#8 Covering & Sealing Using PolyFiber Fabric - oops!

The covering supplies arrived. Here is a shot of nearly $1000 worth of chemicals including the glue, the sealer, the UV paint and the top coat paint plus the thinner for these products.

I hope to have some left over that I can sell to the EAA chapter here. They go through this stuff like water. Decided to have the Tech Counselor help me do the upper left wing panel and then I'd take it from there. Started by putting anti chafing tape on all the potential rub points on the frame that would have fabric contact. I had taken a stab at what I thought would be adequate for taping over sharp areas. Not good enough per my Tech Counselor Ernie. He showed me how this needed to be done. No real tricks here, just had to think about how to best cover the topography with as little tape as possible. Here's a shot of the wing panel after I finished re-taping the root rib gussets. The rest of the panel shows what I thought would be adequate. I had to remove all of what I had done and re-do it right.

Here are some examples of what the anti chafing taping should look like if you are doing a good job of it.

The next step was to apply the leading edge filament tape. I used the directions specified in the original plans that call for three span

wise lengths spaced 3 inch center-to-center from the leading edge of 1.5” filament tape. The purpose is to help minimize the fabric droop between ribs when the fabric is tightened up during the ironing process and the coating process.  After the filament tape is applied it is really easy to bump it with a hand or something on the table or saw horse it's setting on and fold the tape onto itself. After you do this it is really hard to separate the tape. This happened multiple times to me during the process and each time I had to use MEK solvent on a paper towel to redissolve the tape glue so that I could pull it apart again. I could not completely fix an area once this happened but decided it wasn't bad enough to redo it. This shot shows it prior to several accidental collapses that had to be separated.

Next, my Tech Counselor highly recommended I cross brace the ribs midway between the trailing edge and the last row of filament tape. He supplied me with the approved material which was 1/2” wide cloth tape designed specifically for this. I don't think this was necessary since the filament tape and gluing the fabric to the ribs really doesn't allow for any movement of the ribs after the covering is complete anyway but I went ahead as instructed and did it. This shot shows me finishing up the cross bracing tape.

We got to a dead end here as soon as we had tacked down the fabric on the bottom of this wing panel. We were noticing a reluctance of this material to shrink. It became obvious the more we tried to shrink it that it was pre-shrunk polyester cloth....something you might get at a fabric store. When polyester cloth is pre-shrunk, there is about 10% of shrink left in the cloth and it takes a hot iron to get that last 10% (something around 350 F). This won't work for covering material on a "conventional"airframe because you want all of that shrink margin to get a decent, tight and smooth covered surface.  However, this is not a "conventional" airframe, far from it.  The Easy Riser airframe is extremely fragile and weak relative to the techniques and materials used on stiffer, more constrained airframes.  My tech counselor has had no experience with this type of frame so I'm back to re-reading the instructions sheets.  Once I re-read them it was apparent that pre-shrunk material was, in fact, what UFM used to cover the Easy with.  I had saved some scraps of material that I had from the initial covering I did years ago and put them to the iron set at about 300F.  There was almost no more shrinking going on at that temp.  The plans mention a very crude reference to shrinking once the cloth is in place.  It says to set the iron on "wool" and go for it.  You will know if it's too hot because it will melt the material.  So.......the Poly Fiber manual talks about 350F being the highest temp you ever want to take polyester cloth.  Beyond this, the fibers actually begin to relax and then finally melt outright.  My conclusion here is that the original kit cloth was, in fact, pre-shrunk polyester fabric which weighs in at about 1.5 oz/sq yd, significantly lighter than the lightest material you can buy from aircraft supply shops.  The method UFM describes in their plans basically talks about hand stretching the cloth as best you can and gluing it down while holding tension.  Had I read the plan instructions more closely and tested the scraps I had kept from the original material, I could have saved myself a lot of labor and expense.  Although, because my tech counselor assumed he was dealing with a standard covering process, he applied the fabric loosely when we glued the pre-shrunk material so it could not have been salvaged as the bracket holes were consequently in the wrong place.  The photos that follow show the various steps I will now be doing over again with pre-shrunk material.

This shot shows the cuts made for one of the strut gussets using a Weller soldering gun with the blade tip. This was slick and was right on the mark since we made a template pattern before making the cuts.

Here's what happens when you don't make a template and get in a hurry.

A shot showing the rough tension prior to the heat shrinking. This one is the root bay....notice how loose it is. With standard unshrunk polyester, this will shrink up tighter than a drum if you take it all the way up to 350 degrees F.

Here is the Tech Counselor starting to heat shrink the fabric. Notice how loose he strung it. His assumption was that it was standard, unshrunk polyester fabric and very soon after this concluded it was pre-shrunk fabric that I would have to strip and toss.

The next report will take me back to the beginning of the covering process where I will use standard uncertified light fabric material which I ordered from Spencer Aircraft Supply in Washington.....another ~$400 receipt.  I will then discover the airframe is way too weak to support the standard shrinking process and soon be right back to pre-shrunk polyester (basically dress lining material).