Mountain Models Switchback Sport User manual

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Switchback Sport
Builder’s Manual
Thank you for purchasing the Switchback Sport. The Switchback Sport has been designed for the novice
to intermediate pilot who wants a plane with good performance that will fly in a limited space. The
Switchback Sport can also accept the Switchback 3D wing, turning it into a highly aerobatic airplane.
January 31, 2002
Last revised March 24, 2003
Copyright ! 2002, 2003 Douglas Binder, Mountain Models
www.mountainmodels.com
[phone]
[email protected]

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Required Equipment
! Xacto with #11 blades
! Thin and Thick CA – Cyanoacrylate glue (Super Glue)
! 5 minute epoxy
! Sanding block with 200 grit sandpaper
! Smooth, flat work table
! Wax paper to protect plans while gluing
! Needle nose pliers
! Wire cutters
! Hobby Iron for applying covering – also called a sealing iron
! Four channel radio
! Three micro servos: Hitec HS55s or GWS Picos recommended
! GWS EPS 100 A motor with 10x8 propeller. For higher performance, the EPS 300 C or EPS 370
C can be used with a 10x8 propeller.
! Electronic Speed Control (ESC) capable of handling at least 5 amps (10-15 amps for the EPS300).
! Battery pack: 8 cell 300 or 720mAH Nickel Metal Hydride recommended for the EPS 100 motor.
8 cell 720mAH NiMH or 600AE Nicad for EPS 300.
Parts List
2 ea – 3/32” laser cut balsa sheet
2 ea – 1/32” laser cut balsa sheet
2 ea – 1/16” laser cut balsa sheet
1 ea – 1/8” laser cut balsa sheet
1 ea – 1/16” laser cut plywood sheet
1 ea – 1/32” laser cut plywood sheet
1 ea – 1/64” plywood center wing cover sheet
1 ea – 1/8"round x 19” hard wood leading edge
1 ea – 1/8"round x 17” hard wood leading edge
1 ea – 3/32” x 13.5” landing gear wire
4 ea – 1/32” x 18” thin music wire for tailskid and pushrods
1 ea – Plastic Canopy
1 ea - Covering
Bagged Parts:
1 ea – 6” x 3/32” Heat shrink tubing for pushrods
1 ea – 1/2” x 1/8”Heat shrink tubing for wheel retainers
1 ea – 6” Velcro strip for mounting the battery and receiver
1 ea – 2 Tires
1 ea – Motor Mount 1/16” ply sheet
3 ea – 1/8"round x 2.75” hard wood dowel
1 ea – Canopy magnet and tack
1 ea - Tyvek for Canopy Hinges and tail wheel reinforcement.
1 ea – Tail Wheel Rubber
1 ea – 4-40 screw and blind nut for landing gear
Specifications
Wingspan: 35”
Wing Area: 300 sq. in.
Weight: 8 ounces without battery
Wing Loading: 5-6 oz/sq. ft. depending on battery

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Switchback Assembly
Stabilizers, Rudder, Elevator, and Aileron Assembly
The tail assemblies and ailerons are made up from the 3/32” and 1/8” laser cut sheet. Lay the plans out on
a flat worktable and tape them down, and then lay a sheet of wax paper over the plans. This will protect
the plans from the glue. The pieces of balsa are positioned over the plans and glued together. Each joint
can be glued by holding the two pieces in place and applying a drop of thin CA to the joint. In the past,
you may have used pins to hold parts down, but I find this process to be faster and you don’t have to
worry about the pin damaging the balsa. You do have to worry about keeping your fingers far enough
away from the joints or your fingers will become part of the model. Build one part at a time, removing
only that part from the balsa sheet so that you don’t mix the parts up.
Note that the torque rod attaching the two elevator halves is one of the 1/8” x 2.75” hardwood dowels. It
should be glued with thick CA. Give it plenty of time to dry.
Once the parts are dry, carefully remove them from the wax paper then sand them. Round all the edges
EXCEPT the bottom of the vertical stabilizer where it will be glued to the fuselage. Also, the rear of the
stabilizers, the front of the elevator, the front of the rudder, and the front of the ailerons need to have a 40
degree bevel sanded in to them. How you sand the bevel in the ailerons determines whether the aileron
will be for the right or left side. Make sure you make one left and one right.
! Shape the tail wheel wire as shown in the picture. The first bend will create the axle. The second
bend will go over the edge of the wheel, with the third bend running parallel with the wire
between the first and second bends.

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! Measure 5/8" from the bottom edge of the rudder and drill a 1/32” hole in the center of the leading
edge. Gently push the tail wheel wire into the hole. Glue a piece of Tyvek material around the
tail wheel wire where it enters the leading edge of the rudder.
Wing Assembly
! Tape a sheet of wax paper over the plans to protect the plans and to prevent glue from sticking to
them.
! Remove the two vertical spars from the 1/16” balsa sheet. You will note that they fit together with
a V joint to form the center wing. Be very careful to make a left and a right wing. It doesn’t
matter which vertical spar forms the left or right side.
! Slide the ribs into the vertical spars. The 3/32” rib goes in the innermost position. Do not glue yet.
! Position the lower spar caps (the narrower ones) so that they line up with the notches in the ribs.
Ensure that the end of the bottom spar with the arrow shape is towards the center of the wing, that
everything is tight, that the ribs fit fully into the lower spar and that the vertical spar is touching
the lower spar. Once everything is aligned, flow some thin CA into all the joints.
! Position the top spar caps over the ribs. Position as before and glue with thin CA.

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! Position the 1/8” trailing edge so that it is flush with the bottom of the ribs and that it is pushed as
far forward as possible. The end that is shaped like an arrow goes towards the center of the wing.
Glue with thin CA.
! Measure and cut the 1/8” hardwood leading edge dowel so that it is flush with the outer edge of
the outermost rib and only goes halfway through the innermost rib. We only go halfway through
the innermost rib to leave room for the short center leading edge dowel. Glue in place with thin
CA.
! Glue the wingtips as shown in the photos. It is easiest to glue from the spar to the trailing edge
then, once the glue has set, raise the leading edge of the wingtip towards the leading edge dowel
and glue in place.
! We will now glue the two wing halves together. Start by placing the 3/32”x 1.9” x .6” rectangle
with the tab on either end in the slots in the center ribs. Now join the two vertical spars together
and glue with thin CA.
! Glue the top and bottom center spar in place. Make sure you have a good joint and that the top
and bottom spars are well glued to the vertical spars.
! Glue the center trailing in place.
! Cut and glue the center 1/8” hardwood dowel leading edge.
! Glue the smaller 1/64” plywood sheet to the top of the center wing such that it is 1/16” behind the
front of the top spar. The hole should be closer to the front. Take special care to ensure that the
plywood is well bonded to the top spar, especially at the edges of the plywood where it is
outside the center ribs.