Inspection Holes 2

[6319]

I looked at a fabric wing Cessna 140 recently and noticed there were 9 inspection holes in each wing. My metallized C-120 wing has only 4 holes per wing, all aft of the rear spar. Is there a structural reason why Skycraft only put in 4 aft inspection holes?

[V529]

I'm not certain, I haven't seen the Skycraft STC. There were numerous "metalized" wing solutions back in the day, and I don't believe any of them were the same. Unfortunately, unless you have the drawings you won't know exactly how it's supposed to look. And more importantly to answer your question, even if you did have the STC in your hands it may not address specifically the "why" on the panels, other than "they have to be there". Most likely to offer access to some points on the wing, either the STC originator or the approving FAA division thought important.

Most of the metal wing aircraft I've seen had zero "inspection" holes such as you would find on a fabric wing, so yours is a little unique in that regard. "Birtcraft, & Mowatt" were two of the bigger names that offered metal solutions and neither of them had a panel other than the large square panel at the rear strut, such as you would find on any 'V' Strut 120/140.

[8233]

I'm not certain, I haven't seen the Skycraft STC. There were numerous "metalized" wing solutions back in the day, and I don't believe any of them were the same. Unfortunately, unless you have the drawings you won't know exactly how it's supposed to look. And more importantly to answer your question, even if you did have the STC in your hands it may not address specifically the "why" on the panels, other than "they have to be there". Most likely to offer access to some points on the wing, either the STC originator or the approving FAA division thought important.

Most of the metal wing aircraft I've seen had zero "inspection" holes such as you would find on a fabric wing, so yours is a little unique in that regard. "Birtcraft, & Mowatt" were two of the bigger names that offered metal solutions and neither of them had a panel other than the large square panel at the rear strut, such as you would find on any 'V' Strut 120/140.

I have the Skycraft STC on my 120 and have 4 round inspection holes per wing plus the the panel at the strut that you reference.

[6319]

Thanks guys, I'm in Canada and under the Owner Maintenance Category ,similar to your Experimental category. My idea is to put 4 more inspection holes directly ahead of the 4 that are there now, same bay ,aft of the front spar. Like they are on the fabric wing 140. STCs and 337s aside would there be a "mechanical" problem doing this?

[6643]

Why put them in the same bay? I'd think you'd want to see things you cannot already see from the existing holes.

[6319]

I can see the complete length of the rear spar with the 4 in place. Will be the same for the fwd spar with another 4. The lightening holes allow for a good view, however the spar blocks forward vision.The fabric winged 140 I saw was like that, symmetrical I guess you would call it.

[6643]

Ah! The existing holes are aft of of the rear spar. I would not call that the same bay. I thought you meant they were forward of the rear spar, in which case all you have to do is turn yourself around...

[6319]

Sorry but we seem to be going in circles here. Not worried about bays, I know where I want to to put the holes. Just asking if anyone has ever added more inspection holes to a metalized wing, or if there is a reason why they haven't. No answers forthcoming so far on this which seems to be a fairly basic question.

[6643]

I can't be of too much help, but, in general, holes on the under side of the wing, especially aft of the main spar, do not affect the aerodynamics of the wing. They shouldn't have any structural effect, either,

[6319]

Ok, Thanks. I couldn't see a problem but wanted to check to see if anyone out there has. If I decide to go with more holes will post a picture or two.