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| Control Horns: Shown in the left photo is a control horn made from square PVC downspout pipe. This is an inexpensive method of making control horns but the strength they give to the structure is the most important thing. With normal Dubro type aileron horns the "footprint" of the horn and backing is small. When the horn is located near the root of the aileron it can twist and bend leading to less precise control. The wider foot print (1") of the PVC control horn adds strength to the aileron and provide positive control. Preparing the Fence Post: The fence post has one side with corrugations on it. You may leave this corrugation in place making it the bottom of the fuselage or you may cut them off. I used a bandsaw to remove the corrugations and then sand it smooth with 60 grit paper on a sanding block. Cut the fuselage to 22”. This length was derived by trial and error. It is the minimum fuselage length that allows you to fit battery and throttle servo in front of the wing and the elevator servo behind and get the plane to balance at 2.75" back from the LE at the root. Drill holes for a tight fit of two ¼ “ wing hold down dowels. The holes should be approximately 4 1/2" and 14-3/8" back from the front edge of the fuselage. The exact placement of the wing is determined by your flying style. The following is from Don Pruitt regarding CG adn trim: "As you move the CG more to the rear, the plane will get more sensitive in the pitch attitude. I adjust mine so that on 100% throw on high rates it will just snap out on a full control high speed loop. I then reduce that to 70% on low rates and fly it there. I may switch the rates back and forth during a heat depending on how excited I am or whether I am towing a streamer or not. A full streamer attached to the back edge of the fuselage will reduce the pitch sensitivity. I like to have mine set up where it will almost cut my own streamer in a tight loop. When you are doing your initial trim flights you can drill more dowel mounting holes to shift the wing and CG to suit you." Motor Mount: The drawing above is the motor mounting plate used on the Georgia Gorilla. You may use the pattern to make your own from Plastic Cutting Board Material (High Density Cutting Board Plastic), or you may purchase a finished mount for $3 plus shipping from AeroWright as noted in the materials list.The shaded areas are the engine mounting holes and the holes for cable tying the needle valve in place. The 5/8” width of the engine mounting rails was determined through experience. There is enough strength there so that the mount would not break easily but would break just before splitting out the opening in the fuselage. Don't ask how many dirt naps it took before selecting 5/8”. Make a couple of 2” by 1 ¼ ” spacers to fit above and below the engine mount, inside the fuselage. One shoudl be 1/8" thick, the other 3/16" if you are using the AeroWright manufactured motor mount. These spacers allow the whole fuselage to help support the engine mount instead of just the screws. San them to a snug fit if neccessary and coat the surface that will contact the motor mount and fence post with GOOP. Secure the engine mount with two #6 X 1/2" pan head sheet metal screws on each side. Also shown above is one method of installing the components in the front of the fuselage. This is the most common method. I vary slightly by mounting my servos inside the fuselage and moving the battery as far forward as possible as show in the photographs at left. I mount an HS-81 throttle servo in a cut out in the side of the fuselage. The cutout is made with a dremel cutting disc. Make certain that there are no "sharp" corners. Drill each corner with a 1/8" bit before cutting. Orient the cable tie front to rear and leave the connection lock on the top so that it will not get damaged during landings. Secure the battery with Velcro and a cable tie also oriented front to rear. If you orient the cable tie across the battery and servo they may slip out from under the tie during a dirt nap. Make up a throttle pushrod by using two pieces of small gauge piano wire with a Z bend in one end and 1” of ½A size fuel tubing. I don’t remember the exact diameter of the piano wire but it is the same diameter as the standard hole in a control horn or servo arm. This is probably pretty common usage and allows a good enough connection to operate the throttle barrel but will come apart during a crash before you can break a servo arm or strip out the servo gears. Horziontal Stab The horziontal stab is 4 mil Coroplast and should be approximately 20% of the area of the wing. The standard Gorilla stab has a 16” span, a 5” tip and 6 ¼ “ root. The elevator measures 1 ¾ “ (8 flutes). Cut away all of the hinge every other inch in order to reduce hinge friction and the subsequent load on the elevator servo. Mount the stab centered with the elevator hinge line just aft of the trailing edge of fuselage. Secure with 4 #6 X ¾ “ sheet metal screws. Run a shis-ka-bob skewer through the flute just in front of the elevator hinge to improve stiffness. Use a Hitec HS-81MG servo and mount the elevator servo on either the top of the fuselage just in front of the stab using Goop and cable ties, or in a cutout on the side of the fuselage. DO NOT USE A FULL SIZE SERVO FOR THE ELEVATOR - IT IS TOO HEAVY!!!. Vertical Fin Fin is also 4 mil Coroplast and the area should be approximately half the area of the horziontal stab. It can be more but not any less. The fin has the flues running vertically. A tall fin is handy for catching streamers but tends to want to flutter and move around at speed. Short coupled planes tend to want to swim through the air like a fish if they don’t have sufficient fin area. I prefer to have my fin tall enough to catch a streamer or two and I increase the depth so that it extends about 4” past the end of the elevator. This gives adequate stability on the yaw axis. Some combat designs have the fin extending below the stab as well as above it. This helps the stability but I just hate to land on the fin or have to be careful of bending it during storage. Again I run a skewer through the center from front to back to give it some stiffness. Mount the fin using three plastic dry wall anchors and #8 X ¾ sheet metal screws. Glue the anchors into the flutes at the bottom of the fin with CA. Space them about an inch apart starting at the leading edge. Screw them in from the bottom side of the fuselage. |
Georgia Gorilla Fuselage Construction
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