Building a Van's RV-6

A Riveting Experience

Sat, 14 May 2011 21:09:56 -0500

It’s pretty amazing how time has flown. I’ve continued to work on my RV but haven’t really reached the sort of a milestone that I feel justifies a blog. But after many hours of cutting fitting, drilling, dimpling and all I’m finally starting to rivet the right wing together.

The first part of the wing to be riveted is the leading edge. In order to do this it’s first necessary to build a pair of jigs to hold the pieces while they are being riveted. Next I riveted the reinforcing pieces of angle to the ribs and then I primed all the pieces that are not alclad coated, especially where I had machined them. When the rib were ready to go, I reassembled the parts using clecos, starting at the leading edge and working to the outside edges. The assembly went into the jigs and I began to rivet the skin to the ribs, once again starting at the leading edge and working towards the trailing edge.  When I riveted the elevators together I used a technique called “back riveting.” That consists of laying the back of the rivet (the side that is the rounded head on a conventional rivet) on a steel plate and then using the rivet gun to peen over the other end. This time I’m using the more conventional method of applying the rivet gun to the rivet’s head and then using a “bucking bar” to pean the rivet’s other end.  It’s not all that difficult to set rivets but it does take some practice. I must have drilled back out a quarter of the first dozen rivets I set before I figured the trick out. The problem was that I was applying too much pressure with the bucking bar and that was causing the rivets to set without being pushed flush with the skin. But as I said earlier, it just takes some practice. I guess I also got my practice at drilling rivets back out. That’s a skill that I suspect I’ll have plenty of opportunity to perfect.
 Not that the leading edge is assembled I need to fit the ailerons and flaps. I’m working on building the mounting points for them now. Then it will be on to riveting the main skins in place.

Fitting the Leading Edge Skins

Sun, 23 Jan 2011 20:15:55 -0600

There are two parts to the leading edge. About half of the leading edge is part of the wing itself and the other half is a fuel tank. The fuel tank’s construction is similar to the leading edge of the wing but needs to be built separately, as I will describe in the next blog. The tank is not an integral part of the wing. It is held in place with fasteners and can be removed for maintenance.

I have previously described the preparation and fitting of the wing ribs. The prepared ribs and their angle braces were attached to the spar. To keep the ribs parallel to each other I cut pieces of PVC tubing to the proper length and then pulled the entire assembly tight with mechanics wire.

It’s important that the leading edge skin is pulled tightly over the ribs before holes are drilled through them both. I used nylon tie-downs for this purpose. The tie-downs were attached to fixtures that I built out of some scrap metal. I designed them to apply the tension to the rear spar without touching or damaging the trailing the main skin’s trailing edges.

With the leading edge skin pulled in place it was time to start drilling and clecoing it to the ribs and spar. This was more difficult than with the main skins because the back of the rib flanges were hard to see.

Even though I had measured and then double checked my measurements, as with the main skins some of the the holes that I drilled would drift from the centerline of the rib flange. I found it necessary to inspect the inside of the wing with a mirror and flashlight every time that I drilled a row. Even so, the drill went astray a few times, and approached the edge of the flange too closely.

I’ll have to deal with those problems when I dimple and rivet the skin in place.

About half way through drilling the skin I ran out of clecos. I ordered another two hundred and it took a week or so for them to arrive. They too are being used up very quickly. I’m hoping that I have enough left to do the tank.

The wing is starting to look pretty good. Next I’m going to start working on the fuel tank.

Fitting the Main Wing Skins

Sun, 26 Dec 2010 19:12:27 -0600

Several weeks ago I commented about my dissatisfaction with the progress that I was making on the Van’s Air Force forums, a popular site for RV builders. Another member suggested that I spend five minutes every day working on my airplane. That five minutes often turns into longer periods. I tried it and it works. Now that I try to make it out to my shop for just a little bit every day things are starting to move along more quickly.

Before I could progress any further it was necessary to fabricate supports for the aileron bell cranks out of angle stock. A ribs was modified to accept the support which I lightened by trimming unnecessary material.
Next the rear spar had to be fit to to the main ribs. I used the “fake skin” method described in my previous blog entry along with a piece of angle stock that I drilled to use as a drill template.

With the wing skeleton assembled and mounted on the jig it’s weight made it sag in the middle. The wing skeleton had to be leveled before the skin could be fit to it or the bow in it would be permanent.

I preload the skeleton with an adjustable support that I built from some scrap metal, aligning the main spar to a string running between the jig’s two upright posts. The rear spar was aligned vertically to the main spar.

I found that the biggest challenge to fitting the skins to the skeleton is drilling the holes in line with the center of the spar flange. In an attempt accomplish this I took measurements and carefully drew lines on the skin where the center of the ribs should be.
I drilled the bottom skins first, working from the middle of the wing out to the ends and from the leading to trailing edges of the skin (top to bottom on the jig). As I worked my way down the lines that I had drawn on the skin often diverged from the center of the spar flange and I had to make adjustments to compensate.

With the lower skin cleco’d in place fitting the upper skins was more of a challenge. When I drilled the lower skin I could always look at the rib flanges from the other side of the wing. When I drilled the upper skins I had to do so with the lower skin in place to maintain the skeleton’s alignment. As a result the back of the rib flange was no longer visible so I had to come up with other ways to verify that I was drilling in the right place.

After considering the problem I fabricated a small “T” and marked the trailing edge of the skin, using it to alignment with the rib’s centerline

I used the “T” and then double checked the lines that I had drawn on the skin with a tape measure. Even though I made a diligent effort to accurately layout the skin I still found that some of my lines wandered from the centerline of the rib flange and I had to adjust where the skin is drilled accordingly. This shouldn’t affect the integrity of the wing, but I do want this job to look professional.

My kit is an older one and Van’s has made some improvements to the model since it was built. One such is an upgraded brace to reinforce the aileron bell crank support (pictured). At about $20 the upgrade was very affordable and probably took less time to install than it would have taken me to fabricate the part that it replaced.

At this point I’m beginning to think that it’s not really so hard to build an airplane. It requires new skills and a lot of patience but it’s not what I would call so much difficult as just time consuming. It was necessary to layout and drill five hundred holes to fit the bottom skins and another five hundred for the top skins. That doesn’t include the holes I’ll have to drill for leading edge skin, the fuel tank, aileron or flap. And once I’m done I get to do it all over again on the other side. It’s a good thing that I’m working on my airplane every day.

Starting On The Wings

Sun, 28 Nov 2010 20:22:37 -0600

With the empennage pretty well completed building the wings is next. I’m fortunate that the kit I purchased includes the Phlogisto pre-built main wing spar. This $2000 option is said to save about fifty hours of build time. It’s a pretty gold color too.

Having previously prepared the ribs my fist task was to position them properly on the spar. Many of the ribs needed to be cut to fit the spar and then require that reinforcing braces be fabricated from aluminum angle stock.

Positioning of the ribs is very important so that when the skin is drilled all the holes will line up with the ribs to within an eights of an inch. I checked and then double checked that everything is located properly to within a sixteenth of an inch.

Once I’d drilled all of the reinforcing braces to match the holes in the spar I clamped the main ribs in place and measured the distance from the indexing holes (used in their manufacture) to a string that I’d run the length of my wing jig. Much to my dismay I discovered that there was simply no way that I could get them to line up as closely as I would have liked.

After asking several people about it and re-reading the instruction manual a number of times I concluded that I would simply have to live with the situation. The ribs are manufactured by Van’s Aircraft and I have to assume they did it right. So with two pieces of aluminum sheet metal intended to act as a substitute for the wing’s skin and some clamps I aligned the ribs to the spar. After that I used a long bit to drill the ribs to the reinforcing braces and to the spar itself.

At this point all of the main ribs and those leading edge ribs that are’t used in the fuel tank have been fit to the spar.

Next I need to fit the aileron control pivot to one of the ribs and then fitting the rear spar. Then I’ll fit the skin to the skeleton, build the fuel tank and the do it all over again for the other wing. It looks like I’ve got my work cut out for me.
I’m surprised at just how long it has taken me to get just this done. Clearly I’m going to have to relax and just accept that this project is going to take a while to complete.

Building the Trim Tab - Twice

Tue, 19 Oct 2010 11:40:11 -0500

The left elevator is similar to the right side except that the trim tab is attached to it. Consequently it has an additional spar and some internal structure that adds strength and providing a mounting point for the control cable.

The construction of the elevator itself wasn’t difficult. The trim tab turned out to be more of a challenge than I had anticipated.

The trim tab consists of a folded .020” skin, a small spar and a piano hinge that attaches it to the elevator. The skin has to be cut so that it aligns with the elevator’s trailing and inside edges. I didn’t read that until after cutting it as per Van’s drawings. So while the trailing edge lined up nicely, the overall width was about 1/4” narrower than I would have liked.

Once the trim tab has been trimmed, it’s open ends need to be folded to the inside, closing it up. I found it difficult to bend with sheet metal pliers close to the trailing edge, This left an open gap.

I drilled the spar, hinge and skin together and then dimpled the skin and countersunk the spar to match the dimples. That way the hinge would be riveted to a flat surface. I then drilled the bottom of the skin to the spar. After riveting everything together I used my “poor man’s sheet metal brake” to achieve the correct angle on the trailing edge.

With the trim tab clecoed to the elevator, I laid the assembly onto the bench. It was at that point that I noticed that the trim tab had a bad twist to it. I think the twist was introduced when I used the brake set the angle of the trailing edge.

At this point I knew that I had to make another trim tab, avoiding my mistakes from the first one. Fortunately Van’s doesn’t charge a lot for the parts. They came to about $20 plus shipping.

The second time around I started out by using my Harbor Freight sheet metal brake instead of sheet metal pliers to bend the ends of the trim tab. This made for a much neater bend.

Because I had been shipped a pre-drilled trim tab spar, I next drilled the hinge to the spar an then the skin to both pieces. I bent the trailing edge of the trim tab to the correct angle and then with the top of the spar attached to the skin with clecos, I drilled two holes through the skin into the bottom side of the spar. That way everything would line up properly and I wouldn’t introduce any torque into the skin. Even so the spar wanted to move in relationship to the skin and I had to drill a couple extra holes to get everything right.

With the bottom clecos still holding the pieces in alignment I opened the skin back up and then drilled all the holes through the bottom of it and the spar, then deburred, dimpled and back riveted the skin, the spar and the hinge together. This time the trim tab didn’t have any twist in it.

Last I cut a cable mounting horn from a piece of flat aluminum stock, bent it to the correct angle, attached it to the trim tab and then cut a slot into the elevator where the cable passes through it.

With that, the left side elevator is almost done. There are a few details that remain to be taken care of but I’m already starting to lay the right wing out.

I made a few mistakes but fortunately they weren’t expensive ones. The new trim tab came out really nice. It’s a small part but details do matter. And best of all I learned a few lessons along the way.

Completing the Right Elevator

Sun, 12 Sep 2010 20:52:37 -0500

Now that I’ve finished that big software project that was taking all my time up, I’ve taken a couple days to work on my RV project. Things have been slow because I’m learning new skills, but as I become more competent I’m starting to move through the process more quickly.

One thing I’m discovering is that building an airplane just takes time. It’t not that any particular process is so terribly time consuming - it’s that you have to repeat each of those processes so many times. For example the right elevator has approximately 250 rivets. Each of those rivets needs to be laid out, drilled through two or more pieces of metal, de-burred, dimpled, primed and riveted. The time just adds up.

After the stiffening ribs were riveted into the elevator skin it’s necessary to close the skin so that it will fit the spar properly. The bend needs to be at the trailing edge so that the elevator skin does not try to bow outward. To accomplish this Van’s Aircraft recommends what they call a “poor man’s sheet metal break.” It is a pair of two by eights with hinges at the back. I made one and it worked very well.

After the skin has been bent properly it is next fit into a wooden jig that I built to Van’s specs and then the skeleton is fitted into the skin. The skeleton’s location is then draw on the skin. The skin is then removed from the jig and the rivets attaching it to the skeleton are laid out. As was the case with the stiffeners the holes are drilled, de-burred, dimpled primed and riveted.

Learning to rivet was a bit of a challenge. Back riveting like I did with the stiffeners is pretty easy to get right. Riveting with a bucking bar is a different deal, especially with the larger conventional (not flush) rivets. The riveting gun didn’t want to stay on the rivet and would beat the rivet’s head up. I ended up drilling several of them out and re-riveting them.

Riveting the flush rivets was easier once I got the trick figured out. First of all, I’d drop the air pressure down to about 45psi since I’m using a 3x gun which is pretty powerful for a 3/32 rivet. I used a special swivel riveting head that is designed remain flat against the skin so that it won’t mar it. With this head I didn’t have to look at the gun and instead turned my attention to the bucking bar that does the real work. Another thing that really helps is to make sure that the pieces being riveted are on something solid so that they won’t go moving around.

Riveting is really kind of interesting. You would think that the side of the skin that the gun is pressed against would be bent or damaged by the gun but that wasn’t the case. Somehow the energy is transferred to the head of the rivet and the bucking bar (basically a heavy piece of metal) peans over the shank.

I’ll admit that some of the rivets started to go bad but I caught them in time and most everything actually ended up looking pretty good. I found a conflict between what theory says width of the peaned over shank should be (1 1/2 times the initial size) and what the military spec calls for. By the time the shank was peaned to meet the mil spec the head had been expanded well beyond that 1 1/2 - 1 ratio. But having two choices I went with mil spec.

Once the eelevator was riveted together I had to bend the leading edges together and then rivet them in place. Van’s instructions are to take a piece of pipe, duct tape it to the leading edge and then start to bend it by twisting the pipe with a pair of vice grips. Once an initial bend has been made the two ends are held together using duct tape to achieve the desired radius and then pop rivets are driven through the tape to hold the final bend in pace. Once I found the right size piece of tubing this went pretty quickly

With that, I’ve completed my first sub-assembly. Between delays waiting for tools and then getting very busy this has taken me a long time but I think things will start moving more quickly from this point forward. I’m already working on the trim tab for the left elevator and after that is done I’ll be staring on the wings.

Building a Skin Dimpling Tool

Sat, 28 Aug 2010 20:30:00 -0500

A couple months ago I picked up a software development job. It was supposed to be part time but as often happens what was supposed to be a couple weeks of work turned into a couple months of working seven days a week. As result I haven’t had much time to work on my RV project or to do much of anything else for that matter.

In my last blog entry I focused quite a bit on tools. While I’m now pretty well tooled up there was just a couple items that I still needed. One was a dimpling tool suitable for large skins and the other is a 2x riveting gun.

I had two choices on the dimpling tool. One is a “C” frame that holds a punch aligned so that when it is struck with a hammer the it will dimple the skin. This is the “inexpensive” ($200) solution but it takes two people to operate, one to hold the skin and the other to strike the punch. The second choice is also a “C” frame but it uses a lever to dimple the skin. It can be operated single handedly but costs about twice as much as the other dimpling tool.

Fortunately there is a third choice. The manufacturer of the lever operated dimpling tool also sells the head only. It costs less than half the price of the complete unit. Buy purchasing the unit’s head, bucks down builders (like me) can build their own units. That’s the option I chose.

With it on order I discovered that the recommended material for the tool’s body (3” x 6” boxed mild steel tubing) is expensive and difficult to obtain. Surprisingly, the same size tubing in aluminum cost only about half as much as steel so I ordered a 6’ stick. When it arrived I cut it to length before realizing that they had sent me only 2” x 3” tubing. At this point I decided to fabricate the tool anyway. My thinking is that that it might do the job and at worse would give me some welding practice. My biggest concern was that it might flex too much.

After a few hours of fabrication and welding I was done. (See the photo at the beginning of this article.) I got some tig welding practice in and the unit does the job. Yes, it does flex a little but not too much. The one thing I hadn’t anticipated is that being made out of lightweight material, the back of the tool wants to tip up when I press the lever. Clamping it to the table solved that problem.
I’m almost done with the software project and plan to dedicate a couple days to nothing but airplane building. Hopefully I’ll have more to report next time.

Building the Right Side Elevator

Tue, 29 Jun 2010 22:19:54 -0500

One of the great truisms I've learned in life is that you just have to have the right tools to do the job - any job. Over the years I've put together a fair tool kit for cars and motorcycles. But of course building an airplane requires a new and entirely different set. At least I’ve got a medium sizes two piece tool box set (which had been previously replaced by my huge stainless steel Craftman boxes) to put my new tools in.

I'd been waiting for payment from a client for several months and promising myself that I'd pick up the tools I need to move forward on my RV when that check arrived. At the same time I didn't want to be sitting around and doing nothing while I waited. I inventoried the tools I that I did have to see what I could accomplish with them.

Most of the tail section of my plane is was already built and the previous builder did a very nice job of it. What hadn't been built was the elevators so that's where I started.

The first thing that needed to be done was to layout patterns on the skins for where the stiffeners are riveted in. The stiffeners are not real ribs they are just lightweight pieces of aluminum angle stock that are intended to prevent the elevator skins from fluttering. Once the layout was done then each of the stiffeners had to be cut to length and then shaped. I used a pair of metal shears for this and then smoothed the cut edges with a table mounted belt sander. Last I de-burred all the edges on the stiffeners.

Next I had to cut the skin to the proper shape. I was able to accomplish a lot of this with the metal shears but there were some places that were just too tight. In that case I used a Rotozip tool and a steady hand. I then de-burred all of the surfaces on the skins.

At this point I couldn't go any further until I got some more tools. When the check I had been waiting for arrived I ordered an ample supply of drill bits (including 6” and 12” long specialty drills), sheet metal dimpling tools and a $14.95 Harbor Freight air drill. I also ordered about 450 Clecos, temporary spring loaded rivets that can be used to preassemble sheet metal parts.

Once I had the proper size drill bits I was able to start drilling holes through the stiffeners and the skin of the elevator. First I had to lay out where the holes are to be located. To accomplish this I marked the location of the two end holes and then calculated the distance between them so that all of the holes are not be more than 1 1/2” apart. It is very important that the holes in both the stiffeners and the skin line up perfectly. To accomplish this I laid the skin on a piece of dry wall. After positioning the stiffener on the skin I drilled a hole at one end through the stiffener and the skin into the dry wall. I then used a Cleco to hold the two pieces together and then did the same things at the other end of the stiffener. At this point I was able to drill the remaining holes very quickly.

All of the holes need to be de-burred to prevent cracks running from them. This is accomplished by lightly spinning a larger drill bit between my fingers while pressing it against the hole. After that the parts need to be dimpled so that the rivets will be flush with the skin and the rivets will have to be set. The stiffeners are then dimpled with a hand rivet squeezer using the proper sized dies.

Because of the skin’s size I have to wait for a different dimpling tool to arrive before I can dimple it. The head for that tool is on order and I will have to fabricate the rest of it. But doing it this way allows me to built it to my own specs.

I still need to order some rivet guns but have not done so since I'm not quite at the point where I’m ready to use them. But hat time shouldn't be very far off.

Speaking of building things, it can become uncomfortably hot in my shop during the summertime in Texas. I had an old air conditioning unit laying around and it occurred to me that if I could just figure out how to get the heat that it generates out of the shop I could use it as a roll-around unit. So I bought some sheet metal and some insulated 6” ducting and went to work. A couple hours later this is what I had. All the hot air that blows out of the back of the unit is vented into the attic. It’s not very pretty but it makes it much more comfortable working in my shop.

Airplane Construction Begins

Sun, 30 May 2010 20:16:14 -0500

As I described in my previous blogs, until recently I have been focusing on preparing for the actual build. Once I had my shop in order and had received the first of the tools I will need for this project the time came to actually start fabricating my airplane.

Most of the work on the empennage had already been done and the remaining work requires a bunch of clecos, temporary rivets. They were beyond my budget at the time. Because I could do so without spending quite as much on tools I decided to start on the wings.

My task was to prepare the wing ribs. This involves several things: first lightening holes must be cut from the ribs with a fly cutter; then all edges must be de-burred; because the ribs are bent when they are formed they must be straightened; finally the flange where the rib attaches to the wing spar needs to be bent so that the rib is perpendicular to the spar.

I purchased an inexpensive fly cutter from Aircraft Spruce & Specialty Company along with an extra tool bit. At first it wasn't cutting as quickly as I would have liked. After I lubricated the tool bit with WD-40 and that didn't help I started grinding it to get a more aggressive cutting angle. After resharpening it several times it was still cutting slowly and the belts in the drill press seemed to be slipping. I finally discovered that a bolt that holds the pulleys to the shaft carrying the chuck in my drill press had loosened up. Once I tightened it up the cutter started going through the aluminum like butter.

It took me a couple hours to cut out all the lightening holes and then several more to de-burr them. I weighed all the metal that I'd removed and discovered that all this work saved me all of about 3 1/4 pounds. Not exactly an impressive weight loss. However it is inspiring me to take some weight out of the airplane an easier way - by losing some weight myself.

After the lightening holes were cut it was necessary to straighten the ribs. This is accomplished with the use of "fluting pliers." By making indentions into the rib's flange the body of the rib is pulled flat. The trick is to not flute the rib where a rivet will be. I took several hours asking questions and studying the drawings before I started to straighten the ribs because I didn't want to botch the job.

The last operation was to square the rib to the spar. I did this by clamping a rib to a table and then simply bending it near the flange until it was perpendicular.

Now that the ribs have been prepared I need to attach them to the spars. However, before I can do this I need to buy more tools and that means waiting on a check from my clients. I'll describe that process when it's been done.

Doing the Ground Work

Mon, 17 May 2010 07:36:15 -0500

It's been about a month since I wrote my last blog entry, but that doesn't mean that I haven't been busy. As I mentioned at that time there was a lot that needed to be done before I started riveting.

My first big project was to inventory the parts that I purchased. The documents that came with the RV kit include a list of the various parts that should have come with it and what page of the drawings that each part was on. However they didn't say how many of each part is needed. Some of the parts that came in my kit had part numbers marked on them and some didn't. So I entered all the parts that I could identify into a spreadsheet, along with the shelf where I put them and then checked them off the list. Once I'd gone through all of the parts that I could identify, it was necessary to look up the remaining parts on the drawings and match them against what was left.

Considering that the kit was originally purchased fifteen years ago things were in pretty good shape. It looks like I may be short twenty to thirty pieces but they aren't all that expensive so I can live with that. I'm tracking my time on the build and it took about twenty four hours to inventory everything.

Next I had to get the shop cleaned up. This meant pulling a lot of keepsakes in boxes from the shelves where the airplane parts would go and moving them into my cargo trailer. Eventually they will find a home in an old storage building that we have got. I pulled the Fiero's engine from the K-member and removed the transmission and header in preparation for putting it back on the road. I think that the heads needs new valve stem seals but I'm not going to pull the engine down any further until I have a few extra bucks for some gaskets.

Since I am working on a budget I ordered just a few tools that I hope will get me to the next stage, at which time I'll have to order more tools. I'm sure that it's costing me more for shipping this way but it helps by breaking the expenses down into smaller chunks.

Finally I built a wing jig. I attached some 4x4s to the rafters in my shop. I did run into a bit of a surprise. I had to sit on the rafters as I attached the 4x4s which I discovered made them sag just a bit. When I got back down to the floor I found that the boards were hanging free

by about a sixteenth of an inch. Consequently I fabricated some tabs with bolts that I used to preload the wood. This actually worked well because it let me precisely level the 4x4s and then lock them in place.

Now that the wing jig is in place I'm back to studying the kit's documentation and drawings. When my tools show up I should be able to start preparing the wing's ribs. I'll write about that next time.