B-25 J Gunship RC Airplane FlightLine

thingiverse

Designed to convert the nose of the FlightLine 1.6m B-25J into the gunship version used extensively in the Pacific as a low level attack platform. Overview Remove the 'green house' nose canopy and replace it with a 3D printed nose shaped like the B-25J gunship. Barrels are made from carbon fiber rod with a 3D printed skin for scale appearance. Nose skin is 1mm thick. Printed in ASA, the finished and painted Nose assembly weights 46grams (~1.6oz) If you want to support my contributions here, please consider leaving a tip https://www.paypal.com/paypalme/Showmethedenaro Bill of material 1. Printed Nose.STL - 1 each (LxWxH, 144x96x118mm) 2. Printed Barrels.STL - approx 10 each (31x3.7mm) 3. ~400mm of Carbon Fiber (CF) rod with 1.5mm OD (fashion ~10, 29mm long) 4. Canopy Glue, FoamTac or similar foam safe ductile adhesive 5. Thin CA 6. Upol 1K Putty UPO657 7. Acetone 8. Seymour 20-1674 PBE Professional Primer 9. Paint to finish the exterior of the Nose Recommended Tools 1. Small jeweler's files 2. Cordless electric drill & pin vise 3. Drill bits 1.4, 3.0 & 3.1mm - sharp and in good condition 4. Rotary tool with thin abrasive cutoff disks - cut & deburr CF rods 5. Safety glasses, mask and gloves 6. Sanding block with the soft backing and Sandpaper 180, 220, 300/400, 600, 800 grit 7. Fine bristle paint brush, mixing stick & acetone safe mixing container (yogurt container) 8. Mini Transfer Pipette Dropper to apply Thin CA 9. Clamps, Silicon bands, soft foam blocks for fixture while adhesive cures Nose & Barrel Build Steps 1. Print the .STL components. Images show supports I used which are important to the print quality/success. Remove support and deburr. Use caution removing support material from the Nose. Excessive force on the 1mm Nose skin can cause cracks. Light use of the jewelers file cleans up the stringers inside of the square barrel ports in the nose. 2. Inspect the Barrel print quality. Use 1.4mm drill bit in pin vise to deburr ID as needed. Insert 1.5mm CF rod. Fit should have contact at ends but still slide. Cut CF rod to be flush on the back side and ~2mm short on the front side. Transfer Thin CA into mini pipette dropper. With ~4mm CF protruding aft from Barrel, apply thin CA to the exposed CF rod. Quickly use a non-stick flat surface (parchment paper) to press the CF flush with the aft of the Barrel. If you are too slow, the CA will setup before the CF rod is in position. Apply a small amount of CA inside the Barrel hole from the front side. Lastly, apply a small amount of CA the one of the aft most Barrel vent holes. Important to ensure the aft portion of the Barrel which goes into the mounting hole is glued to the CF. 3. Precision drill the thru holes in the Nose to just fit the ~3.1mm aft side of the Barrel. I used an electric hand drill. Be careful to align the drill straight ahead in the middle of each gun port. I used 3.0 and then 3.1mm bits to fit the Barrels. Clearing the plastic from the flutes of the drill bit after each use improves the quality of the successive hole in thermoplastics. Resist the urge to process the bit in the holes. You are trying to clean up material to form a cylindrical hole which points straight forward. Be sure to check the size of your Barrels (~3.1mm) prior to selecting the bit sizes. 4. Test fit the Barrels into the Nose. Jeweler's file can be used to chamfer the aft side of the Barrel mounting pin to ease installation. The fit to the Barrel is intended to be supportive & snug. I can remove them with a slight twist using just my finger tips. Adjust the fit on the barrel not the hole in the Nose. If the fit is too tight, remove material from the barrel with jeweler's file. Be careful to not apply excessive force on the skin when removing Barrels from the Nose. Pushing from the back side with a 2.8mm drill bit can help. Finish the Nose 1. Be careful when handling the Nose print. Seam line cracks will develop in the 1mm skin if excessive force is applied. These can be difficult to detect until after the primer coat is applied. 2. With light pressure, sand the Nose exterior with 180/220 grit to remove the high spots on the print. A flat sanding block with a piece of 1/8 to 1/4" thick foam rubber/mouse pad under the sand paper works nicely. Do not remove all of the print line texture by sanding as this will thin the walls and weaken the Nose. Your goal is to get the shape and profile desired for the final part. Take your time on this step as this is the foundation of the final finish. The next step fills in the low spots to get a smooth finish. 3. Use Upol 1K Putty UPO657 and filler primer to finish the exterior skin of the Nose. YouTube can show you how. https://www.youtube.com/watch?v=BDjVEgaV5jY&list=PLppJpmvu_hpy3Xh0Cxrs39uR3VrPo41iX&index=4&t=519s Note: Avoid getting putty inside of the square Barrel ports. Use the side of the brush to daub around the ports. I found a initial application of 1K Putty LIMITED to only the low spots in the print greatly reduced the total time spent sanding/finishing. a) Fill/sand the low spots with 1K putty/acetone mixed to house paint thickness. 220 grit b) Fill sand the print line texture with a complete exterior coat of 1K putty/acetone mixed to whole milk thickness (thinner than house paint). 220/400 grit. With the surface finish ~90% of my final goal, the remainder was filled with Seymour 20-1674 PBE Professional Primer. 2 or 3 coats seemed adequate. Prime/sand 300/400, 600 grit between coats. Caution: On some of the early versions, I observed a tendency for the aft side corners to flair/curl outward after finish/primer. The trident braces were added to resist this. Be aware to not over expose those corners to solvents (eg limited number of very thin coats, dried quickly). These changes resolved that issue for me. Managing this tendency should make the installation to the fuselage easier. 4. Paint the Nose Be advised to complete the Barrel fit-up prior to final paint. Once painted, careful installation and removal of the Barrels is required to avoid damaging the paint. Fit to the Plane 1. Remove the OEM green house canopy and the forward gun body. 2. Check the fit of the Nose to your plane. It should fit very similar to the canopy to the fuselage. I did not have to modify the foam or the Nose print. It can be insightful to use the slicer to make section cuts on the Nose and fit these partial prints to the plane. 3. Install the 8 Barrels. Careful to not damage paint on the Nose. The tips of the top 4 terminate in the same plane. The tips of the bottom 4 terminate in the same plane. Glue is optional if the fit is snug. 4. Apply a ductile adhesive to aircraft and Nose. Install the nose and remove excess glue. Secure the Nose to the fuselage (silicon bands, clamps with protective cushions etc). Strips of parchment paper can be used as a slip plane as needed to prevent adhesion of the fixtures. Allow to fully cure. 5. Touch up paint as needed. Final Notes CAUTION: Check your planes CG prior to flight.