Structural repair question?

[TheDon502]

Is it bad practice to have a different number of fasteners on each side of a repair? For example a stringer repair, can you have 3 rivets on the forward side and 2 on the aft side of the discrepancy?

 

[berkshire]

It begs the question, if the two rivets are sufficient on the aft side, why would you need three on the forward side?
B.E.

 

[SAITAETGrad]

There are a few good reasons to extend assymetrically due to the existing geometry. You may be on or just short of another change in cross-section so you extend to prevent a stress concentration due to stackup. You may also extend due to being in the shadow of an existing return lip/flange where installation quality may be comprimised due to the confined space. Extending one row beyond the shadow allows a cleaner instalaltion. A skin repair on a Boeing that would otherwise end one row past the inverted hat stringer line is a good example of this.

 

[rb1957]

sure you can, obviously the two rivets are more critical than the three.

fuselage repair ? pressurised or non- ? damage repair or reinforcement (like for an antenna install) ?

 

[737eng]

If the repair is statically acceptable and the durability is adequate, then it is OK. I usually try to get a minimum of three rows for fastener load distribution. However, compliance to the FARs is what you are after, as long as you check the durability of the two rows and implement supplemental inspections as necessary, you are good.

One issue is that you may only be adding two rows due to interference with other structure. Possibly using two rows of larger dia or hi-loks in lieu of rivets, etc.... if this is the case then make sure you don't superimpose stress concentrations. Ending two parts in close vicinity can really emphasis the bending at the end rows. If you only are putting two rows because the part ends, just cut the whole section out and only have one splice.

 

[TheDon502]

thanks for the info