Hole fits in hybrid joints 1

[cires23]

Hi,
I need to install HST315 fastener in a hybrid joint. Per drawing the hole fit is Class II at composite skin (clearance) and Class IV (interference) in the metallic fitting.
If I need to install the 1st oversize at the joint, aircraft SRM does not stated the drilling fit, but to drill different diameter seems quite rare for maintainance. Per my understanding Class II for both strucures should be ok, not to force the composite. Could anyone help?

Thanks and regards,
BC

 

[WKTaylor]

cires23

Details missing.

1OS fastener HST415?

What metallic alloy? how thick?

What composite material? how thick?

Permanently assembled joint? just need to RR 1-fastener? or some? or all?

What drilling/reaming procedure intended? Dose the composite require special methods NOT-compatible with the metal alloy?

Which way does the hole 'get drilled OS': thru the metal-then-composite? Thru the composite-then-Metal?

What do You have to do to the hole wall in the composite? nothing? brush with laminating resin? sleeve it?



Regards, Wil Taylor

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[Stezza]

For our hybrid composite Aluminum structure we use a close tolerance fit for both parts. As you mention installing bolts in interference fit holes in the composite can lead to delaminations in the composite part and reduce the strength of the joint. For the metallic part if you did not have an interference fit you shouldn't have a static strength issue but you have lost the fatigue benefit from the interference fit. In a repair situation if you can find a different location on the aircraft that is more critical in fatigue that has a clearance fit hole then you may be able to justify the clearance fit based on this comparison to more critical fatigue structure. Otherwise you are left with a fatigue analysis to show it good or possibly more frequent inspections.