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I'm looking for pictures/examples of how the upper wing skin fits around the fuel filler neck on some other airplanes with metalized wings. My '46 was metalized with the Ruleto design and I have separate screw-fastened rectangular cover skins (.020" 2024-T3 Alclad) over the fuel tank bays. My fuel caps have never played nicely with the skins as they seem to sit below flush by 1/8" to 1/4". We found some cracks through the old skins during the annual which finally convinced me to fabricate new cover skins. My A&P and I have some ideas for just beveling the edge of the hole for the filler neck on the new skins down just enough to clear the caps, but I'd like to see what this area looks like on some other airplanes before we commit to anything. Thanks!
Bill
Left wing tank cover.jpg (81.01 KiB) Viewed 388 times
Consider that the problem is not the wing skin, but rather the tank, and particularly the neck. I know of a fabric wing with a similar problem. The A&P took a small ball peen hammer and worked the head into the neck of the tank, and pulled the neck up about half an inch.
Thanks John, that's a good point to consider. The forward edges of both caps are more underflush than the aft edges. Maybe they've been yanked forward and down over years of people not being careful to support the fuel nozzle?
I'll see what my A&P is comfortable with on attempting to bring them back up. I just got done reading the thread in here about the odd-ball half weld/half braze joint between the aluminum tank and the steel neck and don't want to to anything to damage that. I've got the cover skin off now and the tank surface doesn't look particularly deformed, but I suppose it wouldn't take much.
Assuming the underflush issue is a tank problem, I'm still interested in seeing how the skin works around the filler. Looking for how much clearance is typical and/or if other airplanes have seals of some kind in there.
With the cover off, you should consider removing the tank and inspecting the "rails" that the tank is strapped to. IIRC the OEM had a felt material under the tank which may have been replaced by a different material, as John C. suggest, picking up on the tank may reveal some "loseness", suggesting the tank has sunk. Also, check the cushion material, others, over the years have discovered tank corrosion due to felt becoming contaminated in salty/coastal enviroments. 2.5c
I got the fuel tank cover skin removed on the left wing, and found some things. My IA and I are surprised and concerned with the holes that were drilled and tapped through the spar caps (both front and rear) for the screws which hold the skins in place. They appear to have been threaded for #8 machine screws which were at some later date replaced with sheet metal screws presumably because the original threads stripped out. Needless to say, not what I was hoping to find. Questions going forward:
- Did the Ruleto metalization drawing package specify drilling and tapping holes through the spar caps for this tank bay cover skin?
- If so, did they define maximum permissible hole diameters along with minimum distance between holes?
Assuming the holes can be there in the first place, the preferred solution is to drill out each hole just enough to remove the threads and reduce points for cracks to start. We can then make a separate nutplate strip that would nestle in underneath the spar cap once new skin screws are installed without doing any further damage. Circled holes in the picture below are the one's we're concerned about.
A huge thank you to Victor Grahn for his help in digging up approved data that got me a path forward with my IA. Once again, this association proves itself to be absolutely essential for keeping these airplanes safely (and legaly) in the air.
