In Part I of this article series, we covered the best ways to build an ARF wing. “How to Build an ARF Trainer Part I” detailed how to build the very best wing possible. In truth, most ARF trainers would fly well if a few steps were left out, as long as the wing halves were correctly aligned. However, if all the steps were followed, your ARF Trainer would be better than 99% of “First Timer” airplanes brought to the flying field.

This article, “Part II – The Fuselage Airframe” will follow the same pattern. When building the fuselage, you will not need to perform every step detailed here for your airplane to fly OK. But if you want the best flying trainer at the field and one that will be problem free and extremely durable, try to follow these instructions as much as possible.

How much you are willing to do so will determine how well your trainer will perform, how easily and quickly you will learn to fly and how long your airplane will last. Remember that all Sport Aviator photos can be enlarged just by clicking on them,

Stabilizer Installation

Photo 1         Photo 2

It is usually best to install the tail feathers first. It is easiest to install the horizontal stabilizer and vertical fin without the landing gear and engine in place. If the engine is installed, the airplane always wants to “nosedive” off the building stand with the slightest nose-forward positioning. Having the landing gear installed makes it difficult to rotate and position the fuselage on the stand while installing the rear surfaces.

The horizontal stabilizer, the funny little wing in the back, is installed first since the vertical fin aligns from it. It is easiest to make all the alignments and measurements if the elevator is not installed during installation. The first strep is to find the exact midpoint on the stabilizer’s trailing edge (photo 1). Once that is located, then draw a straight line from the trailing edge to the front as shown in photo 2. Mark the midpoint of the leading edge as well.

Photo 3         Photo 4

After finding the center on the stabilizer, locate and mark with a strong pin the fuselage center point just forward of the wing saddle (photo 3). Even better, if you have the work space, locate the center of the firewall instead of the front wing saddle. The longer the distance from the pin to the stabilizer tips, the more accurate will be the alignment.

Do not use the outside fuselage edges as they might not always be equal. The idea is to use this measurement to align the elevator so that it is perpendicular to the main wing and the fuselage. Some leeway is allowed here. The elevator leading edge can be as much as 3/64 in. off and the airplane will still fly straight when elevator input is applied. If it is off by more than that, the airplane may skid slightly in a sharp turn. This is still acceptable but can show itself when flying landing approaches.

However, before you can use this measurement to align the stabilizer with the fuselage and wing, you must first center the stabilizer inside the fuselage. Use the two center marks and line you have already marked. Center the trailing edge mark in the middle of the rear fuselage and the front mark in the center of the last fuselage former (the vertical wall at the front of stabilizer slot). As a final check that the stabilizer is centered, measure from the outside rear of the fuselage to the stabilizer tip. Both measurements should be identical. Try not to be off by more than 1/32 in. as roll trim problems can result if you are.

Photo 5

Do not apply any adhesive at this point. It probably would not stick well anyway. The tail surfaces are epoxied in place using 12-minute epoxy for the stabilizer and 5-minute epoxy for the vertical fin. However, epoxy does not stick at all well to the plastic covering. It must be removed before the final installation.

Once the stabilizer is properly aligned with the fuselage and wing saddle, mark both the top and bottom of the stabilizer as shown in photo 5. Use a fine point, felt tip pen for this. The ink can be removed later using denatured alcohol.

Photo 6         Photo 7

It is not easy to remove a stabilizer that you have worked so hard to align. Doing so might even cause psychological damage! But your airplane will appreciate it as will you when the stabilizer remains perfectly aligned 500 flights from now. The stabilizer top should look like photo 6 and the bottom, (you did DO the bottom right?) should resemble photo 7.

Photo 6 shows a slightly “bent” outlined on the rear, left side of the stabilizer top. That was caused by the fuselage’s having been damaged in shipment. We managed to get this ARF very cheaply because of this damage. I elected to make the repair during the installation to insure that the stabilizer would not be “tilted” vs. the wing (extremely important). Before cutting the covering, I just extended the line using a straight edge.

Photo 8         Photo 9

This is an important step. Do the bottom first in case you remove too much covering. Use a Hobbico® Hot Knife™ to cut 1/32 in. inside the lines you made. Leave the outside 1/32 in place to seal the stabilizer/fuselage joint so that the stabilizer covering always remains firmly fixed. Use a “dull” blade in the Hot Knife. Let the heat do the work. Do not cut into the wood as that will weaken it.

Then, carefully remove the covering by pealing it back on itself as in photo 9.

Photo 10

Some ARF models are covered with a commercial brand of heat shrink model covering. If yours is, it will probably peel back without leaving any adhesive residue. But many trainers are covered with something else and these coverings almost always leave some adhesive and color behind (photo 10). This must be removed or it will weaken the final bond.

Photo 11         Photo 12

Alcohol does not remove this covering adhesive very well. In Part I, we learned about the amazing properties in that little blue Coverite® can of Ironex™. Pour a little onto a paper towel and remove any remaining adhesive. TIP: Ironex is extremely volatile and evaporates very quickly. It will slowly evaporate even when the can is tightly closed if you remove the insert that says “cut this out”. To prevent this, just punch a small hole in the insert (photo 12). The Ironex will stay in the can where it belongs.

Photo 13        Photo 14

Ironex will not damage or warp the wood since it flashes off so quickly. BTW – It is a good idea to wear some breathing protection like a paint mask during this process. When cleaned, your stabilizer should look like photo 13. Ironex will also remove the felt pen ink. Do this now except for very short sections at the leading and trailing edges. These “dots” will be used to align the stabilizer when you re-install it. Make sure to remove the covering from the front of the stabilizer, well inside the fuselage so the epoxy will hold it in place against the former.

Photo 15         Photo 16

The final preparation step is to use a modeling covering iron to seal all the covering edges in place. Then use a small torpedo level located at the rear of the wing saddle to level the fuselage. Most any position will work well with flat-bottom trainer wings as long as the level is exactly 90 degrees to the fuselage. Using the rear of the wing saddle insures the 90-degree location and is also the best location to place the level if the wing is not flat bottomed. So get used to it now. If your work stand allows, rubber band the fuselage in place to keep it level during installation. But keep checking it all the time anyway.

Photo 17         Photo 18

Use an “epoxy” brush, available at all hobby shops for about 20 cents, to apply the epoxy to the top and bottom of the fuselage stabilizer slots. Note in photo 17 that there is an interior mounting “plate”. Almost every ARF trainer has such a plate for extra strength. Make sure to cover it with adhesive as well as the spot where the fuselage former meets the stabilizer leading edge.