F

Fl Mac

Well Known Member
On my stabilator, all looks good when the skins are clecoed. When I rivet, and if you look at an angle you can see small indentations left at some of the rivets. Is this just the way it is or is there something wrong. Everything seems to be fitting perfect. The holes lined right up. The ribs were all fluted flat on the table. Any thoughts?
 
small dent like things

Almost impossible to avoid all such things. I had a few areas that did the same. If it looks good when you put the skin on, you just have to accept a few imperfections. ( thats my story anyway ) !

John Bender
Iowa
 
I am getting my fair share of them when the ribs start to turn towards the leading edge. The flat sections are fine. It seems that when I rivet the skin sinks just a small amount more causing a small indentation. I can live with this if it is normal, but if not I would like some suggestions on how to make the curved areas of the skins as smooth as the flat areas.
 
Shim if You Must

If you really want to avoid it you can use small shim washers under the skin to take up the gap. Or use a "liquid shim" - basically a toughened epoxy paste.

www.vansairforce.com/community/showthread.php?t=6750&highlight=liquid+shim

It all adds weight, construction time and expense though - and from a functional/performance point of view probably has no benefit. Also I have noticed that as the assembly becomes bigger and starts to look like a compete aeroplane all of the minor cosmetic imperfections that I fretted about become harder and harder to find - even when I know where they are.

If you have access I have heard of people tapping out the indentation from the back with a mallet and a wooden dowel used as a drift.

Jim Sharkey
 
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BE CAREFULL!

If you plan to build as E-LSA, follow the plans. If it's not in the plans and you don't have written approval from the kit manufacturer, DON'T DO IT!
 
Mel said:
If you plan to build as E-LSA, follow the plans. If it's not in the plans and you don't have written approval from the kit manufacturer, DON'T DO IT!
Click to expand...

Understood. I plan to go E-LSA so I am following the plan to the "T".

They can't be tapped out, they are at and surround the rivet.

I am really not looking for a way to eliminate them as much as reassurances that they are normal to this kind of build. I am sure they have nothing to do with strength and my wife never saw them until I pointed them out. I don't think it looks that bad: it even adds a little character. I just don't want someone to look at the build and say hey those are there because you did not do .......?
 
They can't be tapped out, they are at and surround the rivet.....

You actually tap the tail of the rivet and push the flange, rivet and skin out at once - at least with solid rivets. Not sure how it might work with pulled rivets.
 
I've noticed these also. Not much you can do except flute the flanges per the print, and maybe "tweek" them outward a tad. Can't do anything once it is riveted unless you drill them out.

The skins on the tail cone are worse. Up to 1/32 gap between the the forward most flange and the skin in a just a few areas. I was able to tweek the flange and lessen the gap before pulling the rivet.

Mel, would a shim between the flange and the skin be permissible? Wouldn't this fall under the "workmanship" criteria? Just asking.
 
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jsharkey said:
They can't be tapped out, they are at and surround the rivet.....

You actually tap the tail of the rivet and push the flange, rivet and skin out at once - at least with solid rivets. Not sure how it might work with pulled rivets.
Click to expand...


I see what you are saying. At this point no access to the back.


Not sure how more fluting will help. I have fluted them flat and the holes line up great. It is just that when the rivet is applied it gives a little. It is not that big of deal for me and looks like I am not the only one who is getting these. If the tail section is worse I may have to really watch that area.
 
The short answer is Yes!

Geico266 said:
Mel, would a shim between the flange and the skin be permissible? Wouldn't this fall under the "workmanship" criteria? Just asking.
Click to expand...
But when we start talking about things like "liquid" shim, we are looking at possibly adding weight. Now we get into, what if we add all this weight to the tail, then later decide we don't want to do it anywhere else. Now we have a weight and balance issue. What if the "liquid" shim cracks out at a later time and jams something.
Like almost anything else. it's a judgment call and at this early point in E-LSA things are going to be looked at very closely.
 
Shake, Rattle and ...

Geico266 said:
Mel, would a shim between the flange and the skin be permissible? Wouldn't this fall under the "workmanship" criteria? Just asking.
Click to expand...

Hi Larry,

I'm not Mel, but I do agree with what he said.

In addition, when dealing with any movable control surface, any excess weight can set up conditions conducive to flutter.

Yes, I know it's only a few ounces and >probably< wouldn't cause any problem, but do you REALLY want to be a test pilot every time you go fly?

We're all working to get our heads around the differences between E-AB and E-LSA, and I guess we're going to have to change our aspirations from Grand Champion to Clone (not a bad thing, just different.)

- Tom Tyson
 
Another cause...

Fl Mac said:
On my stabilator, all looks good when the skins are clecoed. When I rivet, and if you look at an angle you can see small indentations left at some of the rivets. Is this just the way it is or is there something wrong. Everything seems to be fitting perfect. The holes lined right up. The ribs were all fluted flat on the table. Any thoughts?
Click to expand...

Beside some of the other causes that have been mentioned, another cause for slight skin dimples is from forcing rivets into holes. If a rivet doesn't easily slip into a hole, with these thin skins, a small depression will be pushed into the skin that can be seen after the rivet is pulled.
 
Thanks for all the suggestions. Here is what I have found so you can pass this along as a suggestion in the future. I had several backwards flutes. I carefully drilled out the skin rivets corrected this problem...riveted the skin back down and it looks good.
 
Fl Mac said:
Thanks for all the suggestions. Here is what I have found so you can pass this along as a suggestion in the future. I had several backwards flutes. I carefully drilled out the skin rivets corrected this problem...riveted the skin back down and it looks good.
Click to expand...

Backward flutes would do it - I guess the indents weren't as subtle as I thought:D
Jim
 
"...if it's not one thing, it's another ..."

Fl Mac said:
... I had several backwards flutes ...
Click to expand...

What you call "backwards flutes" - is this the same as a burr being left on the "back side" of the part from the hole punching process?

If so, I guess it's just something else to look at while building the kit.

Thanks for the heads-up.

- Tom Tyson
 
What I mean by backwards flutes is that I held the pliers backwards in some spots. The pliers have a male and female side. I had the female side on the outside making the hump stick up above the flat of the holes. There was a hill between the rivet holes. You could not see the hill, only the valley at the rivet.

They were fairly subtle, but not enough to live with obviously (the ribs are nicely formed and did not need much in the way of fluting to lay flat) . I had to figure out what was going on. When I got the skin up the problem was glaring at me. Things are back together and I am back on track.

Thanks for all your help.
 
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