[Wes]

I just finished drilling all of the skins of the right wing to the wing skeleton and noticed afterwards that my hydraulic jack (which was used to support the center) apparently lost some pressure during the process. I now have a sag of about 3/16" at the center of the wing. Is this something I can recover from and move on, or will I have to rebuild the entire right wing? I'm not sure what structural implications this may have. Anyone's help would be greatly appreciated.

 

[Frank]

Mis-Drill

When you say all skins are you including the wing tank? If that was the case, nothing would mate at the edge skin joints unless you tapered the skins. Worse case scenario…buy new skins, re-level spar and drill new skins to leveled spar and ribs through existing spar/rib holes.
Never hurts to check with Van’s and get their take also.

Oh. It’s been my experience that many hydraulic bottle jacks may leak a little over time. I use acme thread screw (auto) jacks for that kind of work. Good luck.

 

[Rick RV-4]

Wing Sag

Wes,

I would think if you drilled everything this way, you should be just fine. The only drawbacks I can see are these:

(1) You might be able to see a slight curve when sighting down the leading or trailing edge after you complete the plane. Who cares? All of the older RVs have some slight mismatches, boo-boos, etc. I don't think you'd even notice it. 3/16" over a 10 foot wing is minimal.

(2) If the wing was not perpindicular when you drilled it (i.e., the ribs to the spars) were you able to keep the holes you drilled in the middle (or at least close) of the ribs? If so, I think you'd be good to go.

I agree with the previous post . . . if you drilled everything this way, you should be fine (just IMHO). I think even the tank could be re-fit if that was not on there when you drilled the rest of the wing. If I understand your dilemma correctly, you'd just have to trim a little bit from the skin off the leading edge outboard portion of the tank skin.

When you build your flap and aileron for this wing, just make sure you fit the gap between the two correctly - other wise you might have them spreading apart at the trailing edge (kind of hard to picture).

Hope this helps . . .

Rick

 

[Sid Lambert]

I had the same thing but noticed it just before drilling. I tossed the jack and made a support from threaded rod and a 6x6.

 

[Wes]

I want to thank everyone for their advice. I decided to just deal with the 3/16th inch sag in the wing. This required me to trim the main skins slightly to be ?square? with the wing. It also required me to trim the inboard aft edge of the fuel tank to allow the leading edge to line up correctly. However, when I did this, I encountered another problem since I am installing an inverted fuel system with the fuel sender mounted on the aft wall of the fuel tank. Trimming the tank skin reduced the clearance between the main wing spar and the fuel tank aft wall to a point that it there would be the possibility of the fuel quantity sender contacting the spar. Not wanting to give up the inverted capability of the tank, and not wanting to spend hundreds of dollars on capacitive fuel quantity senders, I had to find a way to mount my fuel quantity sender. The solution I came up with was to recess it into the tank 1/4 inch. I did this by cutting out two 1/8 inch thick rings and mounted them atop one another to the inside of the rear tank wall. On the forward side of these two rings, a .040 plate of the same diameter was mounted. This plate had the center cut out to match the mounting hole required for the sender. This essentially created a socket that the fuel quantity sender fit in, allowing it to be recessed far enough to avoid any potential contact with the spar. I just have to ensure that when I rivet it all together I use plenty of Pro-Seal to prevent leaks. Now with the tank trimmed and mounted, the leading edge lines up almost perfectly, and the chord line is perfect.
The next issue I have to deal with is the position of the fuel tank mounting bracket (T-405) on forward portion of the inboard tank rib. Since the tank skin had to be trimmed by about 3/16 inch to line up the leading edge appropriately, it is now ?short? relative to the position it would?ve been in had I caught the sag problem in time. The solution seems simple enough; just ensure the bracket is fabricated to fit 3/16th inch closer to the leading edge. Not difficult, but just another thing to keep in mind to make up for my mistake. I guess the lesson to all would-be builders is to double and triple check the alignment of the wing while you are drilling the skins, and never trust a hydraulic jack to maintain it?s pressure the entire time. Even a little mistake can have third and fourth order effects later in the construction process.