Wing Final Assembly

by Frank Justice

There are several different methods to use in riveting on the skins. These are described in the construction manual. The method described here is a slight variation of the top-skin-first method. It is a little more work than some of the other methods, but it allows you to avoid pop rivets in both the top and the bottom skins.
Rivet Leading Edge Assembly and Ribs to Spars
  1. Remove the top skin(s), the tank, the leading edge assembly, and the inboard four main ribs (the ones with the flanges pointing toward the root).
  2. Deburr and dimple all the rivet holes in the ribs and spars except where countersunk skins if any will go. Countersink the ones in the spars that you can't dimple, such as where the ribs are.
  3. Put a very slight inward curl on the leading edge skin at the main spar rivet lines so it will not bow up when riveted.
  4. Secure the leading edge assembly with clecos and bolts as shown in drawing #20. Install the rivets that attach the main and leading edge ribs to the main spar. Install the bolts and pop rivets that attach the remainder of the main ribs (except the inboard four) to the main spar.
  5. Install the rivets that hold the leading edge skin to the spar.
  6. Build and mount the pitot tube (left wing only) as shown in drawing #20. Take off the part on the outside of the wing and put it away to avoid damage.
  7. Install rivets to attach the main ribs (except the inboard four and the short rib/aileron hinge bracket) to the rear spar. Do not put rivets in the bottom holes of those ribs outboard of the center spar doubler plate. These will be put in later to also attach the aileron gap fairing. Use flush rivets in all of the holes previously countersunk. Rivet on the short rib and aileron mounting bracket (unless it would prevent bucking a topskin-to-spar rivet; you can rivet it on later instead) using AN470 rivets in all holes.
Installing the Tank on the Spar
  1. Cleco the tank onto the spar. Verify that the outboard edge meets the leading edge skin with no gaps. Trim the tank skin if necessary.
  2. Enlarge the attachment holes to #19 or 11/64". Machine countersink the upper (toward the nose) row of holes along the spar for #8 screws. Remove the tank.
  3. Debur all the holes. Dimple the remaining holes in the tank for #8 screws.
  4. Make the platenut mounting holes in the spar and leading edge flange by attaching a platenut to the spar tightly with a short #8 flathead screw (easier task if it does not engage the locking part of the threads; flathead screws will center themselves in the holes) and drill #40 through its mounting ears into the spar or leading edge flange strip.
  5. Countersink all the platenut mounting holes in the spar and the leading edge flange..
  6. Dimple the screw holes in the leading edge flange strip, the lower row of holes in the spar, and the holes in the tank. At least 12 of these can not be done with standard tooling. The alternatives are: 1.Grind down one side of your dimple die (and the squeezer if necessary) so it will reach the holes. 2. Avery makes a screw-operated tool that will reach 3. Make the tool described in the notes section for dimpling hard-to-reach areas 4. Drill a #19 hole next to the edge of a steel bar and countersink it so a #8 screw just fits; use this as a backup to dimple with a rivet gun and dimple die 5. Countersink these holes, which is cannot be done well unless you clamp on some kind of backup plate, such as about 1/8" thick aluminum with a #19 hole in it. .
  7. Attach the appropriate type of platenuts (dimpled or flat) to the spar with AN426AD3 rivets.
  8. Check each hole to be sure that a screw can be inserted and will easily start into the platenut. If not, enlarge the hole in the spar until it will.
  9. In the area near the root where there are no screws next to the trailing edge, bow the skin inward slightly.
Top Skin
  1. If you are using the two piece top skins:
    Bevel the edges where they meet as shown in drawing 21 section C-C'.

  2. Cut a section out of the outboard skin in the flap area where it overlaps the inboard skin as shown in the construction manual page 7-53.
  3. Dimple the top skin(s) and the top side of the ribs and spars -or- countersink the top skin after doing the next step.
  4. Secure the top skin(s) and wing walk area reinforcing sheet in place tight against the leading edge and tank skins
  5. Rivet the top skin(s) on, making sure you do not put any rivets in that will interfere with getting the four inboard ribs back in later. Back riveting is strongly recommended, especially if you don't have an expert helper. Use the special offset back riveting set with the counter-bored tip (Avery and others). For bucking use a heavy bar or plate with at least a 1 1/2" by 1 1/2" square surface. Handliing the gun is a little tricky but handling the bar takes no skill at all.
Aileron Hinge Bracket
  1. Cut off the jigging tab on the outboard end of the rear spar.
  2. Fit the outboard aileron hinge bracket to the rear spar using the previously-built bearing location template and rivet the bracket on. Also rivet on the inboard hinge bracket and short rib if you have not already done so.
Aileron Bellcranks
  1. Drill the pre-bent bellcrank arms for the bearings #30 and rod end bolts 3/16" as shown in drawing 19. Make each of the two spacers per arm out of either 0.063 or two thicknesses of 0.032 aluninum. Locate approximately as shown and drill the holes #30 for the rivets to hold them in place. While doing this keep track of which piece goes where, and when done tie everything together except the bearings with clecos. Prime everything, then rivet together. Hold the completed assembly up to the picture on drawing 19 and mark the end that goes toward the aileron.
  2. Cut the spacers that go on the bearing support bolt as shown in drawing 19 out of the the short piece of thick-walled tubing supplied. If you are using the VA-126 bushings you must allow room for washers on either side of the bushing; see the notes on bearing assembly for the type of bearing you have. The length of the spacers should be such that they fit in place with slight interference.
  3. Install the bolt head-up using at least one washer underneath the castellated nut. Use more washers if necessary so that the hole in the bolt lines up with the slots in the nut when the nut is tightened.
Aileron Gap Fairing
  1. Using drawing 16 as a guide trim the flat side of the aileron gap fairing W-624 as necessary to allow it to butt up against the rear spar flange and end the proper distance from the spar web. It will be about 1 13/16" wide. Verify the curve of the fairing by holding it against the drawing and the aileron nose rib; modify the curve if necessary a little at a time by hand. Place the fairing in position on the wing and verify that when it is flat against the top skin the bottom edge pushes against the spar slightly. The lower edge of the curved part should lie where the curve of the spar starts; trim if necessary so the fairing will not interfere with the bottom skin. Notch out the ends where they will hit the aileron hinge brackets.
  2. Use double-sided tape to hold the fairing to the top skin and drill the holes #40 for the rivets that will secure it. These should be 2" apart and about 1/2" from the front edge of the fairing. Any farther back and it will be difficult to drive rivets to hold the fairing to the top skin unless you have a bucking bar that will get into an area like that.
  3. Clamp the lower edge of the fairing to the rear spar. Drill #30 through the open holes in the spar doubler plates. Drill #30 through the rib flange and spar holes. Drill additional holes #30 approximately 2" apart along the same line as the previous holes.
  4. Verify that there are no sharp bends in the fairing at the aileron hinge brackets and the fairing is notched enough that it will either clear or not be distorted by the rivets that will hold the brackets on.
  5. Remove the fairing, deburr the holes, and prime it.
  6. Rivet the aileron gap fairing to the top skin, being careful to force down as little as possible to get at the rivets. Then rivet it then to the spar.
Aileron Mounting and Control Rods
  1. Use the two V-shaped airfoil templates made previously to locate the aileron on the wing.
  2. Using the bolt holes in the aileron brackets as a guide mark and drill the aileron hinge brackets.
  3. Put bolts in the holes to hold the aileron to the wing.
  4. Make the inboard hinge spacer shown in drawing #21 It should be about 9/16" long. Put it in place on the bolt.
  5. Make spacer(s) for the outboard hinge.
  6. Secure the aileron bellcrank in its neutral position as defined in drawing #19.
  7. Make an aileron control rod as shown in drawing #19. The tube part must be long enough for the threads of the rod ends to be visible in the inspection hole in the Heim bearing yet not so long that future adjustment (shortening) is impossible. To get the right length, put Heim bearings with rod ends screwed about three-fourths of the way in on both the aileron and the belcrank. Then measure between the shoulders on the rod ends and cut the control rod to that length.
  8. Put the control rod in place and make spacers to hold the Heim bearing in the proper position on the aileron. The spacers must be such that the Heim bearing will not hit the aileron hinge bracket and the control rod body will not hit the edge of the opening in the rear spar as the aileron is moved full up and down. There should even be some extra space to allow for vibration, etc.
  9. Tighten the jam nuts on the control rod ends to lock them in place.
  10. Remove the control rod from the wing.
Flap Mounting
  1. Verify the length of the flap brace against the plans and trim it if necessary (drawing #17). Mark the flange which goes against the wing skin (the sharper bend side; do not be misled by the drawing orientation) Mark the root end. Make the lightening holes as shown in drawing #17.
  2. Cleco the bottom skins on the wing using a cleco in every hole along the rear spar and the last few holes in every rib in the flap area.
  3. Secure the aileron in its exact position by adding the proper washers to the mounting bolts.
  4. Put the flap in place supported by the two airfoil templates. Tape or brace the aileron into its neutral position (lined up with the flap). There should be a gap of 1/4" between the flap and the aileron, and the trailing edges should line up.
  5. Determine where the centerline of the flap hinge-to-bottom-skin rivets will be and draw this line. Also determine if it will be necessary to trim the wing skins trailing edges; all of the hinge eye must be below the trailing edge of the skin. If it is not, mark the skin for later trimming.
  6. Secure the flap so it cannot slip down and drill the bottom skin and hinge #40 along the line at each place where there is a rivet in the flap.
  7. Remove the flap. Trim the bottom skins trailing edges if so marked in a previous step. Bevel the inside edge of the top skin where it will touch the flap.
  8. Clamp the flap brace to the wing skin with trailing edges lined up and drill it.
  9. Pull the pin to remove the hinge half from the flap. Debur everything.
  10. Cleco the hinge on the outside of the wing skin and countersink it (this assumes you are dimpling both bottom skins).
  11. Modify the flap brace so it will connect properly to the rear spar (drawing #17, SK-41, and photo in construction manual). On the short section that sits up on the spar doubler plate, straighten out the bend there and rebend it about 1/4" farther up so that section of the flap brace will be more in line with the rest of it; this is done so that the leading edge of the flap will not hit the brace before it reaches the full up position. Cleco it in place and check to be sure it is not forcing the bottom skin into an undesirable curve; modify the brace flange angles if necessary.
  12. Cleco the flap brace in place. Tape and clamp a straightedge to the bottom skin to keep it straight along the hinge line. Tape the flap brace securely to the rear spar and then drill it #30, 2" apart, including the ribs. Remove and debur.
  13. Dimple the bottom skins and the corresponding holes in the flap brace.
  14. Remove the bottom skins and rivet the flap brace to the rear spar.
  15. A method for securing the hinge pin should be determined at this time. One suggestion that has worked is to remove one hinge eye out of the center of one half of the hinge and one eye next to it out of the other half. Crimp the end of both of the end eyes about half-closed and cut the pin in half so that both halves can be inserted from the middle. The pins will not come out by themselves (as you will realize when you try to get them in) yet they can be removed and reinstalled quickly. It will be helpful to bend down the inside ends of the pins, forming a little tab that you can grab onto when removing or inserting the pins.The hinge ends may also be closed by drilling a small hole through the eye and installing a cotter pin or safety wire.
Bottom Skins Attach
  1. Remove the tank.
  2. Cleco on the inboard bottom skin.
  3. Drive the rivets that hold the skin to the spars between the fifth and fourth (missing) rib. Drive as many rivets as you can in the fifth rib by reaching through the lightening holes. If you can get them all then drive the skin to spar rivets beyond, but do not go any farther on one spar than you can on the other.
  4. Slide the fourth rib into place and cleco it to the skins. Put in the bolts that tie it to the main spar. Put in the rivets that hold the skin to the rib and to the spars between the fourth and (missing) third rib. Put in the pop rivets that hold the rib to the main spar. Put in the rivets that hold the rib to the rear spar.
  5. Repeat for the third, second, and first ribs. Be sure not to leave out any steps as you go.
  6. Put in place any wiring or conduit you plan to use. Secure it with RTV or similar to prevent vibration from wearing it through.
  7. Remove the clecos from all but the fifth rib (or the sixth if you were able to rivet the fifth already).
  8. Pull the skin back carefully, making sure it does not crease at the clecoed rib, and start riveting toward the tip. Do not do the ones at the last rib.
  9. Cleco the outboard skin under the inboard skin, to the next two ribs out, the short rib, and all along the main spar, making sure it butts properly against the leading edge skin.
  10. Reach in through the bellcrank access hole for bucking and rivet to the first two ribs, the row not on a rib, the short rib, and the spars. You can also do most or all of the next rib and spars by reaching through the access hole and the lightening hole in that rib. If you cannot reach all the holes in a rib do not rivet to the spar past the rib.
  11. Remove the clecos past the next rib and pull back the skin and rivet that one.
  12. Rivet the rest of the ribs.
  13. Rivet the flap brace and flap hinge to bottom skin.
  14. The top skin must lightly touch the flap for best performance. With the flap in the up position modify the curve in the top skin if necessary. Place a strip of stainless steel tape on the flap, aligned to prevent the top skin from scuffing the flap. Modify the bend of the leading edge of the flap in such a way that it barely touches the top skin as the flap is raised and lowered. Also check with the airfoil template to be sure that the flap will go all the way to the up position.
  15. The aileron control rod can be re-attached to the aileron bellcrank with the other end taped down to keep it from banging around. Tighten the hardware so that the bellcrank is forced against the round bearing in the control rod end.
Tank Completion
  1. Install the access plate with the cork gasket on the tank. Be sure that all the screw heads are tight against the plate; this alone will seal them.
  2. You can verify that there are no leaks in the tank. Pour a gallon or so of aviation gasoline (the dyes in it will make any leaks readily visible) in the tank and rotate it all around, looking for leaks. Leave it sitting for several days in various orientations. Pour out the gasoline and leave the cap off the tank.
  3. Install the tank on the wing.
Long Aileron Control Rod
Mount the rod end and bearing for the aileron belcrank end of the long aileron push rod W-616 as shown in drawing #19. Leave the inboard end untouched. Install in the wing and tie the inboard end down so it won't bang around.
  1. Assemble the wingtip rib to the wingtip, build in whatever lighting you plan, and install the tip on the wing. You can either permanently bond it on or install it with nutplates and screws. You may want to do the latter if you expect to try to use wingtip antennas or install strobe light power supplies in the wings. If you bond it on, place the wingtip strobe/position light fixture right in line with the aileron push rod so you can pull it out without removing the wing.
  2. Most bulders seem to prefer the three-way lights; red/green forward, white aft, and strobe all in the same fixture, with a power supply in each wing mounted on the outboard rib. This meets the FAA requirements and requires the least work because no other lights are needed. The reason for using the more expensive dual power supplies is that you will not have a long run of wire carrying the noise-generating pulse of current to the flash bulbs; this could interfere with navigation radios. The light fixture must be mounted out far enough that the colored and white lights will be visible from straight forward and straight back. The strobe lights must be visible upward and downward also.
  3. To mount these lights, make a mold out of modelling clay, using water to help make the surface smooth. Bake the mold just enough to dry it out good. Make an aluminum mounting plate the same size as the base of the light fixture and attach nutplates to it to allow easy removal of the light fixture later. If you are bonding on the wingtip there should be a hole in the plate large enough for the aileron push rod to go through (1 1/4" diameter). Make the mounting platform for the fixture by laying up several layers of fiberglass and resin on the mold, with the mounting plate on the inside.
winglast.doc 10/28/94 Frank Justice

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