Applying Polyspan
Since I discovered Polyspan, very rarely do I use plastic coverings or silkspan. To me the product offers the best of both worlds. It allows you to finish the way you want and is stronger and easier to apply than silkspan. The RC guys seem to have gone almost 100% ARF’s with plastic covering but a great number of us in the U control world still take pleasure in building our own planes whether they are from scratch or a kit. Maybe we are just a bunch of old coots set in our ways but I enjoy building as much as I do flying. I am probably a much better builder than I am flyer but that’s OK, because I can fix or rebuild what I put into the ground when I forget which way is out.
Polyspan is a wonderful material to cover with and is quite easy to work with. I have been asked several times how I apply it and I do not want to be redundant here on this thread but thought I would post how we apply the material.
You want to apply at least 2 coats and preferably 3 coats of 50/50 Nitrate dope and thinner to the airframe of the wing before you apply the polyspan.
When you receive the roll inspect it before you apply it and determine which is the shiny side. I have been getting mine from Tom Morris or Jim Snelson at Control Line Central. The rolls are 13” x 20’ long, cost $7.95 per roll, will generally cover 2 planes and the shiny side is to the outside of the roll. The reason it is important to apply it with the shiny side out is to avoid the fuzzies which believe me you will get if you apply it upside down. You will notice the fuzzies when you start doping the wrong side.
I build my wings in one piece on a jig and then remove them when ready for covering. Makes em a heck of a lot easier to cover without those ½” rods messing with you. I cut one piece of Polyspan for each side and overlap about an inch or so at the tips and leading and trailing edges. I use Nitrate dope throughout most of my finishing up until the very final clear coats where I switch to Butyrate. Now some folks will tell you that Polyspan is not good at the tips and I have to admit I have had easier times at the tips with some other material, but if you are patient and don’t mind getting dope on your fingers and occasionally overheating your skin with a heat gun, I have not found a rounded tip yet I couldn’t cover with it. I build a lot with a flying buddy by the name of Dave Shad, AKA the Incredible Hulk, (just kidding Dave) and he showed me a little trick the other day I had not thought of on the tips. He used thin CA to secure it to the edge of the tips and it worked great.
Lay the Polyspan over one side of the wing and start around the leading and trailing edges with unthinned Nitrate dope. The first coat always goes on unthinned . The rest of the way we will be using 50/50 Nitrate Dope and thinner. Try not to “push” the material and brush vertically on the leading and trailing edges. This helps eliminate
bubbles. When you get to the tips, if you have a buddy there with you, get him to kind of stretch the polyspan around the tip and attach with the thin CA. One note here, I do not dope down the center planking at this point.
Give the dope a few minutes to dry and attach itself to the Polyspan, then get out your heat gun and start shrinking the poly span. You can use and iron here too but I don’t. Be careful, you can burn a hole in this stuff if you get the gun to close to it or stay in one spot too long. I keep the dope mixture close to me during this part so I can dip my finger in it and work out a wrinkle at the tip if one appears. A lot of the small wrinkles can be sanded out later.
Once you have it shrunk tight, you are going to start applying you coats of clear 50/50 nitrate dope and nitrate thinner and this is the first time I apply it to the center planking. I put at a minimum of 8 coats of clear at this mixture sanding between every second coat with 400 grit sandpaper. Lowes has these really neat purple rubber pads impregnated with 400 grit that are great for this. Don’t rub to hard or too much on the cap strips.
After the 8 coats of clear, I mix up 4 table spoons of Zinc Stearate, that I got from Randy Smith, in a quart of the 50/50 Nitrate dope and thinner mix. I then apply four coats of this mixture sanding lightly with 400 grit after every second coat. I have used talcum and baby powder and corn starch but this is by far the best stuff I have ever seen for filling in grain. Just don’t let the cops see it, it looks like cocaine. By this time the wing and fuselage are beginning to look like an ice skating rink they are so shiny and slick.
A note about covering the fuselage with silkspan. I know a lot of people do this but I don’t. Some people think it covers the grain of the balsa on the fuselage and it probably adds a little strength but I get a good finish just doing what I have been describing. This is a matter of personal choice.
After all the slurry coats have been applied, I switch to BUTYRATE dope in a 60/40 mixture of thinner to BUTYRATE dope. The 60% is thinner. This is to fuel proof the plane. Remember, you can put Butyrate over Nitrate but not the opposite. I use Randolph brand dopes and this is what John Brodak’s dope is too. I do not have spray equipment so this is also brushed on. I will apply 4 more coats of this mixture as a clear coat over the slurry and sand after the second and 4th coat with 400 or higher grit.
The plane willlook very slick and shiny and you can paint with your choice and brand of paint. My planes will probably never make the front row at the NATS, but they look pretty darn good when finished this way.
Hope this may have answered some questions about using Polyspan.
Mike
Since I discovered Polyspan, very rarely do I use plastic coverings or silkspan. To me the product offers the best of both worlds. It allows you to finish the way you want and is stronger and easier to apply than silkspan. The RC guys seem to have gone almost 100% ARF’s with plastic covering but a great number of us in the U control world still take pleasure in building our own planes whether they are from scratch or a kit. Maybe we are just a bunch of old coots set in our ways but I enjoy building as much as I do flying. I am probably a much better builder than I am flyer but that’s OK, because I can fix or rebuild what I put into the ground when I forget which way is out.
Polyspan is a wonderful material to cover with and is quite easy to work with. I have been asked several times how I apply it and I do not want to be redundant here on this thread but thought I would post how we apply the material.
You want to apply at least 2 coats and preferably 3 coats of 50/50 Nitrate dope and thinner to the airframe of the wing before you apply the polyspan.
When you receive the roll inspect it before you apply it and determine which is the shiny side. I have been getting mine from Tom Morris or Jim Snelson at Control Line Central. The rolls are 13” x 20’ long, cost $7.95 per roll, will generally cover 2 planes and the shiny side is to the outside of the roll. The reason it is important to apply it with the shiny side out is to avoid the fuzzies which believe me you will get if you apply it upside down. You will notice the fuzzies when you start doping the wrong side.
I build my wings in one piece on a jig and then remove them when ready for covering. Makes em a heck of a lot easier to cover without those ½” rods messing with you. I cut one piece of Polyspan for each side and overlap about an inch or so at the tips and leading and trailing edges. I use Nitrate dope throughout most of my finishing up until the very final clear coats where I switch to Butyrate. Now some folks will tell you that Polyspan is not good at the tips and I have to admit I have had easier times at the tips with some other material, but if you are patient and don’t mind getting dope on your fingers and occasionally overheating your skin with a heat gun, I have not found a rounded tip yet I couldn’t cover with it. I build a lot with a flying buddy by the name of Dave Shad, AKA the Incredible Hulk, (just kidding Dave) and he showed me a little trick the other day I had not thought of on the tips. He used thin CA to secure it to the edge of the tips and it worked great.
Lay the Polyspan over one side of the wing and start around the leading and trailing edges with unthinned Nitrate dope. The first coat always goes on unthinned . The rest of the way we will be using 50/50 Nitrate Dope and thinner. Try not to “push” the material and brush vertically on the leading and trailing edges. This helps eliminate
bubbles. When you get to the tips, if you have a buddy there with you, get him to kind of stretch the polyspan around the tip and attach with the thin CA. One note here, I do not dope down the center planking at this point.
Give the dope a few minutes to dry and attach itself to the Polyspan, then get out your heat gun and start shrinking the poly span. You can use and iron here too but I don’t. Be careful, you can burn a hole in this stuff if you get the gun to close to it or stay in one spot too long. I keep the dope mixture close to me during this part so I can dip my finger in it and work out a wrinkle at the tip if one appears. A lot of the small wrinkles can be sanded out later.
Once you have it shrunk tight, you are going to start applying you coats of clear 50/50 nitrate dope and nitrate thinner and this is the first time I apply it to the center planking. I put at a minimum of 8 coats of clear at this mixture sanding between every second coat with 400 grit sandpaper. Lowes has these really neat purple rubber pads impregnated with 400 grit that are great for this. Don’t rub to hard or too much on the cap strips.
After the 8 coats of clear, I mix up 4 table spoons of Zinc Stearate, that I got from Randy Smith, in a quart of the 50/50 Nitrate dope and thinner mix. I then apply four coats of this mixture sanding lightly with 400 grit after every second coat. I have used talcum and baby powder and corn starch but this is by far the best stuff I have ever seen for filling in grain. Just don’t let the cops see it, it looks like cocaine. By this time the wing and fuselage are beginning to look like an ice skating rink they are so shiny and slick.
A note about covering the fuselage with silkspan. I know a lot of people do this but I don’t. Some people think it covers the grain of the balsa on the fuselage and it probably adds a little strength but I get a good finish just doing what I have been describing. This is a matter of personal choice.
After all the slurry coats have been applied, I switch to BUTYRATE dope in a 60/40 mixture of thinner to BUTYRATE dope. The 60% is thinner. This is to fuel proof the plane. Remember, you can put Butyrate over Nitrate but not the opposite. I use Randolph brand dopes and this is what John Brodak’s dope is too. I do not have spray equipment so this is also brushed on. I will apply 4 more coats of this mixture as a clear coat over the slurry and sand after the second and 4th coat with 400 or higher grit.
The plane willlook very slick and shiny and you can paint with your choice and brand of paint. My planes will probably never make the front row at the NATS, but they look pretty darn good when finished this way.
Hope this may have answered some questions about using Polyspan.
Mike
