Vans say replace main spar

[rvbuilder2002]

Originally Posted by BillL

Not arguing with the result, just trying understand the "why". So, I assume the thickness of this flange is insufficient to simply step up to the next size rivet due to the knife edge at the bottom of the countersink affecting the structural integrity of this rivet (these rivets) joint? I am also assuming that the nesting nature of the countersink gives this joint its significant shear strength.

Thanks,

The additional shear strength resulting from a dimpled joint is not relied upon for in the engineering (just taken as extra) but if a skin dimple doesn't fit a countersink tightly, it will have a lower strength than if it was a joint with just a plain AN470 rivet.
The next larger rivet would start getting close to knifing the edge, and it would be breaking the minimum edge distance rule on the wing skins by about .015"

[Norman CYYJ]

Why phone Vans again? RVbuilder2002 has told you why you should not consider using the damaged spar. He knows what he talking about.

[N427EF]

Yes I have a dimpled test piece which nests nicely into the countersink with no play.

Maybe all this is based on miscommunications.

I am absolutely not saying that you should not follow Van's advise.
But $1600 is worth double checking previous communications.

[Mike S]

Originally Posted by rvbuilder2002

the skin dimples wouldn't fit tightly within the countersinks. There would be clearance that would allow lateral movement of the dimple within the countersink.

As I read the above, the area where the problem would occur is hidden from view--------so there would be no visible warning of possible failure.

The lesson to be learned is to set up the microstop in some scrap aluminum before hacking up the expensive parts.

[miko38]

I'm not sure I understand, if you fit the skin over the countersink and there is no play, and the rivit fits in the skin (because it was dimpled to fit that rivit) , and rivets expand to fill voids, where is the failure point?
Still $1600.00 in the overall sceme of everything is not to bad.
Mike

[lr172]

Originally Posted by rvbuilder2002

The additional shear strength resulting from a dimpled joint is not relied upon for in the engineering (just taken as extra) but if a skin dimple doesn't fit a countersink tightly, it will have a lower strength than if it was a joint with just a plain AN470 rivet.
The next larger rivet would start getting close to knifing the edge, and it would be breaking the minimum edge distance rule on the wing skins by about .015"

Good engineering details here. I still wonder how if the dimpled sheet is a tight fit, how could a smaller countersink be correct? Won't the dimpled sheet ride high? I have been countersinking until the the dimple goes in far enough that the sheet and structure mate flat together.

I would still put some playdoh or clay in the countersink, place the dimpled scrap with a rivet and hit it lightly with the rivet gun or light hammer. You will then know what type of gap you are dealing with.

EDIT: Disregard. I just ran a quick test on how I have been doing it and find that I have tight fitting sheets with .008" head depth. That left me a countersink diameter of .200" I don't think that the OP's fittings can be tight with a hole diameter of .230". That would leave the outer hole diameter around .050" bigger than spec.

Larry

[skylor]

Originally Posted by Vbug

Thanks for the responses. Yes the dimpled leading and main skins are riveted to the spar flange. The countersinks are primed with a qtip that's why the look so bad but are indeed uniform and smooth. I inserted a rivet to show depth.
Yes I have a dimpled test piece which nests nicely into the countersink with no play.
I am going to call tech support just to confirm the understanding of the issue since communication has been completely via email.
New spar is $1625. Its not the money just can't believe what I did. I have built a lot of things in my life and never destroyed anything in the process.
Like they say if your gonna be dumb you gotta be tough!

But the real question is, is there no play in the un-primed holes, or is the primer itself masking a sloppy fit of the dimpled test piece?

Skylor
RV-8, Flying

[az_gila]

Originally Posted by skylor

But the real question is, is there no play in the un-primed holes, or is the primer itself masking a sloppy fit of the dimpled test piece?

Skylor
RV-8, Flying

Or is it simply the radius of the back side of the dimple sitting on the sharp edge of the countersink?

[miko38]

If the fit is that critical, and you over countersink by .003 inches wouldn't you be able to add a piece of .003 aluminum to the top of the spar. Match hole drill it, dimple it, and it should be a perfect fit. .003 is less then the thickness of a piece of typing paper.
If vans says to replace the spar I would without any doubt replace the spar. It would make me sleep better at night.

Mike