ETLB Squawk Forums — Archive

Ok folks here is where I am in my build, I have completed all the build and I am in the covering phase, I have covered both wings (polyfiber) I have done a 200 degree calibrated initial shrink just to tighten it up a bit. My question is how do you know how tight is tight enough? Also you obviously cant un-shrink it  lol so I don't want to mess things up this far along. Thanks for all the great input. James

How much the ribs push the fabric out is a good measure of whether it needs more shrinking. The wing picture in the recent Oratex thread posted today is how much the outline of the ribs in the wings should stand out out from the fabric. (A little more too would be fine I think.) If the ribs' upper footprint stand out much more sharply than that, then I think you may have shrunk it too much. Shrinking too much could lift the wing’s trailing edge sooner or later.

Edit: At least the above is how I checked my fabric's tension, besides of course tapping with the fingers and listening for sound. Construction manual says drum tight. Musicians know there are different types of drums  I wish there was a gauge to measure fabric tension.

I had downloaded these notes a couple years ago before I did my covering.
Not sure where I got them from.




>>>>>>>>>>>>
Shrinking the Fabric

Normally, you shrink the fabric in two separate passes.
The first pass uses 200°F, and second and final  pass is at 250°F.
If you’re covering a light structure, like an ultralight,
shrinking beyond 250°F can cause structural damage.
Also, if you are using nitrate and butyrate dope, then you will
only shrink to 250°F. If you used a fabric envelope with sewn seams
or if you want straight seams, shrink the area immediately
along the seam first.

As you begin the shrinking process,  the  fabric  will  shrink
uniformly. If you’re doing a large surface, such as a wing,
begin in the bay near the wing root. Shrink that at 250°F and
then do the bay at the wingtip. You can then work your way toward
the middle of the wing. This will help prevent warping.

Let the iron glide over the surface—no pressure is necessary.
Don’t worry about leaving the iron in one place temporarily.
It won’t scorch the fabric, nor will the fabric get any tighter.
How much the fabric shrinks depends on the temperature,
not pressure or time.

Don’t worry about removing all of the wrinkles on the first pass.
They’ll come out at the higher temperature second pass. Be careful
not to allow the tip of the iron to penetrate protrusions or
rivets and cut the fabric. Also, and this is important, do not
place the iron over cemented seams. A temperature of about 250°F
will loosen fabric cement.

After shrinking the fabric at 200°F, turn the heat up to the 250°F and
iron everything. It’s important that you shrink every fiber of fabric.

[A 350°F setting will shrink the fabric to its maximum of 10 to 12
percent. Failure to shrink to this setting on most airplanes (other
than ultra- lights) will cause the fabric to be loose forever.]

It’s a good idea to mark using a pencil each wing bay or
area that has been shrunk to 250°F. That way if you are distracted,
you will know which areas are completed.

If you are a beginning fabric coverer, I recommend learning the
techniques on a small surface such as an elevator. Perfect your
procedures before going to the wing or fuselage.     

thanks Keith, great info. I agree a floor tom and a snare is like a biwing and a jet lol!

I have not covered yet. The drum tight to me tho (having tuned many drums) is the difference betweene laying the drum head on the drum it will flap and flop when you start and slowly evenly tightens up. The note to me with "drum tight" is that it will not flap and flop when "played". Tune it to what your comfortable with sound look and feel. Also they do have drum tuners which measure the tension... curious what different planes are ... ok its late im tired thats my 2 cents cuz i couldnt help myself

Hi All
Go by the PolyFiber book. Remember you are not using certified fabric. Another idea, ask David Cooper. I see sometimes people forget he manufactures the kits and would have the most experience and some of the best advice!
Bob