Right: Further Photoshop trickery shows fairing used as a "canvas" for traditional kustom paint and graphics. In this sort of "street" application, the outer surface would have a layer of light glass cloth and epoxy applied and finished before painting, for more sturdiness..Bondo brand glass cloth and epoxy can be found in the paint department of Home Depot stores. Un-faired frames lack the surface area for large-scale graphics. This fairing fabrication technique applies to frames with straight top tube. Curved top tubes may be accomodated by using a strip of foamcore slightly wider than the top tube. By giving it transverse relief cuts, it may be curved to follow the top tube. This gives a flat top surface. This is the basis of Kandiru's fairing, which had shaped styrofoam "tank" sections added, with spandex/epoxy stretched over both tank and fairing.

Making a Foamcore Frame Fairing for a Bike Dragster

By Jim Wilson Our IBRKA drag bike rules call for the bike to be fitted with a frame fairing.  The basic reason for this is that it simplifies the design of the photoelectric triggers of our time traps, by giving a large surface not as subject to false triggering as a bare frame. But it also provides a good surface for the bike's class designation, number, and sponsor logos. The frame fairing can be made out of almost anything, even corrugated cardboard from a box; however foamcore mounting board is my personal favorite material for this sort of project, as it weighs almost nothing, yet is strong and rigid, and accepts almost any kind of paint well. This makes it very suitable for use on bike projects. This sort of fairing is also a very good way of having a larger surface area as a canvas for a kustom paint job, so you might want to make one for your bike, even if you don't plan on dragging with it. A bare-tube frame is a very difficult form for a traditional hot rod-style paint job, for example; but a frame fairing is ideal for the purpose. Foamcore board is available at most art and craft shops. I normally buy it in 4' X 8' sheets, as I use a lot of it in my work. That size sheet goes for about $20 at most stores which carry that size, however it is also available in smaller sizes. This fairing was made using one 18" X 30" sheet left over from a recent film job. The sheet cost about $6 at an office supply store. The most common thickness of foamcore is about 3/16", although it is sometimes available in thicknesses from 1/16" to 1/2". It consists of a center core of styrofoam bonded to kraft paper skins on both sides. It may be glued together with white and yellow carpenter's glue, hot glue, epoxy or silicone adhesive. On this project, I used yellow carpenter's glue and masking tape. I used blue masking tape for clarity in the photos, but you will probably prefer to use the more common beige-colored tape, as it is closer to the color of the foamcore, simplifying the painting of it, as less primer will be required to achieve even base coloration. This will also save weight.

Left: I first test fitted the 18" X 30" sheet against the bike frame, to verify that the sheet was large enough to do the job. This is an altered 24" MTB frame, and the sheet was sufficient to do the whole fairing. A larger frame would require more foamcore. It is also available in 30" X 40", 40" X 60: and the aforementioned 48" X 96".

Above Right: Using a T-square and X-Acto knife, I made parallel relief cuts through the paper skin on one side of the board, at 3/8" intervals. These cuts also go most of the way through the foam core. This lets the uncut paper skin on the other side act as a hinge. This allows the normally rigid foamcore to follow the curve of the top tube. The relief-cut section is about 2" wide, half the circumference of the 1.25" diameter top tube. This relief-cut bending is one of the key techniques for fabricating foamcore structures. Once the bent sheet is in place, the relief cuts may be covered by tape, which makes the bent section nearly as rigid as the rest of the sheet. For even more strength, glue may be applied in the cuts before taping.

Left: After making cuts to clear the seat and head tubes, the foamcore is draped over the frame and the other cuts begun. I made the cuts to follow the tubes of the frame. In this photo, the cuts have been started with the seat stay angle.

Right: The cuts have been made following the frame's down and seat tubes. I taped the cutoffs back in place for this photo. Notice the small triangular piece I've removed from the rear cutoff and glued onto the head area. The other cutoffs will serve for making the rear fender sections.

Left: The cutoff sections are taped to the main fairing panels, corresponding to the two sections of the fender section, then cut to a radius, centered on the rear axle. As the bike will  be finally fitted with a 24" X 3.45" 3G Hoggy tire, the radius allows for this larger rubber.

Right: The ;new panels are edge-glued to the main form, then taped on sides. At the same time, tape is applied to cover the top relief cuts. The curved top surface of the rear fender is relief-cut on underside allowing it to curve upward. The inner surface of  this area has a layer of glass cloth and epoxy reinforcement applied, since this bike will have fairly heavy usage by numerous  riders.

Left: All joints are taped, including the outer edges. This protects the fragile foam/paper edges. Now the fairing may  be painted. The foam core can be dissolved by the solvents in typical spray paint. For best results, spray on a light mist of primer. After solvents have evaporated off, apply another, slightly wetter, coat. Follow with others until the coloration is even. This primer buildup may be sanded, but this may not be necessary for racing. Following the same procedure, apply finish coats over primer, which has sealed the foamcore surface, protecting the core.. Below: Photoshop trickery shows fairing in final coloration, with typical racing livery added.

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Right: Further Photoshop trickery shows fairing used as a "canvas" for traditional kustom paint and graphics. In this sort of "street" application, the outer surface would have a layer of light glass cloth and epoxy applied and finished before painting, for more sturdiness..Bondo brand glass cloth and epoxy can be found in the paint department of Home Depot stores. Un-faired frames lack the surface area for large-scale graphics. This fairing fabrication technique applies to frames with straight top tube. Curved top tubes may be accomodated by using a strip of foamcore slightly wider than the top tube. By giving it transverse relief cuts, it may be curved to follow the top tube. This gives a flat top surface. This is the basis of Kandiru's fairing, which had shaped styrofoam "tank" sections added, with spandex/epoxy stretched over both tank and fairing.