September 06, 2010

Mating the Wings - continued - 7.0 Hrs.

It's Labor Day, and I was able to spend my holiday today working on my plane. So my plan was to continue with the wing mating and see how much I could accomplish today. Over the last few days, I've been able to work on some preparation details, getting ready for a day like today. I'll describe them as I go along here. I was also very fortunate to obtain the help of a chapter member and good friend, Shannon Miller. It's not easy to get someone to give up a holiday to come help you, and I'm very grateful for Shannon's help today. Shannon is also building an RV-7A, currently working on his wings. It was great to have him here. He drove all the way across town to help me today. Thank you, Shannon!

It was necessary to bring the fuselage and wings outside onto the driveway again, in a repeat session like before, to finish the tasks at hand. So with Shannon's help, we set everything up out in the driveway. My neighbor happened to be handy to lend a third hand, and the three of us carried the fuselage back outside and prepared to put the wings back on the plane again.

Once the fuselage was in place, these short cushy stools I had on hand made the perfect supports for the wing. We carried the wing out, set it down on these supports, and then eased it into place in the fuselage.

Right wing in place, above, then the left one, below. This was much easier the second time around. Then we carefully leveled everything. I had beefed up my sawhorse earlier, so it was much sturdier this time, which really helped. The tedious leveling process was much easier this time without all the fine wobbling going on.

With the wings on and everything level, it was now time to check the wing sweep. So once again I hung 4 plumb bobs over the leading edges of the wings and staked a string underneath them.

I pounded a stake in the ground and stretched a string across to the other side. Below, here's Shannon on the other end helping me get the string lined up straight.

We took our time and fiddled around with this quite a bit. In preparation a few days before, I had trimmed a slight amount off of the forward half of the rear spar pair of brackets that stick out of the fuselage. Here's a picture, to help make sense of what I'm saying:

The rear wing spar slides in between this "sandwich". The top of this bracket needed about 1/16" trimmed off, tapering down to nothing removed on the bottom end. This is on the forward piece only. The rear half was untouched. I used a file and took my time so as to not overdo it and remove too much. Also, as you can see, I carefully measured for the critical 5/8" edge distance from all 4 sides, and marked a box in the middle of the spar. The center of the hole to be drilled must be inside this little box. There's not a whole lot of room for error, but it's easily doable if you're careful.

While I was doing all this, I realized that I could start a pilot hole part way through the metal, right in the exact middle of the box. This would ensure that when I drill this hole for good, I get it nailed in the exact spot I want. So starting with a #40 bit, I started a small hole, then switched to a #30 and went about halfway through the rear bracket. When you final drill this hole with the wing in place, it's recommended to use a drill guide made of a block of wood or scrap metal, to make sure the bit goes through exactly perpendicular to the spar. Trouble is, the drill guide blocks your view and you can't see where the bit is drilling. So this "starter hole" helps make sure the bit is exactly where you want it. When I did the final drilling, you can feel it. It was easy to slide the drill guide onto the bit first, then put the tip of the bit in this starter hole, slide the drill guide into place, and then drill through. Worked like a charm. There was no worry about the bit wandering off the mark, or missing the mark and not getting the edge distance required here. So, back to the task at hand, Shannon and I worked on the wing sweep until all the plumb bobs were straight over the string.

It's hard to see from these pictures, but we got the sweep as good as you can get it. No discernable errors, plumb bobs centered on the string.

Another way to double-check the sweep and also insure that the wings are both the same is to triangulate. This is done by stretching a tape measure from the tail of the plane to the corner point of the wing. Then do the other side and make sure they're both the same measurement. Plans call for 1/2" or better. By the time we were finished, mine came in at a negligible difference, less than 1/64" as best as I can measure.

Next, with the wing sweep about as good as we could get it, it was time to move on and check the angle of incidence of each wing. This is done with a tool that you make according to the plans. It's basically a straightedge with a 3" block on one end, and it uses a level. Rather than use a bubble level (mine was too short anyway), I used my Smart Tool, which measures digitally to a tenth of a degree. I taped it onto the straightedge angle, which in my case was a scrapped forward fuselage longeron that I had ruined several months ago. It turned out to be just the perfect length for this task.

The forward end of this tool is just forward of the skin butt joint, resting on the flange of the main spar, and the rear end block is resting on the rear spar rivet line. Vans' engineers have designed this tool to give the wings the desired 1° incidence. It measured within 0.1° tolerance. You move it from side to side and check several places along the wing. This test would also reveal any wing twist, if it were present (none in my case, whew!)

Here's the rear spar of the wing, inserted in between the bulkhead brackets prior to drilling. It can be slightly raised or lowered to adjust the incidence, and moved left to right to adjust the sweep. The scrap of .063 is lying there to be used as a shim, but it wasn't necessary and I tossed it aside.

Now you move this tool around from the wing tip to the wing root, checking several spots on each wing to make sure the readings are consistent, adjusting the rear spar of the wing up or down very slightly to get level readings. The Smart Tool is very sensitive, overkill to say the least, and it can make you crazy trying to get every single reading perfect. Plus, the slightest breeze will wiggle the wings a bit and cause the readings to jump all over the place. Fortunately, this was a very calm day. There were only a few moments here and there that the breezes started getting me concerned.

The sun was so bright today that there were positions where it was hard to read the Smart Tool, due to the glare off the wing.

Lookin' good! This is what you like to see. Level readings, and the Smart Tool beeping away at the zero position. When it looks good from wing tip to wing root, on both wings, you know you have it nailed. At this point, Shannon and I put the flaps on to check and see how the bottom inboard flap skin fits against the belly of the fuselage when raised all the way up. To my great satisfaction, it looks as good as it can get, just kissing the belly of the plane when raised up. I wanted to check this before committing to drilling those holes.

So we pulled the flaps back off and double-checked everything again. It looked like it was time to drill, so guess what we did? Time to take a break! We walked away from the plane. We took a break and had some lunch!

Upon returning after lunch, we checked everything again one more time, and couldn't think of a reason not to proceed. So I nervously grabbed my drill and put in my 12" long #30 bit, and slipped the drill guide I made over the bit.

I made sure the tip of the bit was in the pilot starter hole, then pushed the drill guide against the spar, lined the bit up as straight as the drill guide indicated, and pulled the trigger. After drilling #30, I checked with my little inspection mirror to make sure the hole on the forward side was inside the marked box for proper edge distance. Perfect! Then I increased the hole size in several steps with different bits I have on hand, finishing the hole with a 0.311" reamer I bought specifically for this job.

Much to my delight, the AN5 bolts fit very nicely and smoothly into these holes. I'm glad I made the investment in a 0.311" reamer. Had I used a 5/16" reamer (0.3125") I'm sure the bolt would have had some slop in the hole. This one slid right in with no effort. I think the hole could have been even closer tolerance, but it does fit perfectly well with no slop. Edge distance turned out great! So a long day of much effort has culminated in the drilling of two holes. Amazing. I'm very happy to have this done, and very pleased with the results we got. The true test, of course, is to see if she flies straight and true. Am I worried? Uhhh... nope!

Well, with both holes drilled, it was time to relax and have a bit of fun. I put the seatbacks in, grabbed some cushions, and let Shannon sit in the pilots' seat first. I think the RV looks pretty good on him, don't you? Thanks again for all your help, Shannon!

Jamie came home from work, so I was able to coax her into coming out and joining us. We had a great time with some impromptu visitors who stopped by. It's funny, when you have an airplane sitting in the driveway in the middle of a residential neighborhood. You never know what will happen. Anyway, then it was her turn to climb in.

Following some previously established tradition (see last December 10th), we just had to crack open some champagne (thanks, Joe!), make some airplane noises, and toast our friends and family as we enjoy another great milestone along the way.

So what's next? Well, there are some additional tasks that go along with the wing mating that I didn't get to today. I need to drill the holes through the bottom center section skin through the wings and install a lot of nutplates. I need to fit the aileron pushrods to the control column, and the flap pushrods to the flap control weldment and enlarge the exit holes through the sides/bottoms of the fuselage. The inboard edges of the skins on the flaps will probably need a bit of final trimming to fit correctly. I need to install the forward brackets that connect the fuselage to the fuel tank brackets. I need to fit and install the fuel and vent lines that go from the side of the fuselage to the fuel tank, and I need to fit and drill the wing root fairings.

Fortunately, now that these critical rear spar holes have been drilled, these are all tasks that can be done with one wing on at a time. So there's no need to bring it all out in the driveway for each work session, set it all up, and take it all in for the night when I close up the shop. I measured carefully, and figured that I can put the fuselage sideways across the front of the shop, right inside the garage door, and extend one wing at a time back into the shop. I have plenty of room for that and it can be left on for however many days it will take me to complete these tasks for one wing. Then I can take that wing off, turn the fuselage around, and do it again for the other side. Such are the challenges that go with a somewhat smaller shop. At least it's doable, and after all, I can't complain. I'm not paying any hanger rent here at home! I want to get as much done at home as I possibly can.

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