You did it! No one else saw that airplane-eating tree move 20 yards to the right and snag your airplane right out of the sky on final approach. You know you had the airplane in the clear until that tree moved, but no one is going to believe you so you might as well take the blame. Luckily the tree only caught your airplane on its bottom branches so you can reach it. It’s time to put down your transmitter and to take that long, lonely walk out to scene of this very unjust incident.

Not only was this unfair, but it is also an inconvenient show stopper. It is now mid-August and you have soloed only 3 flying days ago. While the airplane is not badly damaged, it can’t fly with that big hole in the wing. Ordering and building a new wing will take until mid-September. After your hard summer’s work learning to fly, you will now have to sit out the best part of the remaining season waiting for parts. Even worse, your new-found flying skills will be getting very rusty and you might have to re-learn some of those piloting skills that are already slowing escaping into the great beyond.

You could go out and by a new ARF trainer at the local hobby shop. But that still requires building and trimming time. It can also get a little bit expensive. Instead, what about spending 15-25 dollars plus two nights work to get back in the air? Even though you may have never built a wood kit, you can fix that wing with a few supplies and a little wood working.

The only tools you will need are all available in the hobby shop. They are:

Gap Filling CAA             Thin CAA          Ambroid® Liquid Cement (I know it is old tech.)

Modeling pins                Pin Clamps       Micro-Fill Modeling Filler

#616 knife blades           #11 knife blades A Hobby knife handle

12” sanding block           Low-tack masking tape   Small flexible sanding block       

Razor saw                     Some assorted balsa wood         Plastic film covering

5-minute epoxy  Micro Balloons Filler

All of these items will be used throughout your modeling career. There is one other tool you will need and that is a modeling iron designed to apply plastic film covering. That costs about $25 on its own, but you should have one already since it is usually required to remove the wrinkles that came with your first airplane.

A few of the items on this list are somewhat vague. That is because different airplanes will require different size wood and brands of covering. So the first task is to make these vague items more descriptive.

 
Photo1     Photo 2

Carefully examine the damaged area. The repairs discussed here work well for damaged leading edges up to three “rib bays” wide. For larger repairs, use the same techniques, but insert a ½ in. strip of .007 in. thick carbon fiber span-wise along the top and bottom of the sheeting, extending onto the existing sheeting on both sides.

Photo 1 shows some internal damage to at least one wing rib. The sheeting is crushed and cracked in many places. But the spar is sound and undamaged. If the main wing spar is cracked, stop right there. While repair is still possible, it is a lot harder to do right and far more critical. If the spar is damaged, it is time to ask a more experienced modeler to help you and it will be necessary to remove most of the wing’s covering for a complete examination.

But your main spar is fine. It is just the leading edge that could use some help. Since most of the factory leading edge is now sawdust, it will need replacing. At least one of the wing ribs is missing its front half and another is cracked. The crushed sheeting cannot be repaired and must be replaced.

Most of the sheeting used in ARF models made overseas is usually about 3/32 in. thick. To be a little more precise, it is 0.089 in. The 3/32 in. balsa sheeting available in the US is usually about 0.093 in. We can live with the 0.004 in. difference since most of it will be removed during the final sanding process. However, be sure to measure the sheeting thickness on your airplane in case it is a different size. Find the lightest, most flexible piece of 3/32 in. sheeting in your hobby shop, 36 in. long by 3-4 in. wide, and buy it.

Photo 3

Next is to identify what size the replacement leading edge needs to be. Use a small fragment of the original leading edge as shown in photo 3. Carefully remove any remaining wing sheeting that may be on it, at least in one small spot. Measure its height, top to bottom. For this repair, the height needed was almost exactly 5/8 in. In order to insure a straight, warp-free leading edge replacement, try to make the new leading edge by laminating two balsa sticks together.

Photo 4

For this aircraft, one ½ x ¼ in. balsa stick and one ½ x 3/8 in. balsa piece were ideal and a perfect match for the old leading edge’s height. The ½ in. width, front to back, was also just right. If it were too short, including a piece of 1/16 in. balsa sheeting in the lamination usually is sufficient.

Cut the individual balsa sticks to about one inch longer than needed to fit the open area in your wing. Laminate them together as shown in photo 4. Use Ambroid liquid modeling cement for this. What? Use a 60-year old adhesive, that isn’t the world’s strongest bonding agent, and then wait two hours for it to dry? Are you crazy? Why not just use thick CAA or at least wood glue?

Ambroid is old technology, but it has three advantages in this application that make it the glue of choice for much of this repair project. First, it sands like butter, leaving no high spots as would CAA adhesive. Second, as it dries, it draws the parts being glued more tightly together for firmer contact and fewer gaps. Finally, it does not contain water, as does wood glue, so it will not cause the two sticks to warp as they dry. The net result is a laminated piece that is straight, tightly bound without gaps and one that can be sanded as if it were made of a single balsa piece.

 
Photo 5     Photo 6

While the new leading edge is seemingly taking forever to dry, (we really have become spoiled by modern adhesive technology), work on some of the internal areas. If any of the wing ribs are just cracked in a few places, like the one in photo 5, then separate the cracks just slightly, apply thick CAA inside the cracks, realign the wood and hold tight until the adhesive sets.

Examine the wing sheeting. Much of it will have to be replaced. But if only a few cracks extend into otherwise sound sheeting, as in photo 6, apply some liquid cement and clamp the sheeting together (photo 6). Again, this area will be sanded and the liquid cement pulls the parts together for a gap-free bond.

 
Photo 7     Photo 8

Now is the time to determine just how much sheeting must be removed. Sometimes, it is just easiest to remove all the sheeting back to the main spar. This makes wing rib replacement easier since it is easy to duplicate the rib. It also makes crack repair unnecessary as most cracks will stop at the spar’s edge. But it also makes for a big covering patch. This can be especially difficult if a color matching covering is not available (more on this later).

My suggestion is to remove only as much sheeting as is absolutely necessary. The sheeting in photo 7 is just too badly damaged to survive. It is dented, crushed rearward and the cracks have separated the sheeting into individual pieces. Use a metal straight edge and a new, sharp No. 11 hobby knife blade to remove the sheeting as shown in photo 8. Do this on both sides of the wing.