Left Wing - Let's rivet...or not

I'm going to have a self-inflicted hiatus from building for a few days.  I started riveting the ribs onto the front spar, and while it went fine, the rivet sets I have are 90% fine for the job and 10% begging for me to screw up.  The manufactured head of the universal rivets (these are the round head rivets, not flush head) goes on the side of the rib flange.  In order to set the rivet, you have to bend the rib out of the way to be able to get the gun perpendicular to the surface being riveted.  The ribs are plenty flexible, but for the top and bottom rivets, the gun still sits at a slight angle because the business end hits the rib web.  The other rivets aren't as much of a problem because the lightening hole in the rib allows at least part of the gun to not hit the rib web.  I could just bend the ribs out of the way more, but then the rib flange gaps and is harder to get flat against the spar during riveting.  With round head rivets, any kind of an angle with the rivet set tends to cause problems because the cupped set digs in on one side or the other, causing squished rivets or dings in the surrounding metal.

I have two cupped sets - one that is just a couple of inches long and an offset one.  The offset one is what is theoretically made for a job like this.  I hate that thing with a passion.  It swivels freely while riveting, and it's never in a direction that is helpful.  The real kicker with it is that because of the offset, the air pressure has to be cranked up quite a bit to get the same amount of energy to the rivet as a straight set.  That higher air pressure makes it bounce like a rubber ball.  I'm sure some people love these for tight quarters riveting, but not me.  The straight set is great, but for the ribs it's just too short.  Sets are one of the few aircraft tools that are pretty cheap, so I ordered a 7" straight set today and am just going to pause the build for a few days until I get it.  The longer length will allow me to get the gun perpendicular to the surface without having to wrestle with the ribs as much.

Left Wing - Assembling...again

With the weather a little cool, the primer is still pretty fragile, but I decided to start reassembly of the wing anyway.  I had to do a little bit of sanding to get rid of a couple of runs.  I think that was the result of the cool weather and my lack of patience to let things dry before I did follow-up layers of primer.  I had to study and re-study the rivet call-outs to figure out what rivets to actually put in since there are a lot of places that get riveted later in assembly.  I covered all of those holes with tape to keep from accidentally putting rivets there prematurely

Most of the rivets in the doublers are universal head, with the exception of 4  rivets in the inboard edge.

I had been scratching my head over the outboard 3 rivets for a long time.  I couldn't quite figure out from the drawings whether or not the doubler needed to be dimpled or if the aileron attach bracket installed later on would simply sandwich it and it could remain flat.  It took a while, but I finally pieced it all together and figured out it should be dimpled to allow the attach bracket to lay flat.  These are the types of things that I've heard Van's has improved on in the modern plans (now they do a step by step approach with detailed drawings at every step in the manual vs just full plans of the entire assembly).  For the older plans like the 9A, they really still leave a lot of steps to be figured out.  If I ever build another plane someday, I think the improved plans are going to feel like cheating.

I clecoed the ribs in place but didn't quite get to riveting today.  Based on the direction the rib flanges face, I left a few of the inboard wing walk ribs out to make riveting a little easier.

Left Wing - Priming

Today turned out to be a relatively warm day, so with just a few minutes of the propane heater running I had the garage heated up enough to prime. I thinned the primer a bit more than I have in the past, which really seemed to help it lay down nicely in the colder than ideal temperature (it was in the mid 50s, which is warm, but still not ideal). I had thought about hanging the ribs so I could do both sides at once to speed things up, but in the end I just used my spray table. It was warm enough that I only had a few minutes of downtime between coats.

After priming I ran to Home Depot to pick up some lumber for the wing stand. Lumber prices have come down a bit, but the cost of a 2x4 is still pretty outrageous! I think I may still actually be able to use more scrap wood from the wing cradle I tore apart last week. I used some of that cradle for my version of a wing storage cradle using the wing crate from Van’s, but I didn’t use all of it. I think I can Frankenstein it together into a useable stand. I’ll either build that tomorrow or start riveting ribs to the spar, just depending on my mood I guess.

Left Wing - Wire Routing & Primer Prep

There are a number of ways to route wires in the wings.  They can either be routed through the lightening holes, through an enlarged tooling hole, or through holes drilled specifically for flexible conduit.  For ease of re-running wires in the future if there is ever a need, I'm going to use conduit.  Luckily, the used wing kit I bought had the conduit from Van's included.  The 3/4" hole to accept the conduit can be drilled anywhere in the lower 1/3 of the main ribs between the first two lightening holes.  The conduit is flexible, so getting the exact same location in each rib isn't all that important.  Just to get in the same ballpark, I made a cardboard template, pilot drilled the hole and then finished up with the unibit.

Beyond that, there's not much to show from today.  I spent a couple of hours cleaning and acid etching everything.  Tomorrow I'll see how well I can heat up the garage to get it all primed.

Left Wing - Rib Prep

I took the spar out of the blocks and laid it down so I could match drill the ribs to the front and rear spar.

And just like that, something that looked like a wing had to get pulled apart for deburring.  

I wanted to try to get a little more room for the wing stand, so did a bunch of reorganizing. It took a while, but I think it's marginally better. 

Left Wing - Fitting Ribs

I had to start tonight with a little shop reorganization.  I think I can actually squeeze the wing jig into my shop bay as opposed to putting it where the car goes.  I moved the drill press and bandsaw closer to the table saw (it's very cozy now, but those won't get used much during the wing construction), then moved the table with the grinder and sander back a few feet.  Pivoting my big work bench 90 degrees gave me a pretty decent size area that should be enough room to build each wing in the jig.  That will at least get keep the car inside through the winter.

The manual calls out priming and riveting the rear spar before moving to ribs, but I'm just going to cleco everything together first then prime all at once.  It's just far easier that way, especially now that I have to set up to prime inside.  First things first, I sorted out all of the ribs I'd need for each wing.  Each wing gets a variety of left and right facing rib flanges, so you really have to pay attention to the plans when figuring out what goes where.

This is where I was reminded that all of those individual parts I've been working on for a while actually go together to make a plane!  Putting the ribs on the front spar really changed how things look!

Once the ribs were clecoed onto the front spar, I put the rear spar in place.  The plans are a little weak when it comes to seeing how the rear spar and ribs connect.  For most ribs, there is only one place for them to go, but for some, there are multiple hole patterns where they could go if you're not paying attention.  The exploded view of the wing doesn't show it in enough detail to figure out, so I had to use the rivet callouts to see which 3 hole pattern in the doublers were for the ribs and which were just the same pattern but for other brackets.  It was pretty easy to double check just by ensuring the ribs were parallel to each other at least.

Most of the ribs are evenly spaced, but the inboard end has double the ribs for the wing walk area.

The next step will be to match drill everything, disassemble and prime, then rivet it all together and build the wing jig to hang it on in preparation for skins and the front nose ribs.

Left Rear Spar - Bad Doubler

Not much to show on the plane today.  I snuck out to the garage for a few minutes and got the doubler plates match drilled to the rear spar.  Since I actually knew which end was up tonight, I managed to do it correctly this time!  The middle doubler gets a big hole cut out of the center for an aileron control arm, so I used the unibit step drill to hog out some material and then hit it with a file to finish it.

The inboard end of the spar gets two different plates: a forked reinforcement plate and then another doubler at the very end.  Easy enough, but I discovered the first manufacturing problem on a part, which slowed things down of course.  On the first doubler I used, the holes on the top edge lined up great, but the holes on the bottom were almost 1/16" off.  That doesn't sound like much, but when it's a 1/8" hole, that's a big variance.  After my screw up the other night I thought I'd double check to see if I was just positioning something wrong. I grabbed the second doubler (for the other wing) to see how it fit.  Everything lined up perfectly on that one.  I took some measurements and sent a few pictures off to Van's to see if I can salvage it or if they just need to send a replacement part.  On the bad piece, one of the holes in the center of the part has a bulge and an obvious hole punch mark that is outside of the actual hole, so I think the tooling may have slipped when they made the part.  Thankfully, because the reinforcement plates and doublers are identical from left to right, I can just use the good parts and deal with the bad one when I get to the other wing.

Tie Downs and Starting Rear Spar

I scuffed up one side of the access plates (definitely easier than waiting until priming day after everything is dimpled), enlarged the holes to match the screw size, then dimpled and deburred the edges.  I won't need these parts until the very end of assembly and paint, but at least they're done.  I'll just prime the inside the next time I do a batch of parts and then set them aside with the other orphan parts.

Back to the spar and a few more nutplates.  These go on the inner portion of the spar as part of the connection to the center section in the fuselage.  I don't think I'm going to actually build both wings at the same time just because of logistics of space, but so far I've done the spars in tandem.  It's just easier to set tools up once and do both spars together.

Next I needed to fabricate the tie down bar.  The basic form is supplied, and thankfully they've already reamed a hole down the center of the spine.  I don't have a tap though, and Home Depot didn't have any sets in stock, so that task will have to wait until I get a set shipped.

The aluminum bar needed holes match drilled to the spar.  I started with one hole located per the drawings, then lined everything up on the spar, clamped it in place and drilled out the rest with the holes in the spar as a guide.  With each hole I slipped a bolt in to make sure the part didn't wander as I kept drilling holes.

I want to be able to attach these to the spars and be done with it, so I grabbed the rattle can primer and primed really quick.  I still can't get over how awful smelling that primer is.  It really makes me appreciate the Stewart water borne stuff, which is almost odorless.  I'll wait to attach these until I've tapped the hole for the tie down ring.

With that, the front spars are pretty much ready to go for wing assembly.  I stowed them back in the crate and pulled out the next batch of parts.  Next up is the rear spar, which is much different in approach than the front.  The rear spar is a thin aluminum Z shaped channel that gets a number of doublers on it, just like the spars in parts of the tail.  Of course, these are double the length.  Once again, I grabbed both right and left sides to tackle both at the same time.  All of the doubler pieces had pretty rough edges - they are about 1/8" thick, which I'm guessing plays a role in how clean they can be punched.  At least these look punched.  I don't think they are laser or water cut.  I hit most of the parts on the sander first to get rid of the big tabs left on the edges, then smoothed everything out on the Scotchbrite wheel.  For the inside edges I used a file, followed by sandpaper.

I didn't get around to deburring edges on the spars themselves yet.  I'll probably wait and do that after I've match drilled everything.  Other than that though, these parts are ready to start initial assembly and match drilling, which I'll probably get rolling on tomorrow.  In the meantime, I need to plan out my wing jig, which is a couple of posts mounted vertically to the floor/ceiling and a metal angle iron shelf for the spar to rest on.  I think I can actually get all of the way through clecoing and match drilling the main ribs to the front and rear spar before having to move everything to the wing jig though.

Once I'm ready for the jig, which isn't too far in the future, I'll have to kick one of the vehicles outside.  The jig has to be pretty rigid, and since I can't go from floor to ceiling because of the garage door, I think I'll have to build a base on each end with plywood and 2x4s, stick them to the floor with a few dabs of construction adhesive (that may not actually be necessary), and brace a 4x4 vertical post.  From what I've seen, the post really doesn't need to be any more than 4-5 feet tall.  Something like this (from Smitty's RV site - a fantastic site I reference all the time):

I was done for the day after deburring all of the rear spar parts.  Or, I should have been done for the day.  After sitting down and updating the blog, I had a few minutes, so figured I'd just go out and start match drilling a few parts.  Two of the doublers are just blank pieces of aluminum with a flange on one side.  These get placed on the spar and match drilled.  The flange on the spar was almost a perfect 90 degrees though, and the doubler's bend was off by a good 10 degrees or more.  That should have been my clue that I had something wrong, but instead I figured it just wasn't bent quite right and I "corrected" it.  I clamped everything together and match drilled.

Just as I finished the last hole, it hit me - I wonder if the top and bottom angle on the spar flanges are different since the top and bottom of the wing obviously have different shapes.  Yep, they're different, and the doubler flange would have matched up perfectly with the other side.  There are only a couple of holes in the other end of the spar that give a clue as to which side is up/down, and I had it wrong, so I match drilled the part upside down.  At this point I should have known that if something doesn't fit perfectly, I probably have it put together wrong. The good news is that I have a second doubler for the other wing that I can use for this spar while I wait for a replacement.  At least I screwed up a cheap part ($9)!  I keep a running list of things to buy from Van's, so I placed an order for the doubler and also some safety wire and tie down rings.

Elevator Trim Tab & Wing Access Plates

The proseal that joins the foam ribs to the skin in the trim tab has been curing for a little over a week, so I decided to finish up the trim tab today.  It's a little fiddly because there isn't a great way to clamp the remaining portion of the hinge to the elevator while the trim tab is actually attached.  I had to do a lot of back and forth until I got the hinge in a place that allowed the trailing edges to line up, as well as left the required space between the elevator and trim tab in the middle where they meet.

I match drilled all of the holes, double checked the alignment of everything, then pulled it all apart and cut the hinge to length.

Everything went together pretty well and the trim tab moves freely.  I still need to bend the hinge pin and safety wire it in place, but I need to order safety wire.  I have a running checklist of items that still need to be done so I don't forget.  Likewise, the counterweights still need to be added to the elevators.  Considering that the elevators can't truly be balanced until they are on the fuselage (and again after paint), I just decided to leave the counterweights off for now and will bolt them in when I join everything together.

With the elevator done and a little more energy from dinner, I decided to keep chipping away at the spar nuplates.  I had all of the tank attach points done on both spars already, but there are also a number of nutplates needed for 3 access plates on the underside of each wing.  These nutplates are slightly smaller for a #6 screw vs the #8 of the tanks.  Each access plate has 4 screws that go trough the spar.  The method for countersinking the screw hole was the same as before, except this time a #40 countersink pilot is what fits in the threaded nutplate hole to keep things centered.

I upsized the prepunched holes in an access plate and dimpled them as a check to make sure my spar countersinking was okay.  The reference I found on VAF said that a #6 countersink should be less than .3125" wide, and mine were just under .3100". The fit with the access plate was great.  Tomorrow I'll drill, deburr and countersink all of the access plates. We'll see if I remember that the 4 holes I did tonight are for #6 screws, but all of the other holes on the perimeter of the access plate get #8 screws.  No idea why the difference.

Organized Chaos

Over the last few days I've finished up the initial pile of nutplates on both spars.  There wasn't much to describe with that since it was the same day by day.  I hit a stalling point yesterday because the next thing to do was to start working on some access plates, which were buried somewhere in the big crate under the wing cradle I got from someone last summer.  In order to get moving with the wing build, I really needed to tackle that crate.  Eventually I'll clean out that entire garage bay and move my car there so I have the open stall next to my "shop."  For now, I have to juggle things back and forth though.

So today I spent most of the day pulling parts out of the crate, getting rid of packing paper, organizing things, building a new wing cradle, etc.

The first thing I noticed when going through parts was that the ID on the wing spars doesn't match the ID on the center section (the portion that the spar is sandwiched between when going through the fuselage.  The spar is 1935, whereas the center section is 1943.  I believe these pieces get match drilled at the factory to make sure they line up correctly, so I'm checking with Van's to see if this is a problem.  It's possible I'm just misinterpreting things.

There are a few things that the original purchaser of the kit bought that I probably won't use, so I'll either sell or give them away to another builder.  The glass panels these days can be set up with AOA systems, so there's not much of a reason to install an old school stall warning vein.  

I jumped in and started wading through paper in the big crate.  Virtually every part is either taped up or wrapped in paper, so I learned very quickly to shake out every single piece of paper after I almost threw away some small parts with what I thought were just wads of paper.  I sorted out the small parts (pretty much anything that wasn't a skin) and put those all together to make it a little easier to find things as I build.  I ran into a problem with the skins though.  I was thinking I could just put them underneath my benches like I did with the skins of the tail feathers, but the wing skins are way too long for that.  So I need a place to store the skins, as well as to store the wings once they are finished.

I had originally planned on using the wing cradle I got from an RV4 builder this past summer, but after looking at the plans, it won't work very well as-is.  The wing is apparently shorter and fatter on the 4, so the cradle would take a significant amount of rework to fit the RV9 wing.  Instead of doing that, I decided to just use the crate that the wing came in.  It's close to the right length and would be able to double as storage in the meantime.

I broke down the wing cradle to use some of the wood and wheels from it.  The big wing crate already had a couple of 2x4s stapled to the bottom, so I attached the wheels to them.  This isn't as stable as putting the wheels at the end, but I think it'll work okay.  If it ends up being too unstable I'll move them to the ends of the crate.

I took the plywood top of the crate, cut it up, and doubled it up for the ends.  The 2x4s attached to them were already stapled to the plywood, so I just left them in place and used them to stabilize everything.  I used a leading edge rib as a template and cut out a pattern on one end (I trimmed these a little bigger than needed and will line them with carpet).  The spar itself will rest on the other end, so it doesn't need the same treatment.  All of the skins and parts have plenty of room in the crate still.  Even when the wings are in the cradle, I think there will still be room to store parts.  That'll be needed once I receive the fuselage kit and have to consolidate space again.

The crate, and now wing cradle, went right back to the same place it was before.  It's still taking up the same space as it was before, but now I have access to the parts I need and the old cradle is out of the way.  Tomorrow I may actually be able to get some real work done.

Deja Vu - Spar Countersinking

Next on the list was to countersink the spar flange for the #8 screws that attach the fuel tank skins to the spar.  While Van's calls out a .007" sub-structure countersink for dimpled skins with rivets, they don't really say much about what is appropriate for something held together by a screw.  Looking on the VAF forums, this has obviously been a head scratching moment for a lot of people.  Some people just make the depth such that a screw head just sits flush in it, but that doesn't really let a dimpled skin seat well enough.  Other people have gone so extreme in countersinking too deeply that they've had to work with Van's to engineer fixes, which don't sound like fun.  I finally found a reference to an old RVator article (an old newsletter written by Van's, but no longer published unfortunately) that mentioned the countersink diameter for a #8 screw in the spar flange.  The say the diameter should be between .365-.375".  They're instructions said to go flush and then 2 clicks of the countersink cage beyond that.  As many people noted in response to that though, that 2 clicks doesn't get you anywhere near .365".  So the bottom line is I need to stay under .375" and anything under that is fine if I think the skin will seat okay.  I finally landed on a happy medium that gives me a little bit of a countersink halo around the screw head.  I tested with a scrap of dimpled aluminum, and I think it'll work okay.  I measured it and the diameter is around .350"ish.  Worst case scenario is that when I mount the tanks I'll find that the dimples aren't deep enough and I'll have to redo the countersinks a little deeper.  That wouldn't be the end of the world.

Anyway, after a lot of nervous back and forth with the cage settings, I started.  I had set the cage to allow for the thickness of the tape - the countersink cages have a metal foot that easily scratches whatever they are up against.  Just like when countersinking the thin material on the elevator trim tab spar, the pilot of the bit doesn't have enough material to guide it through.  That makes it chatter and create a slightly oblong hole.  Van's calls out using a slightly undersized pilot cutter though, with the idea that it'll actually fit into the threaded hole of the nutplate once it gets deep enough.  Sure enough, it worked pretty well.  Things would chatter like crazy until the pilot reached the nutplate and then it would center and smooth out the last small bit of the countersink.  This still creates a knife edge on the material because the size of the hole is bigger than the material thickness allows, so I used a small round file to knock off the sharp internal edge of each hole.  Lastly, I hit each hole with primer, flipped the spar, and then did the exact same thing to the other side.

I was planning on continuing on with the next steps for that spar, but it looks like a lot of the parts that I am going to need are in the bigger crate that is buried under piles of stuff still.  I'm not quite sure where I'm going to store everything, so my plans changed and I decided to just tackle the other spar instead.  At least by doing this I can just use the settings on my countersink cages and not have to redo all of the testing I would have to do by waiting until later on in the build to start the second spar.  So here we go again - match drill, countersink, prime, and rivet on nutplates. 

Spar Countersinking

Not much to show tonight.  I finished installing all of the nutplates in the spar and started countersinking the center hole for the #8 screws.  These are pretty slow going - they are very deep and take a little finessing to keep from chattering.  Initially the pilot doesn't have anything to guide it, but it eventually centers in the nutplate at the very last bit and centers and smooths out the countersink.  Only 60 more to go tomorrow.