Where to countersink the F-718 Longerons

[hk1232]

Trying to verify the dimple/countersink treatment of the F-718 longerons. I'd love a more explicit call out given that I rally don't want to apply the wrong treatment!

From what I can tell in the manual, the longerons get:
1. Countersunk in a half dozen locations along the aft section in the "hole between holes"
2. Countersunk and riveted towards the rear of the after section

And I thought I read that the longeron has no specific treatment elsewhere. Instead, we do a countersink of the aft and forward side skins since everywhere else there is a third layer that will apply over these (e.g. the aft top skin which gets dimpled).

Is this accurate? Anything I should be aware of as I countersink my longeron and dimple my side skins?

 

[skelrad]

If I'm following what you're asking - Yes, you do countersink and rivet those "hole between holes" to help hold everything in place prior to putting the top skins on, but all of the other holes on the longeron still need to be countersunk. You just don't put rivets in them until you have the top skin in place as well. Both the lower and top skins are dimpled to nest in the longeron countersink.

 

[hk1232]

Ok if that's true then this is easy - all longeron holes get countersunk, and matching side / top skin holes get dimpled.

I read through the directions again and didn't find the call-out I recalled that the construction should be:

• dimple top skin
• countersink side skin (which likely has some impact on the underlying longeron given thickness)

Maybe it was a general note from section 5 of the manual that I saw. I do like the idea of being able to match drill the top skins against a standard hole vs. something that is already dimpled/countersunk though. Makes for a cleaner target.

 

[dwollen89]

Not sure if the 9A is the same as the 7A, but there are a few holes on each side on the aft end that don’t get countersunk and the skin doesn’t get dimpled. They are for the horizontal stab fairing.

 

[skelrad]

I read through the directions again and didn't find the call-out I recalled that the construction should be:

• dimple top skin
• countersink side skin (which likely has some impact on the underlying longeron given thickness)

My brain tends to forget stuff as soon as I've done it and moved on, so it's always possible I'm misremembering. I don't recall any instructions to countersink side skins anywhere though. Maybe someone with a better memory will chime in. The only instruction I recall for countersinking a skin was for the forward bottom skin where it attaches to the spar carrythrough (which I chose not to do - I had clearance for the gear tower and dimpled everything instead of countersinking).