Cattail Coupe (oz14854)

About this Plan

Cattail Coupe. Rubber competition model.

Direct submission to Outerzone.

Quote: "THE Cattail COUPE By Stan Fink.

Stan has been a local area rubber model flier of some note for the past ten years or so. He has successfully designed and flown his own indoor and outdoor designs and can be counted upon to develop novel ideas that can be used by others. This month's feature three-view was flown dur-ing the 1986 season to some notable wins. Stan has since left the tree-lined Northwest to ply his professional musician trade in the Philadelphia area.

The Cattail Coupe is a small, fast-climbing model with a decent glide, excellent for thermal flying in turbulent or windy conditions. It is designed for minimum drag and maximum penetration under all contest conditions and has proven itself a worthy competitor during the 1986 contest season.

The fuselage was designed for minimum drag and was tested against a conventional fuselage with a box motor compartment and built-up tail boom. The difference was quite obvious. With the identical wing, stab and prop there was a 20 to 30 second gain in neutral air time with the low drag fuselage. This was a direct result of the higher altitude gained during the climb portion of the flight.

The motor tube is 1-inch diameter rolled out of soft, 1/16-inch balsa ala the Oldenkamp method as described in the June 1986 issue of Model Aviation magazine.

The tail boom is 5/16-inch diameter by 22-inch Cattail stalk harvested from a nearby reservoir. Cattails are best harvested in late summer and early fall as the tails are going to seed and the stalks are turning brown. They are cut near the base with a sharp knife, not yanked out of the ground, and then peeled to the desired diameter. Most of them have some curvature toward the top, so they must be checked for straightness. Bring home a dozen or so and 'weed' them out at your leisure. Cattails have joints like bamboo and a structure in layers like an onion. Peel off the outer layers, trying to get the layers to detach in long sections, This will prevent a knobby appearance at the joints.

Once you have found a decent candidate for your tailboom, paint the stalk with two coats of thinned nitrate dope and cover immediately with lightweight tissue. Water-shrink and dope again. This is done quickly to avoid any further organic breakdown of the Cattail stalk. The tailboom is installed in a 1/16 plywood former which is glued into the rear of the motor tube. A hole is drilled and filed to make a tight fit. Plywood triangles are then added to reinforce the joint. Finally, a balsa or thin aluminum fairing is installed.

The pylon, designed to meet the minimum cross-section required in the Coupe event and to stabilize the model during the climb, is built up into a teardrop shape using 1/32 balsa. Using typing paper to make a pattern for the sides before wasting precious wood. Do not glue in place until all the rest of the airplane is finished and the correct center of gravity is determined with the fully assembled model including rubber.

The flying surfaces are built in the conventional manner as shown on the plans. Because of the relatively small size of the wing, it is very strong and light, and it can be safely flown on windy days. The stab is kept light, coming in at 3.5 grams. The rudder is built up with 1/2-inch trailing edge stock at the rear to induce right turn; the rest is 1/16 x 1/8 balsa strip. The subrudder is 1/16 sheet.

Finally, the noseblock is made out of hard 1/2-inch balsa and plywood laminates. Slight right thrust is built into the bearing and no downthrust is used. The prop is a large diameter, low-pitched one designed for a strong climb and long holds while waiting for that elusive thermal. The prop is carved from 3/8 sheet on computer-generated carving lines.

Of the eight Coupe models I have built over a period of ten years, this to me is the most satisfying one yet. I hope you build one and enjoy it as much as I do. Happy flying, Stan Fink."

Supplementary file notes

Article.

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