Leading Edge/Tanks on Spars

Total time: 694.1 hours
Since Last Time: 33.0 hours
Leading Edges: 75.0 hours

This time we’ve got a two month span since the last post. The leading edges are now complete with leading edge landing/taxi lights in place. The leading edges and tanks are now on the spars. Lot’s of pictures with little to talk about.

The best thing was the birth of Amelia in early September:

 

 

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Tanks Complete

Total time: 661.1 hours
Since last time: 5.2 hours
Fuel Tanks: 117.0 hours

I am finished with proseal for a long time! I finished the last proseal task with 2 days to spare. My proseal expired on 8/12/2012. The last pop rivet went into the rear baffle (described below) on 8/10/2012.

The tanks are finally complete. The only thing that had to be done was the pressure test. I had a scare. The tanks were pressurized with the little 6 dollar kit from Van’s and I sprayed soapy water over all the seams in the tank. Right on the baffle of one of the tanks there was a leak. After a little investigation, I realized no problem. Somehow I had forgotten to install one of the pop rivets that hold the rear baffle to the ribs. I installed that rivet, set the tank aside for a few days to let the proseal cure and retested. No leaks. Both tanks. Hoorah!

There was a scare, however. While wiping down the soapy water I noticed several cracked rivet heads. This greatly concerned me. However after sending pictures to Vans, they said it wasn’t anything to worry about. I’m not happy about this for the sake of looks but it is what it is. If it’s not an issue of safety, I’m not pulling the tanks apart. The issue might have something to do with soaking rivets in MEK for long periods of time, or the rivets might have been older than I thought. Maybe I work-hardened the rivets and didn’t see it in time. The proseal all over the place did make driving rivets a little tricky in some cases because of things sliding all over the place.

Much was said about this issue on Van’s airforce. For more on it see: http://www.vansairforce.com/community/showthread.php?t=89697

Bottom line on the cracked rivet issue: This is email I got back from Vans. The photos referred to in the email are included below.

Joe,
Received both of your E-mails.  At this point if the tanks are leak free I would not do anything. I actually had Van and a couple of the Tech guys look at your photos.  One question was is what shape is your flush rivet set in?  Are there any chips or rough spots?
  — After checking I replied that my flush set is as smooth as when I bought it.
We feel the rivet strength is good even though there are some defects.  You could fill the chipped ares with some epoxy product (JB-Weld, etc) to improve the looks and to add some feel-good strength to it.  Chapter 5 has a section of riveting where Alcoa comments on these types of situations.  You may want to re-read that.
Best Regards, Joe Blank

I did a 24 hour pressure test (see pic below and note the “control” balloon in the center of the tanks). After success there I put the drain valve and the Fuel strainer in place using “fuelube” lubricant/sealant on the threads. The tanks will remain in the “airplane” room until I finish putting the duckworks light fixtures in the outboard leading edges. After that, the leading edges and the tanks will get fastened to the spars.

 

 

Rear Baffles

Total time: 655.9 hours
Since last time: 10.0 hours
Fuel Tanks: 111.8 hours

I learned (or relearned) several important lessons.

  1. MEK hurts really bad when it comes into contact with a freshly opened blister.
  2. Band-aids do not protect freshly opened blisters from MEK.
  3. Nitrile gloves do not protect freshly opened blisters from MEK.
  4. Latex gloves do not protect freshly opened blisters from MEK.
  5. It’s very hard to work with proseal when you have open blisters.

Two 4 hour sessions and the baffles are on the tanks. Both tanks are closed up! I’ll know if they’re closed up for good in about a week when I do the pressure tests on them. That should be plenty of time for the proseal to cure (this time of year). I have no real concerns about leaks – except on the left tank. I fear I may not have used enough proseal. When I looked into the fuel port of the left tank (no picture of this) I thought it didn’t look as good as I would have liked. We’ll see.  Right tank looked great to me (see picture).

Because I primed the Z-Brackets and the entire backside of the baffle (not the front side, only the back), I had to remove primer in several spots. Annoying, but not a problem at all.

The only issue I ran into was one problem rivet. It was one of the blind rivets that hold the baffle to the rear rib flange. I messed it up by not pushing it all the way through the hole before setting it. The result is that it stands proud. I think what happened is that it’s probably not holding to the flange well (if at all). I was concerned about drilling it out considering there is no access to the inside and I’d really rather not have little pieces of metal in the fuel tank. I may revisit this but for the moment, I decided to leave it alone and cover it with proseal to prevent any leaks. Although it bugs me to not have this perfect, nothing depends on a single rivet.

So far at 111.8 hours (and about 7 months), the tanks represent the single longest component of the build to date – handily surpassing the tailcone for the title. And the tanks are still not quite complete. I’m really, really, really hoping they pass the pressure test. If they do, I’m finished with proseal for the foreseeable future. I won’t miss it.

 

Capacitive Fuel Probes

Total time: 645.9 hours
Since last time: 8.3 hours
Fuel Tanks: 101.8 hours

The fuel probes are the biggest thing to report this time. It was an ordeal. Originally I planned to get pre-bent fuel probes from Princeton Probes (pre-bent for the RV-10) but for whatever reason they weren’t available anymore. So I bought the standard probes but didn’t get a long enough bendable section. I sent back those probes and got their NPT probes which are probably better since they should never go bad. The electonics are housed seperately and can easily be replaced. This allowed me to bend the probe and mount it in such a way that I could extend it across two full bays of the tank. Because of the wings’ dihedral this extension will allow me to read fuel closer to full than one normally can with the standard floats or even the pre-bent probes which only go into the first tank bay.

Also complete is the installation of the vent tube and the aft-inboard rib on both wings.

I practiced on scrap copper tubing to try and figure out the best way to bend the fuel probes so they fit and span the highest and lowest points in the tanks possible. After many failed attempts to figure it out by bending and re-bending, I wished there were an engineer I could ask for help. And then it dawned on me that I am an engineer and although my area is signal processing, surely I can apply my vast knowledge of geometry and trigonometry and algorithms to find my answers by design rather than by guessing. So I got out a pen and some paper and formulated my problem. I constrained the problem to limit the probe to a certain distance from top and bottom of tank, a certain bend radius (1″ because that’s what my tube bender will do) and a few other things. Then I wrote some code in Matlab (a software package that does math real good). I used a basic algorithm known as Gauss-Newton to solve for all my unknown variables.

After my algorithm converged I had my answer. I went back into the garage (or shop, rather) and tried my answer. Lo and behold it worked beautifully. This all happened before I got the NPT probes, however, and with the NPT probes I decided to cut 1.5 inches from the end of the probe to get an easier fit, given with the length of 24″ the algorithm computed I would need to drill a hole in the next inboard rib. If I shortened the probe by 1.5″, I could get away with cutting a small slot out of the already existing lightening hole. This makes installation a lot easier since you have to put the probe in the inboard rib before putting the inboard rib into the tank assembly. Otherwise the bends in the probe won’t allow you to install it into the proper position.

For those interested, I ordered a 1/4″ compression nut from McMaster-Carr (just the nut, not the sleeve. I bought two different nuts, actually, they both fit but I don’t remember which one I actually used. Part numbers: 5272K121 and 50915K123). Then on the outside of the rib I used a brass 3/8 washer. I was going to use another washer on the inside (as depicted below), but it didn’t leave enough threads for my comfort so I just used the compression nut on the inside which seemed more than adequate to me – especially considering there is no structural issue here – it’s just to hold the probe in place.

On the inside of the tank, I used proseal where the probe came near the skin and where it passed through the lightening hole – just to elliminate any issues caused by vibration.

Don’t judge me. I know my proseal work is embarrisingly messy. I hate working with this stuff. Early on I tried to keep it neat. Really I did. After a while I gave up neatness in favor of really-sure-it-wont-leak and don’t-take-all-night-to-do-a-rib-because-this-stuff-stinks-and-MEK-gives-me-a-headache-after-ninety-minutes.

Tank Attach Assembly

Total time: 637.6 hours
Since last time: 13.3 hours
Fuel Tanks: 93.5 hours

 

Making good progress. The ribs are in place and the attach assemblies are in place. I’m working on the vent tubing now and am waiting for the capacitive fuel probes from Princeton Probes. As soon as they get here I’ll be able to get the aft inboard rib in place and then close up the tanks. I also ordered a pressure test kit for each tank. I probably only need one, but for the few bucks they cost, I bought two and so I’ll pressure test both tanks at the same time.

A new skill I have is that I can now flare tubing. Ralph Hoover (friendly neighborhood Tech. counsellor) took some time to show me how to do it and to loan me his flaring tool. I practiced flaring a length of scrap aluminum tubing (over and over again) and got it pretty near perfect. So then I flared the ends of the vent tubing.

The only snag I’ve had is with the vent clip which attaches just behind the fuel flange. It should have a 7/16″ hole in it to receive a Snap Bushing. But I never drilled the hole – and I checked the plans and can’t find where it tells me to do so. Nevertheless, I have to deal with it. Using my angle drill I drilled the hole out to #30, then because of the tight quarters, I put a unibit in a black-n-decker battery operated screw driver and slowly drilled out to 9/32″ (just a bit larger than 1/4″ which is the size of the vent tube). I could drill it out all the way to 7/16″ this way, but I’m reluctant to do so. The vent clip is cut from the stiffeners and there are a whole bunch of them. You only need to keep two, which are now fastened in the tanks. I got one of the discarded clips and practiced drilling out to the proper size and found that depending on how I installed the clips, there might be very little edge distance if I drill it out all the way to 7/16″. What I’m planning to do at the moment is not use the snap bushing and just put the vent tube through the clip and pack it up good and tight with proseal. It won’t move, but after everything is in place, it shouldn’t move anyway.  I’m asking around on Van’s Airforce to see what some other builders might suggest.

And here’s a trick I learned. When I countersunk the attach assemblies to receive the dimpled skin, I just drilled #40 holes right into the wood of my table and clecoed the assembly to the wood (see picture below). The cleco does not have to come out the other end of the table in order to hold the metal firmly to the wood. Very handy trick.

 

Left Tank Ribs

Total time: 624.3 hours
Since last time: 9.8 hours
Fuel Tanks: 80.2 hours

Nothing of any real interest. Just lots of pictures. The left tank ribs are now in place. The next interesting thing is going to be the capacitive fuel probes. I had intended to buy pre-bent probes which would have been shipped already bent to the proper shape to fit into the RV-10 tanks, but it was a custom job and the guy could never find the time to do it. So, I’m going to buy the princeton probes and bend them myself. I’ll get some scrap tubing to practice on. Should be OK.

As for the excursions, Scott continues to gain confidence learning to drive. He’s now out in traffic. And I had a nice trip for work out to Colorado Springs where I got to see Pike’s Peak. And lots of fun stuff with the kids in the yard.

 

Right Tank Ribs

Total time: 614.5 hours
Since last time: 7.7 hours
Fuel Tanks: 70.4 hours

Nothing of any great interest to report. All the main ribs on the right tank are in place. They take about 1.7 hours each to get in place. The only rib left on the right wing is the aft section of the inboard rib. That will go on a little later. I’m probably going to do the same thing on the left tank before continuing on to the next steps.

I still hate proseal.