Looking for help with my Koverall application on my 1/5 scale J-3 cub. Please take a look at my video, I hope it's self explanatory.
I've always heard that the curved wingtip can be tricky but I think this one has me stumped. Thanks in advance for any help.


http://youtu.be/qxc0QnJTYh8

You can take your heating iron and shrink a little of that excess out of the fabric before you stick it. Or go ahead and stick it and let the iron pull the wrinkles out afterward (although that makes the iron a little gummy from the glue). Or you can stick it with a lot of little wrinkles and then iron them out later.

I know this sounds a little sloppy, but shrinkable Dacron is a great fabric to work with. Leave the excess material on until you have it stuck the way you want it. Don't be afraid to experiment.

I am sure others will chime in here, as well. You might also look at this website http://www.s****.com/ for helpful hints on using their product, S**** Lite. It is practically identical to Koverall.

A lot of that slack should pull out when you pull it tight to apply it. Cub wingtips are hard to get right with a single piece because the covering needs to both shrink and stretch. I've done my .40 size Cub in both ultracote and solartex. With both, I put the heat gun to it, blowing the heat from the tip into the wing so that it would heat up the whole wingtip area. I then pulled the covering hard right at the spot where the heat was coming from, which made it stretch to pull those side wrinkles out. I did that at probably 10 spots all around the wingtip with each spot stretching the wrinkles out that the previous spot had caused. If you are using stixit to apply the koverall, the same process should work for you. Of course, since you're using koverall and can hide your seams with filler, it won't hurt anything to cut the fabric where that big wrinkle on the side is and fill the little seam that the overlap makes with dope. No one will ever know it's there if you do it right.

rkcruit, I use Koverall alot as well as silk & silkspan. Going around corners is basically pretty much the same with all of them. First off if i watched your video correctly, it looks like you attached the covering to both the leading and trailing edges allready, and still have a tremendous amount of slack in the covering. I try and leave a few inches of material hang over the both the front and rear edges to pull the covering as tight as possible as i work towards the wing tip. It also helps to cut slits in the material on the edge of the curved wing tips. The covering can then be pulled tightly as needed in those areas only to pull the covering tight. ( i use a monokote iron to get the dope( or stix-it) to hold the edges down as i pull the covering tightly.) I have done several build threads here and on other sites but can only come up with this picture of what i'm talking about where i used silkspan. (same process).....Gene

Gene and Jester have it right.

Couple of suggestions.

1. Purchase the fabric application video tape from F&M as it has lots of good tips that a although oriented to the F&M process, which I have used twice and with good success, is generally very good advice.
2. Suggest that first, before applying the fabric, that you might coat the wing, wherever the fabric will touch , with 2 > 3 coats of 50/50 dope/thinner and sand ever so lightly with 320 grit paper. When you apply the Koverall the dope will go thru the covering and join with the dope underneath giving you a better bond. In the F&M process where they use Polytac you want the Polytac to go thru the covering material for the same reason.
3. When using Nitrate dope to attach the fabric experiment with 50/50 vs 75/25 dope/thinner and a small bristle brush. I find that when applying the fabric a slightly thicker dope that is not overly thinned tends to hold the fabric better but your experience may vary. Also controls how fast the dope drys.
4. Suggest that you first adhere the fabric to the rear bottom trailing edge with about 1/2 to 1 inch left towards the middle (towards the leading edge,of the wing and let this dry for an hour at least so that it does not lift at the next step. Make sure that the dope has gone through the fabric to the balsa underneath.

5. Then wrap the covering around the trailing edge to the top of the wing and the leading edge and pull it back to the bottom trailing edge. Do not apply any dope to the leading edge . You will likely find that it is best to also dope down or adhere the fabric at the center of the wing after you wrap it around the leading edge so that when you pull the fabric towards the wingtip you have something to pull against. At this point you may want to dope down down the fabric to the top side of the wingtip also. Wrapping the material around to the bottom. As required, as Gene noted, slice the fabric at the wingtip every half inch or inch , as needed, so that you can overlap it a bit as you pull it around the curve. Don't worry about a little overlap or small wrinkle here and there. You will find that as the leading edge is sanded down to flow to the wingtip that there will be a small amount of extra fabric. What I typically do is slice it down the middle a bit and then dope the bottom side to the leading edge and then when the bottom side is doped down to the trailing edge then dope the small amount on the top side to overlap the bottom side so that the overlaps are on the bottom. If you get small overlaps the beauty of the dope/fabric process is that after a few coats of dope you can lightly either sand the edges down with 320 or 400 dry sandpaper of go over it with a covering iron at around 250 degrees that will soften the dope a bit and smooth out the edges. THis works especially well with the F&M process as the POLYTAC is a heat sensitive adhesive and will smooth out with a covering iron set at a medium temperature. The Polyspray also helps in this. Too hot and bad things happen.

Try and wrap the top side covering material around to the bottom side of the wingtip a bit so that the covering on the bottom, like 1/4 to 3/8" or so. has something later to adhere to without having to overlap on the top.

6. Pull the fabric around towards the trailing edge and stretch it out towards the wingtip as best you can and dope the fabric down to the trailing edge while trying to kept it reasonably taught. THere should be an overlap of the fabric of at least 3/8 to 1/2 inch or when you shrink it will pull apart.

7. THen after you have doped the trailing edge go back to the lower side of the wing tip and repeat the process from the top side. You should be able to dope the fabric along the edge and the bottom of the wingtip to adhere it to the material that wrapped around from the top to the bottom side. THe goal is to hid the overlaps on the bottom.

8. At this point go over the overlaps with a thin coat of dope and set it aside for a while to outgas and throughly dry at least a few hours or overnight.

9. THen take the covering iron and start out with a low temperature, use covering iron with some sort of temperature control, like say 250 > 300 degrees and shrink the wing working the top and bottom at the same time. You will see the covering at the leading edge slide around and the extra around the leading edge will disappear.

10. Work you way up to 300 and then carefully to 350 degrees only in the places where you have small wrinkles that will not go away. Around the wingtip or where there are overlaps/small wrinkles use the covering iron heal (which tends to run hotter), to get the small wrinkles out.

11. When you are happy with the look of the covering, don't over shrink or you will pull the covering away at the edges or warp the structure then use something like 50/50 dope as the first coat with special attention with a bristle brush over the balsa sheet areas and cap strips. THe goal is to force the dope thru the covering to the doped balsa underneath to attach the covering to the the balsa surfaces. When doping over open bays go light on the dope and work quickly or it will go thru the covering. and make runs inside for the first couple of coats.

12. THen apply how ever many coats of nitrate dope you may want. I usually use 75/25 thinner/dope but 50/50 is OK but lots more coats are required. About every send or third coat you can lightly sand the rough edges and where there are overlaps at the wingtips and will see that after about 6 coats of dope that they disappear. With the F&M process the Poly Brush is much thicker and you only need a couple of coats to seal the fabric so you need to be more careful that when applying the fabric it is smoother and that you thin the POLYTAC a fair amount with MEK or the edges get lumpy. Careful use of the covering iron with a sock at a low temperature helps smooth out bumps at the trailing edges/wingtips and overlaps. .

Cheers

ray

Just out of curiosity, why was any reference to S**** or S****.com deleted from my earlier post?

Or this post for that matter?

Oh! I just figured it out. Funny. I'm getting real tired of putting up with spell-checker shirt.