Foam Fix

How to Fix Warps, Dents, Twists, Or
Un-Crunch Foam Airplanes and Parts

by Ed Anderson ([email protected])
I never crash, but maybe you do. Crashing can crunch the foam of a Radian or other foam airplanes to the point that the parts don’t fit or you introduce a twist or warp as you try to put it back together. The repair can also introduce a twist or warp in the fuselage.

I am going to outline a method of getting the foam back to straight or un-crunching 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 glider 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 fuselage, again inverted and then gently stretch the string to the nose. It should track down the center of the fuselage. If it does not, you have a warp. We are going to fix it.

This can happen at the factory, from a fuselage 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 airplane 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 fuselage, take the wings off; you won’t need them. Take the horizontal stabilizer 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 fuselage 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 un-crunch 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 Multiplex Elapor foam models. But it works well with most bead-type foams. Easy Star pilots would crunch the nose of the airplane in a crash. They would plunge the nose, Elapor foam, it into boiling water and the foam would expand, thus the soup reference.

Heat Methods

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 fuselage just a little past straight while it is under the running hot water. The foam beads will expand, extending that side of the fuselage. After a minute or two, 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 100-140° sometimes this is not hot enough to do the job. So we need more heat.

Place 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 such as wings.

My favorite is using a heat gun/hair dryer to heat a wet cloth or paper towels. 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.

By the way, this works well for bagged composite wings, like DLG glider wings. It can take a dent out by heating the foam under the skin. I use paper towels and my covering iron. They magically disappear. This works well for dents in your Radian, Easy Glider, etc. Here 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 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, 120-140° can do it too.

Using these methods I have taken Radians and Easy 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 fuselage. The wings got a few dents, but the fuselage was in five pieces. It flies today!

Regardless of the method, 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 fuselage 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 and 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 may not get it totally flat but you will see the impact. Note that the cup material is thin so don’t heat it too much at once or you will expand all of the beads instead of just the ones on the inside of the curve. The heated beads will get bigger.

When working on a fuselage, wings, or other parts, be sure you don’t introduce a twist as you do this or you will have another problem. But no worries, that can be fixed too.

Clear skies and safe flying.
Ed Anderson