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-   -   RV-3B Dave's in Colorado (https://vansairforce.net/community/showthread.php?t=85658)

Ian 12-19-2014 03:38 AM

Nice job indeed.....but tell me, what's the benefit of riveting the L.E before mains skins ?

David Paule 12-19-2014 12:46 PM

With the main skins on, there's no access to rivet the leading edge skin to the spar flange. With the main skins off, I could get in there with a squeezer and these leading edge/spar flange rivets were easy.

In the photo, you can see the right leading edge assembly in place, to the left of the fuel tank ribs. The spar flange extends aft of the leading edge, and if the main skins were on, I couldn't buck those rivets.



The leading edge assembly is riveted while in a simple jig, after drilling the rivet holes between the skin and the ribs while jigged up on the wing. Then after riveting the ribs to the skin, the whole assembly is riveted to the spar.

Don't forget the spar web to rib flange rivets. They're kind of hidden away in there.

Dave

David Paule 12-24-2014 07:19 PM

A Bit of an Issue and Rivet Removal Tips
 
I was assembling the tanks to the wing before riveting on the tank baffles, just to be sure, and the left tank no longer fit on the outboard leading edge's splice strip. Remember that it was built in place on the wing, with the outboard leading edge attached. This time it didn't fit.

Turns out that the outboard tank rib interfered with the splice strip. Here's the rib and the skin. You can see how close the rib and the reinforcement piece are to the dimpled holes.



This shows the splice strip and how much it would need to be trimmed to fit - clearly a problem.



Later, I marked where I'd need to trim the splice strip and it was very close to those holes. I contacted Van's support and they recommended replacing the outboard tank rib and relocating the leading edge reinforcement plate to the inside of the tank. This didn't please me - I'm not that great at drilling out rivets. So I took a break to think about it.

For my break, I had a friend over and we set the -4 rivets that hold the main ribs to the spar web behind the tank. During the process, I got to replace a few of these and it went reasonably well. Then came the aha! moment. Drilling out these rivets, I was using a #40 drill bit as a pilot drill.

When those were all finished, I went back to the tank and tried to drill out the -3 flush rivets using a pilot drill. This worked a lot better.

This photo shows a few of the first rivets drilled out and the tools I used.

The basic approach is:

1. Center punch the center of the rivet head.

2. Pilot drill just a bit deeper than the head. Use a drill bit that’s 10 number sizes smaller than the nominal one. In this case, for the -3 rivets which used a #40 bit, I used a #52 bit to pilot-drill them.

3. Drill just the head with the correct size drill, in this case #40.

4. Using the unfluted end of the #40 drill bit, pop the head off.

5. Use the pin punch and a very small hammer to punch out the rivet body. That hammer, by the way, has earned its scars. This is its fourth homebuilt airplane.

6. If you’re my age, the magnifying glass comes in handy, and if you didn’t get the head exactly, the needle nose pliers are helpful pulling it off.



That left the rib firmly sealed to the tank. Think glue. Here are the top rivet holes with no more rivets:



How to get the rib out? I bought a set of plastic picnic knives and they were of little use. The sealant was just too tough. I made a sealant knife by wrapping a piece of music wire around a couple of pieces of 1” dowel. I used several pieces of music wire: .015 was too weak. It cut well but broke easily. The .020 was the compromise that worked. The .032 was sturdy but cut poorly in the sealant at room temperature. Going across the dimples was especially difficult.

Then a friend suggested heat. I’ve got an 1,800 watt hair dryer and a few minutes with that let the .020 wire cut through the rest of the sealant. Using a piece of 1/2" plywood as a sort of wedge helped a lot, too, forcing the joint apart. I've got some serious respect for tank sealant now.

These are the tools I used.



Now the rib’s out and parts are on order. They should be here on the 29th.

That light at the upper left of the photo is a sweet thing. It’s a 9 watt florescent under-the-counter light and makes a handy shop light.

Merry Christmas, everyone!

Dave

wirejock 12-24-2014 08:30 PM

Rib
 
Merry Christmas Dave. I'm glad you got the rib out. Looks good.

David Paule 12-31-2014 09:44 AM

Polygone
 
The Polygone remover really works on tank sealant. It's a translucent jelly, slightly golden, that seems quite similar to paint remover except that it can be cleaned off with rags and soap and water. I'm using one of the plastic picnic knives to spread it on and encourage it. It dissolves the sealant quickly.

This is after I spread the first bit on.



After all the sealant was lifted, I wiped the Polygone off with a number of small cut-up rag pieces. Then into the kitchen for a wash and bath in the sink- really. Being of course very careful not to contaminate the kitchen.



I've still got to go over the areas with Scotchbrite again and lacquer thinner before I install the new rib.

The Polygone instructions suggested that some plastics weren't compatible, including acrylic, but these knives did just fine.

Well, that's it for the year. Thanks very much to DR for hosting this site, and best wishes to everyone for a wonderful 2015!

Dave

Ironflight 12-31-2014 11:48 AM

Wow Dave - that has got to be the Holy Grail of anyone who has dealt with tryign to remove tank sealant - going to have to remember this stuff!

Paul

David Paule 12-31-2014 03:32 PM

Made it easy - I put a copy of this in the "Tips" section.

Dave

David Paule 01-04-2015 05:18 PM

First Inspection
 
Since I hadn't had any luck getting a tech counselor to stop by, I had a local A&P do it. He's someone I know and respect, and he's worked on my Cessna 180 before. He found a serious issue on a friend's airplane a few years ago, and has lot of riveting and tank experience on certified airplanes. I particularly wanted this inspection before putting the baffles on the tanks.

His major finding were:

1. Use more sealant inside the fuel tanks, especially on the rivet shop heads.

2. When putting safety wire through sheet aluminum (I've got a place where I'll safety the trim tab hinge rod by safety wiring the inboard end to a hole in the elevator), slip some plastic tube, like wire insulation or shrink tube, over the safety wire. Otherwise the aluminum might eventually crack.

3. I've got a place where some wiring needs to exit a connector and immediately make a turn. There's no room for a plastic connector end - this is the roll autopilot servo in the right wing, with the servo close to the top skin. He said to use some blue sealant to protect them there.

Dave

David Paule 01-10-2015 08:10 PM

Outboard Rib Drilled
 
With the rib removed, I had to locate and match drill to get the new rib in. I used my Vixen file to get the edges straight on the flanges and marked the inside of the skin to show where I had to stay clear to get the tank to fit the splice strip. Then I marked a line for the minimum edge distance to the edge of the flanges. I could view this line through the existing holes in the skin.

I clamped the rib in place - love those Cleco side clamps! - and starting with the forward-most holes, drilled and dimpled. I had to do the first half dozen on either side one by one, clecoing the rib in place because the dimples were pushing the rib aft a bit until I dimpled the rib flanges. So hole, by hole, I continued.

When I got aft of the first half dozen holes, I could simply match-drill the holes.

Here's the rib.



I've also made the leading edge reinforcement, see the plans clarifications for a note about that.

Dave

David Paule 01-15-2015 06:11 PM

All that wouldn't have been any fun if the tank as revised didn't fit, so I figured I'd better try it. It fits. Here it is, with a number of the screws screwed in.



Whew!

So after riveting the leading edge reinforcement on the rib, I used tank sealant and clecos to glue the outboard rib into the tank.



One of the things the inspector wanted me to do was add more tank sealant. I got out the type A thinner sealant and re-dotted all the rivet heads in the tanks. I did that before putting the rib in.

Dave


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