NMPRA

The next series of photos and text represent the process for sheeting a set of foam wings for an EF-1 racer. In this example I use Gorilla Glue. However, if you wish to use epoxy it is exactly the same process.

To start I assemble the end of the joiner tube supports. Each panel receives a 3/16" balsa component capped with a 1/16" balsa sheet.

The cores are marked where to cut the foam to receive the balsa assembly. I use a X-Acto blade to cut through the foam.

Install the end block assy and paper joiner guide tube as shown below. Repeat for the second panel.

Sheeting a foam wing cont:

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Sheeting a foam wing cont:

The next series of photos will show how I prepare sheeting and sheet the wing.

You will need 8 pcs of 1/16" X 4" x 36" balsa to sheet a full wing. Yes you will have some scrap. I use a full width sheet along the LE, a second sheet along the TE trimmed to mate with the LE and then a wedge shape in the middle. The key to having good sheeting is making the mating surfaces square and flat. There are several ways to accomplish this. I use a sanding block and the edge of my bench. The end of my bench keeps the block square and the sheet is sanded relative to my bench. Thankfully, my bench is pretty square. I use the top of one panel to create my sheeting as this is the longest side due to the airfoil shape. It is critical that the finished wing matches the final dimensions on the plans to meet the min wing area rules. You should be shooting for 10.75" at the root and 7" at the tip. This is from the front of the foam core (NOT including the 3/16" LE to the end of the sheeting. NOTE: the foam core is smaller than these dimensions due to the taper of the airfoil.

Assemble the sheeting as shown using Duco cement, (my replacement for Sigment). I tape the sheeting together to dry.

Sand the sheeting and mark the inside to be glued. I also weigh the sheeting. For this wing the top skin was 19g and the bottom was 18g. My buddy Jim DeYoung always uses the following rule when sheeting: .025g of epoxy per square inch of balsa. I am using Gorilla glue but figured I would try to use the same format. In this case we have roughly 168 square inches of balsa and we should only add about 4.2 g of glue per wood surface. Therefore, my glued panels before placing the foam inside should add up to approximately 45.4g with glue. It turned out that they weighed 49 g. Based on how the panels looked for wettness of glue. Which isn't too bad and very close to what it would be had I used Epoxy.

I lightly sand the cores with 220 to remove all the fuzz. And vacuum clean, the same is done with the sheeting prior to adding glue. I keep a tack rag handy to wipe everything down before starting. I mark the top skin for preparation of glass for the aileron servo. The center of this is approximately 7" from the root and 3" from the LE. I use a single layer of 3oz cloth on the top skin as shown. This provides some support for the aileron servo as I glue it to the top skin later on.

In my case I tape the TE to form a hinge at the TE. When opened the gap between the top and bottom sheeting is approximately 1/8". I add tape to the bottom skin full length of the TE and then flip it over on my flat bench. Then add the top sheeting aligning the TE for the entire length. All the while folding the tape onto the top skin to form the hinge.

Add Gorilla glue to the inside of the skins as shown using a credit card or plastic scraper. A majority of glue is removed. The entire balsa sheeting should have glue and no dry patches. Use the above formula to figure out it if you are in the ball park. As well as the pictures below for wettness.

When sheeted the balsa sheeting with stick out past the rear side of the foam schucks (The upper and lower portions of the foam blanks). Due to the airfoil shape, I sand a taper into the last 3/8" of the bottom balsa sheeting. Basically, the TE of the bottom sheeting has zero thickness and is tapered from this zero thickness to a full 1/16" thickness 3/8" in. This allows for the top sheeting to remain a full 1/16" thick along the entire length of the TE of the finished wing. Providing the proper airfoil shape and meeting the 1/16" thick TE requirement per the rules.

Wing cont:

Someone had asked to clarify the taper I add to the bottom sheeting at the TE. I have included pictures of the actual part as well as a small detail from the plans. Hope this helps.

Wing cont:

After the wing sheeting has dried, I trim and sand the wing in preparation of the LE, tips and Aileron hinge line.

First assemble the tips. I use 3 pcs of 3/16" balsa sandwiched with a layer of 1/16" balsa. The order is one pc of 3/16" then 1/16" and finally two layers on top. When assembling be sure to make a left and right assembly. Two layers on top due to the airfoil shape. I use the 1/16" in the center to align the block and keep everything straight.

I use Duco cement to create the tip assemblies. I use Titebond to glue the balsa parts to the foam wing blank.

My trimmed panel prior to adding any additional balsa weighed 68g.