1/2a Control Line Trainer Engine: Cox Black Window.049

Transcription

1 Designed by Bill Osborne & Peter Justin Drawn by Heman Lee 1/2a Control Line Trainer Engine: Cox Black Window.049 This model airplane is made from foam-board that can be purchased at any art-supply store or Target for less than $3 a sheet. For today's youths, it is very rewarding to be able to build their own model and make their first solo flight. Bill makes all of the components for our class from surplus materials. Engines mounts, bell-cranks, control horn are all made from scratch in his home shop. Not only does he supplies these airplanes to our class, he has built hundreds of these for the kids in his own community for free. This model is a great trainer because it is almost indestructible when crashing on grass and easy to build. With minor modifications it can even do basic aerobatics, such as loops. 1

2 Parts List 1 Foam-Board 3/16" 1 Lead-out Guide 1 Plywood 1/16 X 1 1/4 X 12 or Paint Stick 8 Washers for 2-56 screws 1 Plywood 1/16 X 1 1/4 X 9 or Paint Stick 7 Screws 2-56 x 3/4 1 Balsa 1/8 X 5 1/16 X 3 9 Nuts T-Angle Motor Mount 1 Control Horn 1 Lead Weight 1/4 oz 1 Bell-crank & Spacer X 9" Pushrod Wire 1 Cox Black Widow.049 engine with Cox 6 X 3 propeller. Tools Needed Titebond or Elmer Yellow Wood Glue Model airplane dope (clear and color) Xacto Knife No. 1 or Hobby Knife Sand Paper or fine Ruler and Triangle Pliers with wire cutter C-Clamps and some heavy weights (Brick or frying pan) Electric or Cordless Drill 2

3 Building Instructions Step 1 - Outline the Platter. 1. Make a 12" diameter circle on the foam-board. To do this, tack a string to the middel of the circle and tie a felt pen 6" from the center. This will allow you to draw a perfect 12" diameter circle. 2. Measure a distance between 1 to 1-1/2" for the engine mount. (1/2" for Norvel or Stunt version). If you are using the Norvel BigMig Startup with the integrated tank, you can just make it perfectly round. 3. Draw a horizontal line about 1-1/4" for the width of the engine. 4. Make a straight line from the left edge of the engine mount to the left tangent of the circle. 5. Do the same for the right side. 6. Now you have the basic outline of the Platter. Cut the foam according to the outline you just made.. The platter is an 12" diameter plate with an 1-1/2" nose. You can vary this distance down to 1/2" if you want to make it do stunts. The one shown, is a trainer. Mark the center of the Platter using a ruler. Draw and straight line down the center. Mark the center of both top and bottom plywood doublers. Step 2 - Doubler. Glue the plywood longer doublers to the top and the shorter piece on the bottom. Make sure the doublers are exactly in the center on both side. Use a clamp or heavy object to clamp down the doublers and let it dry over night. Apply glue to both doublers and sandwich it to the foamboad. Rub it back and forth a few time. Pull off and apply more glue. Let it tack on for 5 minutes before putting it back on and clamping it down. Alternative: 3/32" softply or go to you local hardware or paint store and ask for 2 paint mixing stick. You can use these as doubler. Just cut one down to 11" or small depending on which version you decide toe build, and the other bottom doubler to 9". 3

4 Step 3 - Fill Edges Use the flat edge of a scissors to crimp the edge of the foam to create a slight taper airfoil. (Optional) Fill all of the exposed foam edge with Titebond or Elmers glue because most paints will actack the foam. Sealing the foam will prevent this. Step 4 - The Elevator (Update) The elevator controls the model up and down movement. Use Scotch's Crystal Clear or packing tape as a hinge, to join the elevator to the main body. Angle the elevator about 30 degree down while applying the tape. Repeat the same step on the other side. Alternative: Use tradition cloth hinges for even dental floss. For better control, balsa wood can be use to make the elevator. (Update - A Better Way To Hinge) This is a better way to apply the hinge. Fist, bevel the elevator with a 45 degree cut. If you are using foam board, apply glue to the exposed foam area the seal it. Place the elevator next to the Platter, but try to leave a small gap (1/32"). Put the first strip of tape on top. Turn the Platter over and using a butter knife to insert the tape into the gap so that is touch the other tape. Carefully work out the tape from the gap. Step 5 - The Rudder. The rudder can be made from any shape you desire. You can use the same foam board material or 3/32" to 1/8" balsa wood. If you decide to make the rudder from balsa, sand the rudder smooth starting with 220 to round and taper all of the edges and finish with 400 grit sand paper. Glue the rudder to the top double of the platter. Set the back of the rudder with an offset about 3/8" to1/2" from 4

5 the center line. Step 6 - Painting Because this is a gas powered model, it must be painted a fuel proof paint. You can use almost any type of paint, although model airplane dope is the best. If you cannot get dope, Rustoleum brand paint will give you enough fuel proofing. Epoxy or Urethane type paints are very fuel proof but don't apply too heavy a coat. You should not use more that 2 coats on this model. One good coat should do it. If you want a smoother job on the rudder section, apply a few coat of clear dope and sand it smooth before applying the final color coat. Also, make sure that all exposed foam edges are sealed completely with glue. Step 7 - Control Horn and Pushrod. Install the control horn first. Use a 2-56 X ½" bolt and nut to hold it in place. Bolt on control horn with 1 washer on the bottom. Blind nut may be substituted for bolt and washer combination. Blind Nut Make the Pushrod from 1/16" X 8-1/2" piece of steel music wire. Make a Z or J-bend and one end. Install the Control Horn and attach the pushrod to it. Make a bend 90 degree up at about 1/4" and position the bellcrank in a neutral position. This will determine the hole for the bellcrank so that the elevator in the neutral position. Custom made control horn can be cut from an aluminum sheet. 5

6 Step 8 - Bellcrank. Drill the hole for the bell-crank and install it according to the instructions diagram. Install lead-out assembly. Make lead-out wires from scrap.015 or.018 cable or music wire. Option: You can purchase 1/2A Nylon Bellcrank and Horn set from Brodak or Carl Goldberg. They usually come with wood screws for mounting the bellcrank and horn. For the bellcrank, throw them out and mount using 2-56 X 3/4" machine screw. Use 1 blind nut on the bottom if you screw if from the top. Bill's scratch built bellcrank 6

7 Step 9 - Leadout Guide. Mount the center of the Lead-out Guide 8" from the back end of the Platter. The Lead-out guide is made from soldering 2 short pieces of brass tubing to a strip of galvanize steel. This make a very strong Lead-out Guide. Bill's bullet-proof leadouts You can use a strip of scrap plastic or 1/16" plywood for the guides. Make a slot into the foam-board and glue it into the slot. Step 10- Leadout Wire. Leadouts can be made from stranded steel cable. Use copper or aluminum tubing for the crimps. Another method is to wrap the end with copper wire. Here is an alternate method of making the leadouts from a solid steel wire rather than using the crimp and sleeve method for stranded steel cable. You can make a leadout wire from.025 music wire. Do the same on the bellcrank end and connector end. 7

8 Step 11 - Engine Mount. Install engine mount made from one aluminum T-bar or 2 L-bar using 2 or 3 screws and blind nut, or use Alternate Built-up Motor Mount Offset Weight Mount engine and check the CG (Center of Gravity). Install the weight offset on the outboard wing at the C.G. (Center of Gravity) point. Approximately 1/4 oz. should do it or just glue 2 pennies to the bottom of the outboard wing. If you look at the bottom of the Platter with the engine at 12:00, the pennies whould be at about 10:00 11:00. Important: The Platter will fly more stable if you add a little positive incidence which is the relationship of the engine thrust line to the wing. To do this, simply angle motor mount 2-3 degress down by adding a washer to each of the top two bolts. Also, DO NOT over tighten the screws to the foamboard sandwich. Over compressing the foamboard will weaken the doublers. Step 12 - Flying. First time flyers should fly the Platter on 25' to 30' lines. Once you have mastered it, you can lengthen it to 30' or 35'. I recommend a Cox 6 X 3 propeller. Use a Sig or Cox 1/2A Control Handle. Connect the "UP Elevator" line to the top of the handle, and the "DOWN Elevator" line to the bottom. The Platter must be hand launched gently. Don't fling it like a freezbie. Use about a 20 degree loft, pointed outward and release. Have fun flying! 8

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