Intro: How to Build a 2.75-inch Folding Fin Rocket (FFR)
The Mk. 4 Folding Fin Rocket (FFR) was an unguided rocket used by US military aircraft during the Vietnam War.
2.75 inches (70 mm) in diameter, it was designed as an air-to-air weapon but was mostly used as an air-to-ground weapon.
Since it was very hard to procure one for my collection, I decided to build one.
Step 1: Tools and Components
42-inch (l) section of 3-inch (w) PVC pipe
5-inch section (l) of 3-inch (w) PVC pipe
1-inch (w) bottle cap for fuze
3-inch PET soft-drink bottle
3-inch (w) PVC end-cap
2-inch (w) PVC end-cap
4 door hinges
Electrical and masking tape
Sandpaper and abrasives
Hammer and pliers
Cement and putty
Saw and blades
Gloss white paint
Olive green paint
Metallic gray paint
Flat black paint
Step 2: Section 1 - Warhead and Fuze
Step 3: Warhead and Fuze
Saw off bottom 3 inches of soft-drink bottle. Total length without cap should be 10 inches.
Step 4: Warhead and Fuze
Affix 3-inch (w) PVC end-cap to one end of 42-inch PVC segment. Carefully attach cut-down soft-drink bottle to end-cap. Total warhead length without fuze should be 13 inches.
Step 5: Warhead and Fuze
Affix soft-drink bottle to end-cap using electrical tape.
Step 6: Warhead and Fuze
Slather generous amounts of white glue for reinforcement. Prime with gloss white paint after 3 hours of drying.
Step 7: Warhead and Fuze
Apply 2 coats of black cement in irregular splotches. Wait 48 hours for cement to cure. Do same for bottle cap.
Step 8: Warhead and Fuze
Smoothen surface with abrasives. Apply coat of white glue to cover all seam lines and prime with gloss white paint to reveal irregularities. Repeat as necessary.
Step 9: Warhead and Fuze
Paint warhead even coat of flat olive green. Apply putty to smoothen major rough spots, carefully recreating pitted surface of cast-iron products. Repeat as necessary.
Step 10: Warhead and Fuze
Apply final coat of flat olive green to warhead. Paint bottle cap flat black. Lightly airbrush both warhead and fuse metallic grey.
Step 11: Warhead and Fuze
Paint 1-inch (l) flat yellow stripe at bottom of warhead. Apply flat black dry transfer letters. Markings are: 2.75 INCH / HE COMP B4 / WARHEAD XM-151 / LOT 31-67-22. Weather and apply ordnance graffiti as desired.
Step 12: Flight Tags
Weather fuze with rust and add scratch-built pressure detonator. Custom-built ‘Remove Before Flight’ tag is printed on gloss red nylon segment.
Step 13: Section 1 Finished!
Finished and fully-weathered cast-iron 2.75-inch warhead section.
Step 14: Section 2 - Fin Assembly
Step 15: Fin Assembly
Make 4 spring segments out of wire. Here’s how.
Step 16: Fin Assembly
Coil wire around any 1-cm (w) cylindrical object. In this case, an old paintbrush.
Step 17: Fin Assembly
Stretch both ends. Make total of 4 spring coils.
Step 18: Fin Assembly
Cut 5-inch length of 3-inch PVC pipe into 4 equal sections. Springs should be equal in length to each corresponding tail fin.
Step 19: Fin Assembly
Affix 3-inch PVC end-cap to other end of 42-inch PVC section. Affix 4 swing hinges lengthwise to pipe. Use wall tacs for reinforcement.
Step 20: Fin Assembly
Reinforce assembly with tape and wire prior to painting.
Step 21: Fin Assembly
Prime entire section with flat black. Install springs with plastic end-caps. Replace wall tacs with aluminum pegs. Detail assembly with wire. Paint even coat of metallic gray, highlighted with silver. Add flat black dry transfers and ignition wire made from cable cord.
Step 22: Section 3 - Motor Tube
Step 23: Motor Tube
Paint motor tube with several coats of gloss white. Weather by spraying with metallic gray paint. Before paint dries, use steel brush to smudge colour on and off certain areas. Repeat as necessary. Add flat black dry transfer letters. Markings are: 2.75 IN ROCKET MOTOR MK. 66 MOD. O / LOT FZD 70.
Step 24: All Done!
Finished 2.75-inch rocket. Total length is 55 inches. Warhead and fuze measure 13 inches. Tail section measures 7 inches. Motor tube measures 35 inches. Now ready for display!
Step 25: Share Your Creations With the Instructables Community!
Step 26: Happy Building!
Total time spent building, painting and weathering rocket? 73 hours! Total cost? Less than USD28!
For more information, contact the builder on Facebook. Enjoy!