A view of the dummy engine.
Model type: Semiscale
Skill level: Intermediate
Construction: Balsa and plywood
Wingspan: 74 inches
Length: 56 inches
Weight: 5. 5 pounds
Motors: Three AXI 2212/34 or
Turnigy C2230-1780 Kv
ESC: Three 18-amp Castle
Battery: 3S 5,000 mAh LiPo
Propellers: APC 9 x 6
Flight duration: 15 minutes
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epoxy is cured, pull three motor wires into the struts ( 27 and
28). Glue the bottom half of the nacelle to the top half. Put
the nacelles aside until you cover the wing.
Make three rings for dummy engines. From 1/32-inch
plywood, cut strips the width of the rings. From scrap balsa,
cut out a disc that is the same size as the inside diameter of
the ring. Cover the ring with clear plastic. Smear epoxy on the
strip and wrap it around the disc three times. After the epoxy
has cured, remove it from the disc and make two other rings.
Sand the outside of the rings to the airfoil’s shape.
The engine’s crankcase can be made by vacuum-forming
plastic over a mold or from a balsa block. Glue the rings and
the crankcase to the plywood ring at the back. Each dummy
cylinder head can be made from a balsa dowel or something
more scalelike. It is up to the builder. Each completed
dummy engine can be held to the firewall with two
magnets and a couple of guide pins.
Cut out the fin, rudder ( 56), stabilizer, and elevator
surfaces ( 62). Mark the location of the ribs on both
sides of the tail surfaces. Pin the surfaces to the
building board. Glue the LE ( 67) and hinge spar ( 63)
to the stabilizer sheet. Glue the blank ribs between the
LE spar and hinge spar.
With a 10-inch sanding block, sand the airfoil into
the first inch of the surface. Flip the stabilizer surface
and glue the rib blanks to this side as was done on the
other side. Sand the LE as was done on the other side.
On the stabilizer, remove 1/16 inch of balsa from the
first ribs. Glue the balsa sheet ( 68) to them. Build the
remaining tail surfaces in a similar fashion.
Cut out the fuselage sides ( 34) and pin them to the building
board. Make sure that the other fuselage side is flipped so
you are building the left and right sides of the fuselage. Glue
the top and bottom longerons ( 33) to the outside edge of the
fuselage sides. (The drawing for former F3 clearly shows how
the longerons are glued to the fuselage sides.)
Pin the longerons to the building board all the way to the
tail. Glue in all of the uprights ( 35) between the longerons. In
the rear, glue the sheet ( 49) to the longerons and the uprights.
Glue all of the stringers ( 40) to the fuselage side, then glue in
the outside balsa doubler ( 51) below the wing saddle.
Flip the sides over and glue on the top plywood doubler
( 36) and the bottom doubler ( 37) on the inside. Epoxy the
hardwood block ( 52) to the top doubler ( 36) in the location
39 Model Aviation JANUARY 2016 www.ModelAviation.com