Saturday, January 26, 2013

Elevation, Round 1

As tempting as it is to dive headfirst into wiring Tony Boy's new instrument panel to coincide with all the learning and GRT EFIS documentation-creation I'm doing at work, this tail kit just really needs to be done. It's going on THREE YEARS now! Granted, a lot has happened, including a tornado, two cross-country moves and the rebuilding of two wings and a rear fuselage. But seriously, it's time to be done with the tail.

I finished up the rudder a few weeks ago. It's not perfect, but it's straight and miraculously dent-free. I say "miraculously" because it's my first control surface made of featherlight .016 sheet metal, and it survived inside a trailer from Yakima Washington all the way to Michigan.  

The elevators are built the same way as the rudder. Draw out the location of the spar on the skin blank, then build on that location to figure the location of the stiffeners, ribs and, in the case of the left elevator, the trim tab. The right elevator was easy, I drew that out in half an hour. The left one caused me some trouble. The dimensions just didn't add up. After drawing the spar, then the trim tab spar and stiffeners, my trim tab cutout would only be 17" long, a quarter inch short of what is shown on the plans. I tried probably half a dozen times to get it right, then asked Ben what in the hell I was doing wrong, thinking he'd see something simple and call me a "crackhead" for missing it. He looked at it, measured some things, and said very quickly, "Let me draw it in CAD and see what happens. If Van's sketch is wrong, we'll find it." So he did. He plotted out all the lines & dimensions given, and when he measured the distance from the edge of the skin to the bend line on the outboard end of the trim tab, the computer came up with 17" for the trim tab opening. HA, I was NOT a crackhead after all. 17 inches, so be it. Build on. 

I had to make stiffeners from raw stock because I used up half of my elevator stiffener stock to remake my messed up rudder back in July. I have to admit, when builders of pre-punched kits complain on VAF about their stiffeners not lining up right or they can't figure out how they go together, I laugh silently to myself. I laugh because they are so easy to make from scratch. See?

First you shear the .025 sheet into 1" strips to make them 1/2" tall, and thus you may trim them to the angle depicted on the plans. The kit includes 5/8" tall stiffeners that can bottom out when you try to bend the trailing edge of the skin, so making them 1/2" tall avoids all that ugliness. See, you're ahead of the game already by scratch-building. 

 Then you set up the brake to smash the strips into angle stock.

And then your dog falls asleep because you're so boring. 

And then you measure out how long each one is supposed to be, trim it off to length, pick out the ugliest end, and measure & draw the angle at the trailing edge so you can cut it to final shape with the band saw. 

Then you file as necessary. There, now you're ready to measure out, mark & drill the rivet holes. And then you realize that those guys crying about their stiffeners not lining up have had enough time to go on VAF, post a question, get a response, fix their problem, put all their stiffeners in place and backrivet them on during the amount of time it took for you to make your stiffeners from scratch. :-) 

Sunday, July 1, 2012

Don't Sweat the Do-Over.

Last week, after destroying my rudder skin, I almost ordered a new one from Van's. New rudder skins are $70, but I just happened to have a new piece of .016" 2024 squirreled away in the garage from a long-forgotten project. I decided, what the hell, I'll make a new one from scratch. I used the original skin as a pattern and cut it out on the garage floor using the air shear. It took all of a half hour to cut it and bend the trailing edge using a 2x6 and an extra set of hands. In fact, it went so fast, I forgot to take a picture of it. Imagine that, me forgetting to take a picture! The flange on the one side was easily done at work on the sheet metal brake.

One week later, as I look at my new skin, I realize that my booboo was actually a good thing. While I was happy with the original one, there were a few things I had wished I'd done differently.

One thing is the dimpling. I set the DRDT-2 up so that it created a crisp dimple, but even after the rivets were driven, there was a slight bit of an upturn on the very edges of each dimple. I know the instructions for the DR say you can't overdimple with it, but this is really thin metal, and I believe they actually were over done just a bit. So, this time I relaxed the preload on the DR and ended up with smoother looking dimples.

I made all new stiffeners for it instead of drilling off the ones I used on the original skin. One night last week, I  tried to drill the first two and ended up with (what I thought were) horribly crooked rivet lines. I just couldn't get the drill to do what I wanted it to that night. I came in the house and complained to Ben about it and he pointed out that the bend radius of a stiffener fits a corner of a 2x4 perfectly, so why not clamp one to the drill press and drill all the stiffeners in the "jig?" He's smart. I remade the two that I drilled by hand (again) and used the 2x4 trick. I was a little mad that I didn't think of it myself. This made the rivet lines straighter.

Another thing I thought of halfway through the last rivet job was the fact that I had no primer and a lot of hand prints on the metal. Last year I decided not to prime the new components of the plane because the fuselage and wings aft of the spar are not primed. No need for all that extra work and money just to have the tail survive after the fuselage corrodes away, right? :-P  However, I did not think to clean the skin or stiffeners before riveting, which can be a bad thing because skin oils can be corrosive. Once you rivet the stiffeners in, oils and dirt trapped between them and the skin is there forever. This time around, I had a few scuffs to clean up anyway with the Scotchbrite, so I cleaned all the parts thoroughly, lightly scuffed them and gave them a quick shot of self-etching primer to protect any areas where the alclad got worn off during the scratch buffing process. This would also protect them from greasy mitts during the assembly process.

The backriveting went fine this time due to increased vigilance and situational awareness. Ben helped hold the other half of the skin out of the way for the aft rivets, and that helped as well. Now it's time to freak out about squishing the finished skin in the archaic hinged wood device according to Van's instructions to form the final trailing edge radius.  Eek!

Sunday, June 24, 2012

Over the Edge

So this morning, we set out to Sears to return our smoking 33 gallon air compressor. Ben decided maybe that one was too small anyway, and it was a noisy little bastard being a single-stage, so we just got our money back and decided to upgrade to a Kobalt 60 gallon, 3.7 hp two stage. It's a big mean-looking sucker but it fits nicely in the corner of the garage near the door and is actually much quieter than the little one, and it runs less, so it should turn out to be the best fit for this suburban paradise we're in.

By 5:30 and after several trips to Ace hardware for fittings & such, including a comical conversation with the hardware guy on the sexual nature of plumbing terms, I was finally able to get to work on the plane. I had laid out my first line of rivets and the first stiffener on the right side of the rudder last night before the compressor blew, so I was ready to go. I had relished the thought of doing this all day... after all, my little backriveting test on the scrap piece turned out spectacular, so I couldn't wait to have a finished skin all nice and pretty. Backriveting is different from regular riveting in that you hit the shop head of the rivet directly with the gun, instead of using a "bucking bar" on the shop head. It works well with countersunk/dimpled flush rivets. You put your rivets in place in the rivet holes, lay a piece of tape over the rivet heads to hold them there, then turn the skin over and lay it on top of the backriveting plate. The backrivet set is springloaded with a plastic ring that pushes down the metal around the rivet, making it easy to hold both pieces down against each other and keep them flat to the plate while you set the rivet.

We put two layers of thin carpet on the work bench and I cut around the plate to form a padded, flush surface around the plate. Ben drew extended edge lines on the carpet to help mark the edges of the backrivet plate. He did not have to tell me that attempting to drive a rivet off the plate would lead to complete disaster.

The first line went great. He gave me a pointer on how to hold the plastic part of the backrivet set in place on the surface so it wouldn't slide, and then I was off like a herd of turtles. I finished the line and turned the skin over, carefully peeled the clear tape away and was relieved to see a pretty row of really nice, flush rivets. Every two holes I checked to make sure the rivets were safely within the boundary lines of the backrivet plate. Soon the right side was done.

I began working my way up the left side of the rudder in the same way. I thought about how easy backriveting is. You really have to try hard to screw the pooch doing this.. I mean, you don't have to hold any bucking bar. The rivet gun feels solid against the plate, which is firmly planted on the workbench and completely & tightly surrounded by carpet so it can't go anywhere. Yes, this is the life. I wish every rivet could be back riveted. And then it happened.

It is not a matter of "if" it will happen, but "when." It's a phrase I've read on the internet, namely Van's Air Force and a few blogs about building. It's the same phrase people use to describe landing a retractable-gear airplane with the landing gear UP, even though no pilot ever believes it will happen to them. Until it DOES. I placed the rivet gun on the last hole on the fourth stiffener from the bottom on the left side. It was over the backrivet plate, but the right side of the skin was in my way so I gave it a nudge. Being the cocky riveter that I was, I neglected to resituate the rivet above the plate. "BLAM-O," I hit it with the typical burst. It made not the strong sharp RAP as the rivet smashed against the plate, but a sickening tinny THUD as the rivet gun smashed the rivet and the skin into the carpet. "MOTHER F.....!!!!"

Ben came running over. He knew what I had done probably before I did. There was indeed a dent. We turned the skin over and looked at the outside. The tape was smashed. He peeled it away like a first responder tears a shirt off a gunshot victim and examined it closely as I sat there on my bar stool, wanting to barf. "Will this thing be polished?" he asked.

"No." He was thinking we could just smoosh the dent down and put some filler on it.  "But it's the last hole, so it will crack eventually," I said. As RV-3s and RV-4s age, they typically develop cracks in the rudder and elevator skins at the trailing edge of the stiffeners. The skin is very thin, only .016", and this is a delicate area that doesn't handle vibration very well. You do everything you can as a builder to avoid any undue stress, scratches, or bad rivet holes in this area.

He looked at me. "It's already cracked. I'm sorry... there's nothing we can do."

It was like looking down on the operating table at a dead... thing. Not a friend, and not really a pet. Nevertheless, I was really pissed that I had just wasted a couple dozen hours creating this thing, and now it was just a useless pile of crap. "GAAHHHH!!"  I wailed. He gave me a beer and a cookie. He's a good man.

I guess the good thing about this is that now I can actually test the hinged wood contraption I need to build to make the final trailing edge bend on my rudder, elevators and ailerons. This is something I have been dreading. What if you oversqueeze it and screw it up? The skin is intentionally under-bent at Van's so that we have room to get in there and rivet the stiffeners. Once they are all in, you squeeze it down to form a perfectly round radius at the folded trailing edge. That edge has to be perfectly formed in order for the plane to fly straight. If it's lumpy on one side or the other, it will induce a turn. If it's creased, it will induce a turn. If you overbend it, you're screwed. You live with it or you start over. Just thinking about it makes me nervous-- but now, I can try it first on my bum rudder.

Time to order some new parts from Van's. At least since we moved to Yakima, Van's is close enough (Oregon) that I won't have to wait a week for stuff to get here.

Friday, June 22, 2012

Ready, set, smoke!

Here's my first attempt at backriveting on an 016 sheet and scrap stiffener. It's the anodized rivet pair on the right. It turned out pretty nice, a smooth surface with oreo-shaped shop heads in back. Then Ben tried a couple (left) with his new/old 1X gun. Then the new Craftsman air compressor fried. The neighbors' ears win tonight.
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Monday, June 18, 2012

Plodding along-- 8 hrs.

I started out the weekend by cutting my rudder skin to shape. The hinge clearance areas are done by drilling holes near the corners, then connecting the holes. I like using the Dremel for cuts like this because it doesn't leave the serrated edges and wavy distortions like snips or the nibbler.  

After half an hour of careful filing, the finished cut looks like this. Now do that 3 more times and watch as Ben pulls his Vertical Stab parts out of the box and clecoes them together.

To keep the whole "match-drilled kit" label in perspective with what I'm doing, I'll post some notes on Ben's progress as he builds his new RV-8 alongside my "old school" non-match-drilled RV-3B. This is Ben's RV-8 vertical stab after just a few hours of work. It took me like 20 hours to get to this point on mine, not including building the friggin jig to make it straight. He had the whole thing clecoed together by the end of the first half-day of work. 

My rudder stiffeners are now taped in place, ready to match drill the skin rivet holes. While the instructions say to drill the stiffeners and skin in one step, I drilled the stiffeners alone first so that, if I screwed one up, I would not also screw up the skin. This also made it easier to drill the aft couple of holes straight since the upper flap of skin is in the way and it would be tough to hold the drill to a mark without the pre-drilled pilot hole. I taped the upper portion to the wall to keep it out of the way, then started drilling them in the middle and worked my way toward myself (forward), clecoing the stiffeners right to the table as I drilled. Then, I moved backward toward the trailing (folded) edge. By the time I got to the last couple of holes, the clecoes held the stiffener and skin flat to the table, making them easy to drill straight.

The new backriveting plate. I just thought the wrapper was funny. "DO NOT USE FOR FOODSTUFFS." Like I would reuse this to wrap my meat.

Rudder skin dimpled and ready to rivet! As usual the DRDT-2 dimpler made it easy and the dimples turned out pretty good. This will be my first shot at back-riveting. I've seen it done a couple times a long time ago. Will let you know how it turns out. :-/

Saturday, June 16, 2012

Light Ordinance? 2.5 hrs

When we moved into our house, it had just two miserable dim bulbs in the garage (and I don't mean us. Or my dog, for that matter). This week, we fixed it with 2 six-bulb daylight fluorescent fixtures and 2 shop lights over the workbenches. I will be careful not to make too much riveting/filing/sawing/air compressing noise after 10 pm in accordance with Yakima's noise ordinance, but I really hope they don't have a light ordinance, or we're doomed to shutting the garage door every night!

Ben started work on his new RV-8 tail kit tonight while I measured, marked and drilled rivet holes in my rudder stiffeners. After 3 hours he has a vertical stab spar all edge prepped and clecoed together, including the rudder hinges, and the ribs are all filed and ready for edge polishing. It took me a couple of weeks to get to that point because I had to make most of the parts from stock and measure & drill all the holes. Pre-punched kits are amazing. If we can find an air compressor tomorrow, we might have a couple more tail feathers sooner than we think.

Sunday, June 3, 2012

First day of RV-3 work in YKM: 5.0 of 236 hours

The first day of working on the -3 in the new shop was a relaxing one. I spent 15 minutes pulling the blue plastic off the inside of the .016" rudder skin very very carefully to avoid making any creases or dimples. It's half the thickness of the VS and HS skin, so it can't be abused at all. Then I got to work with Sketch 7 and measured out all the edges of the skin and the locations of the spar, end ribs and stiffeners. Finished up the day by making most of the stiffeners from pre-bent .025 stock. It's another one of those days where if the -3 kit was pre-punched like the newer RV designs, I'd have saved a day's work. But measuring, drawing and making little aluminum things is very therapeutic. A little NASCAR on the TV combined with a warm soft breeze through the open garage door made for a relaxing Sunday. I'd have finished all the stiffeners, but Ben finished dinner so I came in. What a terrible life I live. 

Last weekend we built a large L-shaped workbench in the garage.
We still need to hang up the shop lights.