#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).

#7 Pre-Rig

When I found that neither set of wings would rig up with the original cabling and not have the rudders binding significantly, I realized I would have to re-rig the entire glider.....meaning I needed to cut ALL the rigging cables and remove them. I ended up doing this using a cutoff wheel on my ¼ inch angle grinder. I had to really be careful not to nick the brackets or tubing but it worked OK. I cut off one end of each negative wire cable leaving a cable bushing on the other end. I used two of these pieces, each with a cable bushing on the end and a cut cable end on the other and clamped them together using the electrical clamp nuts called for in the rigging part of the instructions. I end up with an adjustable cable with bushings on both ends that I used to hold the wing from folding down while I checked the upper and lower spars for parallel alignment.

The photo below shows the right wing set up on the fixture and if you look close you can make out the plumb bob off the leading edge wing joiner on the left hand side of the photo where I am checking for parallel alignment of upper and lower leading edge spars and also the 14” stagger.

You may also have noticed the tape on the floor which I used to mark all the reference points called out for on the pre-rigging sheet in the plans. Here is a shot of what I mentioned can happen in the last post if you don't watch which bolt you're using where (permanently compressed strut).

I have done a bit of sourcing research trying to find the part shown in this photo that is used throughout the Easy Riser rigging brackets. It is called a rivet nut and various other names depending on the manufacturer. The longest barrel length I could find anywhere to date is approximately 0.5 inches. Somewhere, Larry Mauro apparently sourced one with a barrel length of nearly 3/4” which doesn't seem to exist anywhere I've tried looking. He may have had it special order. The ½ inch ones which are readily available, are used on this glider frame in the brackets with only a single cable attached as shown here.

One of my goals in this project is to find sources for all the parts needed to make an Easy Riser from the ground up so I would like to find the longer rivet nut even if I have to find a manufacturer willing to make a custom run of them. Below is a shot showing the longer rivet nut with the half cable bushing which is what requires the barrel length to be nearly 3/4” long since a second cable bushing will need to slip onto the end of it for the quick disconnect negative wire attach point during set up.

That completes the pre-rigging. Next, I need to wrap all seven ribs on the upper left wing panel using the knot shown in the original addendum the plans included for rib stitching (which I also plan to do after attaching the fabric). Wrapping the entire length of the rib keeps the cap strip from pulling off the foam core.  This is probably most important in rough landings where the wing spars might collide with a stationary object whereas rib stitching functions to keep the fabric attached to the ribs.  The other three panels I had already finished rib wrapping from the original build. This shot shows the left upper wing panel propped up on saw horses ready for rib wrapping.

Somewhere I thought I remembered the instructions including wrapping the ribs but could find no reference to it anywhere in the large plan drawings or the rib stitching addendum. I used the same knot shown in the addendum to wrap the ribs. Here is a shot of the last knot being tied on the final rib.  I later decide this is totally redundant since the entire glider will have to be rib stitched after covering and sealing anyway which will accomplish the same thing.

Ordered the fabric glue to do a test on the frame with the old glue intact to see if it would be compatible with the new glue. The tests were good which means it will not be necessary to completely strip all the spars of the old glue. The old glue was Super Seam that came with the original kit. This was really good news since stripping all that glue would have been a real job.

The local EAA chapter has a Tech Counselor that has volunteered to help me attach the fabric to the first wing and shrink it. This requires me to get the trailer ready to haul wing panels so I have been spending most of the time working on that, hence, not much progress on the wings. My next post will include the material order list for the covering supplies I will need through the top coat paint.