CITABRIA RC30 FUSELAGE CONSTRUCTION

47.

  1. Pin the right-hand fuselage side to the plan. It may have to be trimmed slightly to match the drawing.
  2. Cut the cabin frame pieces from 1/8"x5/16" and 1/8"x3/8" balsa as indicated, and glue in place.
  3. Glue the 1/4" square balsa longerons to the top and bottom edges of the fuselage side.
  4. The 1/4" sq. balsa side stiffener (located just forward of the music wire cabin brace) should be glued to the fuselage side 3-5/8" from the front edge. Let dry.
48. Repeat step 47 for the left-hand fuselage side. You can use the plans to build the cabin frame, but be sure to flip the fuselage side over before adding the longerons and side stiffener. (Otherwise you will wind up with two right sides!)

49.

Use the plans to accurately mark the positions of the crossbraces on both fuselage sides (6 on top. 9 on bottom.). Also mark the position of former F-4.

50.

The tow fuselage sides are joined using slow-drying epoxy or Sig Bond applied to the edges of formers F-2 and F-4. Hold the structure over the top view of the plans as it dries to align it properly.




51.

  1. Position the 3/8"x1/2"x4-3/4" balsa cabin brace 1/8" aft of the frame corner and glue in place.
  2. Glue the 1/4" sq. balsa cabin brace to the aft end of the cabin frame.
  3. Add 1/8"x3/8" balsa pieces between the cabin frame and F-4.
52. Taper the aft end of the longerons to allow the fuselage sides to be pulled together. Glue the ends together and allow to dry.

53.

Cut the 1/4" sq. balsa fuselage crossbraces to length over the cross-sectional drawings on the plan and glue them in place. There are six crossbraces along the top of the fuselage and nine crossbraces along the bottom.

54.

  1. Glue former F-3A in place
  2. Add the 1/8"x1/4" balsa stringers between F-2 and F-3A. Notice that the stringers are glued to the back of F-2, flush with the top.

55.

Glue former F-4A to the back of F-4 cross-sectional drawing on the plans for proper positioning of F-4A.

56.

  1. Glue formers F-8 and F-9 together
  2. Add formers F-5 through F-10 to the fuselage. They should all be flush with the front edge of the crossbraces and vertical to the fuselage. Also, be certain they are accurately centered on the fuselage.

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57.
  1. Glue the inner two 1/8"x1/4" balsa stringers to the top of the formers.
  2. Add the outer two 1/8"x1/4" balsa stringers. Notice that the front of these stringers are glued to the sides of F-4A only, not F-4. Be certain all the stringers are glued firmly.
  3. Glue the 1/4" sq. balsa stringers to F-9 and F-10. These stringers should meet at the tail like fuselage sides. They must be parallel to the top of the fuselage when viewed from the side. This step sets the stabilizer incidence and is critical to the good flying qualities of your Citabria.
58.
  1. Glue the 3/8"x1-1/2"x6-1/2" balsa tail platform to the top of the 1/4" sq. stringers.
  2. Trim the 1/8"x1-1/2"x2" balsa dorsal support to fit between the two stringers just ahead of the tail platform. Glue it in place, flush with the top of the stringers.
59. Cut side doublers from 3/32" balsa sheet and glue in place on the front end of the fuselage.

60.

  1. Add the 1/8"x5/16" balsa stringers to the fuselage sides. Use the plans to determine their exact location. A metal straightedge will help align the srtingers as you glue them in place.
  2. Glue 1/8"x1/4" balsa stringers to the bottom edge of the fuselage sides from the doublers to the tail
61. Glue formers F-3B, F-3C and F-3D to their respective crossbraces.


Landing Gear

62.

The landing gear halves are sandwiched between two 1/8"x3-3/8"x5-1/16" plywood landing gear mounts. This allows you to remove the gear while shipping, sanding and painting the fuselage. This also makes it easy to replace the landing gear should it ever become necessary.
  1. Glue the first plywood mount directly to the fuselage bottom between F-3B and F-3C.
  2. The landing gear is made from 3/32" aluminum, so a gap between the landing gear mounts must be formed by gluing a scrap 3/32" balsa spacer directly behind the area occupied by the landing gear.
  3. Glue the second mount to the spacer and formers. The landing gear should now slide snugly into the slot between the mounts.

63.

Position the landing gear on the second mount so that you can see the predrilled holes. Drill through these holes and the two landing gear mounts with a 1/8" drill.
64. Remove the gear and drill the LOWER landing gear mount ONLY with a 5/32" drill bit. Install the gear in the slot and pull four 4-40 blind nuts into the lower landing gear mount using 4-40x3/8" screws installed from the cabin.

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Completing The Fuselage

65.

  1. Add 1/8"x1/4" balsa stringers from F-3B to F-3D. Notch the very front of these stringers to accept sheeting over F-3B.
  2. Glue 1/8"x1/4" stringers between F-2 and F-3B. These should be flush with the edges of both formers.
  3. Extend the stringers from F-3D to the front face of the crossbrace located just aft of F-4 using pieces of 1/8"x1/4" balsa.
66.
  1. Plank the area from F-2 to F-3B with 3/32" balsa. It may be necessary to wet the wood on the outside surface to help make it bend easier.
  2. Plank the top of the fuselage from F-2 to F-3A with 3/32" balsa. Again water will help it to bend.
Window Frames

67.

Carefully taper a piece of 3/16"x3/8" balsa to serve as a base for the window frames (see cross-section at F-3D). Glue in place on the cabin frame.

68.

  1. Assemble the window frame pieces FWF, FWW, WSF-1 and WSF-2 over the plan and allow to dry.
  2. Glue the window frame to the fuselage with the front edge flush with the front of the cabin frame.
  3. Glue and pin window fram pieces RWF and RWF-2 to the cabin frame.
69. Make a cabin window ledge from scrap 3/32" balsa. It should extend from FWW back to RWF-2 and should cover top of the fuselage side, the 1/4" sq. longeron, and the 1/8"x5/16" stringer.

70.

Install the 1/4" sq. balsa diagonal cabin braces as shown on the plan. The bottom end of the front diagonal is glued to the cabin window ledge, about 1/8" from the outside edge.




Joining The Wing To The Fuselage

71.

Lightly sand the top of the cabin as necessary to make it smooth and flat so that the wing will be supported properly. Epoxy the 1/4"x3/4"x1" hardwood wing anchor blocks to the rear corners of the cabin, flush with the top. Be certain that these are glued firmly.
NOTE: The completed wing is required for the following steps.

72.

  1. Prepare P-1 (1/8"x1-5/8"x5" plywood) for installation. Trim the width, if necessary, to fit the center section of the wing.
  2. Cut notches in the bottom corners to fit on the cabin frame.
  3. Using the plans as a guide, mark the location of the two 1/8" dia. holes to be drilled later.
73. Tape the wing onto the fuselage, making sure it is aligned properly. Slide P-1 into position and glue to the fuselage (not the wing!).
Drill two 1/8" dia. holes, side by side, for the 1/8" wire cabin braces. Drill through P-1, P-2 and the 3/8" balsa doubler behind P-2. A thin wedge of balsa between P-1 and P-2 will help steady P-1 as you drill.

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74.

Cut a notch in the top fuselage longeron just forward of the cabin frame and just aft of the 1/4" sq. side stiffener. Make the notch just large enough for the cabin braces to sit flat against the fuselage side.
  1. Trial fit the two 1/8" dia. music wire cabin braces. If necessary, you can slightly "tweak" the bends in a vise for a perfect fit. The upper ends should fit tight in their respective holes.
  2. Thoroughly clean or sand the wire cabin braces and install them in their correct position. Expoy the wires to the fuselage sides and add 1/4" sq. balsa braces behind them at the same time. The cabin braces should be sandwiched between those 1/4" sq. braces and the front 1/4" sq. side stiffeners installed earlier.
    NOTE: The wire cabin braces add strength to the cabin and hold the wing in place - they can't be omitted.
76. Bind the cabin braces at the top with fine copper wire and soldier.

77.

  1. Carefully mark the positions of the wing hold-down bolts on the trailing edge of the wing.
  2. Make certain that the wing is positioned properly on the fuselage then drill through the wing and the wing anchor blocks with a No.7 (or 13/64") drill bit.
  3. Remove the wing and tap the wing anchor blocks with a 1/4-20 tap. You can apply a few drops of thin CA glue to the threads to strengthen them. Redrill the holes in the wing with a 1/4" drill bit to pass the nylon wing attach bolts.



Cowling Assembly

78.

The edges where the cowl halves join should be sanded perfectly straight by gently rubbing them over a piece of 150 grit sandpaper laying on a flat surface.

79.

Hold a length of the joiner strip against the inside of one cowl half, leaving half of the strip extending past the cowl so that it can later be lapped onto the other cowl half. Apply butyrate dope thinner, MEK, or CA glue along the edge of the strip. It will spread along the seam and under the strip using capillary action. Be careful not to get any adhesive under your finger because it will leave a fingerprint in the plastic.
Position the other cowl half in place and apply adhesive along the seams as you did before.

80.

Trial fit the nose bowl of the cowl on the joined cowl sides. Notice that a lip has been molded into the front of the cowl sides to provide an adequate gluing surface for the nose bowl. Notch out the lip at the bottom of the cowl to clear the air filter recess that is molded into the nose bowl. When the fit of the nose bowl is satisfactory, glue it in place.

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81.
  1. Cut out the prop shaft hole and two air intake openings. Also, cut open the air exit area at the bottom rear of the cowl so that your engine will properly cool. The small round dimple molded into the nose bowl below the prop shaft opening simulates the Citabria landing light and should not be cut from the cowl. The air filter recess (located just below the landing light) should be left intact only if you plan to use the optional airscoop, as described in part "b" of this step. Otherwise the air filter recess should be cut out for best realism.
  2. If you have decided to use the optional airscoop, it should be installed now. Carefully cut out the scoop along its edges. The exhaust skirt at the bottom of the cowl will have to be trimmed away to clear the scoop. (The scoop should extend to the rear edge of the cowl.) Position the airscoop as shown on the plan and glue it in place.
82. Scrape the seams on the outside of the cowling with the edge of a razor blade to take out any rough spots or flaws. Low spots in the seam can be filled with Sig Epoxylite Putty. Work the putty into its final desired shape before it hardens using your finger or a razor blade,dipped in water, to smooth it into the low spots. Let it dry overnight, then sand the entire cowling smooth and scratch-free with fine sandpaper. Also sand the back edge of the cowl until it sits perfectly flat.
CAUTION: Do not use coarse sandpaper which will cut deeply into the plastic parts. Deep scratches will often open up wider during painting. Use 220 grit or finer sandpaper to remove as much of the surface gloss from the plastic parts as possible.

Firewall Assembly And Engine Installation

NOTE: You will need your engine and spinner for the following steps.
You should now decide how you wish to mount your engine. An upright cylinder generally makes for good starting and easy access, but tends to spoil the appearance of the model. An inverted installation will allow you to totally conceal most 2-stroke engines, giving the best appearance. However, inverted engines tend to be more difficult to start and have a less reliable idle. A good compromise is to mount the engine cylinder horizontally (side mounted). This installation avoids the problems of an inverted engine and can be seen from only one side. The engine shown in the instructions is a side mounted Saito 45 4-stroke engine.
NOTE: If you have side-mounted your engine, you will most likely have to make a cutout in the cowling to fit over the cylinder head (after your engine is installed). Take your time and make a tight-fitting, good looking cutout. You may need to expand your cutout, or make separate ones, for easy access to your engine's needle valve, carburetor, muffler, fuel lines or throttle linkage.

83.

  1. Using a large sanding block, sand the front end of the fuselage perfectly flat, flush with F-2.
  2. Trim the cowl former if necessary to achieve a snug fit inside the cowling.
  3. Glue the cowl former to the front of the fuselage. The cutout in the cowl former should line up with the cutout in F-2, and there should be an even "ledge" all the way around the outside of the cowl former. Notice that the cowl former "bulges" slightly at the sides - otherwise, it is the same shape as F-2 (without the longeron notches).

84.

  1. The cutout pieces from F-2 and the cowl former are glued together to form F-1 (firewall). Use Sig Kwik-Set Epoxy and use a heavy weight of some kind to hold the two pieces perfectly flat while drying.
  2. Mark the vertical centerline and thrust line on the firwall using the F-1 cross section on the plan as a guide.
  3. Determine the spacing that will be necessary between the two aluminum engine mounts to fit your engine, then position the mounts on F-1 accordingly. Mark the locations of the four mounting holes and drill them out with a 3/16" drill bit.

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85. Tap the four 6-32 blind nuts into the back of the firewall. Bolt the engine mounts to the front of the firewall using 6-32x3/4" screws to be sure the blind nuts are aligned and that the engine still fits in the mounts. Epoxy around the edges of the blind nuts to hold them in place. Be careful not to get any glue on the threads.



86.


Position your engine on the mounts and mark the engine mounting holes. Drill at the marks to suit your engine.


IMPORTANT: The aluminum engine mounts shown in these photos have been replaced by glass-filled mounts.


Glass-Filled Engine Mounts
No Tapping Required
Sig's new glass-filled engine mounts have been included in this kit to replace the aluminum mounts that are shown in the instructions and the plans. The beauty of these new mounts is that they don't require tapping. Simply drill the holes to clear your engine mounting bolts, then fasten your engine to the mounts using 3/4" long bolts and aircraft lock nuts (4-40 or 6-32, depending on the engine.). If you prefer, the new mounts can be drilled and tapped just like aluminum (except you won't need lubricating oil).
87.
  1. Glue the 3/8"x4"x2-1/4" balsa top firewall extension to the back of the firewall, flush with the top edge. Trim as necessary to clear the blind nuts and use a triangle to check squareness as it dries.
  2. Glue the 1/8"x4"x2-1/4" plywood bottom firewall extension to the bottom of the firewall, flush with the bottom edge.
  3. Add 1/2" balsa triangle stock in the corners formed by the firewall (F-1) and it's top and bottom extensions.
NOTE: The firewall assembly (engine, mounts, firewall and extensions) is now ready to mount on the fuselage. The position of the extensions in F-2 will depend on your engine, and is dictated by the length of the cowling. For this reason, it is best to install the firewall assembly and cowling assembly at the same time as described in the following steps.

88.

Mount your spinner (or just the backplate) to the engine and mark the firewall extensions 5-3/4" from the backside of the spinner.

89.

Spot glue the firewall assembly to the fuselage with the marks at the front side of the cowl former. (This may be easier to do if you remove the engine temporarily.) The engine should have no sidethrust and no downthrust.

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90. Fit the cowling to the fuselage. When holding the cowling in place, the engine shaft should be centered between the air intake openings. If it is off center, trim the cowl or slightly reposition the firewall assembly as necessary. Remember to maintain a true thrusting (no side or downthrust).

NOTE: You may want to prepare your fuel tank and throttle linkage installations at this point. (See further down for tips on tanks and throttle pushrod installation.) Once you have done these steps, you should remove your engine and engine mounts.


TO PREVENT COWL CRACKS
The most common cause of plastic cowls cracking is distortion of the plastic from impropper installation of the mounting blocks and screws. If the plastic is fully supported by the block underneath, no strain will occur when the screws are tightened down.

91.

  1. Firmly glue the firewall extension to F-2 and add 1/4"x3/8" and 1/4" sq. balsa braces as shown on the plans.
  2. Glue 1/2" triangle stock to the back of the firewall along it's sides.
92. Glue the 1/4"x2-1/4"x4" balsa side extensions to the sides of the firewall assembly and F-2. Cut off the side extensions flush with the firewall and brace the back edges with 1/4" sq. balsa as shown on the plans.

93.

Cut the 3/8"x3/8"x4-1/2" basswood stick provided into six pieces, each 3/4" long. Glue these six cowl mounting blocks to F-2 in the positions shown on the plan. Carefully trim these blocks as necessary to allow the cowling to slide over them snugly.


94.

With the engine mounted, tape the cowling into it's final position on the fuselage. Drill six holes through the cowling and cowling mount blocks using a 1/16" dia. drill bit. Remove the engine and cowl, and redrill the holes in the cowling with a 3/32" dia. drill bit to pass the six #2x3/8" sheet metal screws used to hold the cowl in place.

Final Shaping Of Fuselage

95.

  1. Use a large sanding block to progressively taper the side stringers towards the rear. They should taper down to nothing right at the back end of the fuselage.
  2. Shape the 3/8" balsa tail platform and 1/4" sq. balsa stringers to blend in smoothly with the fuselage lines.

96.

Taper the front of the 3/32" balsa side doublers with a sanding block. The cowling should be mounted as you sand so that it can be smoothly blended with the front of the fuselage. (Protect the cowling with strips of masking tape.) Taper the front of the side stringers to blend into the 3.32" balsa side doublers.

97.

  1. The bottom formers should be scalloped between the stringers to improve the appearance after covering. This will keep the formers from showing, leaving only the stringers to support the fabric.
  2. The area on the fuselage bottom (just aft of the cooling air exit on the cowling) should be sanded at an angle to help allow the cooling air to flow through and smoothly exit the cowling.

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98.

  1. Sand the top of P-1 to match the wing center section.
  2. Fasten the wing to the fuselage. Roughly shape the 3/4"x1-1/4"x1-1/2" balsa wing blocks to the shape shown on the fuselage top view and F-2 cross section. Glue the wing blocks to P-1 leaving a small gap between them and the inboard wing rib.
  3. Carve and sand the wing blocks to airfoil contour. Sand the lower surface smooth.
  4. Add a small scrap of 1/8"x1/4" balsa to the bottom of the wing block to act as a windshield support and sand to shape.
NOTE: Many modelers prefer to cover their tail surfaces before attaching them to the fuselage. If you choose to do this, be certain that all the hinge slots are cut and the control surfaces move freely with the hinges temporarily in place.

99.

  1. With the wing in place, position the stabilizer on the fuselage and check its alignment carefully. Be certain it is square with the fuselage by viewing it from the top and the rear. When you are satisfied with its position, make small marks on the fuselage and stabilizer so that it can be returned to the same position.
  2. If you have already covered the stabilizer, the covering material will have to be cut away (use a sharp razor blade) where the stab rests on the tail platform, so that you will have a strong wood-to-wood glue joint. Epoxy the stabilizer to the fuselage, lining up the marks you made earlier. Recheck the alignment of the stabilizer as the glue dries.
    NOTE: The elevator must be permanently hinged to the stabilizer before the fin is attached.
100.
  1. Check the fit of the fin on the fuselage. The extended tail post on the fin should be in good contact with the fuselage sides and tail platform. If the stabilizer has been covered, cut away the covering material where the fin attaches.
  2. Epoxy the fin to the fuselage and stabilizer, using a triangle to make certain it is vertical. Also, make sure that the fin is not offset to one side or the other by viewing it from above.
101. The fillet at the front of the fin is formed using Sig Epoxolite Putty. Epoxolite is light and strong, but gets very hard and is difficult to sand when dry. Smooth the putty to its final contour with a wet finger before it dries.


102.

Remove the tailwheel mount from its die-cut 3/32" plywood sheet. Cut or sand a recessed area into the bottom of the fuselage, then epoxy the tailwheel mount in this area so it is flush with the fuselage bottom. The tailwheel and its bracket will be mounted later, after the airplane is completely finished.

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Wheel Pants

103.

True up the edges of the wheel pants by gently rubbing them against sandpaper on a flat surface. Hold the two halves together, then apply butyrate dope thinner, MEK or CA glue to the seam. Apply pressure until the edges are firmly welded together.


104.


Cut out the hole in the bottom of the wheel pant with a Dremel tool and drum sander, or an X-Acto knife. Notice that the scale cutout extends forward of the first bottom surface. The drawings here show two views of the wheel pant with the scale cutout. You can make this step easier by just cutting out the flat bottom surface (but you will sacrifice some scale accuracy). Now go back over the seam from the inside with CA.
105.
  1. Glue the 1/16"x3/4"x1-1/4" plywood attach plates to the inside of the wheel pant in the position shown on the plan using Sig-Ment glue or CA glue.
  2. Carefully locate and mark the position of the axle on the wheel pant using the plans as a guide. Drill only the inboard wheel pant half with a 5/32" drill bit. Cut a slot from the axle hole to the bottom of the wheel pant.
106. Temporarily attach the wheel pant to the landing gear (which should be bolted to the fuselage) using the 8-32x1-1/2" axle bolt and 8-32 nut. Place the fuselage upside-down on a table and prop it up so that the top of the fuselage sides are level. Position the wheel pants so that they also appear level, and mark the two mounting holes through the landing gear onto the wheel pant.

107.

Remove the wheel pant and drill at the marks with a 5/32" drill. Install two 4-40 blind nut from the inside and glue into place. The figure above shows the final installation of the wheel and wheel pant, which should not be done until the airplane is completely finished.


Wing Strut Assembly

108.

Cut the front and rear wing struts to the lengths shown on the plan. The front struts are made from 3/16"x1/2" spruce and the rear struts are 3/16"x3/8" spruce. They should be shaped to the proper airfoil cross section by tapering the spruce slightly, then rounding the leading and trailing edges to simulate streamlined tubing used on real aircraft.
109.
  1. Cut slots in the outboard (upper) ends of the struts using an X-Acto knife with a #27 saw blade. The slots should be 3/4" long.
  2. Drill 3/32" dia. holes into the small pieces of brass shim stock as shown on the plans. Glue these in the slots in the outboard end of the struts using epoxy. Bend these tabs to sit flat on the wing when the struts are in position.
  3. The wing struts are attached to the wing using #2x3/8" sheet metal screws. Drill 1/16" dia. holes into the strut hold-down plates to accept screws.

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110.
  1. The inboard end of the wing struts use short pieces of threaded rod cut to length shown on the plans. Carefully drill the strut ends with a 5/64" drill. Sand the threaded rod clean, file small nicks in its side, and epoxy the rod into the hole in the strut.
  2. Drill and bend the aluminum strut attach tabs as shown on the plans. The tabs fit in slots cut into the fuselage sides, just above the landing gear mount. Cut slots now, but don't epoxy the tabs in place until the fuselage has been covered and painted.
  3. The struts are attached to the tab on the fuselage using nylon clevises on the threaded rod. This arrangement allows you to adjust the length of the struts so that they are not stressed while sitting on the ground. The struts provide extra strength to the wing in flight, and should not be omitted.

111.

The 1/6" dia. music wire jury struts are optional for this aircraft. The plans show how to fabricate and attach the jury struts if you decide to use them.