kite I've flown with an upper T was the >Lite Flite Radial, which broke its upper spreader very frequently. > >Michael Graves > The Talon that I flew was framed in Skyshark 3P, including the top spreader. The top spreader/spine connector was a piece of vinyl tubing, which I think might cause lower stress on the rod than a stiffer connector like those used in my Eclipse. Larry Navarro = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 31 Mar 1995 08:31:21 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3lhhpp$k8s@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article , lord@eskimo.com (David Lord) writes: |>>Dave Lord and I have experimented with wider tips and have found that |>>under turbulent conditions, tracking suffers. We found that additional |>>standoffs, used to generate the washout of the tips, provide the same |>>effect as the wider tips, but work in clean and turbulent air. |> |>Doug |> I agree with what you say except I think that if you design the correct |>size winglets to go with the proper spring constant (leach line tension) |>then you can achieve the same results you get with fixed twist. And you |>would get the added benefit of a wider wind window. I've done some expermenting with both winglets and standoffs to have a fixed lower limit on the washout. Things have been promising, and I'll post details after the next prototype is finished. I also think that winglets provide a better tip shape than what we usually have with a very pointed tip. Theoretically, the point that is at the end of a stunt kite should generate the greatest amount of tip drag... -- 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: Sat, 1 Apr 1995 10:05:32 -1000 From: lord@eskimo.com (David Lord) Message-Id: Organization: Eskimo North (206) For-Ever Subject: Re: Stunt Kite Design Question In article <3lhhpp$k8s@netope.harvard.edu> sasaki@netopd.harvard.edu (Marty Sasaki) writes: >From: sasaki@netopd.harvard.edu (Marty Sasaki) >Subject: Re: Stunt Kite Design Question >Date: 31 Mar 1995 18:31:21 GMT >In article , lord@eskimo.com (David Lord) writes: >|>>Dave Lord and I have experimented with wider tips and have found that >|>>under turbulent conditions, tracking suffers. We found that additional >|>>standoffs, used to generate the washout of the tips, provide the same >|>>effect as the wider tips, but work in clean and turbulent air. >|> >|>Doug >|> I agree with what you say except I think that if you design the correct >|>size winglets to go with the proper spring constant (leach line tension) >|>then you can achieve the same results you get with fixed twist. And you >|>would get the added benefit of a wider wind window. >I've done some expermenting with both winglets and standoffs to have a >fixed lower limit on the washout. Things have been promising, and I'll >post details after the next prototype is finished. >I also think that winglets provide a better tip shape than what we >usually have with a very pointed tip. Theoretically, the point that is >at the end of a stunt kite should generate the greatest amount of tip >drag... Marty Winglets do provide a better wing shape in terms requiring less washout to eliminate tip stall in turns. If they are large enough they can be designed to have no washout. I don't think pointed tips have any special characteristic to create drag its just that they do not create an appreciable lift, either plate (reaction) or Bernoulli. They are just there for the ride and create drag with out creating any aerodynamic benefit. Larger tips move the tip vortex further outboard and thus reduce their effect as a percentage of the total wing thus reducing drag. They also contribute to plate lift. Most kites are so draggy though I doubt this is much of a factor. It is probably in the handling area where you will notice the improvement. Doug is also correct in that if your primary goal is tracking then you want the wing tips to be relatively inactive. He added just enough washout to get rid of the worst of tip stalling. If you check my home page you will see my kite design of the month posted. It is quite similar to your Katana II (I think that is the one, we don't see them here in the northwest). When I designed it I had no knowledge of your design and as obscure as I am I know you knew nothing of mine. But they were both probably reactions to the same aerodynamic problem in delta stunt kites, tip stall in turns. I started out with pointed tips and outboard standoffs but quickly realized dynamic washout was the way to go. I have designed large tips on some kites,but it is difficult to react the aeroloads on the tips to limit washout. Alas, first too little then too much and a whole new set of structure problems. Oh well, buggying is more fun anyway so I am not very driven to work on the problem. Dave Lord check out http://www.eskimo.com/~lord = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 2 Apr 1995 06:23:45 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3lmj2h$on6@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question I sounds like you had the bridle clip location about 1/8 inches too high. Test dive the Talon and make a 90 degree turn before you reach the ground, using push/pull input. If the line tension starts to get lighter, move the clip down, away from the nose, about 1/8 inches. If the line tension starts to get stronger, move the clip up, toward the nose, about 1/8 inches. The manual is very detailed regrading this trimming. Douglas K. Stout Falcon Aero Designs "Designing For The Future" 12-A Mayne Avenue Stanhope, New Jersey 07874 (201) 347-4173 DStoutFAD@AOL.COM = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 2 Apr 1995 06:23:55 -1000 From: dstoutfad@aol.com (DStoutFAD) Message-Id: <3lmj2r$one@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Stunt Kite Design Question The reason we connected the upper spreader to the center spine was to eliminate the movement of the upper wing spars during turns, when we use any of the lighter frames. The upper joiner is standard equipment on our Talon-F and Talon-MF, with Skyshark IIIP and IIP frames, respectively. We use Skyshark VP frames for the center spine of these two models. This was done to bring the center of mass of the design closer to the center and provide strength and stiffness for our tight sail desigsn. Since our kites are designed with stiff sails, this allowed the same performance traits, found in the mid wind speed range, to be achieved at the low and high ends. After a year of less than 2 mph wind flying, we found that this help out performance during low wind routines. As Dave Lord stated, it also maintains performance traits on the high end of the design frame. Sincerely yours, Douglas K. Stout Falcon Aero Designs "Designing for the Future" 12-A Mayne Avenue Stanhope, New Jersey 07874 (201) 347-4173 DStoutFAD@AOL.COM = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 3 Apr 1995 00:37:04 -1000 From: andrewh@holly.harvard.edu (Andrew Hawken) Message-Id: <3loj4g$mg1@epsilon.qmw.ac.uk> Organization: Queen Mary & Westfield College, London, UK Subject: Re: Stunt Kite Design Question Marty Sasaki (sasaki@netopd.harvard.edu) wrote: : In article <3kbq68$pj6@epsilon.qmw.ac.uk>, andrewh@hal (Andrew Hawken) writes: : |>I have been playing the the bridle on my Katana recently, trying to : |>drop the tow point towards the tail, and I find that once the kite is : |>in a stall, that it is very nose heavy, and it is difficult to keep the : |>stall stable. I guess that this is one place where the gravity does : |>overcome the other forces. : I'm not sure what you mean by nose heavy. Does this mean that it falls : away or towards the flyer? Does this mean that the nose drops to one : side or the other? Sorry, not very clear, what I meant was that it falls off to the sides. The lower I set the bridle, the easier it is to stall, but the harder it is to keep the stall stable. I am sure that this is the same for any kite, I was just curious as to the cause, and wondering how we can improve the situation. No criticism of the Katana intended, I love it :-) Andy -- ____________________________Andrew Hawken______________________________ "However many ways there may be of being alive, it is certain that there are vastly more ways of being dead" R Dawkins. Home : 0895 420110 QMW : 071 975 5542 AIIT : 0494 677045 Email : A.Hawken@QMW.AC.UK = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 3 Apr 1995 11:07:49 -1000 From: sasaki@netopd.harvard.edu (Marty Sasaki) Message-Id: <3lpo35$8dh@netope.harvard.edu> Organization: Harvard OIT Network Services Subject: Re: Stunt Kite Design Question In article <3loj4g$mg1@epsilon.qmw.ac.uk>, andrewh@holly (Andrew Hawken) writes: |>Sorry, not very clear, what I meant was that it falls off to the |>sides. The lower I set the bridle, the easier it is to stall, but |>the harder it is to keep the stall stable. I am sure that this is |>the same for any kite, I was just curious as to the cause, and wondering |>how we can improve the situation. No criticism of the Katana intended, |>I love it :-) I didn't take it as criticism. I was just trying to figure out what you were saying. If the nose were actually falling towards or away >From the flyer, then that would be something completely new... Some kites are more stable in stalls than others. Some require a different touch to keep stable. One thing to try if you are having troubles getting a kite to stall is to shorten the outhaul bridles. This will often make the kite easier to stall. You might have to move the center bridle points up to get back forward speed if you do shorten the outhauls. -- 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 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =