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SIG Piper J3 Cub Building And Flying Instructions Download Page 28

. 

b. Round the two outside corners of the fittings with a file or grinder.

c.

 
Lay the Fuselage Strut Fitting back over the plan pattern and mark the bend line exactly where shown. Clamp the part in a 
vise right at the line, and gently bend it to the angle shown.

 
119.

 
Hold the Fuselage Strut Fittings in place on the bottom of the fuselage and mark the location of the two mounting holes. Drill 
the holes with a 1/8" dia. bit. Mount the Fuselage Strut Fittings to the fuselage with two 2-56 x 3/8" Bolts and 2-56 Blind 
Nuts. Glue the Blind Nuts on the inside of the fuselage.

 
120.

 
Inside the fuselage, add a 1/2" balsa triangle to the front edge of the rear landing gear block, between the blind nuts.
 

 

 

121a.

 
Locate four .060"x3/8"x2-1/4" pieces of aluminum for the Upper Strut Fittings. Lay 
them on the Upper Strut Fittings drawing (plan sheet 3) and mark the locations for 
the 1/8" and 3/32" dia. holes. Clamp the part in a vise and drill the holes.

 

 

b.

 
Round the two outside corners of the fittings with a file or grinder.

c.

 
Bend the Upper Strut Fittings as shown on the plan, making two #1 and two #2 
fittings. The difference between the #1 and #2 Upper Strut Fittings is only in the 
slant of their bend lines. Make sure you produce two of each type. Mark the bend 
line exactly where shown, then clamp the part in a vise right at the line and gently 
bend it to about a 20 degree angle.

122a.

 
Locate two .060"x15/16" (tapered) x2-3/16" aluminum Lower Strut Fittings. Lay 
them on the Lower Strut Fittings drawing (plan sht.3) and mark the locations for 
the 1/8" and 3/32" dia. holes. Clamp the part in a vise and drill the holes.

b.

 
Round the two outside corners of the fittings with a file or grinder.

 
123.

 
Epoxy the spruce Front and Rear Wing Struts onto the aluminum Lower Strut 
Fittings. Double check them against the plan to make sure the "V" angle is correct. 
Let dry.

 
124.

 
Next, we need to trial fit the wing strut assemblies on the airplane, in preparation 
for gluing the Upper Strut Fittings into the struts.

RIGHT WING

 

Use a #1 Upper Strut Fitting for the 
Front Strut 
Use a #2 Upper Strut Fitting for the 
Rear Strut

LEFT WING

 

Use a #2 Upper Strut Fitting for the 
Front Strut 
Use a #1 Upper Strut Fitting for the 
Rear Strut

a.

 
Bolt the wing panels in place on the fuselage.

b.

 
Fasten the wing strut assemblies in position, one on each side of the fuselage, 
bolting the Lower Strut Fittings to the Fuse Strut Fittings with 4-40 x3/8" Socket-
Head Bolts and Hex Nuts.

c.

 
Bolt the Upper Strut Fittings to the plywood strut mounts built into the wing with 4-
40 x3/8" Rd.Hd. Bolts.

d.

 
Check the fit of the Upper Strut Fittings into the slots in the top ends of the wing struts. If they don’t line up properly, double 
check to see that you’ve got the correct upper fitting in the correct strut. If it’s not that, you may have to adjust the bend 
angles of the upper strut fittings and/or the fuselage fitting slightly to get a good fit.

Summary of Contents for Piper J3 Cub

Page 1: ... CUB kit This is a computer engineered laser cut kit of America s favorite lightplane Laser cutting is more expensive than the older methods of kit production but it provides incredible accuracy and perfect parts fit We believe that you will enjoy putting this kit together just as much as you ll enjoy its legendary flying characteristics ...

Page 2: ...lying The J 3 Cub was equally at home on wheels floats or skis and it could be flown in and out of places the larger civilian airplanes couldn t get close to Cubs also found work towing gliders and banners doing small field crop dusting and even in air shows Crazy drunken Cub acts landing on moving automobiles and aerobatics in Clipped Wing Cubs are just a few of the things the J 3 could do to ent...

Page 3: ...d it to be red and white Maxey like blue and white and I thought yellow and white would look best As you can see Maxey is the one who actually loaded the spray gun The Cub s Continental A65 8F engine was given a complete overhaul and modified to produce 75 h p instead of its normal 65 New cowlings windshield side windows tailwheel and metal prop were installed Added extras like chromed cylinder he...

Page 4: ... shows the installation of an Airtronics radio system with standard servos In addition you will need two aileron 24 servo lead extensions and an aileron servo Y harness for connection to the receiver Required Tools For proper assembly we suggest you have the following tools and materials available Razor Saw Hobby Knife with sharp 11 Blades Scissors Diagonal Wire Cutters Masking Tape Sandpaper and ...

Page 5: ...enter Section Web F 7 Main Gear Doublers Servo Tray Servo Tray Doublers Wing Tip 1 1 16 Birch Ply Sheet 7 Servo Hatch and Cabin Hatch Hard Points 1 3 32 Birch Ply Sheet 15 CR 1A Strut Mounts W 1A 1 1 4 Birch Ply Sheet 22 F 1 Balsa Wood Sticks 13 3 32 x1 4 x36 Cap Strips Fuselage Side Stringers 5 1 4 x1 4 x36 Main Spars Fuselage 5 3 16 x3 16 x36 Rear Spars Fuselage 5 1 8 x1 4 x36 Wing Spars 3 1 8 x...

Page 6: ...s Elevator Pusrod Throttle Pushrod 1 190 od x36 Nylon Tube Elevator Pushrod Sleeve 1 1 16 od x24 Steel Cable Throttle Pushrod 1 Aluminum Fueler Mount 2 060 thick Aluminum Lower Strut Fittings 6 060 thick Aluminum Upper Strut Fittings Fuselage Strut Fittings 1 7 8 od x17 1 2 Aluminum Wing Joiner Tube 1 880 id x17 1 2 Phenolic Wing Joiner Tube 3 5 32 od x12 Brass Tube for Jury Struts 1 2 x20 Glass C...

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Page 11: ...ont of the cowl by 1 8 Carefully mark the location of the engine mounting holes onto the mounts b Remove the engine mounts from the firewall for drilling of the clearance holes for your engine mounting bolts It s best to lock the mount in a vise and drill the holes with a drill press if you have access to one Note Because some 40 46 engines use 4 40 mounting bolts and some use 6 32 bolts we do not...

Page 12: ...e drill the mounting holes 8 Locate the three window braces sheet 2 Compare the length of the three braces two the same and one is different in length The longer one is glued in the front notch on the left fuselage side at the front notch and the shorter one is glued in the back notch The other short brace is glued in the rear notch of the right fuselage side Be sure to glue these braces to the IN...

Page 13: ...locks of scrap balsa or foam to block the tank in position Note If the recommended fuel tank is used Du Bro 12 oz you can do a trial installation now and then remove the tank for final installation after the airplane is covered b Remove the fuel tank and dry fit a 130 od nylon tube for the throttle pushrod through the hole in the firewall and back to the servo area Slide the fuel tank back in posi...

Page 14: ...e fuselage you need to sand flush any former tabs that may be sticking out beyond the fuselage sides c Now glue the Left and Right Fuselage Doublers in place on the fuselage 21a Carefully cut the Right Window Doubler Left Window Doubler and Door Window Doubler loose from laser cut balsa sheet 23 Handle these parts very carefully as they are easy to break at this point b Glue the Left and Right Win...

Page 15: ... in the hole in the front of the window frame leaving about 3 8 of dowel sticking out the front Now slide the 1 8 plywood Hatch Dowel Support sheet 26 over the dowel and up against the window frame then glue it in place Builder s Tip Use the 4 40 x3 8 socket head Nylon Bolts to keep the hardpoints lined up with the holes in the sheeting while you are gluing the hardpoints in place Don t get any gl...

Page 16: ...s for the rudder pull pull cables Use a heat gun to soften the tube enough to allow you to bend a slight radius in it as shown in the picture Hold until the tube cools b Slide the tubes in the slots of the Rudder Exit Guides and check the radius of the bend The bend is to allow the tubes to have a straight shot to the rudder servo area in the forward part of the fuselage If necessary re heat the t...

Page 17: ... hand held 220 grit paper 40 Two 1 8 od x 6 hardwood dowels are provided to simulate the diagonal cross braces that run from the corners of the instrument panel up to the center of the wing spar on a full scale Piper J 3 Cub Cut the dowels to length bevel the ends to fit and then glue them in place Refer to the front view plan Door And Window Latch 41a Locate the 130 od x28 nylon tube left over fr...

Page 18: ...ge locations Note that the hinge slots should be cut in the outer 3 32 balsa doublers don t try to cut them in the glue line You will also need to countersink the knuckle of the hinge into the bottom edge of the door so that you don t end up with a big hinge gap 49 DO NOT glue the hinges in the wood at this time wait until after covering Cut one 1 2 long piece and one 1 4 long piece of the 130 od ...

Page 19: ... guide sand the edges round 63a Locate parts E 1 E 3 E 4 E 5 E 6 sheet 13 and part E 2 sheet 14 Glue and pin these parts together over the plan b Cut to length and glue in the 5 16 sq balsa ribs for the two elevator halves 64a When the glue is dry remove the elevators from the board and re glue all the joints with Medium CA Use enough glue to completely fill the joints plus leave a small fillet of...

Page 20: ...ard Cover with wax paper or plastic wrap Locate parts FN 1 FN 3 FN 4 sheet 13 and parts FN 2 FN 5 sheet 14 Glue and pin these parts together over the plan b A hardpoint needs to be installed in the fin trailing edge FN 5 for the mounting of the tail brace wires later A 5 16 od dowel with a 5 64 id hole thru the center is provided for making the hardpoint Cut a 5 16 long piece off the dowel and glu...

Page 21: ... are building the Clipped Wing Cub the phenolic tubes should be cut 5 3 4 long 73a Locate the two plywood W 1A ribs sheet 15 Glue one W 1A to each of the W 1 ribs Be sure to make a left and a right rib assembly by gluing the W 1A ribs on opposite sides of the W 1 ribs Match up the cutouts in the ribs carefully when gluing them in place the photo shows the phenolic tube being used to help align the...

Page 22: ...tock provided Glue it in place on the ends of the W 1 W 2 W 3 and W 4 ribs Make sure the back edge of the T E Sheet is right on the line on the plan NOTE If you are building the Clipped Wing Cub cut the piece to 5 7 8 long and glue it to the W 1 W 2 and W 3 ribs there is no W 4 rib at this location 79 Cut a piece of 3 32 x3 4 x21 1 4 balsa from the 24 stock provided This is for sheeting the rear e...

Page 23: ...lace on the wing plan carefully centering the holes in the mounts with the blind nuts on the plan Now lay the wing panel back in place on the plan on top of the strut mounts Carefully line the wing up with the plan One at a time glue the strut mounts to the wing structure making certain you get them in the proper location b Locate the Strut Mount Doublers sheet 15 Determine which doubler fits behi...

Page 24: ...th the entire wing panel The goal is to only level out any mismatched areas not to do the final sanding Sand off any overhanging balsa sheeting or spars flush with the root rib and the tip rib Wing Tip 94 Locate parts TR 1 and TR 2 sheet 11 These are small subribs that go on the outside of the last W 4 rib at the tip end of the wing panel to help support the wing tip sheet Refer to crosssection W ...

Page 25: ... the 3 16 sq rear spar for the rear Hatch Rail Study the plan drawings carefully to understand the orientation of the Hatch Rails Note that the top edge of the Hatch Rail should be flush with the cap strips on the bottom of the wing b Lay the plywood Aileron Hatch sheet 7 in place on the lip of the rear Hatch Rail Now place the front Hatch Rail on the lip so you can determine the exact location fo...

Page 26: ...lon Control Horn to be slid in place alongside the plywood Aileron Horn Mount Before cutting study the wing plan and the cross section drawings to familiarize yourself with how the Nylon Control Horn should be installed in the aileron Notice that the horn should be installed on the outboard side of the plywood Aileron Horn Mount installed in step 205d Also determine how far into the aileron the ho...

Page 27: ...ng the protruding Rear Wing Dowel into the wing panel 116 Use an 8 32 x1 2 Socket Head Bolt along with a 8 Flat Metal Washer from the inside of the cabin to hold the wing panel up tight against the fuselage Remember 8 32 Blind Nuts were mounted inside the W 1 rib for this purpose way back at the beginning of the wing panel construction Wing Struts The Front Wing Struts for the Piper J 3 Cub are 1 ...

Page 28: ...out a 20 degree angle 122a Locate two 060 x15 16 tapered x2 3 16 aluminum Lower Strut Fittings Lay them on the Lower Strut Fittings drawing plan sht 3 and mark the locations for the 1 8 and 3 32 dia holes Clamp the part in a vise and drill the holes b Round the two outside corners of the fittings with a file or grinder 123 Epoxy the spruce Front and Rear Wing Struts onto the aluminum Lower Strut F...

Page 29: ...g the Clipped Wing Cub the Front Jury Struts should be 5 5 16 long b Flatten the ends of the Front Jury Struts and mark the location of the holes Drill the bottom hole with a 3 32 dia bit Drill the top hole with a 1 8 dia bit There are patterns on the plan to use as a guide for bending the Front Jury Struts to shape Be sure to make a right and a left 130a Cut two 4 7 8 long pieces of 5 32 od brass...

Page 30: ...the solder to flow smoothly Also use plenty of solder paste to help the solder flow completely around and thru the bindings Protect the fuselage during the soldering operation with a cloth so that dripping solder or paste will not fall on the wood After both axles are soldered and cooled off carefully remove the wires from the grooved blocks 135 After all the solder joints are cool file and sand t...

Page 31: ... slot in the stabilizer If the hinge is difficult to push in re insert the knife and move it back and forth in the slot a few more times DO NOT GLUE THE HINGES IN AT THIS TIME Now carefully slide the elevator onto the exposed half of the hinges You will find it easiest to slide the part onto the hinges at an angle one hinge at a time To set the proper amount of gap between the parts simply deflect...

Page 32: ...ctly round opening b Cover the bottom of the wing with one piece of covering material Like all open structures you should seal the covering down all along the outside edges of the structure first At the root end of the wing panel seal the covering over the edges and onto the end rib Along the back of the wing panel slit the excess covering at each end of the aileron bay and run the flap of coverin...

Page 33: ...nstruction Glue the other ends of the door hinges into the fuselage Then reassemble the door handle and a latch and make any final adjustments 152 Cover the outside of the door window with covering material We painted the inside with matching Cub Yellow paint Then hinge the door window to the fuselage Covering The Tail Surfaces 153 The stabilizer is covered after it is mounted on the fuselage see ...

Page 34: ...e area in your cowling That ratio will keep a constant stream of fresh cool air moving through the cowling Inadaquete exit space can cause heated air to be trapped inside the cowl which can cause overheating and engine failure This picture shows the size of exit air opening we have at the bottom of our Cub cowlings 159a Cut four 3 8 sq x5 8 long basswood cowl mount blocks Epoxy the blocks along th...

Page 35: ... for the top shrouds the cylinders fins and for any recessed or shadowy areas Flat Steel For the exhaust pipes and cylinders This isn t a standard model airplane color You ll have to mix your own by slowly adding black paint to silver until you get a shade you like It shouldn t be too light colored but must provide adequate contrast with the black painted areas Windshield And Side Windows 164 Cut ...

Page 36: ... to the wing and make the aileron pushrods 174 Use four SIG Easy Hinges to hinge each aileron its wing panel Use the same procedures you did in the section Attaching The Tail Surfaces earlier The aileron hinges should be installed in the 3 32 balsa top sheeting of the wing and aileron see wing cross section drawing on the plan 175 Screw a Nylon R C Link onto the threaded end of a 2 56 x10 Threaded...

Page 37: ...ervo arm hole 185 Slide a 36 length of thin music wire not supplied through the rudder exit guide at the back of the fuselage then forward through the fuselage and out the door opening Tape the unfinished end of the pull pull cable onto the end of the music wire and then carefully pull the cable through the fuselage and out the exit guide Repeat to bring the other rudder pull pull cable out on the...

Page 38: ...ntrol surface Surface Suggested Throw AILERONS 3 4 UP and 1 2 DOWN ELEVATORS 1 UP and 1 DOWN RUDDER 1 3 4 RIGHT and 1 3 4 LEFT Steerable Tailwheel Unit 190 Push the bottom end of the Formed Leaf Spring inside the molded Nylon Tailwheel Bearing Bolt securely with the 4 40 x3 8 Rd Hd Bolts and the 4 40 Lock Nuts provided 191 Prepare the Formed Tailwheel Wire for installation by first grinding or fil...

Page 39: ...ld Du Bro makes a very handy Kwik Fill Fueling Valve part DUB334 for glow fuel only that solves this problem in the easiest way We highly recommend that you purchase a Du Bro 334 Fueling Valve or equivalent and install it in your Cub In this Cub kit we have included a formed Aluminum Fueler Mount shaped like an L that we use to mount the Du Bro Fueling Valve to the firewall It has a 3 8 dia hole o...

Page 40: ...ng edge of the wing IMPORTANT NOTE Balanced means the airplane sets level when supported at the desired balance point not slightly nose down or nose up FLYING The Cub is not difficult to manage on the ground or in the air However being a taildragger there are some differences you should be aware of between flying the Cub and flying most trainer or pattern type models It handles more like a full si...

Page 41: ...se hints make it sound as if the Cub is difficult to fly it really isn t The Cub can be safely flown by anyone who is capable of handling a multi channel model Once you get a few Cub flights under your belt you ll find rudder aileron coordinated flying becoming second nature and you ll be a better pilot with all types of models GOOD FLYING WARNING THIS IS NOT A TOY Flying machines of any form eith...

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Page 44: ...OTLINE for technical support 1 641 623 0215 SIG WEB SITE www sigmfg com Copyright SIG Mfg Co Inc SIG MFG CO INC Montezuma Iowa 50171 0520 LIMIT OF LIABILITY The craftsmanship attention to detail and actions of the builder flyer of this model airplane kit will ultimately determine the airworthiness flight performance and safety of the finished model SIG MFG CO s obligation shall be to replace those...

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