There are as many different opinions as to how and in what order to rivet on the wing skins as there are builders. These instructions are optimized for riveting the bottom skin last; using any other order will cause many of the steps in here to be difficult to do, and a new order for almost everything must be found. Both top and bottom skins as well as the flap and aileron attachment are completely prepared before skin riveting starts. One piece top skins are used by some builders because the finished appearance is slightly better and they are a little easier to install unless you have the newer predrilled skins (the one-piece skin is not available predrilled). On the other hand, the predrilled skins save so much time that the builders who used the one-piece skin now say they would not do it again. Van's at present will not ship them because of their size, but in some areas you can buy two pieces of 4 x 12 x 0.032 2024-T3 Alclad and even have them shear it to size for you. The two piece top skins are joined at one of the ribs with one skin overlapping the other. Some people feel that this does not look good and they would rather do a butt joint and get a smooth skin. This can be done fairly easily. Carefully cut off the top flange of the rib where the two skins join and make another flange that is about two inches wide by bending up a thin strip. Rivet this new flange to the rib. When you put the skins on, trim both of them to meet in the middle of this new flange. Note that the plans call for a double row of rivets to join the skins when using a lap joint; you need to use an equivalent number of rivets in each skin to the new flange in order to get the same strength.

The top skin(s) is drilled as the first step and left attached for much of the rest of the procedure. In the procedure that comes with the predrilled wing skins the bottom skin is drilled to the skeleton first but the very next step is to drill the top skin to the skeleton, so I have left the order as I originally had it, top skin first.

As soon as the top skin(s) is clecoed on the whole wing assembly becomes very rigid. The leading edge and tank skins can then be pulled down to meet the main skin(s) with no misalignment gaps or trimming. While it would be a little easier to put on the leading edge skin and fit the tank without the main skins in the way, having the skins present is helpful in getting rid of any gap between the main and leading edge skins. Just be sure that the whole wing structure is very well supported until one set of main skins is riveted in place.

The inboard topskin (or the one-piece topskin if you have it) may be countersunk because it is 0.032" thick, but the results will be just as good for most people (and better for some) if you dimple these skins. Also, the wing will be stronger.

Marking the Skin Joint Line on the Main Spar and the Rib Rivet Lines

Mark about ten points along both sides of the main spar flange, 1" down from the top of the main web of the spar. This is where the leading edge of the main skins will be.

Verify that the ribs are still straight; modify the fluting if necessary.

If you do not have the predrilled wing skins, draw lines through the rib centerlines onto the top of the main spar and around the bottom of the rear spar where you can see them after you put the skin in place, then mark rivet stay-out areas along the main spar (where the spreader angles and tiedown bar will make it difficult to buck the leading edge skin rivets) where they will be visible after the top skin is put in place.

Top Skin Application (Skip this whole section if you have predrilled wing skins)

Make a rib rivet location template out of a strip of aluminum 29" long (or some stiff material with a straight edge). Make sure the marks correspond to the flat spots on the ribs. Spacing is approximately 1 1/4". Make the leading edge of the top skin correspond to the end of the strip. Include a mark 1/4" from that end (for the rivet line along the main spar) and another one in the middle of the rear spar flange.

Using the template mark and drill #40 the last hole toward the trailing edge in each rib.

Hang the top skin (or the outboard top skin) on the wing skeleton with the tip edge extending 5/8" beyond the tip rib web and the leading edge aligned with the marks previously made on the main spar. Make sure it is a top skin; the top and bottom are not the same width. Secure with tape and clamps as necessary to make the skin conform very closely to the skeleton. The one-piece top skin makes a very accurate straight-edge; if the leading edge of the skin does not line up all the way across with the marks previously made on the main spar, adjust the supports under the rear spar until it does.

Back drill through the hole at the trailing end of each rib into the skin.

Using the template mark the rest of the rivet locations for the ribs onto the skin.

Make a line 1/4" down from the leading edge of the skin and mark that line of rivets 7/8" or less apart. Put a mark on every rib centerline and evenly space the other rivets between them; this keeps them away from the rib reinforcing angles. Arrange the spacing so none of the marks are in the stayout zones.

Drill #41 or 3/32" at all the marked locations (#40 if you plan to countersink instead of dimple the skin). Start in the center of the wing at the main spar and work outward toward the ends. Then work downward along the ribs, again starting in the center. To insure accurate placement in the rib flanges first drill only through the skin at the rib center and look for the line marked on the center of the flange. If necessary push or tape the rib so that the line is in the center of the hole while drilling the rest of the holes. Check occasionally from the back side to insure that the holes are coming out in the center of the flanges. If you have the two-piece top skins do not drill the holes at the edgfe of the skin for the innermost rib.

Make a line on the skin for the rivets that will go into the rear spar flange. Make sure it is placed so as to give adequate room to buck rivets at the root end where the spar flange strips and doubler could get in the way, yet far enough in that the edge distance in the spar reinforcing plates at the middle and tip is adequate.

Mark on the skin where the edges of the spar reinforcing plates lie. Also mark a point 46 7/8" in from the web of the tip rib. Mark the rivet locations 1" apart or less, making sure they do not lie too close to the edges of the reinforcing plates and not within 3/8" of the 46 7/8" mark..

Drill these holes #41 or 3/32" (#40 if you plan to countersink the skin).

If you have the two-piece top skins put the inboard skin in place under the outboard skin (older drawings show the inboard skin on top. It should overlap the outboard skin by at least 1 3/8" and preferably 1 1/2" to allow for the two rows of rivets required here. The inboard end should line up with the edge of the flange of the inboard rib. Place a long straightedge along the edges of the skins to insure that they are lined up with each other. Drill this skin, including the extra row of rivets at its outboard end (see SK-48). Mark a section to be cut out of the outboard skin in the flap area where it overlaps the inboard skin as shown in older construction manuals page 7-53 and SK-46 in newer ones.

Top Skin Application (for predrilled wing skins)

Clamp the wing skins in place on the skeleton with the rib centerlines visible through the skin holes. The outboard skin goes on top of the inboard skin; earlier drawings show this the other way around. Make sure you have the right skins; the top and bottom skins are not the same width. Drill the ribs through the skins #41 or 3/32".

The wing walk area reinforcing sheet can be drilled at the same time if you are careful. After drilling the inboard topskin to the ribs outboard of the wingwalk area, remove enough clecoes to allow you to slide the reinforcing skin straight up from below so it doesn’t make the ribs bow. Tape the reinforcing skin securely to the topskin. Check after drilling a few holes in a rib to see that it has not moved; see the section below for exact placement of the reinforcing skin and some edge smoothing.

Wing Walk Area Reinforcing Sheet

Remove the clecoes holding the skin to the five closely-spaced ribs at the root and to the spars in the same area. Clean out the chips out from between the skin and the ribs. Insert the wing walk area reinforcing sheet (13" x 27.5" x.025") under the skin, making sure its edges are not too close to the rib rivet holes. Align the leading edge butted against the trailing edge of the main spar as shown in drawing #21 with dashed lines and let it overhang the rear spar.

Drill through the skin holes into the reinforcing sheet. Try to make the drill stop as soon as it breaks through and use only moderate pressure; this will keep the bit from enlarging the holes in ribs which might now be slightly misaligned with the skin.

Carefully pull out the reinforcing sheet and replace the clecoes in the skin.

Deburr the reinforcing sheet holes and round the top-side leading and outboard edges so they will not dig into the topskin. You can bevel the underside of the skin on the outboard edge where it crosses over the rear spar to avoid having a sharp step in the topskin. If you plan to dimple the top skin, dimple the reinforcing sheet. Prime this skin on your next painting day; you won't need it for a while.

Aileron Bellcrank Gussets

The two gussets for the aileron bellcrank support can be made and installed anytime after the top skin is in place and must be done before the bottom skin is riveted on. If you do not have the right tools you may not be able to rivet the braces to the ribs, so doing the following procedure next is advisable.

If your kit did not come with them, obtain the new W-425 gussets from Van's; they are easier to install, stronger, and less likely to deform the skin. There is however a slight problem with them in that the lower flange of the lower gusset is right where the platenuts for the bellcrank access plate are on the lower skin reinforcing ring. (This is not a problem with the predrilled wing skins since they do not use a separate reinforcing ring, hence the remainder of this paragraph does not apply.) Drawings 19 and 21 depict these items separately but not the fact that they interfere. This requires that two large chunks be cut out of the lower gusset flange. Van's instructions call for using a 0.040 spacer on the flange of the lower gusset to cause it to be placed in far enough that it will not interfere with the reinforcing ring. A 0.040 spacer is then used over the part of the gusset flange where the ring isn't to allow the bottom skin to be riveted to it. An alternative method is described below; it consists of not using a spacer, cutting away the interfering part of the flange completely, and replacing it with a reinforcing angle where it will not be in the way.

Carefully measure the distance between the ribs where the gussets will go and then bend the outboard end flange down so the gusset will fit without forcing the ribs in either direction.

On the top-side gusset drill the rivet holes #41 or 3/32" (or #40) for the skin and the gusset-to-rib rivet holes #30. Put the top side gusset in place and drill through it into the top skin. Then clamp the gusset securely to the ribs and drill the gusset-to-rib holes.

On the bottom-side gusset drill the gusset-to-rib holes #30. Clamp it to the ribs in a position such the surface of the flange will lay on the bottom skin when it is put on. Drill the gusset-to-rib mounting holes.

Remove the gussets.

If you have the predrilled wing skins or plan to "flange" the bottom skin for the bellcrank access cover rather than making a reinforcing ring, skip this step. On the bottom-side gusset cut off most of the skin-side flange, going about 3/16" into the main part of the gusset, leaving about 4' of flange at the small end, Drill #41 a piece of 3/4" x 3/4" x 0.025 angle about 8" long to the gusset on the opposite side from the existing flange and about 1/4" in from where the skin will be. This keeps it out of the way of the rivets that hold the reinforcing ring to the bottom skin. Deburr and prime the gussets and angle. Rivet the angle to the bottom-side gusset.

It is possible to rivet the gussets to the ribs with them still in the wing but only if you have the right offset rivet set , lots of skill, and two people. The following procedure is much easier: Remove the two ribs that attach to the gussets from the wing assembly. Rivet the gussets to the ribs. Put this assembly back into the wing. (You may have to remove the wing supports, pull most of the rear spar to rib clecos, and bow the rear spar down to do this.)

Aileron Brace Rib and Inboard Aileron Mounting Bracket

The Inboard Aileron Mounting Bracket shown in drawing 16 is supplied already assembled. The outboard aileron bracket cannot be done at this time because the rear spar jigging tab is in the way.

Fit the bracket to the rear spar using the distance from the center of its bearing to the bottom skin line extended (5/16" as shown in drawing 16). Use the template described below.

Aileron and Flap Locator Templates

The above step cannot be done accurately without a template. Later on you will need two airfoil templates to help mount the ailerons and flaps, so make them now and and fix one to be used for a hinge bracket locator. The templates are V-shaped, four feet long, made out of 1/4' or 3/8" plywood. Use the airfoil template supplied with the wing kit as a pattern. One one of them draw a line 5/16" below the lower edge of the opening in the area where the hinge bracket bearing will be.

Place the template under the wing and position it where the bracket will go. Then trim the bracket as necessary until you can see the line on the template through the bearing when it is in place on the spar.

Clamp the bracket in place with the centerline of the bearing 46 7/8" from the web of the tip rib (the centerlinbe is simply the inboard edge of the bracket where it is not doubled up). This should result in the opening for the aileron control rod being about 1/8" from the bracket. This dimension was derived from dimensions on drawing 16. Place the short rib W-625 oriented as shown in drawing 10 with its rear flange centered on the long angle of the mounting bracket.

Mark the eight mounting holes in the bracket 5/16" from the edge of the angles as shown in drawing 21, except use smaller spacing so that the rivets will not be too close to the ends of the flange of the short rib that will be held by the five rivets. Remove the bracket and drill the holes #30.

Clamp the bracket in position on the spar and drill #30 through it into the spar. Remove the bracket.

Clamp the short rib in place, and drill through the spar into the rib. Drill #41 or 3/32" (or #40) the top skin-to-rib rivet holes 1 1/4" inches or less apart.

Remove, deburr, and prime the bracket and short rib.

topskin.doc 8/29/95