In 2001 many combat fliers are looking for more strength and survive-ability. Applying ripstop nylon to foam wings is one sure way to build stronger planes.
What is it? Ripstop nylon is most often used in parachutes and tents. It is a tightly woven nylon or synthetic fabric with a coarse grid embedded in the weave. It can be found in local fabric stores at prices of $3 to $6 per yard. When you go to the fabric store look at the different bolts. There are several characteristics you want to look for. First you want the lightest grade available. I have seen several bolts with the same product name vary in density. Some of the fabrics were twice the thickness and weight of the others. You also want the type of ripstop that is porous and that you finishing material can flow through. Some variations are sealed and liquids will not penetrate them. I hold it up to my mouth and blow through it to see if it’s porous. If the sales person is not looking I may also dab a little saliva on it to see if it goes through. Wearing old pants that you can wipe your hands off is helpful if you use this form of testing.
I’ve seen ripstop in white, yellow, orange and printed patterns. The first few yards I bought were printed in a tie-dyed blue pattern. Many people thought I had tie dyed the fabric and at the first contest I went to with the new planes, a lot of fliers wanted to play some Grateful Dead music to make me comfortable. In any event pick a pattern that is pleasing to you.
What is Water Based Polyurethane paint? Also called WPB it is found in hardware stores and the hardware departments of the Home Improvement stores. I have been getting mine from the local ACE hardware store and it is labeled as a store brand. Minwax also makes it and their can specifically states “alcohol resistant”, which I took to mean I couldn’t get it drunk. Its costs about $13 a quart, which is enough for about a dozen, planes. WPB needs to cure before it is fuel proof. My planes have over 50 flights on them and the WPB is holding up well to the 15% nitro fuel I use. WPB won’t attack white or blue foam and clean up of brushes can be done with soap and water.
One experiment I tried with WPB didn’t work out well at all. All the WPB I have worked with is clear in color, and I usually use the satin gloss finish. I wanted black WPB so I tried to color it. I took a package of RIT dye and dissolved it in a small container of water, no more than ½ pint. I stirred it until the lumps were as small as I could get them then poured the soup into a new can of Minwax WPB. It didn’t blend at all well so I hooked up the electric drill to a stirring paddle and blended it for about five minutes. It was a little thicker than before but not enough to affect application with a foam brush. I got out a scrap of foam and some fiberglass cloth and applied enough to make up a valid test section.
The next morning the test section looked good, just not quite dark enough, so I opened up the can of dyed WPB. Overnight the WPB had changed from a richly colored liquid to a rubbery blob of dough. This stuff was really messed up. Well there goes $13 bucks worth of paint and another idea succumbs to the bite of reality.
How do you Apply Ripstop and WPB? My first attempt worked but I found a better way. Before you start the application, make sure your surfaces are prepared. I have built BAT Tricks and covered them with Ripstop. The wings of the Bats have several strands of fiberglass packing tape on the top and the bottom. The WPB will not stick to the tape unless you give the tape some grip. The way I have done it is to sand the sheen off the tape, but not cut into the strands. Others have sprayed the tape with 3M77, do whatever works for you.
I start with the bottom of the wing and cut two pieces of ripstop about an inch larger than the wing, long enough to go 8 inches past the center of the wing, as I will overlap the pieces. Next I take the ripstop and put it in a pan of water. I push it down so that it is saturated and then let it sit in the water for about five minutes. What happens is that the ripstop absorbs the water in its weave and expands. This good because when it dries it will shrink. If you do not do this step it will start to expand when you apply the WPB to it making the whole wing one big ugly wrinkle that you will have to repeatedly work over to get right.
After the ripstop soaks take out the pieces and hang them off the edge of your workbench. They will drip for a few minutes and then be damp but not wet to handle. While the ripstop is dripping dry, paint the wing surface you are going to cover with WPB. The stuff is self leveling so you don’t have to be Picasso when you put it on, just make sure you get it on the bare surface.
Next lay your ripstop on the coated wing. Smooth it out with your hands, but perfection is not required at this point. Next with chord wise strokes (from LE to TE) paint another coat of WPB onto the ripstop at the wing center section. This will “anchor” it so you can tug it from the wing tip with span wise tension. As you tug continue to paint WPB onto the wing in a chord wise motion until you get to the tip. I overlap both the leading and trailing edge onto the other side.
Repeat for the other side and then the top of the wing. Set it aside to dry for a day. Put another coat of WPB on the whole thing and let it sit for four days before you introduce it to Mr. Nitro methane.
Good Luck…. Lou