First screw up - lots of oversize holes

[Kevin Horton]

Originally Posted by rivetshaver

Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.

But, the MD88 was designed to be riveted with NAS 1097 rivets, so the designers made sure those rivets would be acceptable. How many 0.020" thick skins does the MD88 have?

Van designed the RVs assuming that the builder would use AN426 and AN470 rivets. While it is acceptable to substitute the occasional NAS 1097 rivet, as other have noted we shouldn't do several in a row unless the consequences of that rivet line failing were benign. If the rudder stiffener rivets failed, that would significantly reduce the stiffness of the rudder, which could reduce the speed at which flutter would occur. This could lead to a fatal accident. Don't cut corners anywhere that could affect structural integrity.

Either redimple for 1/8" rivets, or order new parts. Pick your poison.

[DaX]

Thanks for all the input guys. I have had no issues with oversize holes until I started working with the very thin rudder skins. I am going to proceed more cautiously with the elevators.

Tomorrow I am getting together with a fellow RVer and we're going to work it out. Thanks again for all the input. I'm also waiting to hear back from Van's about the matter. I'll post their response when I get it.

[RScott]

Regarding the figure 8's: How does this happen?

I don't know how this happens unless you have the male die on top and the female on the bottom, line it up & then hit it with the hammer, letting it slip out of position in between steps.

Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?

[az_gila]

Originally Posted by RScott

Regarding the figure 8's: How does this happen?

I don't know how this happens unless you have the male die on top and the female on the bottom, line it up & then hit it with the hammer, letting it slip out of position in between steps.

Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?

Another option is to not use the return spring if the male die is in the upper position.
Lift the rod, and let gravity hold the die in position inside the hole, and then hit it.
It's a little more work this way, but practically guarantees no "figure 8's"

gil A

[Ironflight]

Originally Posted by RScott

Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?

Nah, you're not missing anything...your method sounds foolproof! Of course, you know what they say....make something foolproof, and someone will invent a better fool.....

I found that even with the male die in the bottom, you get into a rythm...pound, move, pound, move...and then you get to an awkward spot, you have to bend the skin back or something, and...WHAM! something slips....

Maybe my next airplane won't have any extra dimples or holes...but I bet you can't find the ones on the current plane either! (Bondo covers all sins!)

Paul

[L.Adamson]

Originally Posted by rivetshaver

Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.

This is apparently very true, as I've read much on the subject. There was even a quote on an RV forum from years ago, stating that what some are calling "mistake" rivets, were the norm for some commercial airliner construction.

An interesting subject anyway.........

BTW, someone told me that the rivet heads on an F1 were smaller than the normal AN3 rivet we use. Is this true?

L.Adamson RV6A

[robjohnson]

DaX,

Here is my guideline on something like this, regardless of the part in question. If you have to ask the question about something "being ok", it is probably best to choose a solution that is known to be ok. Now, I know we have several aeronautical engineers on the forum and their advice may be sound -- however, you can't deny the fact that they didn't design the RV. I know if I was in your situation, every time I flew the plane in a little rough air or a super stiff cross wind, my thoughts would immediately jump to that rudder. Are those "oops" rivets going to hold enough pressure when it really matters? Who knows....

If this were my rudder, I would put in the -4's or replace the skins and stiffeners.

[Rick6a]

Originally Posted by DaX

.......... I'm also waiting to hear back from Van's about the matter. I'll post their response when I get it.

Originally Posted by rivetshaver

I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic.....

I think the oft repeated and common notion that too many 1097's in a row as an inherently bad thing is painting with too broad a brush. It all depends on the load path and other anticipated and locally specific demands placed upon a given fastener or series of fasteners. What may be an acceptable fix in one area may be unaccceptable one fuselage station over. This is why the big manufacturers employ stress engineers who's function is to calculate an appropriate fix for any given situation.

In this case, all you want to do is replace AN427AD3 with 1097AD4 rivets in a rudder assembly. Sounds perfectly reasonable to me because the 1097AD4 has a slightly larger manufactured head than the AN427AD3 so it would seem obvious that its manufactured head will be a bit more robust in tension. It gets better because in shear, it is even stronger than the AD3 because it is a 1/8" rivet as opposed to the blueprint 3/32" rivet normally installed in this location. What you are really doing is "bulking up" that general location, making it stronger. That may or may not be a good thing, but I suspect it is. Then to, I have to wonder about the questionable virtue of redimpling that thin rudder skin to accept a larger rivet head when a rivet already exists to fill the countersink just as it is.

I'm not saying this logic will hold up under all circumstances but in this specific case I would have to be convinced otherwise....all the better by a qualified engineer schooled in such matters. I am not (nor should you) be easily swayed by boilerplate bromides dispensed on this and other forums and to be fair....that includes my opinion. Count me among those who advocate the obviously simpler approach of using a series of 1097's to address this particuliar problem.

Let us know what Van's recommendation is.

[az_gila]

Originally Posted by Rick6a

......In this case, all you want to do is replace AN427AD3 with 1097AD4 rivets in a rudder assembly. Sounds perfectly reasonable to me because the 1097AD4 has a slightly larger manufactured head than the AN427AD3 so it would seem obvious that its manufactured head will be a bit more robust in tension. It gets better because in shear, it is even stronger than the AD3 because it is a 1/8" rivet as opposed to the blueprint 3/32" rivet normally installed in this location.
......
Let us know what Van's recommendation is.

Typo above... I believe your AN427AD3 should have been AN426AD3

Rick... I think your comment on the rivet strength in tension may be incorrect...

Yes the 1097-4 rivet head is slightly larger than a 426-3 rivet head - by about 0.012 - but the amount of the rivet head that is resisting a tensile pull is way less for the 1097 than the 426, since we are dealing with the amount of material left in the head after the much larger body of a 1/8 1097 rivet vs. a 3/32 426 rivet.

Do we know if the failure mode in tension is in the body of the rivet, or in the head pulling through the material? - since you use head diameter in your comment, I assume you think it is in the head pulling trough failure mode...

The 1/8 rivet will have a much larger shop head, but when you pull the joint in tension, it seems reasonable to me that it will be the much smaller amount of material at the manufactured head side that will fail.

The joint should be in shear, but all of the practical testing done on RVs (4000+) hasn't measured the difference between shear and tensile loads.....

Interestingly enough, the MIL-HDBK-5 (now MMPDS-01) only gives design strengths for the NAS1097E type rivets in machine countersunk applications.

gil A

[DaX]

OK, I heard back from Van's, here's the conversation:

Matt,

It sounds like you have over deburred the holes initially, then drilling out to
#30 finished it off. What I would suggest is to start over with new rudder
skins and stiffeners. That way you can be ensured that your plane is built to
spec. The skins are .020" rather than .016". We have no technical data on
what issues you would run into if you used all NAS1097 rivets on your
rudder. Let me know if you need additional assistance.
Thanks

Joe
Vans Aircraft

**********

I then replied asking what he thought about re-dimpling for AD4 rivets, and this is his reply:

Matt,

I would think that the AD4 rivets would work fine. They are just a little harder
to rivet due to their size. Good luck!
Thanks

Joe
Vans Aircraft

**********

I have decided to re-dimple for AD4 rivets and use all AD4 rivets to hold the stiffeners to the skins. I'll just be more careful when working the other holes in the thin skins.

Also - I have decided to build-on with the figure-8 - I'm just going to use a doubler plate over where the figure-8 is.

Thanks all for the input!