May 2009 Archives

I began working on the rear spar.  I started by trimming the inboard ends of rear spar reinforcing fork and doubler plates.  I don't have a picture of it, but there is a bit of metal that has to be removed when building the RV-7/RV-7A.

Here are the rear spars.  I've just clecoed the center reinforcing plate on the upper one.

My brother is in town and helped me erect the wing jig.  I'm going to build both wings at the same time when possible, so I've erected two pairs of 4x4s about 2 feet apart.

I clecoed all of the reinforcing plates and doubler plates onto the spar and match drilled them to the spar.

Here are the center reinforcement plates match drilled.  I hadn't noticed the missing hole when I took this shot (can you spot it).

The reinforcing plates have to have an odd shaped hole for the aileron push rod to go through.  This hole is already punched in the spar, but must be cut in the reinforcing plate.  I used a unibit to rough cut close to the line and then files and sanded until they matched.

Afterward, I prepped and primed the reinforcing plates and doublers and riveted them to the spars.  Look carefully at the rivet callouts.  There are many rivets that are skipped and several different rivet lengths.

Here is the center reinforcing plate.  All of the missing rivets will be installed later in conjunction with other components.

Prepping Wing Ribs

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I'm in the middle of prepping the wing ribs.  There are 54 ribs total, and each one has to have the flanges bent to 90º and fluted between each hole to let them lay flat.  I still need to debur the lightning holes and edges before they can be attached to the spars.  This is a really time consuming process, and I'm not even halfway through the process yet.

Here are some of the main ribs and prepping the flanges.  You can see how straight they are compared with the picture above.

Here is a close-up of the flutes that are added between each hole.  Basically, the edge of the flange is longer than the portion of the flange next to the web when the flange is curved.  This causes the rib to bow away from the flange.  By fluting the flanges, you effectively shorten the edge to be the same length as the flange along the web allowing the rib to lay flat.  This is definitely something you just have to get a feel for.  I'm getting faster, but it still takes 5-10 minutes per rib.


I haven't posted many pictures lately because there is really not much to show for the work over the last few days.  I finally finished fluting the wing ribs tonight.  This is really hard on your hands, so you can't work for long stretches.  Anyway, it's done now.  All I have to do is debur the edges and lightening holes and I can get the wing structure up on the wing stands.

I finished deburring the ribs tonight and then drilled holes for the wing conduit.  I made a simple paper template with marks to align with a couple of the bends and the flange of the rib and then center punched the spot.

I then drilled these out to #12.

And finally to 3/4".  A number of builders drill the intermediate holes to 13/16", but the conduit can be worked through 3/4" with a little persistence.  As you can see from this wider shot, I'm putting the conduit where Van's recommends (in the lower 1/3" of the rib between the lightening hole and the reinforcement. 

I finally clecoed the left wing together.  As other builders have said, it feels so good to finally see some structure go together after many many hours of fluting and deburring the wing ribs.

The obligatory shot through the lightening holes for posterity.

I also took a shot through the conduit holes so you can see how well these align even with just a simple paper template for positioning.  I've seen a number of builders spend a great deal of time building a template that aligns with the tooling holes in the ribs to ensure precise placement of the conduit holes, but this is rather pointless as the conduit is very flexible and even a simple method like this basically produces nearly perfectly aligned holes.

I clecoed the wing structure together and temporarily hung it on the wing stand for drilling.

The wing stand uses 1"x1"x1/8" steel (with some aluminum flashing tape to keep from scratching the spars).

Here is the outboard end with a scrap of aluminum angle bolted to the last rib as a mounting point.

I didn't get any shots of it, but I match drilled all of the holes that connect the ribs to the front and rear spars.
I also attached and match drilled the holes that are used to attach the leading edge ribs to the spar.

The last few days have been spent deburring and prepping all of the ribs for priming.  Here are all of the ribs drying after being etched.

And here is a shot of one set of ribs drying after being primed.

I protected the spar bars with some blue tape.  I really should stop using this stuff.  It comes off without leaving any residue on every surface except anodized aluminum.  I had to use some solvent to get all the gunk off the spar after riveting.

We didn't get any pictures during the process, but my buddy Andre stopped by today and we shot and bucked all of the rivets that attach the ribs to the main spars.  We used a straight set and simply flexed the ribs out of the way while shooting.  130 rivets and not a single smiley or bad shop head.  Here, I'm clecoing the rear spar in place so we can hang up the wings.

Here's a good shot of the whole wing.  The four closely spaced ribs at the bottom are for the wing walk.  There will be a double thick layer of skin over these four ribs to handle the load of people walking here.

Here are the wings permanently mounted in the cradle.  I still need to level and straighten them, but that will have to wait until another day.  My wife's heading to Hawaii in a couple of days with a friend and I want to spend some quality time with her before she leaves.

Riveted Rear Spars

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I squeezed all of the rivets attaching the ribs to the rear spars tonight.  Pay careful attention to the rivet callouts because there are a number of holes that must be skipped and there are four different lengths of AN470 rivets used.  Here are a couple of holes that must be skipped where the flap brace rivets to the rear spar.

The outboard ribs attach to the rear spar with AN426 (flush) rivets since the outboard aileron brackets sits on top of this spot and rivets through the 5 open holes just inboard of these rivets.

Fit Top Wing Skins

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The weight of the wing causes the middle to sag a bit, so I put a support near the middle of the rib.  This is basically just a piece of steel tubing and some allthread with a washer and nut.  I put a couple of plastic feet on each end to prevent scratching the spar and to prevent it from slipping on the floor.

I stretched a piece of fishing line across the lower set of holes in the spar and adjusted the support until the fishing line ran through the center of all of them.

The wing walk doublers have to be cut from a larger piece of aluminum sheet.

Then positioned under the top wing skin for match drilling.

Here are both doublers match drilled to the top skins.

It's late, but I just had to see what these looked like clecoed to the skeletons.  I'm really glad I ordered some extra 3/32" clecoes and I'm really glad I have the pneumatic cleco tool.  I know my hands would be killing me if I had to do this with regular cleco pliers.

Here is a closeup of the overlap between the inboard and outboard top skins.  Before riveting these on for good, I'll create a slight bevel on these skins to reduce the bulge.

I got started tonight by fine tuning the lower wing clamps to the point that there is no measurable twist.  I then drilled out all of the skin holes on the top skins (~1000 holes) and this also entailed moving every cleco.

Afterward, I pulled out and attached the lower wing skins.  Here you can see the three access panels that are on the bottom of the wings to make inspecting the wing, aileron control linkage, pitot/aoa, autopilot roll servo, etc. possible.

My buddy Andre stopped by tonight and drilled all of the bottom main skins while I worked on getting the leading edge skins ready to install.  I started with fabricating a simple cradle to hold the skins while fitting the ribs.  This is just a couple of pieces of particle board roughly cut to the shape of the ribs and lined with some old carpet padding I had laying around.  The shape really isn't that critical since it just needs to help hold the skins closed while you get the clecos in place.

Update: Particle board is really the wrong material for this as this fixture will take a fair amount of abuse during the build.  Both of these U shaped pieces broke near the bottom of the U while working on my outboard leading edges.  I didn't need them anymore, so I didn't fix them, but save yourself the hassle and use plywood.

Andre and I clecoed the leading edge ribs into place and fit the leading edge of the left wing in place.

The innermost rib needs to be fitted with a joint plate where nutplates will mount to help hold the fuel tank.  This was a real bitch since there are no holes in either the joint plate or the rib and the fit is really tight.  After futzing with it for about 10 minutes, I finally got everything in place and drilled a few holes to hold everything in alignment.  The only issue I ran into was one of the holes that attach the rib to the main spar ended up with too little edge clearance.  I doubt it will be an issue, but I'll check with Van's just to be sure.

After Andre left, I knocked out the other leading edge in an hour or so.  These still need to be match drilled, but that can wait until tomorrow.

I match drilled the outboard leading edge skins to the ribs and spars.  I didn't take any pictures since it would look just like the picture from yesterday.  I also drilled out the holes for the tie down ring.  Here is one of the tie down rings partially screwed into the tie down bracket through the new hole.

Fit Tanks to Spars

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I used the Checkoway method to fit the tanks to the wings.  Since his site has been taken down, I'm going to document this rather carefully so that other builders can refer to it if necessary.

First up is to assemble the tank.  I've heard of many other builders struggling with getting the ribs to seat fully in the leading edge using the instructions Van's provides.  I'm using an alternate technique that works very well and let me assemble each of the leading edge section in about 5 minutes with virtually no struggle.  The first step is to cleco the first few holes on the top side of the skin near the leading edge.

Next, pad the leading edge with something that is firm but will conform to the leading edge somewhat.  I used a dense foam mat thats folded over a few times.  Stand the section up on the leading edge with the rib you're working with directly over the pad.  Push down firmly with one hand while the other hand puts a cleco in the topmost hole on the bottom of the skin.  By pushing down firmly, you can easily get the hole in the rib close enough that the cleco can be pushed through and the cleco can be used like a lever to pry the holes into alignment (make sure you've pushed all three pieces of metal at the tip of the cleco through both holes before doing this or you'll damage the cleco).

Next, remove the plastic from both sides of the tank baffle and cleco it in place (yes I know I hadn't removed the plastic yet here).

Next, drill a 3/16" (or #11) hole in each of the z-brackets.  The root most bracket should have its hole shifted about 1/16" away from the web (relative to the center) to allow a wrench to be placed over these bolts.

The rest of the brackets should have the hole shifted about 1/16" toward the web.  This will give a little more room on the other flange for the pop rivet tool to seat the pop rivets that hold these brackets onto the tank.

Using this center hole and some scrap bolts, tighten these brackets firmly to the spar (making sure to get the flange orientation correct).

After all brackets have been bolted to the spar, back drill them through the holes already in the spar.

Here is a closeup of what you should end up with.

Next, remove all of the brackets from the spar and attach platenuts to all but the inboard z-bracket.  For the inboard bracket, the platenuts are attached to the rear of the spar.  Go ahead and attach those platenuts as well now too.  After that, bolt all of the z-brackets to the spar.  I used all three bolts here because I found there was some minor hole adjustment that had to be done for the bolts to fit through cleanly and I wanted to make sure that that was done before the z-brackets were match drilled to the tank baffle.

Put the tank on the wing and push it firmly against the outboard leading edge.  Use some straps to pull the tank tight against the wing so that the skins are touching.  Make sure the joints are tight all the way around before proceeding.

Here's a closeup of the joint between the inner and outer leading edges.  You can see that the leading edges are perfectly flush and the joint between the skins has virtually no gap.

I'm doing both wings at the same time.  Here's a shot of both tanks in place.

While the tank is in place, drill the tank to joint plate holes out to #19.

Now, drill the inboard z-bracket to the tank baffle and inboard rib.  This is the only part of the baffle that can be reached right now.

Take off the outboard leading edge.

This gives you access to the outboard z-bracket.  Drill these holes out to full size.

Now, remove all of the clecos holding the tank skin to the spar, baffle, and end ribs.

After removing the skin and interior ribs, you are left with the baffle in the perfect position to ensure tank alignment.

If you zoom in on this picture (click any picture on this site to zoom in), you can see that the centerlines that were drawn on the flanges show through the holes.

Now, drill the remaining holes in the baffles to the z-brackets.

This took me an entire day, but both tank baffles have been drilled to the spars.

Drilled Tanks

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I match drilled all of the holes in the tank skins, ribs, and baffles.

The skins must be countersunk where they attach to the baffles because the baffles have to be slipped in after the ribs are riveted to the skins.  I only got one side of one skin done because I'm exhausted.

I finished countersinking the tank skin to baffle holes tonight and rough cut all of the tank stiffeners.  It's too late to debur these, so I'll do that tomorrow.

The tank attach angles had to be fabricated out of raw angle stock.  I first cut two pieces of angle to length and laid out the cuts.

The first rough cut on the bandsaw.

Both tank attach angles cut to final size and polished.

I cut and deburred all of the tank stiffeners and match drilled them to the tank skins.

Here is a closeup showing how the tank stiffeners provide additional support for the bottom of the tank skins.

There are two options for fuel quantity senders.  The first is to use a float that reads the fuel level with a hollow plastic float on the end of a wire that sits on the top of the fuel in the tank.  The position is read through a resistive mechanism.  This is a well proven design, but has a few drawbacks.  The other option is a capacitive fuel sender.  This has no moving parts, and can measure from the first few ounces in the tank to the last few.  The only disadvantage that I'm aware of is that it must be re-calibrated when you change fuel types.  Since I don't plan on doing that much (if ever), this is a nonissue for me.

The capacitive senders require mounting two electrically isolated plates in the fuel tanks.  The capacitance between these plates and the tank is measured by a small AC signal.  The fuel acts as the dielectric and changes the capacitance.  Once calibrated, this system is easily accurate to a tenth of a gallon.

The first thing is to cut some plastic tubing to length.

These skip over the screws (after putting on a large countersunk washer)...

...and through a UHMW washer...

...and three more UHMW washers on the other side.  As you can see, the screw can't possibly come in contact with the rib.  This is what keeps the plates isolated from the tank.

The screws thread into nutplates that are mounted to the capacitive plates.

Here is one of the plates after mounting it to the rib.  The two outboard plates have to be modified at the bottom to clear the stiffeners.

I positioned the fuel drains and match drilled them to the skins.

For the fuel cap flanges, I drew reference lines at the top and bottom.

I then positioned the flanges in the precut holes in the tank skins so that the hole is centered and the lines I drew are visible in the top and bottom rivet holes. 

Before drilling, I confirmed that the fuel caps are centered in the hole in the skin.

Both fuel caps are now match drilled to the skins.

About this Archive

This page is an archive of entries from May 2009 listed from newest to oldest.

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