Thermic 50X
The front hold-down dowel (above) is glued under the wing with balsa glued on the sides of it. The wing panels (at right) are joined together with music wire
joiners which go into brass tubes. The front joiner is 1⁄8-inch music wire; the rear is 3⁄32-inch music wire. This is optional, the wing panels can also be glued together.
section for wing hold-down, with ¼-inch bal- sa epoxied on both sides of the dowel. Fuselage: Due to the fuselage shape it is constructed a little differently. The bottom keel, K1 is cut from 1⁄8-inch lite plywood, and then formers F1, F2 and F3 are glued to it. Check to make sure the formers are aligned. Glue 1⁄8×¼-inch side stringers in place. The top stringer is ¼ ×¼ inch. This is laminated from two pieces of 1⁄8 × ¼-inch balsa, which bends a lot easier than a single piece of ¼- inch. Glue one 1⁄8 × ¼-inch strip in place, let the glue set up, and then glue the other one to that. On top of this, ¼-inch balsa is glued to form the wing saddle and sanded to match the contour shape below it. The tail boom is made by cutting the sides from ¼-inch hard balsa, then gluing ¼ × ¼- inch hardwood, such as spruce (available from SIG) between the sides, flush with the bottom. This will form a channel for the
pushrods. If you don’t have hardwood you can laminate two pieces of hard balsa to- gether with a carbon fiber strip between them. Once this is complete, glue the bot- tom block on the fuselage behind F3, and the nose block. The rear stabilizer mounts S1 and S2 are glued in then fit the boom in place. The wing and tail surfaces can be set in place and alignment checked. Before the top 1⁄8-inch sheeting is glued in, the control rods need to be in place.
For control rods I used the yellow, inner rods from Sullivan’s Gold-N-Rods pushrods set (#SU 505). Inside of these rods, .047 mu- sic wire was used for the actual pushrods. For the rudder I didn’t want an unsightly pushrod going across the top of the boom, so I made a tiller arm which looks much better. It is made from a 2–56 rod that is threaded
on one end. When installing the tiller arm, a 3⁄16-inch hole is drilled where it goes through
the stabilizer and S2. The hole needs to be large enough so you can wiggle the arm through the stabilizer and angle it out the fuselage side. A 2–56 aileron coupler connec- tor is used on the tiller arm. A Z-bend won’t work here, so I just made a 90-degree bend in the pushrod and wrapped a little copper wire around it for security.
The tail section on my model is a little dif- ferent than shown here. On mine the tail surfaces were moved back a little, with the elevator pushrod going out the back end of the fuselage.
As shown here, the elevator connects in the usual fashion, with the pushrod going out the fuselage side, opposite the rudder. The fuselage is trimmed down at the rear for down elevator. You don’t need a lot of eleva- tor movement since the elevator is pretty ef- fective. About ¼ inch down and 3⁄8 inch up should be sufficient for normal flying.
Close up of the engine. A Cox .049 Medallion (above left) is used, but any engine from .049 to .10 can be used. Electric power is also an option. Note the tank vent lines. A metal control line tank is used since it can’t be removed. The
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engine cowl (above right) is optional. It basically just improves the looks. It is made from heavyweight fiberglass cloth over a Styrofoam™ plug. Use of the cowl certainly gives the model a finished look.
SEPTEMBER 2013
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