Date: Wed, 26 Jan 1994 11:50:44 -1000 From: cora@quads.uchicago.edu (Andre The Great) Message-Id: <1994Jan26.215044.25039@midway.uchicago.edu> Organization: University of Chicago Subject: Standoff placement -how does it influence performance? Hi there, A friend of mine is considering building a kite- the original plan is for a kite without standoffs- however, he wishes to modify the design so as to incorporate a pair. The question is : where along the trailing edge should one attach the standoffs? While I realize that an exact answer would depend upon the overall design of the kite, are there general guidlines? How does moving the attachment points further toward the wing tips or in towards the spine influence flight and handling characteristics? Thanks in advance, Andre = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 27 Jan 1994 10:41:06 -1000 From: reich@nosc.mil (Ronald S. Reich) Message-Id: <9401272041.AA01773@cod> Organization: Division of Applied Sciences, Harvard University Subject: Re: Standoff placement -how does it influence performance? Date: Wed, 26 Jan 1994 21:50:44 GMT From: cora@quads.uchicago.edu (Andre The Great) Subject: Standoff placement -how does it influence performance? Andre The Great, writes: >A friend of mine is considering building a kite- the original >plan is for a kite without standoffs- however, he wishes to >modify the design so as to incorporate a pair. The question is : >where along the trailing edge should one attach the standoffs? The rest deleted: ************************************* Here is a Theoretical Analysis for the placement of the Standoffs for a Delta shaped Dual Line Kite. Assumptions: 1. Nose angle is about 90 degrees. 2. Wing Span is about 8 feet. 3. Depth of Billow is about 10 inches. 4. There is a ridged center spine. Purpose of the Standoffs: The primary purpose of the standoff is to reduce the amount of time required for the Sail to acquire the Billow position. This is a definate advantage in light and gusty winds when flying the kite near the edge of the wind window. Primary Balanced Placement of Standoff: Hang the kite from the ceiling with the bridle side up. Adjust the angle such that the back side of the sail is parallel to the floor. (frame will be tilted nose down) Lay a dowel or kite stick on each side of the center spine. The dowel should create the natural billow. (valley from nose to trailing edge) The point at which the valley meets the trailing edge is the Natural Balanced Position for a Standoff. The center of pressure of the sail should be very near the line created at the bottom of the valley. The flight characteristics will be different for a center of pressure on the outboard side of the valley then for a center of pressure on the spine side of the valley. But that is a whole other design consideration. Theory of Turning: Top View ___ /\ /\ /.|.\ / \ / \ / . | . \ / A B \ / C D \ / . | . \ /------------\/------------\ / . | . \ / A . B | C . D \ __ / . | . \ Line of | \ Wind /------*------|------*------\ Sight \ S S Standoff Standoff Considering the active surfaces for a Right Turn. The Line of Sight represents the effective wind direction when you pull on the right line and tilt the right side of the kite into the wind. The surfaces B and D are positioned "Edge to the Wind" and there- fore have limited effect on the turn. However, surfaces A and C have been positioned to become the active surfaces with more wind pushing on them. Notice that surface A is further away from the center spine than surface C and that the Plane of surface A has increased its angle of attack due to its slope from the trailing edge toward the nose of the kite. Conversely, the plane of surface C has become almost vertical.(flat to the wind) This is a stalled position. Therefore surface A advances and surface C slows down. Consequently the kite turns to the right. Effect of Standoff Position: When you move the standoff out toward the leading edge, the effect is to reduce the area of surface A and increase the area of Surface C. At some point, Surface C will dominate and the kite will have difficulty turning. However, The position of the bridle pick point (Tow Point) will also play a part in the kites ability to turn. The placement of the Pick Point is a whole other design consideration. When you move the standoff in toward the center spine, the effect is to increase the area of Surface A and decrease the area of Surface C. Turns should become faster and tighter. An ex- treme case would be to Standoff the center spine from the cross bar. (No central Dihedral.) The Speed Wing is an example of this concept. (Though it has no center spine) I hope that this has shed some light on the effects of the place- ment of the standoffs for a delta dual line kite. Ron Reich ******************************** = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 28 Jan 1994 07:17:54 -1000 From: sasaki@das.harvard.edu (Marty Sasaki) Message-Id: Organization: Harvard University OIT/NSD Subject: Re: Standoff placement -how does it influence performance? In article <1994Jan26.215044.25039@midway.uchicago.edu>, cora@quads.uchicago.edu (Andre The Great) writes: >A friend of mine is considering building a kite- the original plan >is for a kite without standoffs- however, he wishes to modify the >design so as to incorporate a pair. The question is : where >along the trailing edge should one attach the standoffs? While I realize >that an exact answer would depend upon the overall design of the kite, >are there general guidlines? How does moving the attachment points >further toward the wing tips or in towards the spine influence >flight and handling characteristics? Here is my 2 cents. Anecdotally, moving a single standoff towards the wingtips increases the "oversteer" in a kite. The El Nino from the High Fly Kite Co. has positions on the trailing edge for standoff placement in two places. The postion closer to the spine results in a stable kite with good straight line tracking. Move it to the outside position, and the kite is a little "twitchy", with plenty of oversteer. Overall, standoffs control the shape of the kite at the trailing edge, as well as the shape of the body of the kite. The Katana has two standoffs per side. The outside standoff reduces trailing edge vibration and changes the angle of the sail near the wing tip. At the suggestion of Bert Tanaka, I've been experimenting with this and have even played with three standoffs per side. Standoff length can be important, especially if there is no "give" in the standoffs. Length also depends on whether the kite is flat or bowed as it is flying. If the kite is bowed, then rigid standoffs will tighten the sail as the kite is bowed. -- 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 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =