HOW TO FIX WARPS, DENTS, TWISTS OR UNCRUNCH FOAM PARTS
by Ed Anderson
I never crash, but maybe you do. Crashing can crunch the foam of a Radian or other foam planes to the point that the parts don’t fit or it introduces a twist or warp as you try to put it back together. Or it can introduce a twist or warp in the fuselage. I am going to outline a method of getting the foam back to straight or uncrunching parts. This can also be used to take twists or warps out of new parts and it will take dents out of your foam wings or even bagged wings, like DLG wings.
Let’s suppose your Radian, Easy Glider, Easy Star, etc. has a tendency to turn in the air requiring you to trim in a lot of rudder to get it to fly straight. How can you fix it? Well first you have to find the cause. Turn your foamy over and site down the fuselage seam. It should be straight from nose to tail. Or, tape a piece of string to the tail end of the fuse, again inverted and then gently stretch the string to the nose. It should track down the center of the fuse. If it does not, you have a warp. We are going to fix it.
This can happen at the factory, from a fuse not sitting right in the box or from a crash where one side of the fuselage compressed from an impact. This can also happen if you leave a foam plane in a hot car for a long time. Believe me, what you will learn here will come in handy for the rest of your foam flying life.
Heat does wonderful things to foam. It can stretch it, expand it and help straighten it. You can put twists in or take them out. You can use this when making some foam replacement parts too.
Since we are fixing the fuse, take the wings off, you won't need them. Take the h-stab off if it comes off. Tape the rudder so it is straight.
Try to figure out where the warp is centered. I am going to guess it will start behind the wings, somewhere along the boom. Flex the fuse to see if you can get it to look straight. You may have to use something to apply pressure in the center of the curve on the opposite side to get it straight. If you can flex it to straight, you can fix it.
Basically you are going to apply heat to the inside of the curve as you flex the boom away from the curve and a bit past straight. As you apply heat the gas that is trapped in the foam beads will expand. As the beads expand they extend that side of the fuselage making the heated side longer and helping you take that warp out. If this was caused by a crash this will uncrunch the crunched beads.
This goes under various names, but you might hear it called the Elapor soup method as it really became popular with the Mulitplex Elapor foam planes. But it works well with most beaded type foams. Easy Star pilots would crunch the nose of the plane in a crash. They would plunge the nose, Elapor foam, it into boiling water and the foam would expand, thus the soup reference.
HOT running tap water - You hold the part to be expanded under the hot water while you shape it. In this case you flex the fuse just a little past straight while it is under the running hot water. The foam beads will expand, extending that side of the fuse. After a minute or two you take the fuse out from under the water, still holding it and let it cool. Then site and see if it took. Go back under the water if needed. As tap water is only 100 to 140 degrees sometimes this is not hot enough to do the job. So we need more heat.
Placing the part into boiling water - this works well for small pieces like a rudder a wing tip or a crunched nose. You can also pour boiling water over the area.
Steam from boiling water sometimes works. Use a BIG pot and make lots of steam. This works well for large areas like wings.
My favorite is using a heat gun/hair dryer to heat a wet cloth or paper towels that I place on the area I want to heat. The water keeps you from getting the area too hot and melting the foam. The water itself is not part of the process, it is just for temperature control. When you do this, Don't let the towels dry out completely. You heat the wet cloth till it steams and starts to dry out. You have the part stretched while you do it, just as above.
You may want to protect adjacent areas. I often do this with loosely fit aluminum foil as a heat shield. Make sure there is air under the foil so the heat can be carried away.
BTW this works well for bagged composite wings, like DLG wings. It can take a dent our by heating the foam under the skin. I use wet paper towels laid on the dent and my covering iron. They just magically disappear. Works well for dents in your Radian, Easy Glider, Easy Star, etc. Again, for dents you want to be more focused, so a covering iron or a hot clothes iron is best. Just use the tip to focus the heated area on the wet cloth over the dent.
In each case the purpose of the water is to keep the foam from getting too hot and melting. We want to get it up to about the temperature of boiling water, though sometimes hot tap water, 120 to 140 degrees can do it too.
Using these methods I have taken foam planes/gliders that have been broken into numerous smashed and crushed pieces, reshaped the foam and glued it back together with great success. Recently I shredded my Radian while slope soaring. A high speed crash through bare tree branches did a nice job on the fuse. The wings just came apart and got a few dents, but the fuse was in 5 pieces. It flies today!
In the case of a twisted fuselage or wing, you want to spread the expand over a somewhat broad area, not a pinpoint. Again, in the case of dents in a wing you want to be more targeted. That is why I use my covering iron rather than a heat gun.
In the case of the fuse we are using as our example, you want to expand the most in the center of the warp curve but you want to extend that somewhat forward and back of the center or you will have to overheat one area too much and perhaps not have enough expansion ability to make it work.
Try it! If you have some scrap Styrofoam or other beaded foam you can try this out for practice. Take a foam drinking cup. cut out the bottom. Now do a top to bottom slice. Use the method above and see if you can take the curve out of the foam and make it flat. You will be working on the inside of the curve. You may not get it totally flat but you will see the impact. Note that the cup material is thin so don’t heat it to much at once or you will expand all the bead instead of just the ones on the inside of the curve. The heated beads will get bigger.
When working on a fuse, wings or other parts, be sure you don't introduce a twist as you do this or you will have another problem. But no worry, that can be fixed too.
Clear Skies and Safe Flying.