Finishing Kit

April 16-17, 2011

Fixing a Problem with my Wings - 3.5 hrs.

Okay, I know, this is totally unrelated to my Finishing Kit. So what's going on here? Well, let me explain. Sometimes you have to take advantage of opportunities when they come up.

A while back while I was reading the VAF forums online, a fellow builder down in Texas described a problem he had with the trailing edges of his wings. The top skins, as they extended beyond the rear wing spar above the flaps, had a gap between the skin and the flap. On most RV's that I've seen, the builder has installed some special tape on the leading edges of the flaps. This is because there is a slight rubbing of the flap's leading edge against the trailing edge of the wing as the flaps are raised and lowered, and the tape is installed to reduce any friction or scraping. This implies that the gap between the top skin on the wing and the flap is very small, or non-existent. As I finished my wings and installed my flaps, I realized that in my case, I had a significant gap there. It was roughly 1/8" to 3/16" in size. The red arrows in the photo below show what I'm talking about, although it's hard to see in this picture.

The problem with this is that the profile of the wings' curvature isn't right. There was a "ski-jump" or a raising of the trailing edge of the wing. It was almost as though the flange on the rear wing spar hadn't been bent quite enough, leaving the skin raised up on the trailing edge instead of lying nice and flat. When I laid a straight-edge across the back end of the wing, this became very visible. It was almost as though I had "spoilers" instead of a nice smooth surface profile. When I was at Vans picking up my Finish Kit, I looked at the company's RV-7A in the hanger and examined their wings very carefully. They had a nice flat trailing edge without the problem I was seeing on my wings.

I had a similar problem with the trailing edges of my horizontal stabilizer. If you have been following my build log, you may recall that I documented and took care of the problem back on June 5, 2010. The problem was solved by applying some significant force with my seamer pliers, bending the rear spar flange ever so slightly until the skin was nice and flat. It's the same thing now that I'm talking about on my wings. I know this might sound a bit nitpicky. But I keep thinking of high-speed airflow over these surfaces, and how a little tiny trim tab on the elevator alters the flight of the whole airplane. This is a much more significant surface area than a trim tab. I have to wonder why some builders have a "heavy wing" when they are in the initial stages of flight-testing a new airplane. Could this be the problem? If nothing else, something like this can cause a "bump" in the airflow. That can create unwanted drag. So I have been looking for a way to fix it.

The problem with trying to fix this with the wings is that my seamer pliers aren't big enough. They don't have enough reach, or enough leverage. I had given this a lot of thought over the last couple of years, wondering how and when I might be able to attempt to fix it. Well, once again the VansAirForce forums and some very good friends have come to the rescue! I'm not the only one aware of this. My friend Mike Cencula had this problem, too, and he described a tool he made to fix his wings. He very generously offered to loan the tool to fellow builders if they would pay the shipping cost. The guy down in Texas, who also had this problem, asked if he could borrow the tool. So I jumped in and asked if I could be next in line after him. So when he was finished with the tool a week or so later, he shipped it to me! Here it is, on my bench:

This tool is awesome! It's very simple, but cleverly made. Two heavy steel bars are held together by the threaded bolt in the middle. The distance between the bolt and the right side is the reach that's needed for this job. Notice on the right end of the lower piece, a neat little notch has been machined into the bar. This is cleverly put in just the right place for clearance for the buck tails on the line of rivets under the wing skin, so you don't damage the rivets while using the tool. Finally, note the angle that the bar has been cut off at the end. This is important during use, too. Obviously a lot of thought and care has gone into this item, along with machining skills and equipment that I don't have. There's no way I could have come up with this on my own. The blue tape has been applied to avoid scratching the alclad surface of the wing skins. I was very impressed! Thanks, Mike!

Here's what the tool looks like when you put it together for use. It's basically a big, heavy, powerful clamp and lever.

And here it is, clamped in place on the wing after the flap has been removed. I didn't even have to take my wings out of the storage cradle.

The strategy was simple. Clamp it down and tighten the bolt, then pull it hard toward me. Loosen it up a bit, move it over a bit, and repeat. In a couple hours I had both wings fixed, verified by a straightedge and putting the flaps back on to check the clearance. They just barely touch now. The gap has been closed.

Over and over again, I've been very impressed by the quality of the people you meet in this wonderful hobby, and the generous offers made by fellow builders who only want to help you. Thanks so much, Mike, for making this tool. And especially for being so generous to loan it to us!! And thanks to the online forums! What an incredible resource we have. I'm very grateful.

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