Metalized Wing fuel tank cover

[6843]

Hi All, I have a '46 140 with metalized wings. Along with everyone else, I have no, and can find no, information on the STC used. I am in the process of replacing both fuel tanks (due to leaking). The left cover was attached with a combination of machine and PK screws. The right cover was attached with a combination of Cherrymax type and pop rivets. i was going to replace the screws found on the left, and use Cherrymax rivets on the right but Cherrymax rivets have been on backorder from Spruce for over 3 months now. My question is (1) how are the covers originally attached on a fabric wing? and (2) if you have a metalized wing, how are your covers attached?

On the left wing, the covers were attached with PK screws and tinnerman nuts on the ribs and machine screws on the spars. Someone in the past tapped the holes in the spar. I'm thinking about doing the same on the right but I can't help think that each thread tapped into the spar is a stress riser waiting to crack. Do you think my concern is valid?

Thanks for your collective thoughts,
Dave

[6643]

There are no covers on fabric wings. The fabric goes right up to the filler neck.

How does the plane get annualed with metal wings and no paperwork?

[bc12d]

I just this week found cherry max rivets at B&B aircraft supply at Oshkosh they had a whole assortment of sizes, you can look them up. Yes ACS is out.

[6843]

John,

A great question but as i understand it, people have been looking for metal wing conversion STC data for years with no results. I guess it's just accepted.

[6643]

The only way it could be accepted without an STC is if an FAA inspector signs off on it as a field approval. There has to be an approved 337 in the aircraft records for it to be legit. Is there any mention of the wings being metal in the log books? Any mention of fabric?

I assume you've requested the FAA records, or have them in hand, and there is no record of the wings having been metalized. Is there any mention of the wings ever having been replaced?

It wouldn't surprise me to find that it's been signed off year after year, but that's not the way it's supposed to work.

[dcannon]

My fuel tank covers are both attached with PK screws. Similar to you I have no technical data about my metalized wings.

Logbook entry in 1955 says "Wings metalized" in addition to a 100hr inspection entry. No other detail.

The accompanying 337 says "Fabric removed and 020 metal installed." Additionally, they provide the new weight and balance in a table. The aircraft gained 36 lbs, interestingly. But again, no technical details to share.

[6643]

The accompanying 337 says "Fabric removed and 020 metal installed." ... But again, no technical details to share.

Is your 337 signed off in block 3? If so, that means an FAA inspector approved it as a field approval. Otherwise, the 337 is supposed to (must) cite some other approved data, e.g. an STC. (Still, pretty sketchy! It wouldn't fly today!)

[6843]

dcannon, please share with me whether your tank cover slides under the "flange" where the fuselage top skin extends a bit outboard of the butt of the wing? And if it does, was the tank cover riveted to the end rib that serves to enclose the tank cavity? Mine was riveted and I had to remove the wing to get to the rivets to remove the tank cover. I'm trying to think of a way to engineer it so the wing doesn't have to come off to get to the tank. The "flange" will keep the tank cover from lifting in that area but the rivets are probably adding some strength vis-a-vis triangulating the ribs and spar.

Dave

[dcannon]

The accompanying 337 says "Fabric removed and 020 metal installed." ... But again, no technical details to share.

Is your 337 signed off in block 3? If so, that means an FAA inspector approved it as a field approval. Otherwise, the 337 is supposed to (must) cite some other approved data, e.g. an STC. (Still, pretty sketchy! It wouldn't fly today!)

Yes, under item 3 it is listed as a major repair. I would have assumed major alteration would have been more accurate. Nonetheless, CAA designee signed it off as approved for return to service in block 6. Block 7 accepted by the CAA aviation safety agent.

[dcannon]

dcannon, please share with me whether your tank cover slides under the "flange" where the fuselage top skin extends a bit outboard of the butt of the wing? And if it does, was the tank cover riveted to the end rib that serves to enclose the tank cavity? Mine was riveted and I had to remove the wing to get to the rivets to remove the tank cover. I'm trying to think of a way to engineer it so the wing doesn't have to come off to get to the tank. The "flange" will keep the tank cover from lifting in that area but the rivets are probably adding some strength vis-a-vis triangulating the ribs and spar.

Dave

I will get back to you when I go to the hangar. I have not had to remove it so I will need to take another look. Standby.