Date: Wed, 26 May 1993 04:25:17 -1000 From: zcmh20@hou.amoco.com (Colin Hawke) Message-Id: Organization: Amoco Subject: Parafoil Question A quick question to anybody. I have looked at the pictures in the ftp site, great idea if I may say so. The question I have is about the orchid3.jpg picture - the parafoils seem to have a semicircular piece removed from the bottom edge - what is the idea behind this ? I build foils and never have included anything like this. Is it just for appearance or does it make the foil more stable ? and presumably the ribs must have different aerofoil lengths ? If you don't know about the anomymous ftp site at ftp.hawaii.edu in pub/rec/kites then take a look, don't forget to type 'bin' if you want to retrieve the pics. Cheers, Colin Hawke. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 26 May 1993 16:52:09 -1000 From: jeffy@syrinx.umd.edu (Jeffrey C. Burka) Message-Id: <1u1acq$56r@hecate.umd.edu> Organization: University of Maryland at College Park Subject: Re: Parafoil Question In article zcmh20@hou.amoco.com writes: >A quick question to anybody. I have looked at the pictures in the ftp site, >great idea if I may say so. The question I have is about the orchid3.jpg >picture - the parafoils seem to have a semicircular piece removed from the >bottom edge - what is the idea behind this ? I build foils and never have >included anything like this. Is it just for appearance or does it make the >foil more stable ? and presumably the ribs must have different aerofoil >lengths ? As the kitemaker in question, I'll go ahead and answer... The kite depicted in orchid3.jpg is not a "parafoil" in the Jalbert/Hagaman/ Tucker/etc. sense of the term. It is a Sutton FlowForm, a well known and respected variant developed by Canadian Steve Sutton. The design was originally intended to be a parachute. There are several distinct features to the FlowForm. The four most notable are the use of venting holes in the top, bottom, internal cell walls, and tail; the "legs" which are created by the "semicircular piece removed from the bottom edge to which you refer; the drastically reduced number of cells/keels/bridles (the commercial 252 square foot FlowForm has only 8 cells and 5 keels/bridles); and lastly, the very tall airfoil section used. The "legs" help add stability. On the small sizes (I'm not sure if this is up to 60 square feet or 120) commercially made by Air Affairs (the current owners of the design), the legs are 330f the kite's length (chord of the airfoil section). The internal cells have the same basic airfoil section, but they are truncated. For all 3 internal cell walls, the bottom of the section ends about an inch short of 2/3 of the length of the kite. The top of the section should end an inch or two closer to the front of the kite, and a gentle curve is used along the back edge of the section. As for the cut out section, it is half the width of the kite, centered. When the trailing edges, top and bottom are sewn together, the very center of the cut-out is left open, as a vent. The amount left unsewn is roughly 1/6 of the chord, again with half on each side of the centerline. Venting holes are placed all over the kite. Typically, there are at least two in each internal cell wall. There is also one vent for each cell on both the top and bottom of the kite. On the bottom of the kite, the vents are traditionall placed in a V with the point toward the cut-out. The top of the kite has the vents in a V pointing toward the front. I have built two FlowForms. The first was 8 square feet. Due to the nature of the graphic on that kite (an applique of the NeXT logo) and the small size of the kite, I chose to leave the vents off the face of the kite. All other vents were left intact. The kite seems to fly well despite the modification. My other FlowForm is 16 square feet, and features the orchid applique. Again, due to the nature of the applique, I fiddled with the vents, reversing their placement pattern between the top and bottom. You may also note that the applique partially covers one vent. The kite is extremely stable, though and, in fact, it won "Best Parafoil/Soft Kite" at the 1993 Smithsonian Festival. (my, what a day! the folks from Air Affairs were tickled when they saw my kite...) If you're interested in building a FlowForm, I strongly recommend Margaret Greger's _Kites for Everyone_. This features a pattern for the 8 square foot FlowForm. One final note: FlowForms are *extremely* easy to build, and a great way to get into parafoil-making. They involve far less sewing than traditional parafoils, and the design is rather forgiving. Jeff -- |Jeffrey C. Burka | "When I look in the mirror, I see a little clearer/ | |SAFH Lite [tm] | I am what I am and you are you too./ Do you like | |jeffy@syrinx.umd.edu | what you see? Do you like yourself?" --N. Cherry | = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =