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  #1  
Old 11-14-2017, 12:24 PM
jking jking is offline
 
Join Date: Jun 2014
Location: Tucson, az
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Default Structural Benefit to Filling Hole With Rivet?

Probably a dumb question, but I wouldn't want to disappoint my friends. I have a 1/8" hole in a longeron that I no longer need due to change of plans. It would certainly look better if it had a rivet in it, but with the curvature of the rear fuselage skin this is not an easy slam dunk operation. Its not in one of those places where it will stick out like a big "DOH!" sign. At the same time, I don't like anything weakening the structural integrity and especially if its not doing anything beneficial.
So, will driving a rivet do anything to restore part of the lost strength in this longeron?

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  #2  
Old 11-14-2017, 01:11 PM
219PB 219PB is offline
 
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Adding a rivet will not increase the strength. Only the weight, although miniscule. I am guilty of putting a rivet in a hole so that it does not look like a mistake.
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  #3  
Old 11-14-2017, 03:16 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by 219PB View Post
Adding a rivet will not increase the strength. Only the weight, although miniscule. I am guilty of putting a rivet in a hole so that it does not look like a mistake.
I'm not sure that is quite true.

A filled hole should restore any compressive strength loss that was caused by the hole.

Can an ME verify?
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  #4  
Old 11-14-2017, 03:39 PM
krw5927 krw5927 is offline
 
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Default Not an easy answer...

According to the document linked below, installing a driven rivet produces a local area of residual compressive stress in the material surrounding the rivet, resulting in improved fatigue life for certain loading conditions. See section 14.11, pages 18-19:
https://www.asminternational.org/doc..._Chapter14.pdf

As with everything, a bunch of caveats apply. Care must be taken to also consider the, adjacent structure, maintaining proper fastener spacing to adjacent holes, etc. Whether or not fatigue life is a concern given the part properties and loads is another question.
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Last edited by krw5927 : 11-14-2017 at 03:42 PM.
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  #5  
Old 11-14-2017, 04:07 PM
sblack sblack is offline
 
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ON a fighter jet, or an airliner, there is much effort spent at making every bit of structure as light as possible. Skins are chem milled to thin them in areas where they are not loaded. spar caps are tapered etc etc etc. On an RV the longeron is the same size and cross section throughout its entire length. It probably only has to be that size for a very small portion of its length. In fact, when he was designing it, Van might have sized the angle and then used the next size up, because you can't buy a 37/64" angle that is 7/64" thick (I invented those numbers). The extra material is left in, because who is going to bother trying to get it perfectly optimized.

If you want to do a major stress analysis at each hole, go ahead. It's your airplane. And drilling a hole does reduce the cross section and therefore makes it weaker in tension by definition. But this is only a problem if that part is optimized to be exactly as strong as it has to be. The longeron will be in tension at full rudder 1 way, and compression with full rudder the other way. Same with pitch up vs pitch down. So if you increase the compressive strength for left sideslips, but you don't address the reduction in tensile strength in the other direction, you have not made the structure any safer.

I would only really worry about holes in the longerons up near the steel gussets that tie them to the firewall. That would be the area where they are most highly loaded and there are 4 -3 bolt holes in them. An AD4 rivet hole further down is not going to compromise flight safety.

No, I am not a Vans employee but I have been an Aero Eng for 28 yrs and I do know something about loads and aircraft structures. And I have a 4 that has some holes in places they shouldn't be
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Last edited by sblack : 11-15-2017 at 11:06 AM.
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  #6  
Old 11-14-2017, 08:21 PM
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plehrke plehrke is offline
 
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Quote:
Originally Posted by jking View Post
So, will driving a rivet do anything to restore part of the lost strength in this longeron?
Extra holes in the longeron seems to me to be a condition I would want to fix. Not knowing where you have extra holes or where longeron cross sectional sizing is critical, as an aerospace structural design engineer I would advise to make a repair by riveting on a doubler plate to make up for the lost cross section and strength of the longeron. There probably is a standard repair in AC 43.13. It's an easy fix for assurance of being structural sound. Just by you asking a question means you have some doubt about its integrity.
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Last edited by plehrke : 11-14-2017 at 08:27 PM.
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  #7  
Old 11-15-2017, 02:12 AM
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Tdeman Tdeman is offline
 
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Default Fill it

Without knowing the exact circumstance (regarding where the hole is etc), the one question that can be addressed is:

"So, will driving a rivet do anything to restore part of the lost strength in this longeron?"

We'll see the greatest effect of this rivet itself in compression, where it will in fact carry some compressive loads.
That being said, there is still a benefit of having the rivet in the hole while the longeron is in tension, as pointed out in the article shared above by Kurt W (as well as other texts on mechanical behavior of materials...)

In case anybody didn't read the whole thing , one part that stood out is...

"Both cold working and interference fit fasteners set up residual compressive stress fields in the metal immediately adjacent to the hole (Fig. 14.26). The applied tension stress during fatigue loading must then overcome the residual compressive stress field before the hole becomes loaded in tension. The fatigue improvement due to cold working in 024-T851 aluminum is shown in Fig. 14.27"

Screen Shot 2017-11-15 at 12.42.40 AM by Taylor de Man, on Flickr

So to answer your question, and reiterate what's been nearly beat to death by now, it will likely increase the strength and service life of the longeron by adding that rivet (depending on location of hole etc). Whether or not it's needed, well that's still up for debate
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  #8  
Old 11-15-2017, 02:15 AM
scsmith scsmith is offline
 
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Quote:
Originally Posted by plehrke View Post
Extra holes in the longeron seems to me to be a condition I would want to fix. Not knowing where you have extra holes or where longeron cross sectional sizing is critical, as an aerospace structural design engineer I would advise to make a repair by riveting on a doubler plate to make up for the lost cross section and strength of the longeron. There probably is a standard repair in AC 43.13. It's an easy fix for assurance of being structural sound. Just by you asking a question means you have some doubt about its integrity.
but attaching the doubler means drilling yet more holes in the longeron, just because there is a hole it in it. That actually makes no sense, except in case where the hole in question is at a critical location (such as a peak in bending moment) but the doubler attachment fasteners would be drilled at less critical sections. (Not a likely case in a longeron -- they don't see bending, just tension/compression.)

Filling the hole with a rivet can actually increase the life-cycle strength somewhat, as mentioned above by krw5927. When loaded in tension, there is a stress concentration around the hole that increases the stress locally. By preloading the area around the hole in compression with the rivet, it reduces the net stress increase at the hole. This would likely only be an issue for a very dynamically loaded part that was subject to high-cycle fatigue.

Leave it open or fill it, your preference.
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  #9  
Old 11-15-2017, 06:10 AM
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maniago maniago is offline
 
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If you didnt violate an edge distance with the hole, Id leave it alone and move on. I know what the analysis guys have posted, but IMHO its far far into the analysis weeds for our planes....which, as has been alluded to, are overbuilt and dont travel all that fast comparably for this to be of any critical concern. In anycase also consider that longerons are thick compared to skins (so theres more material support around the hole). Similarly, and just food for thought, if it were in a skin, consider that to stop a crack from propagation, you drill a hole. And dont fill it.

Debur it properly and move on.

Now if you did violate the edge distance, hehe, yeah you gotta reenforce it as mentioned by someone above cause youre now you have a potential crack generator.....

(btw, yes I'm a 30+ engineer too, but I look at this from first principles personally. And yes I have an errant hole in a longeron and skin or two - meh. Lightening hole!)
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Last edited by maniago : 11-15-2017 at 06:16 AM.
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  #10  
Old 11-15-2017, 08:13 AM
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DanH DanH is offline
 
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In summary...

It may or may not be necessary to fill the open hole. However, there are potential advantages to filling the open hole, and there is no disadvantage.

I would only add that open holes make future inspectors a little bit crazy.
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