#15 Rib Stitching, Fabric Sealing, Masking & Painting

Post #15

Finally got going on the build again but it will be tight this fall getting enough warm weather to paint before winter sets in. Rib stitching was the task I had been procrastinating over all summer and when I started my learning sessions on the inherited Easy, it really killed the re-build project. I used the modified Seine knot. I followed a good YouTube video from Cormanairpark that got me finally going on this task. Here's the link;

Cormanairpark Modified Seine knot

I abritrarily chose 3 inches as my spacing partly because I had to keep the fabric tension so low that I was concerned about airfoil deformation during flight. I don't recall what the plans called for but I believe it was more than that. The following shot shows the first panel I did after marking off the 3” lines using a chalk line.

This really made a mess and I marked the rest using a piece of 1 inch wide aluminum strip I got from the motorized parts kit. It was flexible and easy to hold down onto each rib and just mark each position with a pencil. I spent some time figuring out how I could mark out the bottom of each panel so that the stitching cord was close to perpendicular with the top rib cap strip. That way I got a nice, even 3-inch spacing on the top surface and let the bottom spacing vary to maintain the 90 degree angle with the cap strip. Just like the plans show, prop up the wing panel you are going to stitch on a couple of saw horses and go to it. I followed the Poly Fiber (or Stits) covering manual process pretty much to the letter on this. The second step (after marking out the spacing lines) was to apply the adhesive-backed 1/2 inch fabric reinforcing tape which you see here.

The next thing was to take the needle and poke holes through the fabric on both sides of the rib right on the mark up spacing both top and bottom. Once that was done, I propped up the panel onto the saw horses and started the stitching process. I was able to do all the rib stitching with no help and it wasn't all that difficult, just tedious. The hard part was getting the knot good and tight before going to the next knot. I untied many knots that I wasn't satisfied were tight enough to suit me and this really slowed things down. A couple times I broke the cord halfway through the rib and chose to splice it using a water knot (this can be found in most rock climbing books) rather than start the rib over again. I found it fairly easy to tear the fabric with the cord when I wasn't being careful during the knot tightening part. I had to be very careful of the direction I was pulling during knot tensioning.

Once I finished all the panels I wiped down each stitch using the Poly Fiber R65-75 Reducer solvent. Depending on the batch, the wax can be very thick on the flat stitching cord and it ends up all balled up right on the knot. You won't get it all off and it didn't mess up my paint job as I found out later so don't sweat this too much, just give it a wipe down. The next shot shows me using 3 parts Poly Brush to 1 part R65-75 Reducer to saturate the sticky back cloth tape applied over the rib cap strips. The Poly Fiber manual says it normally takes 4 coats to “fill” the tape with Poly Brush. I thought this was excessive and then found out that 4 coats was just about right.

Now you have to start thinking about how you want your taping to come out. I ran a 1 ½ inch tape over the stitched ribs but stopped short at both ends which made it tough to cover with a leading edge tape or trailing edge tape. You decide here what you want to do. I used an 1 ½ inch wide brush in applying the Poly Brush pre-coat doing half the rib.

Now the tape goes down.

Working fast here....you need it to completely wet out the cover tape.

This shot shows me after I top coated the first half and completely wet through the first half of the tape. I'm now doing the second half pre-coat.

Finishing this rib up by going over the tape and pressing it into the wet Poly Brush.

I didn't hesitate to add a little more Poly Brush as I was doing this. The idea is to get the tape wetted completely through without adding any more Poly Brush than you have to in order to accomplish this.

Next, I turned my RV shed into a paint booth. Here's the results of the first spray coat of Poly Brush.

I borrowed an HVLP turbine from the EAA club nearby but bought my own gun.  I could have borrowed the gun also and actually did for the first panel of Poly Brush.  I then reverted to the gun I'd bought which I felt I had more adjustment with.  I just followed the Poly Fiber manual on this and it was fairly easy except for the leading and trailing edges. It was really touchy keeping these areas from forming drip lines. When this happened, I had a 2 inch brush handy in a jar of R65-75 Reducer and I quickly brushed any drips away. This worked well as long as I was very conservative on the amount of reducer on the brush. I ended up with some contamination streaked areas in spots that would not take the Poly Brush. After freaking out, I decided to wipe those areas clean right down to the cloth and then re-brush and then re-spray. I got the areas to “take” but you could easily see the brush marks left even after the final color coats. I believe this must have been something on the rag I used to wipe down the panels since they had been brush coated nearly a year ago. Once I got the panels all coated with a couple of passes of Poly Brush and was convinced they were sealed, I went on to apply the Poly Tone color coat. I was surprised at how much I had to apply to cover the pink Poly Brush (I used a white color coat). It turned out I really couldn't see what I was doing in this shed so I added 8 four foot dual tube flourescent shop lights and hung them with about 3 feet of clearance over the panels. What a difference! I ended up doing a second session and getting the panels I didn't quite get covered the first time. The keys here were;

a) spend most of the time doing a good job masking (the paint will go EVERYWHERE)

b) use multiple light passes on the leading and trailing edges to avoid runs

100. you can't have too much light.

I didn't get any photos of the white base coat but one of the issues was getting even coverage. Since the idea here is to put as little paint on as is needed to just cover the panel and no more. This stuff addes weight but you'd be amazed at how hard it is to get enough on to completely cover the pink Poly Brush. I tried both chord-wise passes with the gun and span-wise passes and really had no preference in results although it was much less tiring to go span-wise. I found that aiming the center of the nozzle right at the line of the last pass gave me the right amount of overlap to avoid serious banding. It just takes practice.

Once the base coat was on I started masking the next day for the accent color stripes. Here's where you'd better be real careful about COMPLETELY and I mean COMPLETELY mask off where you don't want to have paint going where you don't intend it to. I've already shot the red accent and this is the gold going down last.

Remove the masking and we have.......

Looks good to me!

I didn't find it necessary to mask the bottom of the panel off entirely when I applied the red stripe on the top surface and when I flipped the panel to mask the bottom side, found a nice, ugly mist of red way out on the main, perfectly painted white base coat surface. Great!, re-mask the entire bottom of the panel and re-set up for a second session of white base coat, etc., etc......shot a day on this little error.

Some thoughts;

Spend the money and get the good masking tape. I found that 3M Vinyl Tape 471+ works and will give you good, sharp lines. With all the effort this takes, using this quality of tape on all your actual lines will be worth the cost. Use that blue stuff used for home painting walls , etc. on all the other areas where you are not painting against it. I used the blue stuff (Blokit or Frog tape) on my actual lines and got bleed through. If you were really diligent about going over every inch of the line with adequate pressure to get a 100% seal, you might get by. I was being careful and got a significant amount of bleed anyway. Use a ¼ or ½ inch vinyl tape on the line and then use the blue cheaper stuff to tape to that.

Next I will shoot the bottom of the bottom two panels. You can be darn sure I'll have the top surface COMPLETELY masked off tight after what happened doing the top surface. If I had this to do over again, I'd mask the entire wing off for red and paint both sides since my plan was to do the same pattern on top and bottom of each of the lower wing panels. This would have eliminated the overspray issue I created and also been more efficient use of a spray day. I just wasn't confident of the process or technique and didn't want to risk the entire paint job without knowing it would work OK.

I've already found out through experience that using standard 3M blue painters tape can still be easily removed after two weeks. I did this in a heated space where I store the wings which may have helped keep the tape pliable. This is really important otherwise going on advice from the EAA guy, he'd have me remove it within a couple hours after painting which would mean I'd have to mask right before I paint and then get it off right away. Two concerns he mentioned were having issues removing tape from a painted surface and having the paint pull up along the edge but he also had never tried to leave the tape on for any length of time. I saw neither issue at two weeks. In fact, there was no hint of an issue. I'm inclined to believe I could leave the masking job on the wing for several weeks at least while waiting for a good day warm enough to paint now that winter has settled in here. What that means is that I can (and will) mask everything now and then paint when I get a good day where the temps get above 55 F. Yesterday I painted with a temp of 56 -57F and raining some with no issues. This shot shows me finishing up masking for the underside of one of the bottom wing panels. The top is all done.

Notice that the 1/4 inch tape line is the 3M vinyl stuff  I mentioned which will define the boundary of the red field I will shoot next.  I'll move the paper up to the 1/4 inch tape and then use the blue stuff to tape to it.  Also notice that I'm not going to use the vinyl tape to mask off where the gold will go down after I finish the red.  What I ran there was 1 1/2 inch painters masking tape.  Since this is the bottom of the panel, I figured it wasn't worth running two lines of the vinyl since no one but pilots below me looking up will ever see this side.

Still haven't decided on what I'm going to do with the top wing panels. If I do the same pattern, it's gonna add more weight but if I don't I think it's going to look cheezy. Decisions, decisions......  It will be a miracle if I get enough weather to get this all painted without having to wait until next spring now.  We're really settled in with rain and cold weather here in Oregon already.  Anyone out there want to volunteer use of their heated paint booth?