CITABRIA RC30 WING CONSTRUCTION

NOTE: The basic structure of the Citabria wing consists of three separately-built components - a flat Center Section, A Right Wing Panel and a Left Wing Panel. The three components are then permanently joined to the single-piece wing.

Right Wing Panel

1.

  1. Locate the 1/4"x3/4"x36" balsa sticks for the front internal wing spars and the 1/4"x3/8"x36" balsa sticks for the rear internal wing spars. Cut a 4" long piece of each size stick and slide four R1, nine R2 and five R3 wing ribs onto these short pieces. Pin the stack of ribs and sand lightly with a sanding block to true up the edges.
    CAUTION: It isn't necessary to sand the entire stack perfectly flush - just sand enough to take off any prominent high spots or burrs. Excessive sanding may distort the sirfoil shape.
  2. Check rib length against the plan and, if necessary, sand the leading and trailing edges to bring the ribs to their proper length.

2.

Taper the outboard ends of the front and rear internal wing spars as shown on the plan.

3.

Pin the flat side of the spars to the plan and mark the rib positions using a pen and straightedge. These marks will help you keep the ribs vertical when you glue them in place later.

4.

  1. Pin the 1/16"x1" balsa trailing edge sheeting to the plan. Do not cut the sheeting at the aileron break yet.
  2. Pin the 1/4" sq. balsa bottom spar to the plan using scrap pieces of 1/16" balsa to raise the spar 1/16" above the plans.
5.
  1. Slide the nine R2 and five R3 wing ribs into place on the two internal wing spars. Be certain that the tapered ends of the spars are positioned correctly (tapered side downward).
  2. Position the rib/spar assembly over the plan. Use scrap 1/16" balsa to block up the ends of the R3 ribs and the outboard R2 rib.
  3. Once the ribs are all positioned correctly, glue them to the internal wing spars. Also glue the R2 ribs to the trailing edge sheeting. Use a triangle to insure that the inboard R2 rib is perfectly vertical.


6.

  1. Glue the 1/8"x3/8"x36" shaped balsa trailing edge in place. Use a straight edge to be certain the trailing edge continues in a straight line in the aileron area.
  2. Glue the 1/4" sq. balsa top wing spar into place on the ribs. The top wing spar will have to be sanded later, so choose a relatively light piece of wood for this use.
  3. Glue the 3/16"x5/8" balsa leading edge to the front of the ribs.

7.

  1. Glue the R4 tip rib in place. You may notice that the bottom edge of this rib slopes up towards the rear. This provides built-in washout to the wing which helps prevent tip stalls at low speed.
  2. Saw off the top wing spar and leading edge flush with the outboard R2 rib. Glue small pieces of leading edge, trailing edge and top wing spar material to the wingtip. Block up the trailing edge with 1/4" sq. balsa scrap.

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8. The wing uses three gussets to provide extra strength in the corners. Cut the gussets from scrap 3/32" balsa. Be sure the grain direction is oriented as shown on the plan.

9.

Glue the 3/8"x7/8"x14" balsa aileron spar to the back of the R3 ribs and the two R2 ribs on each side. This spar sits flat on the plans - it is not blocked up.


10.

The 3/16"x1"x14" balsa aileron leading edge will have to be beveled before pinning it to the plan. Prop it up along a table edge as shown in this diagram and sand until you have the correct bevel. Now measure 3/4" from the cut-back corner to cut it to the correct height. The aileron leading edge can now be pinned to the plan with its beveled edge down and the top edge resting against the aileron spar.

11.

Glue the A1 and A2 aileron ribs in place. They will require some trimming for a good fit. Use a strip of 1/16"x3/16" capstrip material to block up the front end of the aileron ribs.

12.

Glue the 1/16"x1" balsa trailing edge sheeting to the top of the wing and pin it firmly in place until dry. Add the small trailing edge top piece to the wingtip.


13.

Remove the wing from the plan. Cut loose the aileron from the rest of the wing structure and lay it aside.

14.

Add the 1/4" sq. balsa bottom wing spar to the wingtip.

15.

The 1/4" sq. balsa top wing spar and the leading edge can now be sanded to the contour of the ribs. Be careful to avoid sanding the ribs and changing their shape. Double check all of the wing joints to make sure they have been properly glued.


16.

Set the Right Wing Panel aside and repeat steps 1 through 15 to build the Left Wing Panel.

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Center Section

17.

Start the center section by cutting a 1/4"x3/4" balsa front center section spar and a 1/4"x3/8" balsa rear section spar from the 15" long pieces provided. Cut them to the exact length and shape shown on the plan. The angle on the ends of these spars provides the proper dihedral, so they must be cut accurately. Mark the tops of these spars.

18.

  1. Pin the 1/16"x1" balsa trailing edge to the plan.
  2. Pin the 1/4" sq. balsa bottom spar to the plan using 1/16" scrap balsa to keep it raised.
19.
  1. Slide the four R1 ribs over the two center section spars and set the assembly over the plans. Be certain the inner two R1 ribs are spaced wide enough to accept the aileron servo that you plan to use.
  2. Use the Dihedral Guage shown below (glued to scrap balsa) to position the two outboard R1 ribs at the correct angle. Glue the ribs to the spars and trailing edge.


20.

  1. Glue the 1/4" sq. balsa top spar to the center section. When dry, remove from the building board.
  2. Glue the 1/8"x3/8" shaped balsa trailing edge in place.

Finishing The Wing


21.

  1. You can now prepare the center section and wing panels for joining. Sand the inboard ends of the wing panels, bringing the spars, leading edge, and trailing edge flush with the end R2 rib. Cut holes in the end R2 rib of each wing panel just large enough to accept the front and rear spar splices.
  2. Sand the top spar of the center section to the contour of the ribs. Sand the ends of the spars and trailing edge, being careful to leave the two splices sticking out on both sides.
22. Pin the center section down firmly onto one end of your building board. Glue one wing panel at a time to the center section using Sig Kwik-Set Epoxy applied to the spices, spar ends and between the R1 and R2 ribs at the joint. The wingtip should be blocked up 1-1/4" under the outboard R2 rib (not the R4 wingtip rib). The solid balsa wingtip blocks supplied in the kit just happen to be 1-1/4" wide, so they can be used to support the wing during this operation. Repeat to attach the other wing panel.

23.

  1. Cut a slot in the inboard R2 rib of each wing to accept the 3/8"x1-3/16"x9" balsa filler and doubler.
  2. Glue the filler and doubler in place. When dry, shape it to rib contour.
  3. Glue the 1/8"x1-1/4"x5" plywood plate called P2 to the front of the filler and doubler. Sand the top and bottom edge to rib contour.

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24.

The leading edge of the wing is sheeted on the top and bottom with 1/16"x2"x36" balsa sheets. Apply the bottom sheeting first. Start gluing at the leading edge and working back to the spar, pinning or taping the sheet in place as you work. Cover only half the edge of the outboard R2 rib with the sheeting. Be careful not to build in any warps during this step. Let dry.

25.

Turn the wing over an apply the top leading edge sheeting, just like the bottom sheeting. Pin the wing to the building board during this step to help avoid warps. When dry, trim the excess overhanging top and bottom sheeting flush with the front of the leading edge.



26.

Glue small pieces of the leading edge sheeting to the top and bottom of the wingtip area. Let dry and then trim flush.

Aileron Control System

NOTE: The Citabria uses a bellcrank/pushrod system to actuate the ailerons. Steps 27-29 describe the installation of this system.

27.

  1. Using a hand-held drill bit or piece of brass tubing with a sharpened end, drill 3/16" dia. holes just above the lower edges of the ribs, about 3/4" aft of the front internal spar, to pass the 1/16" dia. music wire pushrod.
  2. Cut four small pieces (1/4"x1/2") of scrap 3/32" plywood to serve as pushrod guides. Drill each piece through the center with a 3/32" dia. drill bit.
  3. Put a "Z" bend into one end of the pushrod, then thread it through the wing, installing two of the scrap plywood pushrod guides in their proper position as you go. Don't glue the pushrod guides to the ribs yet.
    NOTE: At this point some modelers may prefer to use R/C solder links (not provided in kit) instead of "Z" bends on the pushrod.
28.
  1. Remove the two aileron bellcrank mounts(1"x2-1/4") from their die-cut 3/32" plywood sheet. Drill a 3/32" dia. hole in the center of the mount, then assemble the bellcrank as shown in the diagram above. Apply a drop of epoxy to the nut to hold it permanently. The bellcrank should twirl freely when properly installed.
  2. The bottom surface of the bellcrank mount is positioned 7/16" above the lower edge of the ribs (see cross section on the plans). Attach the bellcrank to the pushrod, then position the mount as shown on the plans and glue it in place. Brace the mount to the ribs with scrap pieces of 1/4" sq. and 1/16"x1/4" balsa.
29.
  1. Splice the ends of the two pushrods together using a 1" piece of brass tubing soldered to both pushrods in the center. Use tape to hold the bellcranks in the neutral position (as shown on plans) during this step.
  2. Allow the joined pushrod to seek its natural position, then epoxy the plywood pushrod guides to the ribs. When dry, the entire pushrod/bellcrank assembly should work freely, with no binding.
30. Cut two filler blocks from the 3/8"x1"x2" balsa stick provided in the kit. Glue these in place at the trailing edge of the center section and sand them to rib contour when dry. The filler blocks reinforce this area for the wing hold-down bolts.

31.

  1. Sheet the top and bottom of the center section with 1/16"x3"x36" balsa.
  2. Add the middle sheeting to the top and bottom of each wing panel using one piece of 1/16"x3" balsa and one piece of 1/16"x2" balsa on each section.

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32.

Sheet the area under the aileron bellcrank assembly with 1/16"x3" balsa. You may cut the pushrod slot as shown on the plans, but with a bit more care and patience a more attractive crescent shaped slot can be made, as shown in the photo.

33.

Glue the 1/16"x3/16" balsa capstrips to the top and bottom of the ribs as indicated on the plan.

34.

  1. Glue 1/16" balsa sheeting in the control horn area of the aileron on the bottom surface only.
  2. Add capstrips to the top and bottom of the small ribs in the ailerons. When dry, sand the top of the aileron leading edge to shape.
  3. Install aileron control horns as shown on plan. Use a 1/4"x3/8" balsa spacer.

35.

Glue the 1/4"x5/8" balsa leading edge caps and the 3/4"x1-1/4"x8-1/2" balsa wingtip blocks in place on the wing. Let dry.
36.
  1. Carve and sand the wing leading edge caps to the shape shown on the plan. Take your time with this step and try to keep the shape uniform along the entire leading edge.
  2. Sand the wingtips to the shape shown on the plans.
  3. Sand the 3/8" aileron spar flush with the top of the wing contour.

37.

Remove the four hold-down plates (1/2"x1/2") from their die-cut 3/32" plywood sheet. Install the plates as shown on the plan by cutting out the 1/16" balsa sheeting and epoxying the plates flush with the bottom surface of the wing. Secure the plates to the ribs and spars with scrap balsa.

38.

If you plan to use the optional jury struts, install 1/2" lengths of brass tubing at the positions shown on the plans, with the ends flush with the bottom surface of the wing.

39.

Carefully block sand the entire wing until all joints are smooth and even. Use a large sanding block to avoid sanding down any one area too much.

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TAIL SURFACE CONSTRUCTION

Stabilizer and Elevator

40.

  1. Build the 5/16" sq. balsa stabilizer frame by first cutting pieces to fit the plan from the 36" long sticks provided. Glue and pin the pieces together on the plan.
  2. Glue the 1/8"x5/16" sprice braces to the front and rear of the stabilizer frame.
  3. Cut the 5/16" balsa center sheet to shape and glue in place.
  4. Add the 1/8"x5/16" balsa diagonal ribs.
41. When dry, remove the stabilizer from the board and sand all of the edges round. You may find that a line drawn along the center of all the frame pieces can help in getting a consistently rounded edge.

42.

  1. Cut to length the 5/6" sq. balsa pieces for the elevator halves. Glue and pin to the plan.
  2. Cut the elevator trailing edge pieces and gussets from 5/16" balsa sheet and glue in place.
  3. Cut the elevator tip pieces from the 5/16"x1/2" balsa sheet and glue in place.
  4. Add the 1/8"x5/16" balsa diagonal ribs and allow to dry.

43.

  1. Remove the elevator halves from the plan and sand them to the correct outline. An easy way to do this is to make a tracing of the elevator half and cut it out. Place the tracing over the elevator, draw around the outline, then sand down to the line.
  2. Taper the trailing edge to the contour shown on the plans and round all the edges.

44.

Temporarily pin the elevator halves to the plan. Mark the leading edges where the wire joiner will attach. Remove the elevators and drill 3/32" dia. holes into the leading edge, then cut a groove to accept the wire joiner. Sand the wire joiner lightly and epoxy it to the elevator halves. Place the assembly over the plans while it dries to be certain that everything is aligned properly.

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Fin And Rudder

45.






46.

  1. Cut to length and pin the 5/16" sq. balsa fin frame over the plans. Notice that the rear edge of the frame extends to the bottom of the fuselage.
  2. Add the 1/8"x5/16" balsa diagonal ribs.
  3. Glue the 5/16" balsa fillet to the leading edge.
  4. Remove the fin from the board and sand the leading edge, trailing edge and top edge round. (Don't round the bottom.)
  1. Glue and pin down the 5/16" sq. balsa rudder frame.
  2. Add the 5/16" sheet balsa gusset.
  3. Add the 1/8"x5/16" balsa diagonal ribs.
  4. Remove the rudder from the board and sand the edges round.

Hinging The Control Surfaces

Poly-molded hinges have been included in the kit for all of the control surfaces. They are easy to install and can't clog up with glue or paint like pinned hinges. Even though they may feel a bit stiffer than pinned hinges, the "stiffness" is nothing compared to the air load from the control surfaces that the servos have to work against. Much of the initial stiffness can be eliminated by pre-flexing the hinges to extreme angles. The Sig Factory Fliers have used these hinges for years on hundreds of models with complete success.
To avoid any binding, the hinges must be properly aligned. The best way to insure this is by drawing a line on the control surface using a straightedge and soft lead pencil along the entire hinge line. Cut the initial hinge slots using an X-Acto knife with a #11 blade or a special hinge slotting fork. Then widen the slot to fit the hinge with a #15 or #27 saw blade.

IMPORTANT NOTE: The ailerons on the Citabria are hinged about 1/16" below their top edge. Cut the slots so that they angle downward in both the aileron and the wing (see cross section on plan). When the ailerons are in neutral,the hinges will already be deflected, but this won't affect their smooth operation.




Notice that the hinges have a flat side and a rounded side. For best operation, the hinges on any control surface should all be installed with the same side facing downward. Install hinges using plenty of Sig Kwik-Set Epoxy in the slot and on the hinge. The thin, bendable portion of the hinge should be completely out of the slot and free of glue. Excess epoxy can be easily peeled off after it has dried for 7 to 15 minutes.