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Mountain Models J-3 Cub, Manual, Page: 5 / 27

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Mountain Models J-3 Cub Manual Download Page 5

5 

Step 1: Assembling the Fuselage 

The first thing you are going to assemble is the fuselage of your airplane. This involves 

assembling the fuselage sides, formers, stringers, firewall, etc. 

1. 

Glue the 3/32” balsa fuselage side parts together with thin CA.  Ensure that they are seated 

properly with no gaps.  

 

 

To remove the pieces, gently flex the balsa sheets until the pieces fall out. 
You may find that you need to carefully trim the extra pieces of wood that 

originally held the piece to the sheet. You can also use a #11 X-Acto blade to 

trim them out of the sheets.

 

2. 

Glue the 3/32” balsa reinforcement piece F9A to F9 and F10A to F10 with the engraved text 
forward on both parts. Make sure the parts are flush with the bottom and lower sides of the 

parts as shown in the left image below. 

 

3. 

Press the 3/32” balsa part C8 into the 1/8” balsa part F8. The text on F8 should be facing 

TOWARDS C8 and the text on C8 should be facing UP. Reference the above right image. Do 

NOT

 glue the parts together yet. 

Summary of Contents for J-3 Cub

Page 1: ...ingspan 48 in Length 30 in Wing Area 332 sq in Standard Wing Weight Ready to Fly 13 4 17 oz Depends on motor battery Wing Loading 5 8 7 6 oz sq ft Standard Wing Revision History Date Revision Notes Comments 11 28 2006 1 0 Document initial release ...

Page 2: ...shless out runner motors Please let us know you experiences building and flying this model We look forward to customer feedback and want to know how you re doing with our products Thank you Brian Eberwein Mountain Models PO Box 6815 Colorado Springs CO 80934 www mountainmodels com Phone 719 630 3186 Before You Begin Check to make sure that all of your parts are there and in good shape Parts List N...

Page 3: ... 3 4 40 x 3 8 Socket Cap Screw 1 Allen Wrench 3 32 2 Wheel Retainers 1 1 2 Double Sided Velcro 1 3 4 Sticky Backed Velcro Pile and Loop Sides 1 Spider Wire 12 feet Building Materials You Will Need Smooth and flat work surface Wax paper or clear plastic wrap to protect the work surface Thin and thick Cyanoacrylate CA glue 5 Minute Epoxy Hobby knife with 11 blades Needle nose pliers Wire bender or p...

Page 4: ...xed up or disappear Do NOT glue anything until told to do so Join all of your pieces using thin CA Cyanoacrylate glue unless we tell you otherwise In general only a small amount of CA is necessary to glue parts together Don t over force your pieces together If they aren t fitting together properly make sure you have the right pieces and that they are oriented correctly If needed you can lightly sa...

Page 5: ...t you need to carefully trim the extra pieces of wood that originally held the piece to the sheet You can also use a 11 X Acto blade to trim them out of the sheets 2 Glue the 3 32 balsa reinforcement piece F9A to F9 and F10A to F10 with the engraved text forward on both parts Make sure the parts are flush with the bottom and lower sides of the parts as shown in the left image below 3 Press the 3 3...

Page 6: ... nut flange Make SURE you do NOT get CA on the inside threads 5 Insert the reinforcing triangles as shown in the below left image 6 Slide the 1 8 Lt Ply F5 onto C8 as shown in the right image above Make sure the text is facing away from the other parts Do NOT glue yet 7 Press the 3 32 balsa F12 into F11 The text on F12 should be facing UP and the text on F11 should be facing forward away from F12 ...

Page 7: ...ft fuselage side into place on the formers from the previous step as shown in the above right image Make sure the formers are at a 90 degree angle to the side and tack glue them to the left fuselage side Make sure the C8 part is all the way in F8 and F5 and tack glue them together 10 Insert F9 and F10 with the text facing FORWARD into the right fuselage side Place the F11 F12 assembly from step 6 ...

Page 8: ...the center line Weigh the fuselage down to the plans as shown below After you are sure all the formers are fully seated and everything is straight glue the formers and the top stringer in place with thin CA 12 Glue the 3 32 balsa cabin sides together over the plans Make sure you have wax paper or plastic wrap over the plans of course Make sure that the bottom sides of the parts with marks from the...

Page 9: ... and seat against the cabin top C8 part 15 Insert the 3 32 balsa reinforcements as shown in the image below They are on the same sheet as F10 Make sure they are fully inserted before gluing them in place 16 Insert the 3 32 balsa F3 and F7 parts as shown below with the text facing FORWARD Secure with thin CA ...

Page 10: ...ides together to mount the firewall as shown above right MAKE SURE that the text on the firewall is facing FORWARD Make sure the sides are straight and glue the firewall in place You can trim the front on the fuselage sides back slightly if you want so they are about 1 8 in front of the firewall 19 Insert the 3 32 front hatch as shown below Secure with thin CA Do NOT glue the hatch portion of the ...

Page 11: ...bottom They are the ones with the square ends Place them so the lasered side is inside the part Not outside like in the image Secure them in place with thin CA Double check that the fuselage is still straight before gluing these into place 23 Insert the 1 16 balsa hatch shelves in place as shown below They tab into the slots in the fuselage sides Secure them with thin CA ...

Page 12: ...1 8 sq hard balsa stringers as shown below Trim any extra from the rear to be flush with the aft former F11 It will stick out further than the middle formers This is so the edges of the formers do not show through the covering when you re done 26 Install the side stringers also shown in the above image They will only fit in the right spot top or bottom so if one doesn t fit try the other or rotate...

Page 13: ...ed and glue it in place with thick CA Trim any overhang with a sharp blade or sandpaper so it is flush with the firewall and F2 29 Glue the false ribs together as shown below and on the plans BE SURE to make a left and right side and that the back of the parts are flush 30 Sand the parts as shown in the image below and on the plans Glue them to the fuselage as shown in the image below ...

Page 14: ...tch tabs marked R into place as shown in the left image below The rectangular RH part goes behind the magnet to reinforce that section of the hatch 33 Trim the tabs holding in the forward hatch and remove the forward hatch from the fuselage Glue the second magnet into place on the engraved circle on the front hatch Glue in the remaining 2 1 16 plywood hatch tabs as shown in the right image above 3...

Page 15: ... joints later and DO NOT wrap the center joint With the center joint wrapped the gear is extremely stiff and has no shock absorption 3 Glue the 1 16 balsa landing gear core to one of the 1 32 ply parts as shown below If the center holes do not line up rotate one of the parts 180 degrees so they do line up It is best to use 5 minute epoxy here to make sure you get a very solid glue joint After the ...

Page 16: ... glue is dry After everything is dry remove the single spider wire holding the center joint together 6 Trim the 1 16 balsa landing gear fairings to fit as shown below We made these slightly oversize to account for differences in assembling the landing gear wires Glue them to the wires using thick CA 7 Bend the tail wheel wire as shown on the plans using the 0 039 wire ...

Page 17: ...e to the elevators with thick CA or epoxy 3 Assemble the vertical stab and rudder over the plans After the parts are all pressed together secure with thin CA Make sure you don t glue the rudder to the vertical by accident so assemble them separately MAKE SURE the top rear of the vertical and the inside corner of the rudder are square at a 90 degree angle so they fit together nicely after they are ...

Page 18: ...tter fit If they are a bit loose use some thick CA in the joints to make sure you get a good glue bond 1 Below are pictures of the rear firewall mount The front firewall mount goes together the same way The taller 1 16 ply firewall parts are for the mount pictured Press the 1 8 sides onto the 1 16 ply part with the lasered sides of the parts facing inwards Place the top part with the text facing o...

Page 19: ... less strain on the wood less chance of breaking the pieces and a smoother finish Using a tack cloth carefully remove the balsa dust once you are done sanding What to Sand On the tail parts first lightly sand each side of them so all the part joints end up nice and smooth Use a sanding block long enough so you don t nick the edges of the internal structure as you sand Start out with 320 grit to ge...

Page 20: ...g with your iron Using a heat gun increases the risk of melting a hole in the covering so we prefer an iron Fuselage We like to do the sides then the bottom and then the top In the area where the covering goes from the side stringers to the rear window area we like to have the covering attached to the stringer and then the inside edge of the windows so it flows nicely and doesn t sink down Tail Fe...

Page 21: ...u ve triple checked the fit glue the wire in place with thick CA Take care not to get CA on the covering as it can leave a nasty white residue that doesn t look good Slide the tail wheel onto the tail wheel wire You can keep it in place with a drop of thick CA kicked with accelerator immediately so the CA does not go into the wheel BE VERY careful so the CA does not go into the wheel You can do mu...

Page 22: ...all the stab and vertical to the fuselage again making sure that the stab sits flat on the stab mount area Make sure the vertical is at a 90 degree angle to the stab BEFORE the glue sets Allow the glue to dry before continuing 4 Set the rear fuselage fillets in place on the stab Mark the covering on the stab and elevator where the fillet meets them Remove the covering in these areas just inside th...

Page 23: ...below 2 Slide the servo connector onto the pushrod wire and use aggressive double sided tape or some drops of thick CA to secure the servos to the sides of the fuselage as shown above Trim the extra wire sticking out but leave some for adjustments Step 9 Windows and Plastics The easiest way we have found for trimming the vac formed plastic parts is to use sandpaper Trim the parts out of the sheets...

Page 24: ...u can t sand the edges like above but you can use sandpaper on the back of the part to get there This is a lot easier than using an X Acto blade to start with especially if you slip and cut into the part We ve all been there and done that so take your time and try the sandpaper method it works 4 For really nice air inlets for cooling the motor ESC and battery try the following Trim the front of th...

Page 25: ...cause the motor mounts unbolt you can change mounts later 2 If you use the rear firewall mount pictured below mount the motor to the firewall and then bolt the motor mount to the firewall using the included 4 40 hex head bolts 3 If you use the stick mount for a GWS geared brushed system use the included 2x3 8 wood screw to secure it to the motor stick 4 Slide the cowling onto the fuselage lining u...

Page 26: ...r itself Step 12 Finishing the Kit Well you re almost there the end is in sight just a few more steps and you can go flying assuming the weather is cooperating Attaching the Battery Attaching the battery 1 The battery mount location is flexible to handle the different weights of motor and battery options We mounted the stick on the bottom of the formers to allow the battery to be changed from the ...

Page 27: ...l be hard to control requiring constant input to keep the plane flying straight and level For the Cub start with the CG at the front of the range on the plans Use this as a starting point and then you can slowly move it back as you like Scale Additions and or Modifications The outlines of our Cub kit are very true to scale Of course in making a kit easier to build we did simplify some areas For a ...

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