We got all of the prepared parts primed today. The final finish isn’t anywhere near what I am aiming for, but it is fine for a light primer coat. I think I probably didn’t apply enough air pressure at the gun. I’ll do some tests before we take the paint booth down this week.
Ugh… That was a long day of acid etching and alodining in preparation of primer tomorrow. Maybe I should do smaller batches of parts next time. There is a picture of the “pile of parts” that I’ve been talking about (minus the skins). There were a few small glitches in preparation, but nothing major. Primer is next.
I also got the elevator counterbalance skins and ribs aligned, match drilled, and deburred today. The instructions sure are getting sparse. Much plans interpretation is required at this point. I have a lot of assembly and drilling to do for the elevators that isn’t even mentioned in the instructions. I guess this is preparation for the wing kit. Oh yeah, I ordered the wing kit yesterday! We should see the parts for the wings in two months!
It was a full day of match drilling the rudder skins to the skeleton, deburring all the holes and edges. I also machine countersunk the trailing edge wedge. That wasn’t fun at all. I don’t have any words of wisdom on that. Once again we just have a pile of parts.
I finally have progress to show today. I decided that I must prime and rivet the rudder stiffeners to the skins before I could continue with rudder construction. The stiffeners are critical to the shape of the rudder skins and I don’t think the match drilling of the rest of the skeleton would come out right if they were just clecoed together.
So, I scuffed the (fluted) stiffeners with a scotchbrite pad, scuffed the skin insides with a nice new Sioux orbital sander with a scotchbrite pad on it. The sander worked great with the scotchbrite for the skins. Note that I scuffed the skins before I dimpled them. I can see using this method for final paint on external surfaces. Then I washed the parts with soap and water and rinsed. Then they got scrubbed with MEK for final cleanup before priming. I primed the parts with Sherwin Williams 988 in a spray can. I decided to do this for these parts because I’m not quite ready to do my big batch of primer. So shooting primer from a spray can is only for when I have to have something primed quick and it is only a few parts.
After priming, I loaded up the skins with rivets and rivet tape to hold them in place, flipped them over on the back rivet table, and back riveted the stiffeners on. Believe it or not, these are the first rivets that I have driven on the plane. Of course I practiced on something else. I’ll repeat the general consensus: A monkey could produce perfect flush rivets with this method. They all came out just fine. That was a lot of fun.
With the skin stiffeners primed and attached, I clecoed the skins to the skeleton that I had previously constructed. This is where we pickup next time. Next is to match drill the skins to the skeleton, fit and match drill the trailing edge wedge, and machine countersink it (not looking forward to that).
Ok, here is an interesting process that I haven’t been able to find any reference to; I noticed that the manufacturing process to bend the rudder stiffener stock leaves the pieces of angle stock a bit warped or bowed in both directions (not quite flat, not quite straight). Then, after dimpling the holes in them, the bow (flatness against the skin) in the stiffener is even worse. Still not catastrophic, but I got to thinking about the physics of a rivet in a hole in a part that is in tension… All I saw (I do most of my heavy thinking in my sleep) was eventual failure. I sent a quick message to Vans (content below), and based on the response, spent an hour or so fluting both surfaces of the stiffeners to make them straight and flat against the skin. I am much happier that they are now flat against the skin and the holes line up perfectly (everything is relative) straight. I haven’t been able to find a single previous builder or instructional note describing the need to do all this, but I am very happy with the results. I have however seen / read about other completed RVs with large pervasive cracks forming around the ends of the skin/stiffener joints. It seems that many people use proseal at this location to try to help this. I’ll probably do the same. But, could some of these failures be occurring because of builders installing stiffeners that aren’t straight and flat? I am thinking maybe so. I would love to hear from somebody that did this operation on their rib or elevator stiffeners.
*** message to Vans builder support ***
Builder: 91070
Rudder Stiffeners slightly bowed.
I find that my rudder stiffeners were slightly bowed in both directions. This bow increased a little after dimpling. Is it appropriate to very slightly flute the stiffeners in either direction to make them more flat and/or straight? It seems that if the stiffener isn’t perfectly flat on the skin, the skin will either end up with a slight curve in it, or some stress in the rivets if they are holding things straight in tension. Or, maybe it wouldn’t be a good idea to flute at all on the stiffener surface that is on the skin (to straighten the holes), but ok to flute the perpendicular part of the stiffener in order to make it sit flat on the skin?
The bow in the stiffeners really aren’t all that bad. It would probably all work out if I didn’t touch them, but it sure would make me feel better to make these sit flat and straight.
Any suggestions?
*** Vans builder support response ***
Joe,
Do what ever is necessary to straighten the stiffeners to your
satisfaction. The slight curve is a result of the manufacturing
process and can’t be helped.
***