Flap spar countersinking

Hey guys,

I'm working on the flaps, countersinking the flap spar to accept the flap skin dimples, using the hinge to back up the countersink pilot as per the instructions.

The issue I'm having is - In order for the countersink to be anywhere near deep enough to accept the skin dimples, I'm ending up with a slightly knife edged countersink on the spar. The spar is sandwiched between the skin and the hinge, so I suspect it isn't an issue, but I'm interested to hear about your experiences.

Knife edged countersinks feature quite a lot on our aircraft (wing spar platenuts come to mind....) but in this case carefully dimpling the hinge, skin and spar instead of countersinking may be a better option?

I'd trust Van's and carry on with countersinking per the instructions, dimpling could result in problems with distortion of the hinge or spar. I seem to remember the spar is fairly thick material?

-goose said:

I'd trust Van's and carry on with countersinking per the instructions, dimpling could result in problems with distortion of the hinge or spar. I seem to remember the spar is fairly thick material?

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I believe the problem is with the soft hinge material distorting when it is dimpled. Try it on a scrap piece.

Dumpling flap spar

If you dimple the flap spar, you will have to countersink the hinge and probably end up with knife edge holes in the hinge which may be a bigger issue. Dimpling a hinge causes distortion.