Why do so many builders cleco EVERY hole?

[pfarber]

I've been told (and done) a cleco every 4 or so holes. I see 'builders' putting 100's cleco's in a simple skin.

Is there something I'm missing?

 

[Kyle Boatright]

My rule of thumb is a cleco about every 3rd hole. But I'm sure putting one in every hole would improve my build accuracy a smidge.

 

[N804RV]

There are times when sticking a cleco in every hole as you final/match drill is a very good thing to do. If you've ever final drilled then took it all apart to deburr, then prime, and when you cleco'd it back together to rivet, and rivets and the end of the row would not fit, .... more clecos when drilling would've helped that!

 

[TFF]

Thin metal can have a pinch; bunch up a bit. Thick may not seat. It happens especially on long lines where the sheet can move a bit. Clecos don’t fill the holes perfect. What ever you call the screw in clecos, are nice to help lock in spots. About a gallon and a half of clecos will do a RV nicely.

 

[MadRocketScientist]

When you are building something with .020" or .016" thin skins, things can pucker up between clecos and then holes won't line up as you rivet the sheet down. Or you end up with wrinkles between the holes. I guess it wouldn't be needed so much on thicker skins.

 

[wsimpso1]

On long straight runs, every 4th is probably fine. On highly curved areas, I can see every hole. Here is why:

With flat stock wrapped around a curve, you get secondary curves. The outside of the curve gets longer around the curve and shorter across the straight line. The inside of the curve gets shorter around the curve and longer across the curve. The piece wrapped around the outside of a curve ends up sort of saddle shaped, with the edges lifting. You can see this where skin panels abut on a wing or turtledeck. This is plate theory...

To keep all the holes aligned, some folks put Clecos in every hole as they follow around the curve trying to keep it all laid down. In addition to getting the holes lined up around the curve, this will usually reduce wrinkling and puckering that comes with the tendency of the skin to become saddle shaped. Sometimes you can get the straight lines across the curve misbehaving - Clecos in every hole can help that lie down and make sure the holes are all aligned too.

Billski

 

[gtae07]

Depends on the curvature, what I'm doing, etc.

I clecoed every hole when sealing my tanks, to keep the assembly tight. When drilling non-prepunched items I cleco every hole for the first few next to where I'm drilling, then as I work along they spread out behind.

On my aft wing skins, or long fuselage runs, I did every 3 or 4 holes.

It also depends--am I drilling? Just attaching the skin/item for fitting purposes? Riveting? The answer will change cleco spacing.

 

[CRG]

Thicker skins can do it too. Not chasing the skin can help greatly, by that I mean don't rivet in sequence. Pin the sheet in a few places along its length with rivets, then fill the gaps.

When you are building something with .020" or .016" thin skins, things can pucker up between clecos and then holes won't line up as you rivet the sheet down. Or you end up with wrinkles between the holes. I guess it wouldn't be needed so much on thicker skins.

 

[narfi]

Thicker skins can do it too. Not chasing the skin can help greatly, by that I mean don't rivet in sequence. Pin the sheet in a few places along its length with rivets, then fill the gaps.

I like to divide an unriveted section in 1/2 with my next rivet. Then cut those two halves each in half, etc...... Playing the mental game with myself to see how perfect I can end up at the end...... Playing with the math to see if my final run can be every other hole......

 

[cblink.007]

On long straight runs, every 4th is probably fine. On highly curved areas, I can see every hole. Here is why:

With flat stock wrapped around a curve, you get secondary curves. The outside of the curve gets longer around the curve and shorter across the straight line. The inside of the curve gets shorter around the curve and longer across the curve. The piece wrapped around the outside of a curve ends up sort of saddle shaped, with the edges lifting. You can see this where skin panels abut on a wing or turtledeck. This is plate theory...

To keep all the holes aligned, some folks put Clecos in every hole as they follow around the curve trying to keep it all laid down. In addition to getting the holes lined up around the curve, this will usually reduce wrinkling and puckering that comes with the tendency of the skin to become saddle shaped. Sometimes you can get the straight lines across the curve misbehaving - Clecos in every hole can help that lie down and make sure the holes are all aligned too.

Billski

Billski, you literally took the words out of my mouth. I had contacted a close friend who works the assembly line at Bell Helicopter, and he said the EXACT same thing, almost to a T!

 

[David L. Downey]

I am one of the wacko's that use as many clecos as I can. As previously stated, especially on thin skins wrapping curves, the line-length delta can cause a gradual difference in the spacing at the interface...and that causes bunching when riveted. I have also been accused on this sit of being uselessly passionate about beburring. I am. And I step drill everything and deburr between steps. painful but allows the skins to pinch tightly to the skin or frame below, thus minimizing the developing error along the matching interface.
I always insert clecos alternating the orientation of the center blade ans they are not - as mentioned above - hole filling. they are however oblong in section when clamped so alternating the blade orientation locates the line of holes better in both axes.
just my experience - no one has to hear a word.

 

[wsimpso1]

David L Downey, what you are doing by using a lot of Clecos and deburring as you walk the surfaces to each other is ensuring compliance between the two parts, ensuring coaxial holes for the rivets to fill and then clamp, and ensuring that the worst defect will still be a safe joint. It might be excessive on long straight runs, but in any place with a lot of curvature, it sure looks right to this engineer.

The ideal rivet fully fills the hole with residual loads in both radial and axial directions that firmly clamp the joint against movement. With firm clamp loads that prevent movement within the joint, the rivets stay tight and do not fatigue. Preloads in other directions, burrs between the clamped members, and shifted/pinched/bulged rivet forms after setting all make yielding and then loosening of the joint much more likely in use. High standards and modest defects are what we should be aiming for - Aim small, miss small, FOS is generous, life is good.

Alternatively, if we allow ourselves less then perfect fit up, poor deburr, etc, then side loads, shifted/sheared rivets, pinched or thick waisted rivets, joints not firmly pulled up, etc become the norm, and the joints become subject to yielding in use, which relaxes the usual clamp loads, loosens rivets, and then allows fatigue in the rivet and joint. And, if you allow yourself poor fit up, what other quality deficits are then being allowed?

Billski

 

[ScaleBirdsScott]

I generally have followed the rule of putting a cleco in every hole as they are drilled, and then after 3-4 solid start pulling them out to where there is no more than 2 empty holes between any two clecos.

Sometimes when just rough fitting something up, focusing my attention to one part of the panel after its been on and off a few times, when putting it back up, the areas away from where I'm working will be held on by only a few, maybe one every 5-8 holes.

But when we go to do final riveting it's usually every-other-hole gets a cleekon.

 

[pfarber]

But cleco's won't fix poor match drilling and deburring.

This is what I would consider normal:

JerMo's RV-10 Project

The RV-10 is a four-person airplane, not just an airplane with four seats. It will carry four FAA standard people, full fuel and sixty pounds of baggage. The cabin accommodates four full-sized adul…

rv10project.wordpress.com

Then you have this:

http://joesrv12.com/Photo/A_06_04_03A.jpg

There are not a ton of compound curves on E/ABs, they are kinda designed out of the projects to make the buildable, or are supplied/purchased formed.

 

[wsimpso1]

But cleco's won't fix poor match drilling and deburring.

True, but that is not what we are talking about. Wrapping a skin around a nose rib, the skin goes further as it goes around than the rib does, and is trying the whole time to straighten out. If we skip holes with the Clecos as you go around, the holes in rib and skin will end up match drilled to a skin that is at larger radii than it should be. Then when we do pull it down with rivets, holes no longer match OR the holes will match but the skin will not be pulled down everywhere. So, you Cleco everywhere around a curve.

This is what I would consider normal:
...

Those are flat surfaces. There is just about zero positional error going with a Cleco every three or four holes on flat panels, unless the flat stock took a set when rolled or was otherwise curled. Then you have the same problem as putting flat stock around a curve.

Then you have this:
...

Now that looks like gratuitous Cleco-ing. As if building an airplane did not take long enough already.

There are not a ton of compound curves on E/ABs, they are kinda designed out of the projects to make the buildable, or are supplied/purchased formed.

Maybe you should read post 6 (mine) again. A simple curve does not really exist. RV wing leading edges, fuselage lower chines, and turtle decks are designed as simple curves, but during the elastic bending of the sheet around the form, it unavoidably is a little saddle shaped. Even if the shape is rolled or hit on a brake to plastically deform it and hold a curvature, the plastically deformed part will be slightly saddle shaped, and that combined with the remaining elastic deformation to lay it down will still result in raised edges on the panels.

Easy places to see this on RV's is the outboard edges of the wings and stabilizers. In places like that you have work to get the skin fully down on underlying ribs, and Clecoing every hole around the curve really helps. The skin dips (slightly thin stabilizer that you can see and feel) a couple inches from the outboard ends and then the edges are flared. On airplanes where the builder did not straighten these edges, you can see it and feel it really easily on the outboard end of the horizontal or vertical stabilizer. Put the thumb and index finger of one hand on opposite sides of the stab and draw it spanwise, you can feel the thickness change or simply lay a (plastic) straight edge spanwise on the stab. It is usually apparent at the front edge of the turtledeck too.

I have seen birds where this flared edge was fixed. I guided a friend through fixing this in his RV8 project - he had a seamer with one jaw gently crowned in a collection of tools he bought from another builder. Working that tool along the edge and very gently bending the flared edge in also raised the depressed section just inboard too. With a nicely crowned/polished seamer, patience, and working back and forth along the edge, it can be straightened out invisibly. Some elevators and rudders have this shape and can be improved similarly. When I have seen RV's without the flare, I have talked with the builders, and they usually admit finding the mishape, and to then working the edges. I have also talked to builders who filled and faired the end of the sheet metal to the fiberglass cap - no screws or rivets visible. They usually admit that they did it because there was a gap to the tip cap and the skin was deformed near the tip. Yeah, there are others that keep it a secret, but I know what they did. Now so do the rest of us.

Billski

 

[pfarber]

Now that looks like gratuitous Cleco-ing. As if building an airplane did not take long enough already.

Not buying 'better cleco ever 3/8ths an inch so the skin doesn't warp/wrinkle/oilcan. No one is slapping a flat sheet over wildly curving and complex forms and hoping it stays in place with cleco's. They are forming it to a large extent. In A&P school you have to do all sorts of rivets (flush, countersunk etc) and once you get the first few set the skin does not move the remaining cleco's are really there to just keep the sheet against the substructure. Once you establish the inital alignment, you really can't walk a cut/formed skin wildly off kilter.... to to the point where a cleco in every hole vs every 3-4th hole would make a difference.

Best practice would be a cleco 'around' the rivet you are setting (as much as possible. That 437th cleco 6 feet away is not doing anywhere near the amount of work you think it is.

I follow an RV build on youtube and the workflow is just garbage. I get not wanting to make an expensive mistake, but when you take (and I timed this) 2 minutes per rivet (remove cleco, put down cleco pliers, insert rivet, tape over rivet with a tiny piece of tape, pick up gun and bar, rivet, put down tools, measure head with tool, clean off tape, move to the next rivet) there's gonna be a few weeks worth of wasted time there.

 

[N804RV]

But cleco's won't fix poor match drilling and deburring.

This is what I would consider normal:

JerMo's RV-10 Project

The RV-10 is a four-person airplane, not just an airplane with four seats. It will carry four FAA standard people, full fuel and sixty pounds of baggage. The cabin accommodates four full-sized adul…

rv10project.wordpress.com

Then you have this:

http://joesrv12.com/Photo/A_06_04_03A.jpg

There are not a ton of compound curves on E/ABs, they are kinda designed out of the projects to make the buildable, or are supplied/purchased formed.

Those are nice flat panels going onto a fairly uniform substructure. Try the mid-side skins on an RV-8 fuselage, where the sides curve slighlty to meet longerons with compound bends/twists. You have to start by clecoing every match hole, then final drill those match-holes before you drill into that virgin top longeron. And, you've gotta drill the skin onto the longeron, clecoing every hole as you go.

Then, after you take it all apart and debur, prime and back rivet miscellaneous substructure to those side skins, you've gotta line it all up and futz with cleco's until you can put a rivet into every hole without cheating and augering out a few holes at each end.

That's the only way you're gonna get those skins on tight with good looking rivets.

Maybe once you get it all lined up, you can pull clecos out of every other hole. But, not before. Even Van's says repeatedly, "use as many clecos as it takes to get everything to fit correctly, even if it takes a cleco in every hole."

 

[pfarber]

Those are nice flat panels going onto a fairly uniform substructure. Try the mid-side skins on an RV-8 fuselage, where the sides curve slighlty to meet longerons with compound bends/twists. You have to start by clecoing every match hole, then final drill those match-holes before you drill into that virgin top longeron. And, you've gotta drill the skin onto the longeron, clecoing every hole as you go.

Then, after you take it all apart and debur, prime and back rivet miscellaneous substructure to those side skins, you've gotta line it all up and futz with cleco's until you can put a rivet into every hole without cheating and augering out a few holes at each end.

That's the only way you're gonna get those skins on tight with good looking rivets.

Maybe once you get it all lined up, you can pull clecos out of every other hole. But, not before. Even Van's says repeatedly, "use as many clecos as it takes to get everything to fit correctly, even if it takes a cleco in every hole."

If you need to use them, then use them. But I showed the ridiculousness, or maybe just inexperience or lack of understanding that I see all over the E/AB world. Making a battery box? Better add 300 cleco's to turn a 30 minute project into a 2 day affair etc.

 

[TFF]

It’s not that you can just use a few and be happy. If it’s your own homebuilt, quality control is your own standard. Be happy in your work.
If you are trying to do a job and the owner is not happy with the work, you start loosing money. Maybe a lot. A&P school is not the real world. There is a reason Vans goes to the lengths they do for an average but game person to be successful. The guy that builds the show perfect RVs goes through multiple airplanes worth of skins for his perfection addiction. Sure you can put something together with a minimum amount. Can you put together a Bonanza tail skin without flaw? I know a few that can. I can’t.

 

[Marc Bourget]

For the reasons discussed above and adding an unmentioned benefit learned from guys who were "fitters" in the WWII shops in Lockheed, North American, etc.,

I argue for more cleecos because "things move around" while you're riveting up a structure - for example, outer wing panels.

More cleecos reduce "assembly creep" as riveting progresses. They maintain better shape conformity during the assembly process so, as things start to go "cattywhumpus," the variance(s) will show up (rather than have any variance "absorbed" by the looser fitting assembly held with less cleecos).

Devise a means to determine variances in alignment as you go - on a rivet by rivet basis. I can remember one outer wing panel where I had to have a friend introduce a "counter-twist" as I progressed. The variance decreased as I progressed because the wing, itself, was increasing in being "fixed" as more rivets were installed.

Onward and upward