FOUR-STAR 120 RC65 FUSELAGE CONSTRUCTION

Fuselage Subassemblies

Before starting fuselage construction, there are a few subassemblies that should be built and set aside until needed. This is done to avoid interruptions during the flow of fuselage construction.

32.

  1. Glue together the two die-cut 5/32" plywood F-1 pieces using Kwik-Set epoxy or slow CA. Use a heavy weight of some kind to hold the two pieces perfectly flat while drying.
  2. Mark the vertical center line and thrust line on the F-1 assembly using the cross-section on the plan as a guide.
  3. The engine mount included in the kit will fit most of the 1.20-size four-stroke engines on the market. Positon the engine mount (or another mount of your choice) on F-1, mark the location of the mounting holes, then drill them out with a 3/16" drill bit.

33.

  1. Lightly hammer four 6-32 blind nuts into the back of F-1. Pull the blind nuts into their final position by bolting the engine mount to the front of F-1 using four 6-32 x3/4" socket head bolts. Apply medium or slow CA around the edges of the blind nuts to hold them in place. Be careful not to get any glue in the threads!
  2. Position your engine on the mount far enough forward for the propeller to clear the fuselage "cheeks", mark the engine mounting holes, then drill at each of the marks. If you plan on using the four #8 x1" sheet metal screws provided in the kit, use a 9/64" dia. drill bit. The sheet metal screws are self-tapping and won't loosen from engine vibration. If you prefer, machine screws can be substituted, but you'll have to drill and tap the mount.

34.

Temporarily bolt the engine to the mount so you can locate the best spot on F-1 for the throttle pushrod to exit and line up with your engine's carburetor control arm. A 2-56 solder clevis is provided in the kit to attach the flexible cable pushrod to the engine's carburetor. The solder clevis should work well for 2-stroke engines, but most 4-stroke engines may require a different type of connector. Remove the engine and engine mount, and drill at the mark with a 9/64" dia. drill bit.











35.

  1. Glue the two die-cut 5/32" plywood landing gear mounts together with epoxy or slow CA. Again, weight the assembly down until dry.
  2. Carefully center the aluminum landing gear over the landing gear mount and mark the location of the mounting holes through the three holes in the landing gear. Remove the mount and drill at the marks with a 13/64" drill bit.
  3. Lightly hammer three 8-32 blind nuts into the holes and secure them with medium or slow CA.

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36.
  1. Notice that the die-cut lite-ply former F-2 has two dimple marks which are used to locate the holes for the wing hold-down dowels. Glue F-2D to the die-cut lite- ply former F-2 so that the dimples remain showing.
  2. Drill at the dimples in F-2, first with a 1/8" drill bit, then with a 1/4" drill bit, and finally with a 5/16" drill bit. Use a chunk of hardwood behind the formers to keep the plywood from splintering as you drill through.

37.

Glue the die-cut lite-ply tailwheel mount (TWM) to aft end of FBR (Fuselage Bottom, Rear).

Basic Fuselage Construction

38.

  1. The fuselage sides are spliced from two die-cut pieces. Align the pieces directly over the plan (protected with wax paper), then apply medium CA to the splice joint.
  2. Glue the die-cut fuselage doublers to the fuselage sides using slow CA or Kwik-Set epoxy, and allow to dry. Be sure to make one left side and one right side!

39.

  1. Carefully slip all the fuselage formers (F-1 through F-G) into place between the fuselage sides. Put a rubber band around the fuselage at each former location to hold it tightly together.
  2. Slide the die-cut lite-ply part FBR (Fuselage Bottom, Rear) under the rubber bands until it snaps into its proper location between the fuselage sides. Do the same thing for the die-cut lite-ply part FT (Fuselage Top) and the die-cut lite-ply Stab Support.
NOTE: The "Tee-Lock" tabs on the formers, FBR, and FT are made oversized to protrude past the fuselage sides. These will be sanded off after the fuselage has been completely assembled.

40.

  1. Place the fuselage over the top view on the plans to check its alignment. Even if some of the plywood is badly warped, the interlocking parts are designed to be self-aligning. If there are any persistent warps or twists, now is the time to fix it! Once the fuselage is glued, it can't be re-aligned. Double check that the opening at the back end of the fuselage is square with the fuselage top. If necessary, gently twist or push the parts in the desired direction and use masking tape to hold them there.
  2. Carefully glue all of the parts permanently in place, preferably working from inside of the fuselage, using medium CA. Start with small patches of glue in the corners, checking the fuselage alignment as you go. Then go back and glue all of the joints on both sides. Leave the rubber bands and tape in place until all of the glue has dried completely.





BUILDER'S TIP:

To assist in keeping the nose section of the fuselage straight, you can install the die-cut lite-ply tank floor at this point, but it is very important not to glue it in place during part "b" of this step. The tank floor should not be glued in until step 45. Notice that if you use the provided engine mount, you will need to cut some clearance notches at the front of the tank floor to clear the two bottom blind nuts and mounting bolts.

41.

  1. Glue F-4T and F-5T to their slots in FT.
  2. Add the die-cut lite-ply headrest HR to the top of FT. Use the 25 deg. side of the Dual Tool to get the correct angle.

42.

  1. Glue the five 3/16"x3/8"x24" balsa fuselage stringers in place. Notice that the top stringer and the two bottom stringers sit in notches in F-G, while the two middle stringers butt against the front face of F-G.
  2. When dry, trim off the front of the stringers flush with the front of HR and the back of F-G. Save the scrap stringer material for later.

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43.
  1. Install the landing gear mount to the fuselage by gluing it firmly to the sides, the doublers, and the bottom of F-2.
  2. Bevel the bottom edge of F-1 as necessary to allow FBF (Fuselage Bottom, Front) to seat properly in its grooves on the bottom of the fuselage.
  3. Tape FBF in place, then glue it using medium CA. Be sure to firmly glue the joint between FBF and the landing gear mount from inside the fuselage.
NOTE: The hole in FBF is provided to serve as an oil drain hole, as well as a convenient place to route the vent line from the fuel tank and/or the breather line from the crankcase of a four-stroke engine.




44.

  1. If the tank floor was installed earlier for alignment reasons, remove it now. Cut two 1-3/8" lengths from the 3/4"x30" balsa triangle stock to serve as braces for the landing gear mount. Notch both braces to clear the blind nuts, then glue them in place.
  2. Cut two braces for F-1 from the 3/4" balsa triangle stock and notch them as necessary to clear the blind nuts on the back of F-1. Apply slow CA to the braces and press them firmly in place.


45.

  1. Now you can permanently install the tank floor. Make sure it is seated on the fuselage doublers and against the back of F-1, then glue it in place.
  2. Trim the die-cut lite-ply nose triplers as necessary to fit, then glue them firmly to the fuselage doublers and F-1.
  3. Glue the small top deck formers T-1 , T-2, and T-3 into their notches in FT.

46.

  1. Bevel the top edge of the fuselage sides with a sanding block to provide a firm seat for the fuselage top deck when it is installed. Notice that the angle between the top deck and the fuselage sides varies along the entire length. Use the top deck formers as a guide to the sanding angle. Don't worry about perfection - a few swipes with a sanding block on each side should do the trick.
  2. Tape the die-cut balsa top deck in place. You will probably need to apply some warm water to the upper surface of the top deck to make it easier to bend into position and prevent it from cracking. Apply medium CA from inside the fuselage as much as possible. When dry, remove the tape.

47.

Check the fuselage for joints that could use another application of medium or slow CA. Fill any gaps at the Tee-Lock tabs and slots with CA.

The fuselage should now be ready for final sanding. Sand off all of the Tee-Lock tabs, then round the bottom edges of the fuselage and the corners of the balsa top deck. Use a sanding block, starting with 80-grit sandpaper. Switch to 150-grit, then 220-grit or 360-grit for the final sanding.



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Mounting The Wing To The Fuselage

NOTE: The wing must be completed through step 18 before proceeding.

48.

  1. Trial fit the wing to the fuselage. Align the wing (see the General Alignment Diagram on page 20 of "The Basics of Radio Control") and make accurate pencil marks on both the wing and fuselage so that the wing can be returned to the same position later.
  2. Locate the two 5/16" dia. x2" wing dowels and sharpen one end of each to a point - keep the point symmetrical and centered. Push the dowels into the holes in F-2 so that only the points remain sticking out into the wing opening. Slide the wing into position, making sure it is centered on the fuselage. When you remove the wing, there should be two small indentations in the leading edge.

49.

  1. Drill 1/8" holes through the leading edge at the indentations. Re-drill the holes, this time with a 5/16" drill bit, and continue drilling straight through the lite-ply wing dowel supports that are already installed in the wing. Keep the drill aligned as best you can with the wing center line.
  2. Remove the wing dowels from F-2. Put a piece of wax paper over the face of F-2 and reinsert the dowels, forcing them through the wax paper. Push the dowels in only 3/8", leaving most of their length exposed.
  3. Trial fit the wing in position, sliding it onto the dowels. Check to see that the wing seats properly on the fuselage. If not, slowly enlarge the holes in the leading edge until it does seat properly.

50.

When satisfied with the fit of the wing and the wing dowels, coat the inside of the holes in the leading edge with epoxy. Slide the wing back into position on the dowels. Also apply epoxy to the aft end of the wing dowels and the wing dowel supports by working through the openings in the bottom center sheeting. Hold the wing in place until dry, then remove the wing and fill any gaps around the dowels with another application of glue.




51.

  1. The two 3/4"x3/4"x1-1/2" basswood wing hold-down blocks key into pre-cut notches in the -fuselage doubler. For an accurate fit, the side of each block that contacts the fuselage needs to be beveled slightly to match the aihedral angle of the wing. Temporarily tape the wing in place on the fuselage, then check the fit of the blocks by working through the lightening holes. The blocks should seat firmly against both the fuselage side and the top surface of the wing.
  2. Again working through the lightening holes, install the wing holddown blocks in the notches, making certain they are in full contact with the wing upper surface. Tack glue the blocks to the fuselage with slow CA, then remove the wing. Finish gluing the blocks in place using medium CA.
  3. Cut two 1-1/2" lengths of 3/4" balsa triangle stock to brace the wing hold-down blocks. Glue the triangle braces firmly to the top of the holddown blocks and the fuselage doublers.

52.

  1. Fit the wing in place on the fuselage and check its alignment one last time. When you are satisfied that it is aligned correctly, tape it so that it can't move.
  2. Carefully mark the drill locations for the wing bolts. Visually confirm that a hole drilled at the marks will pass through the approximate center of the basswood hold-down blocks.
  3. Drill through both the wing and the wing hold-down blocks with a #7 (or 13/64") drill bit. Keep the drill perpendicular to the bottom surface of the wing so the heads of the nylon wing bolts will seat flush against the plywood plates.

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53.
  1. Remove the wing and tap the wing hold-down blocks with a 1/4-20 tap. Apply a few drops of thin CA to the holes to strengthen the threads. When you are absolutely certain that the CA has cured, clean up the threads by re-tapping the holes.
  2. Redrill the holes in the wing with a 1/4" drill bit to pass the nylon wing bolts.

Servo And Pushrod Installation

54.

The servos need to be mounted in the fuselage so that the nylon push rods can be routed properly, with the least amount of curvature. Refer to Chapter 2 of "The Basics of Radio Control" and the plans for information on where and how to mount the servos in the fuselage. Start by cutting two 4-1/4" long servo rails from the supplied 3/8" sq. basswood stick. The ends of the servo rails searin the die-cut lite-ply servo rail supports (SRS), which in turn slide against the "flat" inner edge of the fuselage doubler. Use your servos (or servo tray if you plan on using one) to properly space the servo rails. When satisfied with their position, glue the servo rails and servo rail supports in place.


55.


  1. Lock the rails in place by gluing a scrap piece of lite-ply or balsa at each end of both rails.
  2. Mount your rudder, elevator, and throttle servos to the rails.







56.

  1. Locate the two .270 o.d. x36" nylon outer pushrod tubes (black), and roughen the last 4" of each with sandpaper to aid glue adhesion.
  2. Slide the outer pushrod tubes forward through the pushrod exit slots in the fuselage sides and the notches in F-6. Continue sliding the tubes until only about an inch sticks out past the slots.
  3. The outer pushrod tubes should nearly meet (but not cross) at the notch in F-5. Glue a scrap of balsa below the tubes to hold them in place.
  4. Apply glue (either slow CA or epoxy) to the outer tubes at the push rod exit slots, from both the inside and the outside of the fuselage.
  5. Use a single-edge razor blade to trim the outer pushrod tubing flush with the outside surface of the fuselage.

57.

  1. The nylon push rods must be supported at each former to keep them from flexing under load. Use the die-cut lite-ply pushrod straps, F-3S and F-4S, to support the push rods. Notice that the pushrod straps haven't been marked for push rod location because the routing of the pushrods will vary with different servo installations. Ideally, you want to have the push rods to come through F-3S pointed directly at fhe servo arms of the rudder and elevator servos. Carefully mark the pushrod locations on the plywood straps, then drill at the marks with a 9/32" drill bit.
  2. Cut off the front ends of the outer push rod tubes about an inch forward of F-3. Slide F-4S then F-3S into position on the push rods, but don't glue them in yet.
58.
  1. Cut two 4-40 x 8" threaded rods to an overall length that is equal to the distance from your servo arm to the end of the black tube (this distance will vary depending on your servo placement). Solder a 4-40 solder clevis to the smooth end of each rod.
  2. Screw the threaded end of the rods completely into the two .200 o.d. x36" nylon inner pushrod tubes (yellow).
  3. Slide the inner pushrod tubes into the outer tubes from the servo end. Attach the solder clevises to the servo arms and hook them up to the servos.
  4. With the push rods hooked up to the servos, you can now glue F-3S and F-4S to the front of F-3 and F-4, respectively, in such a way as to keep the bends in the push rods to a minimum.

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59. Now is a good time to install the .130 o.d. nylon outer tubing (clear) for the throttle pushrod. Route the tubing with as little curvature as possible, and support the aft end with a scrap balsa standoff. A SIG pushrod connector is supplied in the kit to hookup the cable to the throttle servo arm.

60.

Now is also a good time to plan your fuel tank installation and routing of fuel lines through F-1 (see "Engine and Fuel Tank Installation" for more information on fuel tanks for the FOUR-STAR 120). Mark the locations of the fuel lines on F-1, then drill holes through F-1 at the marks with a drill bit that is the same diameter as your fuel tubing. If you haven't done so already, remove the engine, fuel tank, throttle cable, and inner nylon pushrods before proceeding.

NOTE: The final step in the fuselage assembly is to attach the tail fairing blocks and shape them on the fuselage. Since this requires a completed stabilizer and fin, the instructions for this step are included under the next section, "TAIL CONSTRUCTION".

TAIL CONSTRUCTION

Stabilizer and Elevator

61.

  1. Cut the 1/4"x3/4" balsa stabilizer trailing edge to length and pin it in place over the plan.
  2. Glue the 1/4" sq. x9" spruce stab brace to the balsa trailing edge.
  3. The 1/4"x2"x12" balsa sheet provided in the kit must be used for both the stabilizer center block and the fin base. There is very little excess, so cut these parts carefully. First, cut out the stabilizer center block, using the plans as a guide, then glue it firmly to the stab brace and pin it to the plans.
  4. Add the 1/4"x3/4" balsa leading edges and tip pieces.
  5. Add the 1/4" sq. balsa diagonals to complete the stabilizer frame.

62.

The stabilizer is sheeted on both sides with 1/16" balsa. Cut two pieces of 1/16"x4"x30" balsa as shown in the diagram, and glue the parts together to make two stab skins.
BUILDER'S TIP: Use Sig-Bond for gluing the sheets, and sand the joints smooth BEFORE attaching them to the stabilizer frame. Sanding the skins after attaching them to the framework can result in a "ripple effect" due to the underlying structure.


63.

Sand the top and bottom of the stabilizer frame to smooth out the glue joints. Also sand the ends of the leading and trailing edges to match the tip pieces.


64.

  1. Apply slow CA or Sig-Bond to cine entire side of the stabilizer frame, then immediately press it onto one of the stabilizer skins. Trim the first skin with a modeling knife, then repeat for the opposite skin and allow to dry.
  2. Sand the sheeting flush with the stabilizer frame, then round the leading edges with a sanding block. Sand a small flat spot at the center "point" of the stabilizer so that it will seat against former F-6.
65.
  1. Locate the two pre-cut 3/8" balsa elevators and sand their trailing edges round. Draw a hinge line centered on the leading edge of each elevator, then use a sanding block to bevel the front of the elevators using the hinge line as a guide.
  2. Imbed the die-cut 1/16" plywood elevator horn support (EHS) in the bottom of the left elevator. Drill two mounting holes for the elevator control horn, and reinforce the balsa around the holes with thin CA.
  3. Use the plans to mark the elevators where the 1/8" dia. music wire elevator joiner will attach. Drill and groove the leading edges to accept the elevator joiner. Sand the joiner wire and wipe it clean before gluing it to the elevators with Kwik-Set Epoxy. Be certain to keep the leading edges of both elevators aligned as the glue dries.

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66. Temporarily tape the elevators to the back of the stabilizer, then use a sanding block to sand both of them at the tips until they match perfectly. The tips can be left square or sanded round if you prefer.




Fin and Rudder

67.

  1. Cut the 1/4"x3/4" balsa fin trailing edge to length and pin it in place over the plan. Notice that the fin trailing edge extends to the bottom of the fuselage.
  2. Cut the fin base from the remaining piece of 1/4"x2" balsa sheet. and then pin it in place over the plan.
  3. Add the 1/4"x3/4" balsa leading edge and top piece.
  4. Add the 1/4" sq. balsa diagonals to complete the fin frame.




68.

Cut a piece of 1/16"x4"x30" balsa as shown in the diagram, and glue the parts together to make two fin skins. Use Sig-Bond for gluing the sheets, and sand the joints smooth BEFORE attaching them to the fin frame.

69.

  1. Sand both sides of the fin frame smooth with a large sanding block. Trim the ends of the fin leading and trailing edges to their final shape.
  2. Draw a line on both sides of the fin trailing edge 3/8" below the fin base.
  3. Apply slow CA or Sig-Bond to one entire side of the fin frame except for the area below the line that you have just drawn.
  4. Repeat the above step for the other side of the fin.


70.


When dry, trim the sheeting flush with the fin frame. Use a sanding block to sand the fin leading edge round. Finish the fin by sanding a small flat spot at the bottom of the leading edge to fit against former F-6. Temporarily pin or tape the stabilizer to the fuselage, then trial fit the fin in place. You may have to trim the length of the fin trailing edge to allow the fin base to seat firmly on top of the stabilizer. Leave the fin in place until after the tailwheel has been fitted.


71.

  1. Round off the trailing edge and bottom of the pre-cut 3/8" balsa rudder, and bevel the leading edge.
  2. Imbed the die-cut 1/16" plywood rudder horn support (RHS) in the right side of the rudder. Drill the two mounting holes for the rudder control horn, and reinforce the balsa around the holes with thin CA.
  3. Cut a slot in the bottom edge of the rudder to accept the tailwheel wire.

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72.
  1. Tape the rudder to the fin so that its bottom edge is aligned with the fuselage bottom.
  2. Sand the top of the fin or rudder as necessary so that they will line-up when installed later.
  3. With the rudder still taped in place on the fuselage, trial fit the tailwheel assembly. Adjust the bends in the wire as necessary until the nylon bracket seats properly on the fuselage bottom and the tailwheel itself is aligned with the rudder.
  4. When satisfied with the fit, sand and wipe clean the top of the tailwheel wire, then glue it into the slot in the bottom of the rudder with epoxy. Tape the nylon tailwheel bracket to hold it in position on the fuselage until the glue dries.
  5. Allow the epoxy to dry, then reinforce the tailwheel area with a 2-1/2" long piece of 2" wide fiberglass tape applied with another batch of epoxy. When dry, remove the rudder along with the entire tailwheel assembly from the fin.
    NOTE: The tailwheel bracket will be attached to the fuselage during final assembly.
BUILDER'S TIP:
Two #2 flat washers are included in the kit to act as retainers for the tailwheel. Of course, you can use 3/32" wheel collars (not included in kit), but the soldered washers give a more "finished" look.
1. The secret to successful soldering is cleanliness. Sand the wire and the washers, then wipe them clean with alcohol. Begin the job by soldering the inner washer, which can be held in place with a temporary piece of heat-proof silicone fuel tubing.

2. When cool, install the tailwheel followed by a thin cardboard spacer and the outer washer.

3. Solder the washer, allow to cool, then remove the cardboard spacer. Grind off the excess wire and file the end smooth.
Done properly, this installation should be completely trouble-free.



73.

The balsa tail fairing blocks can now be glued to the fuselage using the stabilizer and fin to position them accurately. Cut two 4" lengths of 3/4" balsa triangle stock to serve as tail fairing blocks. Make sure your fin is centered on the fuselage (as viewed from above), then carefully glue the fairing blocks to the back of F-6 (not the tail surfaces!) Gently slide the fin and stabilizer off the fuselage and apply a second coat of glue to the front of the fairing blocks.


74.

Temporary spacers are used to support the fairing blocks during shaping. Spot glue the 3/8"x3/4"x2" balsa spacer to the stab support centered under the fairing blocks. Glue a scrap piece of 3/16"x3/8" balsa to the top of the spacer between the fairing blocks. Finally, spot glue the fairing blocks to the spacers.

75.

Carve and sand the fairing blocks to blend in smoothly with F-6 and the fuselage stringers. Usea sanding block with one end wrapped with paper to protect the stringers from the sandpaper. When done, carefully cut away the glue spots holding the spacers to the fuselage and the fairing blocks. You can remove the spacers now; just be careful of the fragile fairing blocks during covering.

76. OPTIONAL:
If you plan on installing the optional tail brace wires (see "Final Assembly" for more information), you need to reinforce the attach points on the fin and stabilizer. Use the six die-cut 1/16" plywood brace wire pads (BWP) for hard points. Use a sharp knife to carefully cut away the balsa sheeting in the positions shown on the plans (four places on the stabilizer, two on the fin). Glue in the plywood pads, then drill three attach holes with a 3/32" drill bit, right at the center of the plywood pads. Harden the balsa between the pads by applying a few drops of thin CA directly into the holes.