Conference vmszoo::rc

Well, Tom, don't expect perfection on the first shot; tissue is
something you have to handle a little if you want to get it
right.  I am assuming that you are not a rubber twister, and this
will be your only, or one of few projects.  The reason I say this
is that the right way to do the job is to use nitrate dope.
Since the stuff is relatively hard to find, and comes in big cans
anyway (I buy quarts), I'll give instructions for using common
clear butyrate dope.  This stuff is a little hard to handle, but
what the heck, a better modeler than me uses it on his rubber
jobs, so it cant be all bad. 

First, start with the tail or rudder to get the feel of the
process.  Give the surfaces that will receive the tissue a couple
of good coats of 100% dope.  Now, thin a quantity of the dope
about 50% using either automotive acrylic lacquer, acetone, or
butyrate dope thinner.  Cut a piece of tissue about an inch
oversize and lay it over the surface.  For flying surfaces, I
start at the leading edges.  Soak a little of the thinned
butyrate through the tissue to soften the 100% stuff below.  Let
this corner dry a little.  This is where the automotive thinner
is best; it flashes off relatively quickly, allowing the work to
proceed.  Now comes the "feel" part.  Stretch the tissue just
right, taking care to keep it flat over the surface, with just
enough tension to lay it flat across the edge.  Tack the other
end down.  Do this procedure for all four sides of the surface,
pulling up and redoing until you see no creases on the tissue.

Now, just go around the surface with the thinned dope, making
sure that it all lays flat with no creases.  The secret of the
process is not to get the tissue flat, but to be sure that there
are no points of stress; that is, that the tension on the tissue
is equal at all points.

Trim the tissue to just a little more than the width of the balsa
around the edge of the surface, using a brand new THIN, double
edge razor blade.  Throw the blade away after using on one model,
or when it starts to tear the tissue. It should cut with little
more force than its own weight as it goes around the surface. 

Wrap the tissue around the corner of the part and tack it on the
other side just a little.  This gives nice edges; you may have to
cut the tissue at right angles to the edge in several, use as
many as you want, places to get it to wrap properly.   This takes
some experience, don't get frustrated.

Do both sides of the surface.  After the dope is dry, use a coat
of alcohol (I use rubbing), to stretch the tissue.  For a small
rubber model, it is best to wet one side, pin or weight the
surface flat, and let it dry.  It will look stretched in about
1/2 hour, and you can do the other side, but it will continue to
stretch for 2 or 3 days afterward.  If you got the tension on the
tissue just right, you should have a nice warp-free surface.

When all is dry and stretched, use a coat or two of 50% dope to
seal the tissue.  You can use color, though it adds weight, so be
careful.

On wings, the book says to do the lower side first; I try to do
this, but I always forget and do the top first -- it seems to
come out ok, except when there's undercamber (then even I
remember to do the bottom first!).  

For the fuse, the process is similar, except that you may have to
use small strips.  Sometimes, on a complex surface, such as a
Mustang, you wind up using little strips, on one or two sets of
stringers at a time.

I'll tell you why I always use silkspan or tissue, and very
little plastic covering.  Its because I have a little kit of
stuff I need to do the covering job.  I get a can or two of beer,
go into the yard to a comfortable spot and cover to my heart's
content.  Plastic is sterile compared to the feel of dope and
tissue. 

Finally, rubber is tricky.  Chances are if you built the kit
using kit parts and methods, its too heavy to really fly.  For
instance, I routinely substitute 1/32 for 1/16 in the kit (if I
build from a kit, or the same from plans).  Especially true for
wing ribs.  Use some SIG rubber just a tad longer than the
distance to the motor peg, lubricate if you can.

Good luck.  If I missed anything above, don't hesitate to ask; we
need all the rubber twisters we can get!

     re.1  John, I have made about one hundred or so rubber models.
    They were all when I was between 10 and 16 (I'm now 25). I made
    them to fly not to look at so I didn't paint them. I used to build
    them in two nights so I could get out there and fly them. I used
    HOT-STUFF so I didn't have to wait for it to dry. When I came to
    covering them I just doped on the covering fast. It came out tight
    and no wrinkles but if it got wet or oil from my fingers got on
    it, it tore. I applied dope a few times and the weight of the plane
    was high. I was wondering is there any way to keep the weight down
    when painting it.
    
    TOm
    

The method in my note, that of putting down 2 coats of 100%,
and using 50% to stick the tissue down is the time-honored
method. I've tried to shortcut it, like with only 1 coat of 100%,
but it doesnt pay off. 

As you well know, weight control starts from the first stick;
every stick and joint has to be thought about.  The performance
goes up (or down) according to every gram.  I'll leave it at
that since I assume you're familiar with it all.

This is where the advantage of nitrate comes in.  Not only is it
easier to use when sticking the tissue, but you can do little
tricks like diluding a couple of drops of silver Floquil (a
railroad paint) in the thinned nitrate to give the color.  I used
this on my Mustang.  Unfortunately, Floquil is incompatible with
butyrate.  Nitrate is also marginally lighter.

The best you can get is to use color tissue with no more than 2
coats of 50% thinned clear dope for finish.  If the structure is
light to begin with, this should do the job.

1.  Silver colored tissue is unavilable.  You have to put down a
white tissue and then color it.  For butyrate, you should use a
silver dope thinned 50% or more.

2.  I recommend a free flight silkspan for a rubbe model in that
size range.  It is stronger and easier to handle.  I can never
get the numbers right I think its graded 0 as the lightest, and
000 as the heaviest.  I just ask to see the stuff and feel it
till its right.

3.  If you do get some nitrate, the Floquil is called "Old
Silver", or something like that; give a nice flat finish.

    John thanks for the input. I might try the nitrate and color mixed.
    I have used silk span in the past but I never doped it after covering
    it seemed very heavey compaired to tissue. Of course this practice
    of mine led to alot of repairing but I enjoyed watching them fly
    more than how they looked.The longer they flew the more I wanted to
    keep the weight off the next one I built. When I built my first SIG kit
    I loved how lightweight it was. That was the first time I put dope on
    the covering but I didn't color it. I was told to paint on thinned
    dope on to a strong piece of toilet paper that was on the surface
    of the tissue. Then pull the toilet paper across the surface untill
    the dope ran out. Then paint more on the toilet paper and pull it
    across till the surface was complete. This insured that the dope
    was the same consistency across the surface. I tried it and it seemed
    to work well plus keep the weight of the model down. Did you ever
    try that or is it better with a brush alone, or some other trick
    not to put to much on. What about spray cans?
    
    Tom
    
    

No I never used the toilet paper trick, sounds neat.  I prefer to
adjust the ratio of thinner to dope to control the flow.  Using
the automotive acrylic lacquer thinner (I emphasize this; its
very different from garden variety lacquer thinner), you can vary
the evaporation time by using different grades.  I buy the medium
rate stuff, but I'm tempted to try the fast stuff some time.  The
dope/thinner ratio can go down to 25% dope if you wish.  Again, I
stick pretty much with the 50/50 mix, and adjust my brushing
technique to suit the job.

If you intend to get the nitrate, you can still use it on your
gas models.  You can put butyrate over nitrate, but not vice
versa.  Since the nitrate is better to use for sticking the
covering, I put it on with the nitrate.  Then to finish, I use
the butyrate as I described earlier.

Wish me luck, I'm about to venture into the world of fabric
covering.  My next model will be covered with acrylic dress
lining material.  Its similar to Coverrite, and much cheaper than
silk.  Al Alman's column in Model Builder described the process
in detail a couple months ago, and I have been admiring the great
jobs at the field -- scalers use it a lot.  I understand that the
secret to that stuff is to apply the finish coats with a foam
brush; I'll find out... 

I always use the nitrate dope on rubber models. The nitrate dope shrinks less,
and is less likely to cause warpage. I usually use 1 coat thinned 50/50 sprayed
with a badger airbrush to seal the tissue. 

Wayne