Countersinking side skins for F-425 top rear skin?
 

Previous builder has riveted the fuselage side skins to the longerons and left holes open for rivets common to top and side skins. However, longerons are not countersunk nor are the side skins dimpled.

Plans call for AD4- rivets. The 0.025 F-425 top skin will have to be dimpled. Countersinking the 0.032 side skins for AD4- (1/8") flush rivets will go well beyond the allowed countersinking for a 0.032 skin.

Manual does say that countersink of skin held between sheets (in this case between dimpled top skin and partly countersunk 1/8" longeron) is OK. So I shouldn't worry and just go ahead and countersink for AD4- flush rivets?

I'm thinking of simply doubling number of rivets and using AD3- instead of AD4-. Would two AD3- rivets be as strong as one AD4- rivet?

Finn

It's not that simple. Call vans or a structural engineer. Vans will be less expensive. What about using NAS1097 rivets what everyone mistakingly calls oops rivets. Anyway call vans.
By the way the 1097 rivet is commonly used in Boeing skins, it's the big head ones that are for screwups.

You mean the small head ones?

OK, I sent an e-mail to Vans.

Finn

Do what Mel says?
 

No answer from Vans yet.

So I did a more thorough search and came across this thread:
http://www.vansairforce.com/communit...sink+longerons

Mel replied:
"Since the side skin will be "sandwiched" between the top skin and the longeron, it is acceptable to countersink the side skin and longeron together. Then dimple the top skin."

So I see my options as:
1) Countersink the side skin (and longeron) to accept top skin dimpled for AD4-6 flush rivets, or
2) Use Oops rivets (1/8" rivets with 3/32" flat rivet heads)

In any case I think I'll add doubling AD3-6 flush rivets with side skin countersunk for AD3- flush rivets.

Finn

Pictures???

A common approved mod was to substitute -3 rivets on 1" spacing in place of the -4 rivets on 2" spacing. Dimpled the outer skin into countersink below.

Oh, good. I do intend to add AD3- flush rivets in between original 2" spaced holes, countersinking side skins.

So now the question would be:
Would 1/8" oops rivets overall be stronger (side and top skins, shear and tension) than countersinking side skins for AD4- flush rivets?

(I had countersunk original holes in side skins for AD3- flush rivets. Then I looked at the plans and saw AD4-6 flush are specified. Existing holes are slightly bigger than 3/32" but would probably fill out with AD3- rivets. But now I feel I should drill them up to 1/8" and either countersink further to AD4- flush or use 1/8" oops rivets.)

Countersinking for AD4- flush would enlarge original holes in side skins. However those holes would be filled with the dimpled top skin, being sandwiched between longerons and top skin. I'd have to check edge distance for those larger holes in side skins, but think they'll be OK.

On the other hand, oops rivets next to AD3- rivets would just look like a line of AD3- rivets with 1" spacing, perhaps looking better than alternating AD4- and AD3- flush rivets.

Sorry for getting so verbose.

Finn