Got another stiffener angle from Vans and remade the E720 L stiffener than became damaged in my previous attempt to get them back riveted to the left elevator skin. I have also realized that I have not posted any pics in several posts so it's time to change that. So bear with me while I take a short trip down the past.
Here is a shot of the measurement for the E720 L stiffener where Van's wants you shorten the back end by a specified amount from the second to the last rivet. In this case the measurement is 2 inches from the hole.
And now for something I just could not pass up, even though it is not exactly airplane related. Back up on the mountain for some deer hunting. My son Adam was able to hunt this year so we both went up the mountain to see what we could see. So with that in mind, I ask you, what is wrong with this picture?!
And here is one with the skin being dimpled using the C frame. No extra holes poked in the left skin like I did on the right elevator skin - thank goodness for that!
All the stiffener holes dimpled. One thing about this process that I do not like. Since you don't really get to match drill any of the other holes for the attach points for the spars and ribs until after you bend the trailing edge of the skin, you are forced to prime areas with holes that are both undrilled to final size and that have not been dimpleed yet. Some have questioned the integrity of the primer if you primer first and dimple later, but I ahve not seen any appreciable flaking or detatchment of the primer from the area where the dimple was formed, so I guess it's not such a big deal.
Napa 7220 self etching primer in a can being applied to the stiffeners and the trim server mounting access plate, etc. My little chicken wire paint box works quite well for the smaller parts.
Inside left elevator all scuffed up with scotch brite pad (maroon) and cleaned with microfiber cloth and acetone. Ready for primer.
Too bad halloween is over! Warning! The following pic is very grotesque and not for the faint of heart! You better watch out if you get a can of primer in my hands - lethal and extremely dangerous for sure!
On a more serious note - please, if you use this stuff, remember that it contains ACID that EATS METAL. This is about the last stuff you want to be breathing, so the mask is an absolute MUST, even though the primer comes in a rattle can that looks like any other spray paint in a can. Here is the skin after priming. I really like the way way this stuff lays down.
Tape applied to the rivets for back riveting the trim access plate and the the stiffeners.
The trim access backing plate after back riveting. Interesting to me that the side next to the forward spar has NO rivets to hold it on the skin. I think the curved flange sits up against the back of the spar but not 100% sure about that. The other holes that you see are for the nut plates that will secure the cover. Some additional holes will drilled as well to accept the rivets for the two brackets that will hold the trim servo in place.
Stiffeners on the bottom back riveted with no problems.
And then the problem occured. I was on the last stiffener E720L. Although it is hard to see in the pic, the area where the primer is scratched off is the side of the dimple that became completely caved in. Even worse is that it happened to the very last hole in the stiffener, closest to the trailing edge of the skin, where a lot of stress can occur. Not a great place to have a potential defective part or assembly. How this happened is still a huge mystery to me. The only thing I can figure is that I did not adequately hold the skin back far enough to clear the rivet gun set retaining spring, and the back rivet set may have slipped to the side and started driving the rivet at an angle. After two attempts to drill out and reset this rivet as per my previous post comments, the stiffener was damaged beyond usefulness.
The last two pics are the result of many steps to fix the problems that this caused:
- fabricating a new stiffener to replace the damaged one
- setting the skin back on my close quarter dimple tool to try to reshape the dimple in the skin so that the 1097 4-3.5 Oops rivet head would sit more flush after drilling the hole to 1/8 inch to accept the wider diameter oops rivet
- using a 1/8 inch drill bit and the same sized hole in the skin as a guide to mark the surface of the center of the last hole in the stiffener. Remember that Vans makes you drill this final hole in it's entirety. It is not predrilled like all the other holes, so you have to drill this hole out all the way.
- drilled the hole from the previous mark using a #40 drill bit first, so that the correct 3/32 dimple could be formed arund the hole
- dimpled all the stiffener holes with 3/32 dimples
- drilled the last hole in the stiffener a bit larger to 1/8 inch using a #30 drill bit so that the oops rivet would fit through the holes in both the skin and stiffener
- primed the stiffener
- inserted and taped the rivets into the skin, ensuring that the 1097 AN4-3.5 rivet was in the last hole, and the normal AN426AD3-3.5 rivets were in all the other holes
- Got my kid outside to hold the skin back so I could focus entirely on holding the back rivet set steady and the stiffener firmly to the skin
- Successfully back riveted set all the rivets on this last stiffener.
The pic above shows the oops rivet sitting nice adn flush on the skin. HEad is the same as the other rivets, but the shaft is thicker. WHEW, am I glad that worked out.
So I have officially set my very first oops rivet. An interesting thing about these rivets is that they have a slightly raised center section on the manfactured head side that you don't see on the regular AN426 flush rivets. This initially caused me to think that the rivet was going to sit a bit proud of the skin, but in reality it sits just as flush as all the other ones. Another concern was proper rivet length. I was not sure that using a 1/8 inch thick rivet of the same length as the AN426 flush rivets would result in the proper shop head dimensions, but this seemed to work out just fine as well. Checked it on my rivet gauge and everything seems to measure up correctly. I am still a bit concerned about clearance with the rivet head on the opposite side of the skin once the trailing edge is bent, but I'll worry about that later. For now I am just glad that I got the stiffener replaced and riveted to the skin correctly.
There - all caught up now! Next is bending the trailing edge of the skin and trimming off those pesky tabs.
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