[aarvig]

I am deburring the rear wing spar doublers W907B and C. These are the thick doublers near the root of the rear wing spar. After deburring to get rid of the nicks and roughness of the factory cut edge (using a file and 400 grit sandpaper) the edge distance along the entire top row of rivets on both 907B and C is shy by 1/32nd of an inch.
I spoke to Vans this morning and I was told it was not going to be a problem HOWEVER, I don't feel comfortable with this answer being these are the rear spar doublers. There is no way to deburr these doublers without coming up 1/32nd short. Is this really not a problem, am I being to worried about standards? Or should I replace the parts? Again, replacing them may put me right back where I started due to the deburring required.

 

[David Paule]

While I can't comment about this particular issue, I can comment about the topic in general.

There are several ways for a designer to establish the minimum edge distance. The easiest is to simply pull some numbers from MIL-HDBK-5 or its later version. This is sort of a broad-brush approach and works pretty well for a variety of situations.

The next one is to go into some tables that predict the strength of the hole or the surrounding material and look at the specific geometry involved. This can be somewhat time-consuming but is pretty effective.

Finally, the designer can make a finite element model of that specific part, and carefully account for the part geometry, fastener preload, thermal expansion effects, the axial pressure from the fastener(s), the neutral axis locations of them, other fasteners in the pattern and so on. This is fairly time-consuming to get right and involves a lot of person/computer interaction.

The thing is that these different methods of calculation give Van's the knowledge to offer a solution to a specific problem. Also, they know the actual load on a part, which the easier cookbook approaches don't take into consideration. So if they say that a part is okay in a particular case, they are basing that judgement on a lot more than a simple mechanic's rule.

Rest easy, and follow their guidance.

Dave
An old aerospace stress analyst

 

[VNS]

Snap!
Just did mine last night - sorry to talk in metric but we are like that in New Zealand.
I have 4.9mm from the edge of the 3mm hole which is fine. Check how much you are removing. You only need to deburr not grind smooth

 

[Andrew M]

edge distance

Minimum edge distance is also known as tear out distance. The aft spar is primarily in compression (as in anti drag) where the main spar carries the lifting load. The top row of rivets you describe being below minimum recommended edge distance does't really give me any heart burn because it's not loaded in a direction that will tear out those fasteners.