LH skin dimpling, some HS riveting

January 9, 2010

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This morning, I snuck out into the garage and starting dimpling the left hand HS skin with my new (borrowed) c-frame.

After thinking about the setup and trying a few things, I quickly realized I wanted the female dimple die underneath and the male dimple die on top.

I set up the skin on 3 2x4s (I haven’t built a dimpling table yet because I wanted to see how I liked doing it) which was less than a 1/4″ above the female dimple die. Then I basically moved the c-frame around until the male dimple die was lined up (this way I don’t scratch the skin with a male dimple die while trying to locate the hole from underneath, like some builders do). Then I held the male dimple die down into the hole and…WHACK! Perfect dimple. I am far happier with these dimples than the pop-rivet dies. Keep in mind here, I am dimpling with the standard spring-back dies here, not the tank (deeper) dies.

Here's my setup for now. I like this because you move the c-frame, not the skin.

After finishing each row, I put a line of blue painters tape on the outside of the skin. I learned on the practice kit to protect whatever I didn’t want to scratch. The tape will come off just before riveting.

Blue tape on the outside of the skins. Hooray protection!

After I finished both sides, I scuffed up the internal lines, cleaned, then primed the inside of the left HS skin.

Here's the inside of the left skin, all suffed up, ready to prime.

While I waited for skins to dry, I riveted together HS-705, HS-702, and HS-704, but only the middle two holes. The rivets didn’t bend over, per se, but set a little crooked. (My fault for not keeping the squeezer steady.) I drilled them out perfectly, and then decided shooting them might be a better idea. After practicing with a piece of scrap for a minute, I actually ended up shooting these rivets. They look really good.

Shop head picture. Rivets 7 and 8.

Machined head picture. This just looks good.

This is not the order the directions has you rivet, but I was getting antsy to get some primed pieces together. Notice I didn’t slide in the HS-710 and HS-714 yet (still need to finish those), as you can set HS-404 to HS-702 to HS-405 without them. Then, it is off to run some errands.

When we got home from running some errands, my latest Avery tool order had arrived. Finally, a scotchbrite wheel! 6″x1″x1/2″ CP-7AM “Cut and Polish” Medium wheel. Also, I’ve heard some good things about the Permagrit line of products, so I picked myself up one of the 12″(?) ones. Fine on one side, coarse on the other, flat (I heard not to get the curved (convex) one.. Much better for making a straight edge than my regular file.

More tools!

First thing after mounting the scotchbrite wheel, I finished the edges of HS-710 and HS-714 with the wheel. So easy. I should have ordered the wheel at the beginning. (Serves me right for trying to piece together a toolkit instead of buy one all at once. I thought the scotchbrite wheel was a luxury. It is not.) Then I countersunk the holes in HS-710 and HS-714. I had done this before, but sized the countersinks perfectly for a AN426AD4- rivet. When you cleco the dimpled HS-702 front spar to either piece, the spar doesn’t sit flush, so you have to enlarge the countersinks.)

Enlarge countersinks. Check.

Then I finished surface prep, cleaned, and primed those two.

While waiting for the primer to dry, I clecoed HS-707 (leading edge “middle” rib) and HS-706 (tip rib) to the left skin to get in the mood for riveting. The girlfriend and puppies are taking a nap, so I’ll have to come back to this later, but I’m getting excited to start skin riveting.

HS-707 and HS-706 all clecoed to the left skin and such.

Anyway, I put in a few minutes of right HS skin deburring, scuffing, and dimpling before coming in for the day. (Notice I decided to scuff the interior of the right skin before dimpling? It’s easier to scuff the skin without all of the dimples getting in the way. It’s these little things that will save me time the second time around.)

Let’s see. 9am to 11am, 2pm to 4pm. 4 hours today.

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Practice Kit – Finished

October 4, 2009

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Sunday morning, I managed to finish off the practice kit. Here are the pictures.

Here are the skins riveted to the spar. Notice how I didn't make the jig to hold it to the table.

Here are the skins riveted to the spar. Notice how I didn't make the jig to hold it to the table.

Another shot of the skins riveted to the spar.

Another shot of the skins riveted to the spar.

After the skins were riveted to the ribs and the trailing edge wedge, I rolled the leading edge and clecloed it together. I haven't edge formed the top skin yet, hence the ripples.

After the skins were riveted to the ribs and the trailing edge wedge, I rolled the leading edge and clecloed it together. I haven't edge formed the top skin yet, hence the ripples.

The finished product.

The finished product.

Overall, I am happy with the results. I don’t think they are airplane worthy (I don’t know if I will ever be happy with the final product), but I feel like I am ready to start on the real kit. All of the riveting came out nice, but some of the other aspects (dimpling, countersinking, edge rolling) are still not up to par.

Biggest lesson so far:

1) Go slow, take your time, read the plans, and be careful.
2) The skins don’t look too bad, but I have a feeling there will be too many scratches to polish the final airplane. I’m planning on paint anyway, so I should be okay.
3) Other things, I want to acquire some of the tank dimple dies for the understructure. Some of the skin to rib seams didn’t sit as nicely as I wanted, and I think the slightly deeper dimples in the ribs will accept the dimple in the skin better.
4) Buy a bigger backriveting plate. I just have a 1 x1/2 x 36 inch steel stock. I had to be really careful to keep the rivets lined up. With a wider plate, I wouldn’t’ have had to move the skin around, which caused…
5) …scratches in the skin. Next time I removed the vinyl from the skin, I am going to immediately replace it with painters tape. All of the scratches on the skin are where I removed the vinyl. This can be prevented.
6) Priming. Using the self-etching primer is so easy, I think I may do all of the interior skin next time ( I only primed the rivet lines, where two pieces of metal would meet this time).
7) I need a no-hole yoke for the rivets near the rear of the trailing edge. I managed with a thin bucking bar, but I didn’t like the results. A no-hole would make this a non-issue.

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Practice Kit – Riveting

October 2, 2009

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I started riveting today. I got the skeleton riveted together and back-riveted then stiffeners to the skins.

Skeleton riveted together.
Skeleton riveted together.
Skins back-riveted. Nice, huh?
Skins back-riveted. Nice, huh?

I’ll try to finish up tonight, but I need to figure out a way to dimple the ribs near the trailing edges. I should probably follow the directions and fabricate the special dimpling tool described in the plans. Off to the hardware store for some steel…

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Practice Kit – Priming

October 1, 2009

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I decided to prep and prime the practice kit to smooth out the process before starting on the airplane. i don’t know if this is the final process, but it was I did for the practice kit.

First, I scrubbed all of the surfaces to be primed with a soapy red scotchbrite pad. Then clean with acetone and let dry, then prime with a medium gray self-etching primer. I’ll continue tomorrow.

One of the skins, primed and de-blued.

One of the skins, primed and de-blued. Stiffeners, doublers, trailing edge wedge, spar, and ribs ready to rivet.

Stiffeners, doublers, trailing edge wedge, spar, and ribs ready to rivet.

Stiffeners, doublers, trailing edge wedge, spar, and ribs ready to rivet.

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Practice Kit – Stiffeners and Skins

September 30, 2009

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I started on the real practice kit today. First, you have to make the stiffeners. Easy as pie, except the stock I got in my kit was cut short by about 1/2″ in each case. I got two shorter sections, the kit shows it comes as one long piece. Maybe George gave me some extra that was laying around. No biggie, but that’s why in the pictures below the stiffeners are different lengths. Then I edge prepped the stiffeners, ribs, spar, and skins. I also practiced using the soldering iron some more, with pretty decent results. Here’s a shot of the stiffeners and skins ready to match-drill.

Skins and stiffeners ready for match drilling.

Skins and stiffeners ready for match-drilling.

And the stiffeners match-drilled to the skins…

Match-drilled and cleco'ed.

Match-drilled and cleco'ed.

After this, I assembled the skeleton, matchrilled both skins to the ribs, spar, and trailing edge wedge, then disassembled everything. It got late, so I stopped after getting all the holes deburred. Here’s a shot of the skeleton clamped together, ready for drilling.

Skeleton Clamped

Skeleton Clamped

Next step is to figure out a priming process and test it out before dimpling and riveting.

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Finished the first assembly in the Practice Kit

September 29, 2009

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Tonight, I finished the first assembly in the practice kit. Only a few notes, and some lessons learned.

Big lessons learned:

  1. The soldering iron leaves a mark if you aren’t careful, be gentle, and go slow enough that it melts the vinyl.
  2. Deburring holes was very easy, even with just an oversize drill bit.
  3. Buy a nice countersink. I faked it with a drill bit, and the results will not be acceptable on the real project.
  4. Less scratches tonight, but still a lot. I need to get some scotchbrite pads and self-etching primer to rehearse the prep and priming phases.
  5. I want to experiment with priming before dimpling. I’ve heard people have had good results (said another way, no bad results due to priming a weirdly angled surface in the dimple.)
I got out the soldering gun and tried my hand at removing the vinyl covering in a straight line.

I got out the soldering gun and tried my hand at removing the vinyl covering in a straight line.

MY FIRST RIVET. It is so beautiful.

MY FIRST RIVET. AN426AD3-3. It is so beautiful.

Three more rivets. I squeezed and bucked with flush and cupped sets. I am using a 4X gun, which means I had the pressure all the way down to 20 psig. It worked really well for the AD3s, but I might need more pressure for the AD4-4s.

Three more rivets. I squeezed and bucked with flush and cupped sets. I am using a 4X gun, which means I had the pressure all the way down to 20 psig. It worked really well for the AD3s, but I might need more pressure for the AD4-4s.

The final (and blurry) product. It's probably for the best that you can't see the fingerprints and scratches on it.

The final (and blurry) product. It's probably for the best that you can't see the fingerprints and scratches on it.

I am very happy that I did this part of the practice kit first. Now I know how to proceed on the real kit, and nothing with drilling, deburring, dimpling, countersinking, or riveting will be new to me, even on the practice kit. (I plan on displaying the practice kit prominently, so it better look good.)

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Started on the Practice Kit

September 28, 2009

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Today, I started on the practice kit. The directions point back to (and the kit actually includes) sections 3 and 5 of the construction manual. I threw my extra copies away, I’m going to just keep the ones from the Preview Plans I have.

The kit tells you to make some useful tools before starting. I found 3: A wooden hand seamer, a stand for your practice kit (basically a place to clamp the front spar so the skins stand up vertically) and an assembly with an 11 inch long piece of angle riveted (with various rivets) to two more pieces of 2.25″ x 11″ aluminum sheet. I’m not sure if this is a useful tool or just something to rivet before starting the pretend control surface. Hmm… I’ll make it nonetheless for the practice. I’m going to pass on the hand seamer, but get started on the other two.

Interesting note, the directions tell you that if you don’t have dents, scratches, and mistakes on your practice kit, you aren’t doing it right. Apparently, they want me to get out all of the mistakes now before I start on the real airplane. Right…

Here’s a picture of everything that comes in the kit.

Everything that comes in the kit.

Everything that comes in the kit.

Closeup of the Hardware

Closeup of the Hardware

Closeup of the skins.

Closeup of the skins.

I didn’t get very far on the practice kit. I made it through step one, which is to drill the weird angle assembly in 24 places for the appropriate flush and blind rivets of various sizes. Even the practice kit is going to be slow going. I did learn a ton, though.

  1. Everything is so tiny. I’ve been staring at picture on all the build sites, thinking things were bigger. The -3-3 rivets are TINY! The skins are a lot thinner than I thought they would be.
  2. Don’t take the blue off the skins if you don’t want to scratch the skins. I thought my workbench was clean, but after deburring one of the small sheets, there were small pieces of aluminum everywhere. I slid one of the sheets on the table and scratched the hell out of it.
  3. My cheap clamps are nice, but not perfect. I’ll need to get some higher quality ones. Also, I need to use the duct tape on the clamp face trick. They scratched the hell out of the sheet, too.
  4. I had to measure, mark, and drill the holes. No big deal, but I just noted that they really have you jump right in. I drilled into a spare piece of MDF I had laying around, but I didn’t drill far enough, so the clecos don’t have a fantastic grip. Oh well.
  5. I played around with pressure on the bit while drilling. I learned as a kid that when you have the spiral piece of metal coming off in one piece as you drill, that is the right pressure (which wasn’t that much more than the air drill itself). Anyone have any other advice?
  6. I learned that building is not going to be a piece of cake, but is going to be a lot of fun. That’s kind of a fluffy statement, but it’s true.

Here’s the picture of what I got done last night.

Step one. Drill appropriate holes.

Step one. Drill appropriate holes. Don't make fun of my erroneous markings. The instructions said I have to make mistakes on this practice kit, and not the real airplane, so I made sure there were some errors.

Also, I had to cleco the skin to the end ribs. I don’t know why, but I wanted to do it. I promise not to skip steps in the future.

Top skin cleco'd to the end ribs.

Top skin cleco'd to the end ribs.

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Purchased Practice Kit from GBI

September 27, 2009

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I am a lucky guy. I live about an hour away from George and Becki Orndorff of GeoBeck, Inc. See their website at fly-gbi.com. Last night, after a wonderful day of flying a Cessna 310H to Gilliam McConnell and having lunch at the Pik-N-Pig, I drove down to see George and Becki and purchase a practice kit. After graciously forgiving me for bothering them on a Sunday evening, George showed me their RV-7A (N289GB). It was immaculate. I asked George about a few things, the answers to most of which were expected. Example: Why shouldn’t I build? (“You should!”) Do you love it? (“Absolutely!”) Everyone I ask has nothing but wonderful things to say about their RV. Sounds like I need to go ahead start!

Two of his answers were more interesting. I asked him about tip-up versus slider, noting that everyone seems to like what they have. His simple response: “I’ve built both, and the slider is better. I won’t build another tip-up.” I was sold, but I pushed to find out why. Basically, he explained that the slider was more sturdy, cooler (both hero-pilot style and temperature style) and easier to build. Easier to build? That’s contrary to what I’ve heard, but George is obviously trustworthy in the RV expertise area, so I’ll take is word for it.

The other answer was to “What modifications should I do to the RV-7?”

He told me to put the RV-8 rudder on the RV-7 (instead of the RV-7/9, larger “uglier” rudder). I haven’t seen pictures side-by-side (to determine if I agree with the ugly part), but George said the larger rudder on the 7/9 is for spin recovery. I’ll need to think about this some more. I am not too concerned about spin recovery (he said it only improved the recovery from 1.5 turns to 1 turn), so I think the choice will come down to aesthetics, and the fact that the trailing edge of the 8 rudder is bent, while the 7/9 rudder is double-flush riveted.

Anyway, I got home with the kit, and had to join the girlfriend for dinner, so all I did was unpack the kit, and lay it out nicely so I can take pictures tomorrow before I get started.

Most importantly, the kit is a Van’s kit (some other builders were wondering what the difference was), but also comes with GBI’s sheet metal tools DVD. $55, which, with some subtraction skills, puts the DVD at $20. I watched the DVD last night, it runs about 60 minutes, and was really helpful with introducing me to some of the tools and techniques I am going to become intimately familiar with over the course of the project. He also walks through the actual construction of the practice kit. It’s worth the $20. I also bought the pre-punched empennage kit videos. Those should come in handy soon enough.

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Posted by Andrew