Standardized Round Inspection Covers Made on a Lathe

Source: 2025 Q4 Beartracks, George Huntington
INSPECTION COVERS WITH A LATHE
This is how we made our inspection covers, so they are all the same hole spacing. Every plate fits anywhere. We roll a small edge like the Cessnas so it holds its shape and doesn’t warp when installed. Take a piece of 3/16 or so steel big enough for the inspection cover. Weld a tube on it long enough to accept Clecos from the back side while mounted in the lathe. Turn the plate down on the lathe to the correct diameter and add a small chamfer to the outside edge. Drill the mounting holes, be precise as possible. Use it as a drill jig to drill the inspection plates and the mounting holes in the airframe, mount the inspection plates to the tool with Clecos and use the lathe to cut the plates to size and deburr. Make a tool with a roller bearing mounted in it and gently roll the edge of the inspection plate over the chamfer.

Closing up the wings

As we talked about in the general riveting section, the shortest, least painful and most efficient way to close out the wing skins is to befriend a local RV builder (or two) and have them help you with the riveting chores. With one of those to help, you can close both wings on a long Saturday.
Whether you have one of the Van’s Armada to help or not, you’ll still need an extra set of hands to handle the bucking and riveting chores. Put the most skilled of the two inside the wing with the bucking bar, as that’s where a lot of dings come from.
This is also true when you install the tank bay stiffeners.
Working With the Wing Skins
The most common question asked about putting the wing skins down is “How to you reach inside to do it?” The answer is, you don’t reach inside. You roll the skin back, toward the leading edge, and one of you stands on one side with the rivet gun and the other stands on the open side with the bucking bar. You work each row of rivets spanwise, rolling the skins down, as you go.
Working this way, you can reach all but the last three or four rivet rows at the trailing edge in front of the rear spar. Then you recruit someone with smallish hands to reach through the lightening holes in the rear spar with a small bucking bar. Since most of the rivets are AN3 size, the bucking bar can be quite small. For access, you’ll have to drill out the temporary aluminum pop rivets that hold the aileron cove covers in place during shipping. When finished, you pop rivet those back in place.
They are non-structural so aluminum pop rivets will work nicely.

Note that the original Bearhawk 4-Place came with the top skin ready to rivet, while the Patrol, LSA, and Model B come with the bottom skin ready to rivet. The process is the same either way.


This one picture answers almost all the questions, including how much easier it is, if you find a local RV builder to help you. The skin is rolled back until the last three or four rows of holes, then you reach in through the lightening holes.

Trailing Edge Stiffener at Flap Bay

In earlier kits, you’ll need to install the stiffener that lays in the open area behind the rear spar in the flap bay, although it has been done by the factory in later kits.

The goal here is to attach the stiffener and have the back edge of the sheet metal remain perfectly straight. The reason we mention this is because, when a rivet is driven, it expands the hole very slightly and, unless you plan ahead, it’s possible to get distortion in the skin. It will manifest itself as a wavy or slightly curved skin. This can be avoided with just a little planning.
There are actually two stiffeners, one top and one bottom, and they overlap the flange of the rear spar and are flush, or very close to being flush, with the trailing edge of the skin. Wings have been supplied in several different degrees of completion in this area, as the kits were improved.

Drilling the Stiffener
In most of these cases, the stiffener has no holes in it, but both the spar and the skin are drilled and dimpled but an additional line of holes and dimples needs to be made between the spar flange and the edge of the skin. Use the front row of holes as guides to drill the stiffener and hold it in place while drilling the rear holes.
To visualize what you’re trying to do, look at Plans Page 9. You can drill the holes either direction, meaning have the wing right side up and drill from the bottom up (with the edge hanging off the work table) OR turn the wing over and drill down. Most people are more comfortable drilling down, but that’s up to you.

Clamp the Stiffener in Place
What follows is a general instruction of how to drill and install the stiffener. It is assumed the stiffener has no factory-drilled holes in it, nor is the second, rear-most line of rivet holes drilled in the skin. In most later kits the stiffener and all holes in the top skin and spar flange will have been drilled and dimpled. The bottom stiffener may also be finish riveted. If that’s the case, much of this can
be skipped.
The first step is to position the stiffener so it’s flush with the trailing edge (or close to it) but the front edge overlaps the holes in the spar flange enough to give a distance from the center of the holes to the edge of the stiffener of at least 3/16 inch (twice the diameter of the rivet).
Once you have a couple of holes drilled you can hold the stiffener in place with clecos and it won’t move while you drill the other holes. However, getting those first holes in without the stiffener moving takes a little forethought. The stiffener must be clamped in position until you have at least four holes drilled in it to accept clecos. Make one hole at each end and space two through the middle. To clamp the stiffener in place the best solution is about half a dozen side-grip clecos, or small C-clamps padded with masking tape to prevent marking the aluminum as you clamp the stiffener in place.

Drilling the Holes
Make a back-up block out of a six-inch piece of two-by-four or something similar that will be held against the stiffener and drilled into. This will keep the stiffener from flexing while being drilled.
You’ll use the existing holes in the skin and spar flange to drill the front holes in the stiffener. Drill a couple of holes in the middle of the stiffener. Put clecos in the holes, then space out three more holes evenly spaced down the length of the stiffener. Make sure none of the clamps have slipped.
Once you have those clecos in place, the stiffener definitely isn’t going to go anywhere so go ahead and drill the rest of the holes. Don’t start at one end and work to the other end as the stiffener will creep. Start at the middle and work our way out. Once the holes are drilled, debur them and, if they aren’t already dimpled, dimple using a squeezer, but don’t squeeze too hard or you’ll get distortion.

Riveting the Stiffener
While it is entirely possible to simply drop the rivets into the holes and whack away with a squeezer, chances are you won’t be satisfied with the result because it’s hard to keep the trailing edge straight and from curving as the rivets expand and push the aluminum around. However, there is a way to prevent that. Buy a heavy, extruded aluminum angle (1/4” thick, 2” or so wide) and squeeze the rivets using the angle as both a straight edge and as an interface between the squeezer the heads of the rivets. The procedure is as follows:
1. Drop all the rivets into the holes.
2. Position the stiffener over the rivets.
3. Lay the angle down over the rivets.
4. Clamp the angle and stiffener together. Make sure it’s clamped tight in about a dozen places.
5. Adjust your squeezer to properly compress the rivet by squeezing the angle against the
rivets.
6. Don’t rivet in a straight line. Do several in the middle, the end rivets, then every third one starting in the middle and working out. Then come back to the middle and, working your way out, finish the rest of them. Using this technique, you won’t drive the expansion all one direction and will limit distortion.

Mismatched Stiffener/Rib Intersection
A few wings were shipped with the lower stiffener riveted in place but it is about three-quarters of an inch too long and has to be trimmed to let the flap bay root rib fall in place. Just drill out a couple of rivets and cut three-quarters of an inch off the inboard end of the stiffener. A Dremel tool is the easiest way to cut it. Protect the wing skin beneath by inserting a piece of aluminum scrap.

Wing Inspection Covers

Fuel Tank Bay Cover
The fuel tank bay cover comes with about 100 holes pre-drilled to the wing. The tank cover must eventually be attached using #6 flush head machine screws (MS24693-S26). To accommodate these screws, we need to install nutplates (also called “Anchor Nuts”) in the wing. There are several varieties, but the lightest and least expensive are the K-1000 or MK-1000 anchor nuts. The MK-1000 are miniature versions of the K-1000.
After installing all of the nutplates for the tank bay cover, prepare the cover by rolling the edge for a nice tight fit with the wing. This process is detailed here.
Next, drill the tank cover holes with a #27 bit, debur the holes, and dimple them with a #6 screw dimple die:

In the picture below, the tank cover is temporarily fitted to the wing with 8-10 screws. There is no need to secure it permanently any time soon.

The last step for the tank cover is to drill the hole for the fuel tank quick drain. This will require locating a hole based on a reference that we can’t see when the cover is in place. To get around this problem, we’ll remove the tank cover, make two reference marks on the skin, reinstall the cover, and transfer the skin marks to the cover. That sounds like a complicated process, but it’s simpler than it sounds. Start with the fuel tank cover off. Mark a line on the skin that intersects the center of the tank drain hole and one of the screw holes on the wing. Make a small mark on that line that is 5 inches from the center of the drain hole.

Next, mark a second line that also passes through the centerline of the drain hole, but is perpendicular to the first, as you can see in the photo below. Make a mark on that line that is also 5 inches from the drain hole center.

Now replace the tank cover and secure it with a few screws to assure proper alignment. Use the ruler to transfer the lines onto the tank cover:

The two lines should intersect where the hole needs to go. The 5 inch measurements provide a redundant check to make sure that the hole is located exactly.
Remove the cover and use a step drill to make the hole large enough to clear the quick drain. Be sure that the hole is large enough to remove the drain without needing to remove the tank bay cover. A flush drain like the Saf-Air SA18 will rest under the skin and minimize drag. Select a hole size based on the outer diameter of the socket that you will use to install the drain valve. The SA18 fits in the 1/8” NPT threads supplied in your fuel tank.

Wing Inspection Covers
The kit comes from Bearhawk Aircraft with the inspection holes cut into the wing skin, and pre-cut inspection covers and doubler rings. The cover and ring are pre-drilled with one hole in each corner to help you get the alignment correct. Each ring will need two sets of holes- one set for the rivets that will hold the ring to the wing skin, and one set for the nut plates that will hold the cover screws.

The first step is drill the cover plates to match the doubler rings. Draw a center line on each side of the doubler ring, connecting each adjacent set of corner holes. Lay out the hole locations for the inspection cover screws on each line based on 1-1.5” screw spacing, and drill the holes with a #40 bit. Next, attach the doubler ring to the hole cover, using the pre-drilled corner reference holes. The corner reference holes are drilled to screw size; if you don’t have a cleco that fits this hole snugly, use screws. Match drill each #40 hole on the cover plate, placing clecos as you go to ensure good alignment. These will eventually be the holes for screws and anchor nuts. Since these pieces are now uniquely match-drilled to each other, mark the pair with orientation arrows and identifying names.

Next, we’ll drill the holes for the rivets that hold the ring to the skin. Lay out a line exactly 1/4″ in from the outside perimeter of the inspection cover ring. Drill these holes with a #40 bit as well. The result:

Next you’ll need to locate the inspection ring perfectly centered in the wing inspection hole. To do this, cleco the inspection cover on the inner side of the inspection ring, which is the opposite side from where the cover will make contact after final assembly. It’s too confusing to talk about the top and the bottom of the ring, since we are working with an inverted wing. Then, place the ring and cover assembly in the hole, and make sure that the cover is centered in the wing inspection hole. You may need to file the edges of the cover and/or the hole in the wing for a proper fit. The goal is not a zero-gap fit. Leave enough space for paint.
Double check that the cover is in the wing inspection hole, drill and cleco the inspection ring to the hole. Be careful to not push down too hard while drilling these holes. There is no support rib underneath and in pushing down you might deform the wing skin downward while drilling. This may cause the inspection hole area to be a low spot in the wing instead of level with the surrounding skin. Just let the drill do the work and cut the hole.

Now you can take the three apart and debur the holes. Put the inspection ring under the skin and cleco it in place to test fit everything.

Now test fit the cover in the hole to make sure the holes line up properly.

If it all fits well, drill the screw holes to final size and remove the cover and doubler. Add the nutplates to the doubler and dimple the cover. Dimple the rivet holes and rivet the doubler in place with -3 rivets.

Builder Greg Charest adds a few more notes:
Wing inspection plates require a bit more attention to accuracy than other portions of the build process. Several less experienced builders, myself included, have marked and drilled holes for the inspection panel nut plates and have been unpleasantly surprised to find that the holes are too close to the edge of the cover, backing plate or skin. If you are, like me, a first-time builder, it is worth taking a little extra time to understand why this mistake is easy to make and hopefully avoid. There is more than one way to complete the inspection plates, but the following method has worked for me.
Looking at the parts supplied in a kit (or the plans) you will see that the backing plate frame is 7/8” wide. In my case, they are very slightly less. The inside half of the frame side will support the cover plate and the outside half will be riveted under the skin, so we have one-half of the 7/8 width available for our nut plates – 7/16. On the inside of the plate, we want to maintain the standard edge distance of not less than twice the rivet diameter – 3/16. We need about the same 3/16 distance on the other side so that the screw hole on the cover does not get too close to the edge. This is a total of 6/16ths so to get this right, the center of our rivets needs to be within a 1/16” zone in the middle. Not much margin for error!
Before going further, a couple of notes:

  • Don’t even think of using that sharpie with the bashed and battered tip that draws like a magic marker. Use a new one and preferably, get a new one with the very fine tip.
  • Use a decent rule and try to measure to 1/32.
  • As soon as you cleco the cover to the backing plate for the first time, make registration marks on each piece. Accidentally rotating or reversing one of the pieces later will cause you grief.
  • Check the fit between the cover plate and the wing opening. You are going to want to cover to be centered in the cutout. In my case there is about double the clearance in the short direction compared to the short direction for the 4×6 openings.

Kit parts are extremely well made but the inspection plate parts are not CNC machined and so are not 100% identical or symmetrical. The backing plates and covers come with 2 or 4 holes drilled in the corners that are used to align the two pieces. In the picture you can see that, at least in my case, the pre-drilled hole is not located exactly on the centerline of the half that supports the cover. This is no problem for the corner holes due to the radius, but it does mean that if you simply draw a line between the corner holes the line will be closer to the inside edge.

If you have a set with only two pre-drilled holes, cleco the cover to the backing plate and carefully
locate and drill the remaining two corners. I found it helpful to draw the center lines for a visual aid. At a minimum add the registration marks.

Double check from the top side. Again, the corner holes/nut plates are a little more forgiving due to the nut plate orientation, but you can now see better where the rest will fall in comparison.

Now layout and drill the remaining holes. Pay careful attention to keeping the holes centered on the lines. In the picture below, (right side where I did not complete the line) you can see that I very slightly favored the outside to compensate for the pre-drilled corner holes that were not quite centered.

You can now upsize the #40 holes and use your handy nut plate jig to drill the rest of the rivet holes for the nut plates. After drilling all the additional holes and de-burring them you can dimple the screw holes for #6 screws and the rivet holes for 3/32 rivets. This is a lot of dimpling in a small backing plate and it will cause a certain amount of distortion. This is easy enough to flatten out just by bending it by hand.

Counter sunk nut plates for #6 screws (K1100) are super expensive. Some people manually countersink K1000 nut plates but you have to be careful not to remove too much material. K1000s will work perfectly well just as they are but it does require a bit of technique to get them to pull down and line up properly. The scratch builder B-Spot has a great YouTube video on making inspection plates and I have found his method to work perfectly. Watch the video but the short version is this – install a #6 screw hand tight in the center screw hole. Drop an extra-long standard rivet in one side just to hold the nut plate in alignment. On the other side, insert a flush rivet and give it a gentle, partial squeeze. The goal is to have it expand only enough to hold the nut plate in place. If the other side pulls way up, you have gone too far. Now remove the long rivet, replace it with a flush rivet and fully squeeze it. Then put the final squeeze on the other side. Both sides should now be nicely pulled down and aligned. The screw should be easy to remove by hand. If not, you have probably pulled the plate off to one side and you will have to drill it out and try again. It is worth the time to vertically mount your squeezer to your work bench since you have quite a few nut plates to add.

The final step is to rivet the backing plate to the skin. Screw the cover and backing plate pieces together and carefully draw the outline of the cover on the backing plate. After separating them, insert the backing plate into the hole in the wing and use the outline to line up the plate with the cut-out in the wing. Look at this from various angles to get it to match exactly. Once you are satisfied with the alignment, use cleco clamps to hold it in place. There are 4 in the picture, but more is better. You do not want it to move when you drill the holes through the skin. In the picture you can see from the outline that the fit is tighter on the short sides which matches what we saw earlier when checking the fit.

You can now layout and drill the holes through the skin and backing plate, de-burr and dimple them and rivet in the backing plate. One advantage of this method is that you can see where you are drilling into the skin so getting too close to the edge is easy to avoid. Again, it is helpful visually to transfer the outside edge of the backing plate to the top of the skin by measuring in 7/8” or if you really want to be sure, by using a pair of dividers to measure each side. In my case you can see that there is a bit more than 14/32” to work so drilling 7/32 from the inside of the cutout will be about right. Start by drilling and clecoing diagonal corners to fix the position of the plate and then fill in the rest.

Locating the Filler Neck in the Top Wing Skin

Source: 2017 Q2 Beartracks, Mark Richardson
Well, in keeping with a lot of tasks on my scratchbuilt Bearhawk, I had been dreading the whole process of cutting the fuel tank filler neck holes in my wing skins. I was really worried that I would mess something up and cut the holes in the wrong spot (like that NEVER happens, right?) and wind up trashing some expensive sheets of aluminum. Well, turns out it was really easy and I did both holes in my left wing (I have an Aux tank) in a little over an hour and they both turned out perfect. I figured since I bored you in the last issue with some building tips, I might as well do it again since this actually worked out.

I was a little leery about using some of the methods I had read about, including the one about smearing some kind of liquid/putty/whatever on the rim of the filler neck and then pressing that against the inside of the skin. I didn’t think that would be very accurate.

This is what I did (your mileage may vary, batteries not included, objects in mirror are closer than they appear…)

1. I took a square of paper and drew a 2″ circle on it.

2. With spray contact cement, I attached the paper perfectly centered on the filler neck. I then put duct tape on paper facing up (towards the inside of the wing skin) along the side closest to the edge of the tank.

3. I then positioned the tank where it needed to be (vertically and horizontally) and then used a long wooden coffee stir stick to reach through a lightening hole and press the tape to the skin.

4. The tank was then removed. The duct tape easy overcame the stickiness of the contact cement, so the square paper template was now stuck EXACTLY where I needed to drill the hole. I drilled a #40 hole through the center so I could mark the hole on the top side of the skin.

5. Using a #40 drill, I worked my way around the hole and then used a Dremel tool and file bit to remove the waste in the center.

6. I used a spiral bit in an air die grinder to round out the hole and make it 2 1/4″ in diameter (1/8″ all the way around the hole). Why not go straight to 2 1/4″ at first? In case I buggered something up; you can’t put material back in :-)



That’s it. Quite easy actually. And nobody is more surprised than me …..

Leading Edge Forming with a Vacuum Cleaner

Source: 1996 Beartracks, Bob Barrows

Note: this method was revised here: http://bearhawk.tips/1957

I am slowly building up a collection of past issues of Sport Aviation. It was in one of these past issues I came across an article by Ben Owen in the April ’86 issue (pp 61-62) about forming leading edges with a vacuum cleaner! Bob has ruined a few wing skins in his time so I showed it to him. He thought it would be a good idea to include it in the newsletter. We have not had a chance to try this yet but it sure does look good. If any of you do it this way let us know so we can pass your results along to the rest! If you want a copy of the Sport Aviation article contact EAA and they can get one for you. Here is an abbreviated and edited for BEARHAWK construction version for vacuum forming of the Leading Edge Skins. – Mike

You can now vacuum form your skin without worry of leaving any evidence of your work on the aluminum (scratches, knee dents, footprints, etc.). Just fold the skin over and use nylon or mylar tape to hold it back and seal the seam. Leave some overlap to trim off, and make sure that you are folded back square. (Masking or duct tape can be used, just be sure to use an extra layer to avoid surprises as the aluminum will want to return to a flat shape) Next, seal up the open ends with large heavy weight plastic trash bags taped to the aluminum. The bags must be large enough as to guarantee that they do not offer any resistance to the pull of the vacuum. In the bag on one end cut a hole Just big enough to slip the vacuum hose into and seal it up with tape. Turn on the vacuum and watch the skins draw together! If you are using a very powerful vacuum you could over form the radius, but by operating the on/off switch you can control the process with ease. If your
vacuum is a bit on the weak side you may need to persuade the radius a bit with the 2×4 method as shown in earlier newsletters. Check your radius with a nose rib as you go along.

If you use this method please get back to us as to how it worked out.

Wing Leading Edge Forming with a Vacuum and a Pipe as a Die

Source: 1997 Beartracks, Bob Barrows

Based on some recent discussion with other builders, testing done in the shop and present production of the wing skins for the latest set of Bearhawk wings, I felt that we needed to revisit this subject.

The following method is by far the best approach and seems to give the most accurate constant repeatability.

In photo (A) a 1 1/2″ plastic pipe (1 3/4″ 0.D.) is taped across the leading edge skin where the bend is required. Wrap the skin around the tube as shown and hold in place with a wood 2X2.

Tape the end of the skin with a strong 2″ wide strip of tape, two or three layers to hold in place.



As shown in Photo (B) tape both ends of the skin with a plastic film. Trash bags will work but a piece clear plastic will allow you to see what is happening. Tape film on with masking tape making sure that you have it air tight.



Photos (C) & (D) show the skin being sucked down to the proper shape by applying full vacuum from a household vacuum cleaner. The plastic pipe keeps you from kinking the skin and will give you the best results. Let us know how you like this method.



Making the Wing Skin Stiffeners for the Fuel Tank Bay

Source: 1996 Beartracks, Bob Barrows
The Wing Skin Stiffeners used in the fuel tank area on the inside upper surface (2 per wing) need to be preformed to match the airfoil shape.

First cut the aluminum blank about 3″ longer than needed and bend up as shown using a sheet metal brake.

We did the contouring as follows:

Using the wing nib form block as a base attach the stiffener as shown below.


Screw the front end of the stiffener to the form block as shown and clamp the back end as shown.

We then heated the entire length with a torch (use a propane torch if you have one) being careful to heat evenly. If you heat too much in one place the stiffener will break at that point.

Check to see if enough heating has been done to cause the part to take a permanent set by loosening the front screw.

If any of you builders would like to set up a rolling fixture to make this part, give me a call.

Bob

Bob’s Method for Skinning the Wing

Source: 1995 Beartracks, Bob Barrows
The wing skins are .025 & .032 2024-T3 ALCLAD as per the drawings. The basic skinning procedure is to install the wing skin in sections as shown on the wing assembly drawing. The .025 skins are installed so as to cover from the bottom of the main spar flange around the nose and back to the end of the aileron or flap pockets. See sketch below.

The bottom of the wing is covered by one large sheet from the tip rib to rib #5 and a strip approximately 9 1/2″ wide from rib #5 to rib #2.

The .032 skin between rib #1 and rib #2 is one piece from the back of the rear spar around the nose and back to the rear spar.

When forming the skin to fit around the nose rib refer to the method shown in the Winter ’95 newsletter. DO NOT over bend the radius. It is very difficult to remove much of the bend without deforming the skin. Practice with some scrap aluminum.

Hold the skins in place around the nose ribs by using 1/8″ nylon cord and sections of tire tube (or big rubber bands if you have them) as shown below.

A view of the tight wire running through the nose ribs mounted in the wing jig.

A view of the wingtip section mounted in the wing jig. Note the middle support in the lower right corner.

As per plans and information in the Fall ’95 Newsletter cut and form the the wing skins, leaving about 1″ extra material all around.

Before fitting skins mark each rib with a black line down the center of the flange of all ribs (Fig 1).

We started fitting the skins from the wing tip area inward (Fig 2). Fit all the skins that go around the nose first then fit the large and small bottom skins.


Fit outboard skin to ribs as per Fig. 3 using rubber bands and rope to pull skin down tight against ribs. “C” clamp skins to spar and rib flanges to keep from moving.

Mark wing skins on the outside with straight lines (Fig. 4) indicating where the rivets will go. Be sure to measure so that the rivets will be located in the center of the rib flange when the ribs are straight!

First drill all rivet holes at 3/32″ – holes needing to be enlarged to 1/8″ will be done after fitting adjacent skins.

Drill rivet holes for nose ribs first at the hole nearest the leading edge. Be sure rib is moved off to the left or right so that the hole only goes through the skin and not the rib flange.

Looking through the hole, move the rib back into position so that the black line marked on the center of the rib is visible and centered in the hole – now drill rib flange. Install cleco to hold skin and nose rib in place. Drill remaining skin and nose rib holes using the same method and cleco as needed.

Insure that all the center ribs are lined up and drill the remaining rivet holes being sure the drill goes through the center of the rib flange and in proper location on the spar flanges. Comply with the rivet spacing as shown on the drawings.


Install clecos as needed to insure a tight fit with the ribs.

Remove the clecos from the outboard skin and remove the skin.

Locate in place the next skin inboard and apply the rubber straps and clamp to hold in place. Reinstall the outboard skin using rubber straps and clecos (Fig. 2&3). Drill and cleco skin #2 as was done on the 1st skin. Holes at skin overlaps may now be drilled out to 1/8″.

After fitting skins and drilling all holes to finished size the excess material should be trimmed off and edges made smooth.

Continue down the length of the wing using the above outlined procedure.
After all skins are fitted drilled and clecoed to the wing assembly to your satisfaction all skins should be removed from the assembly and all holes deburred and dimpled for flush riveting. Rivet skins to nose ribs first then large bottom skin, followed by skin to top of center ribs.

All fitting, drilling, and riveting is done with the wing in the jig. This ensures that the wing will be straight and twist free.

Install backup rings and plate nuts, for access holes on bottom wing skins as needed before riveting skins in place. Fit fuel tank cover panel and install plate nuts after installing wing skins.