Completed match drilling holes in main wing skins

I'll start this post with a quick pic of the new overhead light that I described in my previous post that was mounted to the underside of the shelf:

Since I finished match drilling all the main wing skin holes to the spar and the ribs on both wings, the next step will be to remove the skins and debur ALL the holes. This also means that it is time to remove the vinyl by using the wonderful soldering iron method once again. At this point I was tired of having problems trying to get anything from a 25 watt to a 40 watt soldering iron to generate enough heat to melt the blue vinyl coating on the metal. It just would not heat up the vinyl enough to melt through it the way that it should.

So I trekked off to HD aviation department and found this new 60 watt iron:

Just as I have done with other irons before, I used my scotch brite wheel to remove the sharp point which will scratch the aluminum very easily if left "as is." Then I took some 320 aluminum oxide sandpaper and smoothed the tip. Then I took what I think was a trim bundle piece that came with the wing kit and ran some tests to determine if the iron would melt the vinyl better and that it would not scratch the aluminum. It was successful on both counts. Finally I think I have an iron that will do the job easily. I then did some of the rib sections on the left wing, but determined that trying to do this with the skins on the frame with all the clecoes in the way was not the best way to go. So I will remove the skins and finish the vinyl stripping that way.

Next I wanted to show a pic of the area where the inboard and outboard skins overlap. This pic looks down from above the spar where the skins meet the spar flange, and shows the bulge that occurs in that area. the skins also also butt up against the fuel tank skins, and the overlap creates an ugly mismatch in the joint between all of them. This of course translates into additional parasite drag, and so the area is supposed to be trimmed down so that all the skins join together at a bout the same depth. It is referred to as a scarf joint. The drawings in the plans try to show what this trimming is supposed to look like from a couple of different angles, but I found that I just get confused about what I at looking at because I cannot figure out the orientation unless I stare at it for along time. Basically you only have to address the 1.5 to 2 inch square area where ALL the skins overlap at the main wing spar flange. Once the joint is trimmed down by reducing the thickness of the wing skins in that area, it should appear as though it is just one continuous thickness that should roughly match the same thickness of the fuel tank skins.

A couple more lighting improvements to the shop and continuing with drilling the skins

Thanks again to my niece's fiance Steve, who is a licensed electrician, I was able to add one more light fixture to the far side of my garage. I put in a 48 inch x 2 bulb T5 54 watt florescent fixture under my large shelf that held most of my larger wing parts all this time. I picked it up from HD after staring at it for a while and then realizing that I was almost blinded by the amount of light it was putting out. It really lights up the entire bottom side of my right wing, as well as the band saw.

Steve hard wired it to an existing light socket and switch, and now that area of the garage is completely illuminated. Now I just need to figure out how to heat the damn thing during the winter months. The holiday weekend was literally a "wash" in that we were inundated with heavy rain, wind, hail, and tornadoes. Heck, a pic of the street in front my house even made it in the Saturday newspaper with a huge funnel cloud over the school right next to my house. Scary to think that came that close to losing the house, and even more disconcerting to think that I almost lost everything I have put into the airplane. Luckily the funnel dissipated and the clouds wondered on to the north.

So not much time was spent working on the wings, except that I did manage to finish drilling the bottom left wing skins. I spent some quality time vacuuming the shop, since I had not done that in a while, and the debris from cutting and drilling the steel support brackets for the stands left my work benches covered in steel remnants. I also tried to follow another section of instructions from Vans that tell you to "draw a couple of lines on the skins that intersect the center of the holes from the wing tie down bracket."

The problem is this:
The main wing "skins" do NOT intersect the tie down hole. The bracket and the hole for the wing tie down ring are located at a point along the leading edge skins, NOT the main wing skins, and the main wing "skin" does not but  up against the leading edge skin in that location. Instead, one of the removable inspection plates is what actually butts up against the leading edge skin. SO the procedure should say to temporarily mount the inspection plate to the bottom wing skin, and take a straight edge to align the center of the tie down ring hole in the bracket to the inspection plate cover, as shown in the following pic:

The leading edge skin will butt up against the inspection plate cover, and the mark from the cover can be transferred to the leading edge skin. The LE also has a small pilot hole that was drilled very close to the access hole for the left wing, and I wondered what the extra hole was for at the time I was messing with the access hole cover plate support bracket. Now I know that this was intended as the starting point for enlarging the hole through which the tie down ring can be inserted into the tie down bracket. THe next pic shows the hole:

The idea is that Vans designed it so that the ring is removable and is stowed in the airplane to reduce drag. This hole is not an exact placement, since the position of the final hole for the ring depends on the accuracy and attachment of the holes drilled in the main wing spar and tie down bracket. Therefore you need to measure carefully and file this starting hole in the correct direction as necessary to establish the true center point of your tie down bracket hole. I'll have lots of vinyl removal and deburring and dimpling coming up, as well as leading edge prep work and some fuel tank prep work. Wow, I can't believe I am about to start prepping my fuel tanks already..... Very cool. I just wish Vans did a better job on their manual instructions for the wing section - pretty piss poor as I have said before.

Finally done setting up the wing stands

All 4 bottom brackets are now bolted in place, and I have all 4 plumb bobs mounted from the next cleco inboard from the one on all 4 end ribs. I chose to suspend the fish line and plumb bob from this location so that I could keep all clecoes attached to the end ribs and allow the fish line to swing freely. I will use my square to obtain the necessary measurements to determine if I need to adjust the wing for any twist. I put gorilla tape on all bracket surfaces,especially the ones that will come into contact with aluminum and steel. A nifty chart I got from Cleaveland tools along time ago shows the compatibility (or lack thereof) of various metals. Aluminum alloy attach brackets are NOT compatible with steel, and will start to react/corrode if left in contact with each other for extended periods of time.The layer of tape between the 2 surfaces should prevent that from happening.

You can't see the steel bracket too well in this first pic, which shows the the two inboard ends of each wing clamped at the rear spar attach point. These are the ends that will be adjusted if there is any twist in the wing. You can also see the two plumb bobs suspended from the clecos at the main spar:

Next are the pics of the left and right wing outboard attach points with plumb bobs suspended.

Wow. Now maybe I can start drilling wing skins again for a change. I'm tired of drilling holes in 1/4 inch thick steel. Next time I'll have some pics of a recent visit to a hangar at KFTG last week where our EAA chapter visited 2 RV-7A projects that are very close to completion. John Tetter and Lyn Langer's aircraft are looking great, and I took a lot of pics from my camera phone of everything from fuel systems to landing light and fuel tank assemblies and fittings and more. Lyn also had a backup alternator on his engine. Lyn's engine is also one that I am considering to purchase from Superior in Texas, so I spent quite a bit of time examining that.

Recent wind and weather events here in Colorado also have me contemplating my decision to build a nose wheel or tailwheel aircraft. More later.

RIght WIng outboard lower wing stand bracket completed

Same measuring, cutting, grinding, fitting, drilling, as the left wing, and the lower bracket for the right wing is done. Everything fit just as well as with the other one, so am pleased with the way this one turned out as well. 4 more lousy holes to drill in the other stand for each wing to install the other brackets. The other ones will be clamped into place against the rear spar mounting flange after checking both sides for any twist.

Here is the shot of the right wing outboard bracket wide shot:

And the close up:

I had to grind down about 1/16 of an inch of the inboard section of the steel bracket as it was just a bit too close to the rib. All this means is that my measurements for the placement of each wing stand were a bit different between the left and right wing stands. Not a big deal. The 3/16 inch hole for the tolling hole in the rib was spot on, so my exhaustive approach to accurately transferring measurements from one part to another are paying off. I need to buy some more 2 inch steel angle to fabricate the remaining two brackets, and then I can get back to drilling holes in wing skins - FINALLY! These wings ain't goin' anywhere any time soon.

More about wing stand bottom support brackets......much, much more......

IN my previous post I mentioned that I was going to use clamps to avoid measuring and drilling more bolt holes in my wing stands. The Vans plans do not elaborate on the bottom support brackets, nor do they show a detailed inset of the assembly for the bottom bracket like they do for the top ones. Well since the last blast of winter moved out of town, for some reason I changed my mind and decided to proceed with all the necessary cutting, drilling, fitting, and leveling of the bottom support brackets. Call me a sucker for punishment I guess.

Part of the reason for doing this is to document it for other builders. I could find pictures from other build logs showing how others have done this, but I never see any details written about how the did it. That would leave one to believe that the procedure may be so simple that it is obvious, but I say that could not be further from the truth.

For the bottom brackets on the tip end of the wing, you have to deal with the proximity or distance of the ribs and skins to the lower angle bracket, the overhanging skins from the tip rib (about 1/2 inch), and ensure that the wings are mounted on the stands in such a way that the the lower tip bracket can be mounted to the tip rib without interfering with the overhanging wing skin at the trailing edge of the had to reverse the right wing on my stand because of this.

Anyway, a whole lot of tools and measurements and drill bit changes and fitting and cutting and so on later, I managed to get the bottom bracket fitted exactly the way that I wanted it. The only less-than-desirable thing was the 3/16th inch #10 hardware that I had to pick up from the specialty hardware store in my area to attach the angle to the tip rib, since the big box stores don't really carry bolts in this size at all. I ended up getting some screws that are threaded all the way to the pan head, and I really need something similar to the tank attach bracket bolts, but they are not quite long enough for the job.

ON to the pics.I started by using my top brackets as a template for the length of each bottom bracket. I measured and cut them from some existing 2 inch steel angle that I still had lying around. Note that I am using 2 inch angle on the bottom brackets, which is necessary for me because of the 1.5 inch angle I used for top, combined with the 2 inch short angle pieces that attach to the rib and set over the top of each top support bracket. I did this to add the necessary gap between the extended skins that exceed the flange of the final rib to act as the attach points for each wing tip. I used bar clamps to secure the angle to the bottom of the wing stand,and quickly discovered how close to the bottom wing skin the angle would come (less than 1/8 inch.) I also had to check it for level since I was going to drill another bolt hole to attach the angle to wing stand. It all had to line up correctly to avoid interfering in a number of different ways.

I measure and drilled the 1/4 inch hole in the angle bracket as shown below:

This hole is 2 inches in from the end, which should center it along the 4 inch side of the 2x4 steel post.  the Perhaps I should have started with the step where I drew the reference line across the top of the angle after leveling it against the post and positioning it the way I wanted it. Here is both the inside bolt hole that was transferred by an ultra fine sharpee pen from the hole drilled in the angle. This made marking the first bolt hole rather simple.

I then used my straight edge and clamped it along the reference line so I could use my tape measure to measure the line from the top of the post down,which is the most common area to use to ensure the measurements are transferred accurately over to the other side of the post.

THis next pic shows many things. First is the line transferred to the outer side of the stand, and the bolt hole and bolt that were ultimately drilled and secured along with the angle to the post. I should also point out that I ground down the edges of the steel angle and smoothed them on my scotch brite wheel. I don't want any of the heavy metal marring up the airplane parts so this was essential.

Next is shows how closely this angle comes to the top and bottom skins, and how level it aligns with the rear spar and rear rib flange of the tip rib. It also shows the sharpee outline of the small aluminum angle I used as the attach angle to the rib. It mounts to the steel angle and then also to the forming hole in the rib. It also shows the level on top to ensure that everything was in alignment.

Here is another view

For the attach angle I used some scrap 1.5 inch aluminum angle from HD aviation department. THis is the same angle that was used as a backer plate to countersink all those pesky tank attach nut plates to the main spar. I cut it to size and smoothed it with the scotch brite wheel.

Next came the 1/4 inch hole in the attach bracket which I just eyeballed and decided where I wanted to drill it.

Then I transferred the mounting hole from the attach bracket to the support bracket:

Then I removed the steel support bracket and drilled the hole. THen I was able to take a short 1/4 inch bolt and attach the two angles together.

Then came the fun part of figuring out how to transfer the exact measurements of the location of the forming hole in the rib to the other side of the aluminum attach bracket. I removed the attach bracket, ensured the support bracket was level, and used my straight edge to mark a line on the front and back sides of the forming hole on the rib, and I extended these lines above the top marks for the attach angle so they could be seen after the attach angle was placed back on the support bracket against the rib. I then transferred the lines from the rib to the attach angle and then took the final measurement from the top edge line down. From this I had enough dimensions transferred to the attach angle so that I could drill the necessary 3/16th inch hole. I was very pleased with the alignment:

I put a piece of gorilla tape on the back side of the attach angle so that it will not mar the side of the rib, and then used the 3/16th inch hardware to attach the angle to the rib. It fit like a glove (thankfully). I even was able to insert my arm through the next to the last lightening hole to hold a nut driver on the nut on the inside of the rib that holes the screw in place. Everything is secured nicely, and it only took me most of the day to get it all done.

One down and one to go......

Tonight was a research night for several things

As I am drilling out the rivet holes in the wing skins, there are a couple of things that I need to address. I was not quite sure how to attach the bottom supports to the trailing edge of each wing while it is in the stand. This needs to be done so that the wing can be kept square without any type of twist or bend.

Vans has a very straight forward method for doing this which involves hanging two plumb bobs from lines suspended vertically from clecos holding the two end ribs at the main spar. You then measure the distance between the suspended lines and the top-rear corner of the rib/skin at each end. The measurements between the plumb line and the corner of the rib at the root and the tip of the wing should match if no twist exists. If they do not match, then there is a twist, and you need to use the bottom brackets and some clamps to secure the trailing edge of the wing after removing the twist.

After reviewing some other build sites online, I think I have figured out how I will set these up. I think I can do it using only C clamps, a couple more metal brackets, and some wood braces where needed. Anything to avoid drilling more holes in the wing stands, which was a laborious process the last time that I had to do it.

Next, I noticed some oil canning in the last bay of the bottom wing skin for the left wing (at the tip). There are other posts on VAF that report the same phenomenon, as well as potential solutions that range from self correcting when everything is riveted, to attaching stiffeners to the affected area, to double checking and correcting the bends in the rib flanges in that area. The main thing is that apparently Vans is aware of this, and says it is a cosmetic issue and is not a structural concern. So I will spend a little time checking the rib flanges and checking that the wing is level on the stand, as well as correcting for any twist that may also be causing this to happen. Otherwise I am not too concerned.

The weather turned cold again for a few days as winter tries one last time to hang on. So it was a good night to stay inside. The forecast says that we might even get snow on Mother's day this Sunday, which will not make my mother very happy at all.

Also saw that Dynon issued a service bulletin for their heated pitot tube system because they confirmed what several well known and respected RV drivers have been telling them for a while now: ice can form in the lines beyond the pitot tube because it does not do a very good job of separating and draining water from inside the tube. The water travels up into the lines and freezes in the lines causing erratic or no airspeed indication at all. I am expecting a recall and a full replacement with a new pitot tube sometime in the future when they come up with a solution.

Found more clecos (Thanks EAA Chapter 301 Members!), attached all the wing skins and I'm drilling all those holes

I sent out a call for help to the members of EAA Chapter 301 for any spare clecos they may have, and they delivered in spades. I need to send a personal thank you to Bob Meer, Rudy Kniese, Darrel Herk, and others for answering the call. Also thanks go to Mel Keuthe and Mike Rettig for responding. This saved me about 250.00 in new clecos, and I now have enough to slam the skins onto both sides of both wings.

Through that experience I got to see Bob's beautiful IFR equipped RV-7A,  and Rudy not only gave me some clecos, but also invited me on a flight in his nicely painted Glastar up to KGXY for breakfast last Saturday morning. He even let me fly it most of the time! What a nice flying machine that was. He has the same Infinity grips that I plan to install on my joy sticks, and it was great to be able to get the feel of them during the flight.

Before I get more into the main wing skins, I have some more detailed pics of the process I used to match drill the holes into the wing walk doubler of the right wing, which I could not do until I got more clecos. The first pic shows the beginning of the drilling process after I had positioned the top edge the required 9/16 of an inch from the top of the inboard W702 skin for the right wing:

Note that I started in the middle and worked my way to the top, clecoing every other row as I went, working out any slack in the skin as I went.

Next shows the piece of tape that used to mark the recessed alignment of the edge of the doubler against the wing skin. It also shows the enormous amount of aluminum residue from the drilling that forever threatens to scratch anything that it comes into contact with.

And here is what it looks like when all the holes are match drilled into the doubler and the W702 skin:

With doubler all drilled for the right wing, I deburred the holes on both sides and then proceeded to slap the skins onto the wings. This pic shows the bottom skins of the right wing and the top skins of the left wing. This is due to the opposite directions that I placed the ends of each wing spar. I don't know if there was a reason for this, but so far this is how I intend to work on both wings. One thing I confirmed that I had already pretty much figured would happen is that I will need more light on the other side of the right wing next to the garage wall. It is just too dark back there to see anything.

Kudos to my niece's fiance Steve Lindsay for helping me cleco all the skins in place. He was full of questions about the process and I think he enjoys learning how all this works. Hell, he even said he would go for a ride when I get it finished. He truly has no fear! Thanks for the help Steve!

This next pic shows the detail of the inspection access holes along the bottom of the right wing. The left wing has the same ones. If you read any of my left elevator/trim tab posts you know what the access cover plates look like that will attach to nut plates surrounding these holes. It was interesting to find out that the support flanges that support each of the cover plates are actually joggled from the wing skin. There is no additional sub-support bracket that has to be riveted to the wing skin. That was a nice surprise. Also on the right wing in one extra hole that does NOT appear on the bottom of the left wing. This is the venturi-shaped hole for the naco air vent intake which routes air to the floor vent for the rear seat passenger. a hose connects to the intake and to the air vent on the other end. Nifty setup for that as well.

The inboard (short) skin gets attached to the spars and ribs first, and the outboard longer skin has a row of two rivets that you can see in the above pic toward the center. Remember that you can click on the pics in each post to get a much larger, more clear image. That goes for every pic in this blog. The top side skins go on exactly the same way, except that the wing walk doubler goes on the inboard section under the W702 skin and over the 4 closely spaced ribs. The skins are actually fairly easy to hold and attach, but having a helper for the larger one is definitely  plus. the last thing you want to do at this point after all this hard work is drop a skin on an edge - a very expensive and frustrating mistake.

Lastly, I took a pic of the outer web of the tip rib to show that the tooling hole in this rib was NOT widened for any wire bundle tubing or antenna coax or other wires. This hole is left undrilled because it is used to help align the neutral position of the aileron with the wing after those get built. I also took this to show just how nicely the top and bottom wing skins form over the ribs. I am very pleased to see that all that hard work to ensure that the rib flanges were 90 degrees to the web seems to be paying off nicely. Out of 28 ribs, I only needed to nudge a couple of them into place while fitting the wing skins. This is also a testament to how straight I was able to make each rib. Simply amazing when you consider how bowed they were when I first open them out of the box. I have to say I am enjoying this part of the build. Check back with me later when I am trying to contort my body into weird unnatural positions to try to rivet them together, to see if I still feel that way :)