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1097 rivets for a hinge?

atalla

Well Known Member
Elevator Trim Tab Hinge Machine CS / Dimple issue

As the subject states can I use oops rivets or 1097 rivets to lessen the counter sink at the elevator trim tab hinge line? I have use this method for Nut plates and it works quite well. On a scrap piece of trim tab I?m having a difficult time setting a countersink to get a standard 426 rivet head down into without enlarging the hole. Skin is 020

Thanks in advance.
 
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As the subject states can I use oops rivets or 1097 rivets to lessen the counter sink at the elevator trim tab hinge line? I have use this method for Nut plates and it works quite well. On a scrap piece of trim tab I?m having a difficult time setting a countersink to get a standard 426 rivet head down into without enlarging the hole. Skin is 020

Thanks in advance.


Why not simply dimple the skin / hinge?
 
I think I see my error. I believe the skin is dimpled the spar is Machine Countersunkand the hinge it flat.
 
Still having issues

I am having the same trouble with the spar. I?m not able to counter sink the spar enough to fit the dimpled skin without oversizing the # 40 hole. The manual isn?t very clear. I experienced a warped hinge after dimpling it during a practice kit so any advice you guys have would be great.









 
I ran across this issue a few months ago on my -14A and it has stopped me in my tracks. Per the plans, you countersink through the spar and into the hinge leaving a knife edge in the spar. I contacted Vans and was told this is correct and they've been doing this since the beginning and that there's never been any problem with it. So far.

I wasn't happy with that answer. My day job is aircraft structural analysis for the big B. This is a condition that is not acceptable because it gives you an initial flaw for a crack to start growing. In the GA maintenance world, it's acceptable to countersink to the bottom of the first layer in the stack-up but you must stop there.

My concern is with the "never been any problem with it" statement. Has anybody ever inspected this location after a while in service? How would you inspect? The only viable method I know of that's affordable to the EAB crowd is dye penetrant. However, you need to have the crack grow to the edge (in the spar, which is sandwiched between the skin and hinge) before this method will detect it. You can also use low frequency eddy current to inspect the spar through the skin, but the training and equipment to use this NDI method costs more than most can afford.

Because I'm cursed with way too much knowledge on this particular subject, I've decided I can't live with the status quo. I'm going to have new spars made for the tab and elevator out of 0.050 in. sheet. I talked to a local metal bending shop and it'll cost about $300 to duplicate these parts. And yes, I ran this idea by Van's and as long as I maintain the proper control surface balance I'll be OK in terms of flutter.

Now before I get jumped on, I'm *not* saying this is a design flaw. Van's is probably right that it will never be a problem. You need three things for a crack to grow: 1) an initial flaw (got that), 2) sufficiently high stress (probably not), and 3) enough cycles to grow the crack (probably not with these aircraft).

For me, being the very conservative type, I'm unwilling to live with this. It'll be in the back of my mind every time I fly. It's all for my peace of mind.
 
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I ran across this issue a few months ago on my -14A and it has stopped me in my tracks. Per the plans, you countersink through the spar and into the hinge leaving a knife edge in the spar. I contacted Vans and was told this is correct and they've been doing this since the beginning and that there's never been any problem with it. So far.

I wasn't happy with that answer. My day job is aircraft structural analysis for the big B. This is a condition that is not acceptable because it gives you an initial flaw for a crack to start growing. In the GA maintenance world, it's acceptable to countersink to the bottom of the first layer in the stack-up but you must stop there.

My concern is with the "never been any problem with it" statement. Has anybody ever inspected this location after a while in service? How would you inspect? The only viable method I know of that's affordable to the EAB crowd is dye penetrant. However, you need to have the crack grow to the edge (in the spar, which is sandwiched between the skin and hinge) before this method will detect it. You can also use low frequency eddy current to inspect the spar through the skin, but the training and equipment to use this NDI method costs more than most can afford.

Because I'm cursed with way too much knowledge on this particular subject, I've decided I can't live with the status quo. I'm going to have new spars made for the tab and elevator out of 0.050 in. sheet. I talked to a local metal bending shop and it'll cost about $300 to duplicate these parts. And yes, I ran this idea by Van's and as long as I maintain the proper control surface balance I'll be OK in terms of flutter.

Now before I get jumped on, I'm *not* saying this is a design flaw. Van's is probably right that it will never be a problem. You need three things for a crack to grow: 1) an initial flaw (got that), 2) sufficiently high stress (probably not), and 3) enough cycles to grow the crack (probably not with these aircraft).

For me, being the very conservative type, I'm unwilling to live with this. It'll be in the back of my mind every time I fly. It's all for my peace of mind.

Isn't experimental aviation great? If you don't like something you can start your own experiment an do it different.

The definition of "never been a problem with it" is that with 10,000 plus RV's flying, nearly all of them have the trim tab attached this way.

Machine countersinking the outer skin would be a very bad idea structurally because the skin is only .020 (and in some cases .016). There would be very little skin area being retained by the rivet head.
You could dimple countersink all three layers, but the hinge material is rather thick. It doesn't dimple well and if you do, you will find that it gets rather distorted out of shape. The hinge is also a softer material than the spar and skin so machine countersinking that is not recommended.

The plans method sandwiches the machine countersunk spar flange between a full thickness dimple countersunk skin, and a full thickness, un-distorted hinge segment.
This is the strongest method, and in 30 + years, there has as far as I am aware, never been a single report of a problem discovered. With the # of hrs in the RV fleet, even if cracks were occurring and hidden between the layers some indication of a problem would likely have been noticed by now.

But like I said, it is experimental so do what every makes you feel comfortable, though without some major redesign.
 
I am having the same trouble with the spar. I’m not able to counter sink the spar enough to fit the dimpled skin without oversizing the # 40 hole. The manual isn’t very clear. I experienced a warped hinge after dimpling it during a practice kit so any advice you guys have would be great.

The portion of the manual to refer to is machine countersinking for a dimple, in Section 5.
If you follow the instructions, it will produce a structurally sound rivet joint, but the counter sinks will not be deep enough to allow the skin to lay fully flush and that is on purpose..... the explanation of why is in other threads here in the forums.

Here is one post -
http://www.vansairforce.com/community/showpost.php?p=1287720&postcount=29
 
So your saying it?s ok to enlarge the hole in the spar as long as I use the hinge as the pilot but not enough so the dimple lays flat? Is there a measurement we have for the size of the countersink?
 
The recommendation in Section 5 is to countersink so the rivet head lies flush with the surface, then go an additional 0.007 in. deeper. You can read the recommendation in Section 5.5 under "Machine Countersinking".
 
If countersinking two layers of aluminum bugs you, add into the mix a structural adhesive. Done. Many airplanes don't have rivets in their primary structure.
 
I was under the impression I was to never enlarge a rivet hole. I mean that?s why I use a reamer to bring the hole to an exact size. Doing so in a control surface hinge seams odd. I will have to look at my counter sink and calculate what each notch is in depth for the .007 and than run some more test pieces. Anyone have pictures of a similar hinge line?
 
My pictures

I know this shows these parts assembled, and on an RV-9, but I think this is what you're after. I noticed when I countersunk the trim spar that the hole was enlarged a little, but I stopped worrying when I thought hard about the whole assembly of the skin/spar/hinge sandwiches together, and there are around rivets along that line.

5yc6ip.jpg


jt6n2f.jpg


2zzm2ad.jpg


k50iom.jpg
 
I will have to look at my counter sink and calculate what each notch is in depth for the .007 and than run some more test pieces. Anyone have pictures of a similar hinge line?

All of the micro stop tools I have ever used were indexed in .001" increments per each notch/detente. They usually have a marking on them somewhere that says .001".
 
If countersinking two layers of aluminum bugs you, add into the mix a structural adhesive. Done. Many airplanes don't have rivets in their primary structure.

Brilliant! This is a solution that eases my mind. I'm going to do this and save some cash. Much appreciated.

Funny thing is I knew of this being done on old 737 classic skins to create a pad up at the fastener lap joints. Some of the fuselage skins on that old bird are 0.032 in. I didn't even think about the adhesive solution applied to this situation.

Thanks!
 
Still lost a bit

So what?s the consensus here then?
do I countersink as far as a rivet +.007 or do I counter sink until the dimple lays flat enlarging the hole and just being OK with the total sandwich as a whole being strong enough ? I like the idea of structural adhesive however 10k of these things air flying and iv never heard of a trim tab failure so Do I follow the manual and have a slight bulge in the skin where do I carry-on like the rest of the masses.
 
I?d do as the plans suggest in section 5.5. Countersink until the rivet head is flush, then 0.007 in. (7 clicks) deeper. The skin dimple will not sit perfectly within the countersink. This is normal.

I?m going to do the extra step of bonding the hinge and spar together before I countersink. This is not called out in the plans. You don?t need to do it either.

As I stated previously, I?m not comfortable with knife edges but given the relatively light usage of these airplanes it?s highly unlikely you?ll accumulate enough cycles for a crack to grow.
 
When I built my trim-tab, I just dimpled everything (Skin, spar, and hinge). Worked fine, the only downside was the limited access for riveting. The small additional space consumed by the dimples just made it harder. Probably still less trouble than making a new spar.

I ran across this issue a few months ago on my -14A and it has stopped me in my tracks. Per the plans, you countersink through the spar and into the hinge leaving a knife edge in the spar. I contacted Vans and was told this is correct and they've been doing this since the beginning and that there's never been any problem with it. So far.

I wasn't happy with that answer. My day job is aircraft structural analysis for the big B. This is a condition that is not acceptable because it gives you an initial flaw for a crack to start growing. In the GA maintenance world, it's acceptable to countersink to the bottom of the first layer in the stack-up but you must stop there.

My concern is with the "never been any problem with it" statement. Has anybody ever inspected this location after a while in service? How would you inspect? The only viable method I know of that's affordable to the EAB crowd is dye penetrant. However, you need to have the crack grow to the edge (in the spar, which is sandwiched between the skin and hinge) before this method will detect it. You can also use low frequency eddy current to inspect the spar through the skin, but the training and equipment to use this NDI method costs more than most can afford.

Because I'm cursed with way too much knowledge on this particular subject, I've decided I can't live with the status quo. I'm going to have new spars made for the tab and elevator out of 0.050 in. sheet. I talked to a local metal bending shop and it'll cost about $300 to duplicate these parts. And yes, I ran this idea by Van's and as long as I maintain the proper control surface balance I'll be OK in terms of flutter.

Now before I get jumped on, I'm *not* saying this is a design flaw. Van's is probably right that it will never be a problem. You need three things for a crack to grow: 1) an initial flaw (got that), 2) sufficiently high stress (probably not), and 3) enough cycles to grow the crack (probably not with these aircraft).

For me, being the very conservative type, I'm unwilling to live with this. It'll be in the back of my mind every time I fly. It's all for my peace of mind.
 
Well I followed the instructions and this was my result. I?m not sure if this is addiquite. I like that the hole is not compromised.





 
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