Rivet questions

[DesertBearhawk]

Guys, About to start riveting my flap together and have a couple of questions: As the nose skin to nose ribs are blind dome head rivets is there any reason I can't use 470's on the skin to spar flange area and not dimple them? I test dimpled some holes for #3 rivets and find that the "hole" grows significantly after dimpling resulting some sloppiness around the shank of the rivet. I even tried drilling the holes with a #41 drill...any thoughts on how to improve this condition? Thanks for your replies guys!

[jaredyates]

Here are a few thoughts. I found that the fabric doesn't lay down very well around 470 rivet heads, so that may be worth considering. If I remember correctly, aren't the spar rivets in the breeze when the flaps are up, while most of the nose rivets are not? Also, I think the dimpled holes provide more strength in shear, making me think this would be a change you would want to clear with Bob. The rivets should expand to fill the sloppiness when you squeeze them, so I wouldn't let that concern you.

[marcusofcotton]

Dave, I seem to recall using a 3/32 drill may have resulted in better fitting after dimpling, perhaps worth a try.

Mark J

[DesertBearhawk]

I'll be looking at the plans for the possibility of them "being in the breeze", although I cant imagine that the amount of induced drag would be worth considering. I do find your statement about strength interesting, where do you think I could find more data on that?

I hate to call Bob on stupid stuff like this, I would rather save my calls for the big issues that I have no doubt will come up!

[marcusofcotton]

Bob in the past has stated that the wings are to use dimpling for strength. There is a very good short read for all of us at:

http://www.kilohotel.com/rv8/rvlinks/marvelrivets.html

Bill Marvel funded strength testing comparing both AN470 and AN426 rivets in under driven, over driven, and correctly driven samples. Note that a grossly under driven AN426 in dimpled material is still slightly stronger than a correctly driven AN470.

[bestbearhawk1231]

Dave, I had the same problem on the first flap. Watch the deburring on the nose skins, it only takes about a quarter to half turn too much to go from deburring to countersinking. I dimpled everything that needed to be and even with the "slop" around the rivet shank, they drove nicely. Oh ya, I am sure you know this, but when you are checking your rivet length make sure you go from the bottom of the dimple, not the the bottom of the rivet flange. I "got" to drill out most of them and try it again after an A&P instructor pointed that out (the look on his face was priceless once I admitted that I had been using a length gauge but apparently had been using it wrong). I felt like such a schmuk. I ended up with half sizes on a pile of them to get them to drive correctly. The rivets on the top can be a bear with the angle of the flange. Oh ya, have fun on the tail end of the corner gussets..those ones are great. I ended up putting in stainless pop rivets in the last 2 or 3 since I couldn't get a bar of any type in there to buck the rivets. I agree with Jared on the 470s, I think it will be a royal PITA trying to get your fabric to turn out later. Trust me, the flap looks so much better with flush rivets. I also read somewhere that dimpling/countersinking the aluminum makes for a stronger joint in shear and virtually identical joint in tension, something about the rivet is mainly being used in tension since the dimple provides the sheer strength.

Oh, one last thing, make sure you keep all of the layers tight against each other when you drive the rivets...it sucks trying to remove rivets that have "flowed" between the sheets while the shank was expanding. I have heard that putting an o-ring on the tail as you drive it helps keep multiple sheets together, I might try that on my ailerons and the other flap that need to be riveted. The A&P instructor suggested using a #42 bit for drilling out the rivets...not that you will need to know that. I can tell you from experience that it worked much better than the #40 bit I had been using.

Good luck and may the force be with you!

[jaredyates]

Bob has fielded far more stupid questions than this... from me, and probably others. I don't think it's in the stupid question category.

[bestbearhawk1231]

Dave, just wondering if you called Bob for clarification and if so what was his answer? Thanks.

[DesertBearhawk]

I did not call Bob, I have pressed on with the 426 rivets. ON a side note, getting in to rivet the ribs on the flap is a PITA…..

[bestbearhawk1231]

Yes it is...an offset rivet set definitely helps out.