Overview about Plans for Traction foils

This book is always mentioned as the basis for most of the work that is mentioned at rec.kites, if people report about the own experiences with developing new type of (mostly dualline) traction foils. For the first time, a designer of a traction kite (Nop Velthuizen) has explained in very detail, which are the design characteristics of modern traction foils and which are the limits that should be observed when starting a new development.

In the book, Nop describes three different sizes of the Sputnik 4. Most commonly known is the 5m^2 variant, because also this is the most useful size. Nop also introduces for the first time a symmetrical profile for the traction foil. This has several advantages. One of them is that through the thick end of the profile, the sewing of the profiles is much easier. The symmetrical profile should also generate less pull, when it is flying overhead.

Another important improvement for the interested readers of the book is the availability of a software, which enables to scale the sputnik (or any other profile) to just the dimensions you want it. The software will also calculate and print the bridle dimensions.

There is an errata list for this book available somewhere on the net. Concerning the Sputnik, the most important fact to know is that the bridle dimensions in the book should not be used. Let the program calculate the right dimensions!

First version of the Bebop foil, published in the issue 3/93 of the Drachenmagazin, page 38. Christoph Gmelin has a background as mechanical engineer for aerospace. The plan therefore covers many interesting topics about thickness and speed of profiles, outlines and the shape of profiles, etc.

The plan and the way to build the kite itself are rather complex. This is certainly not good for beginners and newbies. But on the other hand, Drachenmagazin claims that Peter Lynn was interested in using the new method of attaching the bridle line to the kite.

All the crossvent holes shall be covered with gaze! The bottom sail consists of three different curved parts (one gaze, two ripstop). Top sail consists of two curved parts. The attachment of the bridle lines is somehow similar to the peel method, but the corresponding parts of the profiles shall be reinforced with dacron. Profiles are given in a spreadsheet with 6 digits...

This plan was published in the book of Peter Rieleit "Leistungsstarke Lenkdrachen zum Selberbauen". I have only seen very few foils built according to these plans, although they contain again some interesting features.

Peter is the only one to use an asymmetrical s-shaped profile, which will be self-stabilizing. He therefore only needs one bridle attachment point per profile. A similar profile can be found on the flexifoil-type of kites.

To avoid the aerodynamic drawback from having few profiles with large spacing between the profiles, Peter has introduced the concept of having small parts of the profiles which are sewn in the middle of a cell. These semi-profiles are only 15cm long and will help to shape the front part of the airfoil, where the most lift is generated (theoretically). For another kite he also used small pieces of ripstop which were used to connect the top surface with the bottom surface right in the middle between two profiles.

For buggying the Quattrofoil is very well suited. As with most of the Quadrifoil based kites, this kite is easy to be used even by beginners. It creates the power rather smoothly and is comparatively small. The kite can be recovered from virtually any situation; as it can be "parked" at the edge of the wind window, this all makes a nice beginner kite for buggying.

The plan is published in a series of other plans produced by a group of German kite shops called "handkerchief".

Additional comment January 1999: this kite is now out of commission, because one bridle attachment ripped nearly the whole kite apart. But it does not matter that much anymore, because I have now "standardised" on the Sands quads as daily kites or kites for beginners. These kites are much easier to handle and have better performance. I would not recommedn any longer to build this type of kite.

Additional comments January 1999 I have now build the 2m^2, 3m^2, 4m^2, 4m^2 with DRips and the 6m^2 kite. I can recommend all of them, except the 6m^2. The small kites are very easy to build, very easy to fly but still powerfull. No tendency to luff and especially with the 4m^2, if you need extra power just pull the brake lines a bit and that's it. These kites are ideal beginner kites. They easily outperform any other of the standard quadrifoil type of kites, such as Quattrofoil, Undertaker or Apollo.
The problem with the large kite might be my fault. I have introduced cross ventilation to all rips and it seems that this is the reason for a strong tendency to fold together at any turn. I will try this autumn and close the holes again in the profiles and report back afterwards.

The directions to build the kite are on the usual high Drachenmagazin level. A friend of mine has build the kite and did not detect any errors. The plan also contains a guideline on how to minimise the waste of ripstop. Contrary to the original, Jens suggests to use the "Peel"-method of attaching the bridle line to the profiles, using a seperate v-line on the profiles.

The plan was published in Drachenmagazin, issue 2/96, page 14.

Before building an Apollo, please read my comments to the Sands Quads.

From the outline, the Ajax resembles the C2 Competition a lot as Jens also uses a bielliptical outline. Contrary to the C2, the rip-spacing is constant. For the bridle, Jens suggests to use a Polyester line (brand name Cyclone PES), which might result in some unexpected stretch in high-wind situations.

I haven't build the Ajax yet, but the building seems to be rather complex, because of the use of reinforcements for each profile nose, necessity to have 11 different profiles, a very complex bridle, etc.

At the end of the plan, Jens mentions that he had first developed a small version (2.4m span) and the scaled up all dimensions to get the 4.6m kite. He suggests that scaling could easily be done to come up with any other size such as 3.6m span or 7.2m span. When planning for the large version, he denotes that the rip-spacing should not be too large and that in this case additional profiles might be needed.

Author	Jens Gaulke
Size [m^2]	4.5
Aspect ratio	aprox. 4
No. of profiles	22
Profile thickness [%]	??
Wingspan [cm]	4600
Bridle type	two point bridle
Cross vent.	Yes

to be added

If you are interested in getting the plans, then send 5£ to the address above and you will get 1:1 drawings of the profiles and detailed building instructions.