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#1
I started building a 100cm wing span j3 cub based on FT simple cub plans but modified .

I used HK 5mm modeling foam (similar to depron) , recycled polystyrene sheets, some balsa wood, 3mm plywood, kraft paper (brown) , as main building materiel.

I mainly used polyurethane glue to bond things , as it gives the best adhesion strength to foam & wood . Also used some PVA white glue, hot glue & water based fast set construction adhesive.

The wing was hotwire cut using 50mm polystyrene sheet with Clark-Y airfoil. wing cord is 17.5cm and span is 102cm with 2 degree dihedral.

I used brown kraft paper with PVA white glue to cove the foam which stiffened up the foam wing really well. I didnt have to use a spar as the strength from the kraft paper was so strong and made a nice rigid foam core. after covering with paper I made a bevel cut in the middle and slightly bend the wing to set the dihedral angle and glue the center cut with polyurethane glue. then used a strip of kraft paper with white glue to cove the glue joint and also the increase the strength.

I used kraft paper to cove the fuse and tail which strengthened the whole structure really well.

In the fuse where the battery and landing gear goes I used some 5mm balsa , 3mm ply to reinforced the foam .

I used racerstar 1300kv motor from banggood with 30A ESC and 8x4 APC prop. This combo generated about 750g of static thrust drawing 13 amps.

4x 9g servos from ebay .

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#2
I used gray primer 1st to coat the paper. The cowling was made from a block of polystyrene foam then shaped it to fit the firewall. after shaping I covered it with few layers of kraft paper and white glue which stiffened it like plastic. Then I cut a cavity in the foam for the motor leaving around 5-10mm thick foam wall . Then I cut a hole for the motor shaft and put a later of water based construction adhesive and sanded it down before applying few coats of primer (pics above) 20180718_220132.jpg 20180718_220224.jpg