Oh crap...covering gone wrong

[avidflyer]

I'm just looking in the Poly Fiber manual, and there it talks about shrinking to 350 degrees. It says that at about 375 degrees, it starts to soften and loose all measurable tension. At 415 degrees it starts to disintergrate. I was under the impression that all these fabrics were the same. I've been wrong before though. If you have any fabric left, you could make a small test panel with some wood 1"X2" screwed into a square and try shrinking it up to 350 and then if it's real tight, later on heat it up to 375 and see if it starts to loosen. If you have enough fabric, you could try some kind of punch test with one heated to 300, another to 350 and then finally up to 375. If it was equally strong at 300 and 350 and starts to loosen at 375, I probably wouldn't worry about it. Jim Chuk
Avid MK IV (flying)
Kitfox 4 (building)
Northern Mn

[cap01]

the manual i have is vintage 92-93 with some of model III and IV . the section on covering does mention the fabric being dacron 1.8 oz and " do not shrink the fabric to anything over 248 degrees f unless absolutely necessary" and it does mention that distortion of the frame could occur if the fabric is shrunk at the higher temps .

[Geowitz]

Thanks for the thoughts and ideas. I'm somewhat convinced that what I have may be fine, but I keep looking at the rib stitch holes and how some of them seemed to tear a little more than I would expect so I think I'm just gonna bite the bullet and leave no doubt by recovering them with new fabric and I'll use the medium which is preferable for the wings anyways. I don't think anything else will put my mind at ease and atleast it's enjoyable work.

[t j]

Here's my covering story. Shortly after I purchased my Kit in 1994 I attended a covering workshop put on by PolyFiber at an aviation conference. One of the first things the polyFiber rep said was, "You Kitfox guys be careful, you can bend your airframe if you shrink the fabric over 300 degrees"

I asked him about the light weight dacron supplied with my Kitfox kit. He said it was fine to use it. He said if I planned to ever put a high horse power engine on the plane or if it would be subject to rough use like hitting brush on remote strips or or be kept outside in snow and ice conditions, medium weight fabric would be better.

A tip he gave me on shrinking was to have a helper hold a straight edge against the structure being shrunk. Shrink the whole structure at temperature intervals increasing 25 degrees at a time. If the structure started to pull away from the straight edge stop right there with the shrinking.

I ended up using the light weight fabric on the fuselage and bought some medium weight for the wings, tail feathers and verticle fin.

I shrunk everything except the wings to 300 degrees like the Kitfox builder's manual suggested. I had my hepler hold a straight edge on the trailing edge of the wings and increased the temperature to 325 degrees. The trailing edge stayed tight against the straight edge so I increased the temp to 350 degrees. As soon as I started to iron a wing at 350 degrees the trailing edge started to pull away from the straight edge. I stopped right there.

I found the light weight fabric is much easier to work with for making doilies. It is much easier to make them lay nice and smooth over the inspection rings. I started using medium weight for doilies on the wings but switched to the light weight when I couldn't get all the rinkles out of the medium weight.

[t j]

If anyone is wondering about the condition of fabric that has been stored for some years it is pretty easy to test the strength of your fabric. Here's a link to the fabric covering section of AC 43.13-1B The method for testing fabric strength starts on page 35.
http://rgl.faa.gov/Regulatory_and_Gu...apter%2002.pdf

[Mark]

but I keep looking at the rib stitch holes and how some of them seemed to tear a little more than I would expect

I have found that you can tear out the rib stitch holes of most fabric at any temperature. Tearing is a function of the knot tying technique. Try pulling up and away from the hole rather than pulling down toward the fabric.

[Geowitz]

t j - Thanks for the synopsis. I actually reinforced the trailing edges in anticipation of bending with 3/8 aluminum tubing placed in the cavity of the trailing edge with hysol 9460 as I believe the SS7 has. I really don't see any other place that shouldn't hold up to 350 degrees shrinking. Anyone have thoughts on this? I mean, really, where else could it warp if you heat it evenly on the top and bottom?

Mark - I was pretty gentle with the stitching, atleast I think I was, but I'm sure I could have been better. I guess it's probrably more unsettling to me because I'm used to seeing it done on medium fabric.

[cap01]

it sounds like from the old kitfox manual that they are concerned more about warping the frame that melting the fabric . if it passes the straight edge test , you might get ahold of someone at poly fiber and get their take on your situation . i also have the poly fiber info pack that says the same thing as tj for light structure a/c about going to 250 then checking for deforming going on up to 350 . thats with poly fiber fabric of course .

[Dave S]

George,

If the information to not shrink at a temp over 300 degrees F was part of the kitfox manual or Kitfox information It might be good to take a look at the details in the manual. At least in later model KFs the manual says to stop at 300 on the wings if you do not have the trailing edge reinforcement bonded into place. These are 3/8 inch diameter tubes that are hysoled into the void in the trailing edge. If you got them - the manual says to go to 350 - if you don't stop at 300. This is in line with Chuck's comment regarding structure. In the case of the KF trailing edge - too much tightening can bow the trailing edge if the reinforcing tubes are not bonded in.

If the information to not shrink at a temp over 300 degrees F was part of the covering material supplier's instructions then it may be a fabric deal , not a KF trailing edge issue.

Sincerely,

Dave S
KF7 Trigear
912ULS warp

[Geowitz]

Thanks everyone. My manual is "pre" trailing edge reinforcement so I wasn't aware of the real reason for 300 until you guys pointed it out. It's a good thing I saw that mod mentioned on this board and I'm glad I took the extra time to do it.

All in all I'm pretty sure I would have been ok, but I don't want to have any doubt in the strength because I know I went over 350 in just a few spots, not to mention medium is really a much better choice anyways. I've dealt with some medium and figured the light dacron wouldn't be much different, but I could really tell a difference while stitching. Now it's all really about peace of mind. Besides, I really like covering. It's very relaxing. I've already gone ahead and ordered medium covering and will go just shy of 350 since I did add in the 3/8 tubing.

Heck, the old covering is already off with the wings awaiting their new dress. I love the Stewarts system.