Hobby Shack's AirMaster40T

	The kit and engine in their original boxes. The anticipation for building and flying this R/C airplane are at an all time high. Hobby Shack has put a lot of colorful imagery on the box and an attractive price to match. Looks easy to build and fly. The Fuji 40 engine was purchased for $40.00 and quite a bargain for that price.
	We're building this kit on a solid core door in the basement. The glues and box of clamps didn't come with the kit. First we open the box and find the instructions. Reading through these and identifying all of the parts is a good first step for all kits. The examination of this kit detected missing horizontal and vertical stabilizers, commonly referred to as the "tail feathers". A call was placed to Hobby Shack to get the missing components. They were very courteous on the phone are sent replacements.
	The next step is to find the three dihedral braces and glue them together for the main wing. It is important to check the fit of these parts in the wing. Several ARF kits built by this author were not the correct size and had to be shortened by as much as 1/4-inch. The correct length will allow both main wing halves to be butted against each other with NO gap between the wing halves. These parts fit perfectly. Shown here is a plywood doubler which will be laminated (at the same time) with the servo tray. This allows for a more solid servo installation. The wood is thicker, giving the servo mounting screws more of a bite.
	A thin film of 30-minute epoxy is spread on all the wood surfaces. The temperature is about 60 Degrees, so the epoxy will take hours to harden. We will clamp and weigh the pieces down to prevent warping and movement while the epoxy cures.
	Two of the three clamps used on the main dihedral brace (dihedral joiner) are shown here. Also, the doubled servo tray has been laminated. Alcohol is used for cleanup and waxed paper was put down on the "table" to prevent gluing the parts to the table. All excess epoxy is wiped off the parts, once the clamps have been tightened. Check that the parts are lined up one last time. Don't move them for at least an hour!
	While mixing the epoxy enough was mixed so that the excess could be used for fuel proofing the interior of the fuselage. If the fuel tank were to leak, or a fuel line come loose, alcohol and nitromethane will go all over the place. The AirMaster fuselage is really easy to work on because the top of the fuselage comes off! We reglued any suspected weak wood joints and fuel proofed the interior of the fuselage. Extra epoxy was added around the landing gear blocks. Care was taken not to get the epoxy in the landing gear holes!
	An acid brush and heat gun (used a little heat, don't overheat the epoxy until it smokes!) was used to spread a thin coat of epoxy. The heat will make the epoxy thin to a water like consistency, which makes it easy to apply. The epoxy will set (cure) much faster when it is heated. Don't use a lot of epoxy, since it is heavy and cures, not dries, meaning it will weigh as much "dry" as it did when you put it on! Other stuff you can use for fuel proofing include Balsarite from Coverite, Sanding sealer, Urethane paint, and of course epoxy. Some modelers don't use any fuel proofing to keep the weight down or to save time. Epoxy was sparingly used on this model and all exposed wood on the front of the firewall was thinly coated as well.
	When the laminated servo tray was cured, the servo openings were cut to the size of the servos. We will be using some HITEC RS425 standard servos. The openings needed to be slightly enlarged. Next the servo tray was epoxied into the fuselage and held in place by clamps until the epoxy cured. It is a good idea to put scrap wood between the model and the clamp jaws to prevent leaving marks on the model.
	A test fit of the Fuji 40 two stroke engine was done early on to see how the components and controls would need to be routed (done much later). At this early stage it has been decided to fully enclose the engine in the cowl and provide cooling through the cowling. This meant the engine will be mounted inverted. This is not a good practice for a first time modeler. The engine can be troublesome because accessing the glow plug for starting is trickier and the glow plug can be flooded with fuel when it is located at the bottom of the model. However, on this model, the inverted engine allows the carburetor fuel inlet to be approximately centered with respect to the center of the fuel tank. (More about this later).
	When the epoxy has set on the servo tray, we started on the main landing gear. A razor knife was used to cut away the covering. After this, the wire gear was pressed into the holes. We actually had to wiggle the gear while we hammer lightly to get the gear in. The landing gear straps will be added next. Small pilot holes are drilled into the fuselage and then the screws are tightened. We are going to use 3-inch Sullivan Skylite wheels, not the kit wheels. The larger diameter wheels make taking off and landing from our grass fields easier.
	We are now installing the laminated main wing spar into the wing. Vaseline was put into the holes at the back of the wing where the aileron torque rods and bearings are. As shown in the photo, a toothpick was used to insert the Vaseline. This will prevent epoxy from entering these holes and gluing the control linkages to the rest of the wing. A golf tee was cut off and pressed into this hole to help align the two wing halves when they are joined together. A generous film of 30 minute epoxy is spread into the spar sockets and the mating surfaces on both wings. The wing spar joiner is coated as well, and then pressed into the sockets. As before, alcohol was used to wipe the excess off the wing. Use the alcohol sparingly because it may remove some of the color from the covering.
	Most ARF kit instructions show the spar joiner glued into one wing and allowed to cure, then gluing that assembly to the other wing half. I like to glue both wing halves at once. This technique requires that you test the fit before applying the glue and the wing must be supported while the epoxy cures. 30-minute (or longer) should be used. This is a high stress area of the model! The wing was taped and held in place while the epoxy cured, so that the two wing halves stayed together and aligned at the center. Recheck the alignment several times, but try not to move the wing halves unless there is a need to fix the alignment. A small misalignment is not a major cause for concern. Some ARFs built previously had two different widths for the wing halves. The differences should be centered. As shown here, the wing parts in this kit fit perfectly! .
	A dremel was used to grind a flat spot on the landing gear where the wheels area mounted. This gives a better surface for the locking screws to bite into. The wire was also measured and cut off even with the outside wheel collar. The kit wheel collars were replaced with an allen setscrew type. These work better than the slotted screw type, since the screw can scrape on the wheel. The wheels are Sullivan SkyLite 3-inch (as mentioned before). Each of the wheel collar setscrews was given a drop of CA to prevent it from coming loose due to vibration..
	Although not in the included instructions, I like to use fiberglass reinforcement on the main wing. Six ounce per square yard fiberglass and epoxy is used. First, the covering is removed form the center of the wing. Care must be taken not to cut through the wing balsa wood. This will weaken the wing, not strengthen it. The covering is carefully removed about three inches wide. Notice the extra wood at the back of the wing to prevent the rubber bands from crushing the wood. This model is well built from the factory.
	Vaseline was put into the slots for the aileron controls rods to prevent the epoxy from gluing them to the wing. Epoxy was then mixed and spread onto the wing. The fiberglass was laid onto the wet epoxy. A head gun and new acid brush was used to spread the epoxy. The excess epoxy was scraped off with an (expired) credit card . Next, toilet paper was used to blot still more of the excess epoxy from the wing. Finally, the wing was cleaned up using alcohol and a paper towel. The epoxy was allowed to cure overnight.
	The fiberglass and epoxy should look like this as it is curing. Note that the weave of the fiberglass is still visible and the epoxy has a dull sheen. All large air bubbles have been carefully removed by brushing the air out from the center to the edges of the fiberglass.
	As we wait for the epoxy to cure, a look at the completed landing gear installation.

Last Updated 10/15/00

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