Wings: Ribs. A cracked rib scare that wasn't.

I've been waiting to post this for 7 months.  What was holding me back was the final resolution, which was completed today.

On 4-Dec-13, I decided to remove several rivets along a rib line as their shop heads were less than perfect.  This was a bad day:  I botched the removal of four rivets ending up with slightly elongated holes.  On the fifth rivet, I removed the factory head just fine.  Thinking I was on a skin-spar joint, I gave the rivet shank a good smack with my punch.  Out popped the rivet, like it should.  I was  then horrified to find that I was actually on a skin-spar-rib joint!  Meaning, now I bent the rib flange out.  I took my low quality boroscope to the inboard side of the rib to get a closer look at what I had done.

Oh no!  It must be a cracked rib!  How can I fix this?  The top and bottom skins are already on.  The rib can't realistically be replaced.  Maybe I could run a rat tail file in the rib notch and work out the crack then re-radius the edge.  This isn't good!  I was ready to give up and start saving a few decades for a Cirrus.

To investigate how feasible my filing fix might be, I went in to get some better pictures to check clearances and angles for running the rat tail through there.  On the outboard side of the rib (not shown), I noticed the surface of the rib in the area of the alleged crack was completely undisturbed.  That was perplexing.  If there was a crack, I should've seen it on both sides.  With a simple Canon SD1100IS consumer camera, I adjusted the camera angle and lighting and it turned out it wasn't a crack at all!  It's actually bucking bar damage from when the rivets were bucked, as shown below.  My bucking bar is rectangular and the edge got slightly driven into the rib since it was resting on the spar flange.

You can see why I went in to remove the rivets:  Of those in focus, the one on the left is damaged and the two on the right are over-driven.  Though it looks like the dimples are cracked on the right, it's actually the primer unable to conform to the metal expansion when the rivet is driven.  Ya, it scared me too when I first saw these popping up.  Turns out it can be a good indicator of an over-driven rivet.

Anyway, how does that tab look after being pulled in by a cleco?  Compare the left and right sides below.  Clearly, this tab won't sit flush on its own and certainly not with the pulling power of a cleco.

So, to pull it flush, I could use a strong pull rivet like a CCR-264SS-3-2, but I really wanted to have a normal AN426AD3-4.5 in there.  The challenge then becomes how to keep the flange flush whilst riveting.  Well, I had a "moment of clarity" and devised the following methodology:  Use a normal mushroom set on the factory head but instead of a bucking bar on the shop end, use a back rivet set with the shank of the set inserted into a bucking bar with a hole.  The spring loaded collar of the rivet set will push the rib's flange flush onto the spar flange, whilst the bucking bar it's inserted in will provide the mass for forming the shop head.  As the rivet expands, it should pull in and lock the flange tab in as flush as it can be.  Here's what that looks like in concept.

So, I tested how far the tab would be pushed down onto the spar flange with the back rivet set, as shown below.  Turns out, it has a way to go.  I looked around for stronger springs, but decided on another method instead.

I've read that some folks use a rubber grommet between the bucking bar and the shop head to help keep two parts flush against each other.  What kind of grommet would be strong enough to withstand the brutality of a bucking rivet gun and of the appropriate elasticity to allow the bucking bar to push everything flush?  Well..uhhh...these will...

So here's the bucking bar with the..uhhh..."ring".  The Popsicle sticks were attached so the bucking bar could rest on the spar.  The shop head of the rivet will go into the ring and the bucking bar is then pushed very hard into the flanges, keeping everything flush.  Then the rivet is set with the gun.

Bucking bar in position.

And here's the result.  Not perfect, but far, far better than had I just bucked it normally.  And it's clearly better than had I used my back rivet set as the bucking bar, as the image four above suggests.

Whew.  Ya, I ain't so smart.  But managed to get myself out of this jam and still feel okay trusting my life to these wings.

Wings: Ribs. Riveted to spar.

The ribs have been riveted to the wings.  Except for the outboard ribs (as per plans) and the most inboard on the right side (W-1010-R) since I need to redo the torque tube support bracket due to...operator error.  This was a full 7.5 hour affair with the help of my friend, a successful RV-9A builder.  We drilled out and replaced about 6 rivets.  That's not too bad.

Wings: Ribs. Prime rib.

2 hours later, all ribs are cleaned and etched, including all the smaller parts like brackets and so forth.  I decided to use Stewart Systems' offerings, including EkoClean, EkoEtch and EkoPoxy/EkoPrime.  Getting these guys to dry is a challenge, so here they sit, under the ceiling fan (pardon the wing tips, that's the best place to store them until they're needed).

Here's the priming extravaganza.  I practiced with the spray gun using water.  I tried to calibrate the air pressure, air volume and fluid volume.  I knew this was going to be a learning experience.  I wasn't sure how much to spray on the parts.  The instructions call for 3 mil.  How to measure that?  I don't know.  Thus, I sprayed enough so it appears that the metal is covered.  Sometimes I sprayed too much.  Sometimes too little.  The latter was easy to fix.  If the former is too bad, I can sand it down.  EkoPoxy dries slowly, so you can't turn over parts to prime the other side.  That was a challenge.  Overall, it took 2.5 hours to prime the ribs and the other parts from Sections 11 and 12.

It's probably fair to say that each rib will have received at least 1.5 hours of work associated with it prior to riveting on the spar.  28 ribs=42 hours.

Wings: Ribs. Final drilled to spar.

Flap-brackets are final-drilled and their associated ribs have been match-drilled.  The torque tube support assemblies are ready.  Conduit holes are drilled in the ribs.  Most holes needed to be enlarged, however some holes needed to be created.  Using a punch is not the way to go as it deforms the web.  So I used a smaller bit, about 1/32", to create the hole, enlarged it with a 1/8" then used the unibit for final-sizing.  Some of the conduit holes are 1/2" so using the hand deburring tool was a non issue on these larger holes.  For the smaller holes, the 400 grit sandpaper worked fine.

Next was removing the bolts from the web of the spar.  Some of these came out easy, others were extremely challenging.  Almost as though the hole they were sitting it wasn't big enough.  With the bolts removed, the ribs get cleco'd onto the spar so that 1) the #30 holes in the spar web and rib forward flange can be final-drilled, 2) the forward flanges of the ribs can have the bolt holes match-drilled with a #12 and 3) final-size drill the #40 holes on the rib tabs (which I had done previously since I looked ahead at the plans).  Using a #12 bit to start a hole on the forward flanges is not a good idea.  So I used a #30 bit to start the hole and final-sized it with the #12.

Left spar and right spar.

    

Cleco'ing in the ribs on the right spar.

Next comes prep for priming.

Wings: Flaps. Brackets straightened.

I asked one of my shop-master friends how I might straighten the W-1025A Flap Hinge Brackets, since I couldn't visualize how to do it with the tools I have.  They are, after all, 3/16" thick aluminum.  He suggested his hydraulic press.  The brackets are much better now.

I also had to order a #12 bit to final drill the aileron bellcrank brackets as required on page 13-05.  That is on the required tools list from page 3-02, so that's my fault for neglecting to purchase it earlier.

Wings: Ribs. Prep for systems holes.

I organized and labeled all of the ribs according to their position from inboard, 1-14, for each wing.  Then I could locate their systems holes, label their sizes and mark the locations for drilling (upper-aft, lower-aft, lower-forward and ground lug holes).  Since not all ribs get the same holes and each wing has different holes, this made the most sense.  Here they are, stacked, top to bottom, inboard (1) to outboard (14).  Left stack is left wing.

Wings: Ribs. Deburring, dimpling and other stuff.

This marks the 54 hours mark.  Not much to show for all that time.  Nothing that looks like an airplane, that's for  sure.

I continued prepping the ribs by finishing up the #40 hole deburring and starting their dimpling.  For the holes, I was originally using the hand deburring tool but it didn't seem to be taking the burrs away.  So I ran over the holes with 400 grit sandpaper.  That was taking away the burrs quite nicely, but it was a lot of manual labor.  Turns out that handy 3M Scotch-Brite Fine-Finishing Sander was perfect for the job.  You could hear the burrs "ticking" off the flanges.  Plus, it's like free scuffing in preparation for priming.

There were a number of self-inflicted scratches on the ribs which I needed to remove.  Here is one example "before" and "after".

 

Then I had to sand out some minor nicks from the factory in the spar.  I wish I took a "before" picture, but here is one area sanded with 400 grit and polished with 600 grit, prior to priming.

When it came time for dimpling the ribs, the plans call for only the lower flanges to be dimpled.  That seemed odd to me.  Why wouldn't you dimple the top flanges?  So I peeked ahead in the plans and found that in Section 16, page 16-02, you're asked to dimple the top flanges, but not on the inboard 4 ribs.  That's because those ribs support the wing walk doublers.  Thus, I decided to label those 8 ribs (4 each, left and right) and draw a line down their upper flanges to avoid accidentally dimpling them (pic below).  I could dimple the top and bottom properly since it's easier now with them off the spar than later with them on.  That took a while.

Then it was on to the torque tube support brackets.  Those had to be match drilled as a single structure, then again when on the ribs.  Here they are as separate assemblies.

And here the right one is on its rib.  It was extremely difficult to fit this into the rib.  In fact, I plan to pull it out and adjust things to get a smoother fit.  I'm concerned that I may have gouged the W-1010-L in the process, in which case I'll be buying another one.

You can see how it doesn't quite sit well in there.

Now, the left rib torque assembly bracket was impossible to fit.  Why?  Take a look below.  The W-1029A-L isn't properly shaped.  It's as though they bent it at the wrong locations to make the flanges.  This isn't something I can fix since the holes wouldn't line up with the ones in the ribs if I just somehow rebent it.  So Van's sent me a replacement part.

Wings: Ribs. Deburred, drilled, staightened and fluted.

So far, I'd say each rib has received about 45 minutes or more of attention.

• All edges on the main ribs are deburred.  
• All #40 holes are final-sized.  
• All flanges are straightened.
• All main ribs are fluted and flat.

The 3M Utility Cloth Roll 314D did the trick on deburring the tabs and other hard-to-reach areas.

 

The rib straightener rocked every flange.  I taped part of a cereal box underneath the pressing lever to get the edge as close to the rib bend as I could by just kissing the top of that part of the rib that curves up.

Fluting was an interesting experience.  Chapter 5 of the plans has little guidance, so off to the web I went.  One gentleman has a nice video explaining the whole process, so I tried that originally.  But I found it to be time-consuming and too much of a shot-in-the dark.  I had remembered reading that it isn't necessary to flute every space between holes, so off I went to the Internet for more ideas.  This fellow had a great technique which I adopted.

Step 1:  Notice that rib is curled here.

Step 2:  Start by fluting the part of the rib with the largest curl and work your way out.  As you press on the fluting pliers, the curl is reduced.  You can watch the rib get straighter as you press.  Notice that not every portion is fluted below.  That is the same rib as above.

Here is a nicely fluted rib.

 

All main ribs fluted.  You'll notice that each rib is fluted in the same general area and each one is done differently, according to its needs.  Initially, I was concerned that my table wasn't flat.  But I checked it with a straight edge.  Upon closer inspection of unfluted ribs, they tended to be curled in the same way.

This stack used to have a lot of springiness to it.  Now that they've all been fluted and are straight, this is a fairly rigid stack of ribs.

Next, these ribs need to have their #40 holes deburred on both sides and then dimpled properly.

Wings: Ribs. Deburring ribs made easy!

Here it is, the solution to all weight-saving hole deburring problems:  3M Scotch-Brite Fine-Finishing Sander.

Mounted in the drill press, it makes deburring the holes as easy as pie.  Already ran it through the main ribs.  Beautiful results.  You can hear the burrs coming off as satisfying audible "ticks".  This will make deburring the leading edge ribs go by so much quicker.

Then I will try 3M Utility Cloth Roll 314D for the little tabs and such.

Also, J-stiffener match drilling is complete as I received the replacement J-stiffener from Van's.

Wings: Ribs. Rib deburring 2.

Deburring continues on the ribs.  This is a tedious, repetitive, repetitive, repetitive process.  I've nearly completed all of the trailing edge ribs (as opposed to leading edge ribs).  I have only the little tabs to complete on each one.  That's not an easy task.  So I picked up some 400 grit aluminum oxide cloth to get into those little nooks and crannies.  I also picked up a finishing sander to speed up the weight saving holes on the leading edge ribs.

Main ribs, mostly deburred.

Once I'm done with these ribs, I'll go ahead and knock out the leading edge ribs too.  This way I can prime all ribs at once.

Leading edge ribs, untouched.  That right there is a stack of tedious boring work on deck.

Some things I've learned:

• Be careful with the hand deburring tool.  If you get overzealous you can skid the blade right off the edge and along the body of the rib. It causes a scratch.  I've marked each scratch so I can go over it with some maroon Scoth-Brite pads to buff them out.

• If you don't remove a big burr with the cutting wheel, the hand deburring tool will just skip right over it, neither deburring around the big bur, nor removing it.
• Sometimes the hand deburring tool will picket-fence down the edge causing little bumps.  Seems it's a function of speed and surface profile.
• The edges are sharp and cut into the cutting wheel.

Looking ahead a bit, these are the flap hinge brackets, W-1025A.  As you can imagine, they're quite thick to bear the requisite loading.  The plans call for straightening them out.  Mine are a little curled.  How on earth one straightens this stuff is beyond me!

I also scanned the plans into a pdf file and ran them through some OCR software.  Now I can study the plans wherever I am.

Mistake #2.  Can you spot the problem?  I can attest that ribs are about $22 each.

 

Wings: Ribs. And other updates.

• Bought Napa 7220 self etching primer for the spar countersunk holes.
• Ordered the replacement J-stiffener.
• Ordered the two missing parts.
• Spoke to Scott at Van's about the spar issue.  He asked the guys who build the spars what they thought.  If I understood Scott correctly, the shavings occur when the rivet is placed in the hole.  If any gap between the rivet and spar exceeds 0.005", then it would be out of spec.  He suggested I use a feeler gauge to measure it.  After he explained to me what one of those was (I was thinking the round spark plug gap checker), I went to O'Reilly's to buy one.  There is no gap.

Whilst I wait for my replacement J-stiffener, I continued working on the ribs.  I decided to cease straightening the flanges until after I debur.  So, I spent 3 hours deburring today.  It was the first time using the Scotch-Brite wheel on the grinder, so there was a learning curve:  At first I was timid with the wheel and wasn't happy with the smoothness of the edges.  But after being more aggressive with it, I could really get a nice smooth edge.  For some edges I used the hand deburring tool since I couldn't get to all sides with the wheel.  But, I didn't do the edges that are along the weight-saving holes in the webbing.  I'm going to do those after I'm done with the outside edges. I also found that I needed to pad the tool rest on the grinder with some electrical tape since the rest was scuffing the ribs.  Finally, I placed a fan to blow on the grinder to keep it cool.

 

Deburring edges.

Left:  The corner (the outside of the wheel is obviously not effective).
Right:  The pile on the left has their outside edges deburred (3 hours!).  The pile on the right doesn't.  Then I have to go through them all once more for the middle holes.