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Making Kapton tubes for FAI contest models

by George Gassaway

Keith Vinyard & 40mm Kapton main body S9A Copter model at 2008 WSMC
George's 40mm Kapton main body
S9A Copter model at 2008 WSMC

This info shows how to make parallel wound tubes out of .002"Kapton sheet (from Jim Fackert), for 30mm FAI models. Making them for40mm models, or any other diameter, is the same process (justdifferent diameters require different sheet widths).

Tailcones are not made of Kapton. The heat of ejection andstiffness/strength required for a cone just is not suitable. Sotailcones are best made out of fiberglass, or as a less desirableoption, paper cones.

When the straight Kapton tube is done, it can be glued (using CA)to a tailcone using the method shown in the following GIFdrawing for a jig for aligning and gluing 40mm bodies. If youhave a "real" FAI body mandrel, that can be used instead. But be sureto keep the main tube and tailcone slid far enough down 1/2" to 1" sothat you do not accidentally get CA onto the mandrel itself.

All photos are thumbnails for larger pics(not including Gif drawings)

A suitable mandrel is needed for rolling the tube. For thisexample, the mandrel was some 30mm aluminum tubing from Andy Tomasch.That tubing is exactly 30mm O.D., assuring that the Kapton tube willmake the FAI minimum diameter by some margin for measurement error.The tubing might have a little flaring-out or burring where it wascut, use some 100-150 grit sandpaper or even a Dremel tool withcut-off wheel to sand or grind the tube to de-burr it and give it aslight rounding. This way the completed tube will slide off of themandrel more easily. This deburring step does not apply if using acustom made mandrel for making full FAI bodies.

Other special supplies needed are Scotch 1/2" double-sided tape,and a fine line marking pen as shown above (Both available fromWal-Mart or office supply stores).

The Kapton sheet should be cut to 3-7/8" wide (orient it to gowith the curl of the sheet), and as long as the desired length of thecompleted cylindrical tube. The width of 3-7/8" is about 5/52" widerthan needed to wrap once around the mandrel. The extra 5/32" allowsfor enough overlap to join the sheet together with the double sidedtape. Using a fine line permanent marker, draw a line 5/32" as shownabove, to be used as a reference line for the overlap area.

Use masking tape to tape the Kapton sheet down to a buildingboard, curled-side-up, 5/32" marked overlap at the bottom. The boardshould be dust-free. Tape in 4 places as shown above, careful not toput tape over the two lower corners where the overlap is. Peel off alength of double sided tape longer than the length of the sheet, andmoving from left to right carefully start to lay the double sidedtape down across the drawn overlap line. Do not go above the line, asthe adhesive in the tape might stick with the foam plug at ejection.If the tape does not go on right, you might be able to peel it up abit and reposition it. But if you do it too much that you contaminatethe adhesive of the tape, just throw away the tape and start overwith a new strip. After getting the tape down properly, carefully runyour finger across the tape to press it down all the way intoplace.

With the tape successfully applied, lay a straight edge or rulerdown across at the bottom edge where the Kapton sheet ends, to act asa guide for cutting the tape off flush with the end of the Kaptonsheet. After cutting the tape horizontally using the ruler, also maketwo vertical cuts at the left and right sides to trim off the rest ofthe tape along the 5/32" wide overlap area.

Pre-curl the sheet and hold it that way for awhile so it will curlaround the mandrel more easily. Be careful not to contaminate theadhesive of the tape.


The mandrel should have a line drawn along it that is parallel tothe length. This line will help in aligning the sheet so that thejoint overlap will be parallel and now skewed. Orient the Kaptonsheet so that the unmarked side is at the top of the mandrel, themarked side with tape coming around from the other side. Use maskingtape to tautly hold the upper part of the sheet parallel to themandrel, leaving some clearance for the overlap.

This is the trickiest step, joining the overlap without anysignificant slop in the resulting tube diameter. Carefully bring thetaped edge of the sheet around towards the top edge of the sheet,while holding the sheet as tightly to the mandrel as possible. Withpractice, this step will go better. Concentrate on getting the middlepart as tight as possible, and press the taped edge down only in themiddle, leaving the rest unjoined for now. Then repeat that stepconcentrating on the left side, then the right side, pulling thesheet tight each time. The result ought to look like the above photo,where the tape is tacked down in three spots. If everything lookseven and tight, then go ahead and run your finger across the overlapto make the rest of the tape press down and stick to the overlap.

Final result above, a completed tube, ready to remove the maskingtape and slide off of the mandrel.



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