Rear Ejection Bomb Rocket

thingiverse

There is a newer version available at https://www.thingiverse.com/thing:3920822 . This new design utilizes an Estes BT-60 body tube in place of the paper towel tube, resulting in a slightly improved rocket. After showcasing my Pringles F-Bomb model rocket to my kids (https://www.thingiverse.com/thing:3123333), my eldest suggested that it would be awesome if the parachute came out of the bottom, simulating a real bomb's descent. I concurred and began brainstorming. I rummaged through my desk drawer and found a Pringles can, a paper towel tube, Tinkercad, and some spare time, sparking my creativity. Thus, this rear ejection bomb rocket was born, built using the same materials as before. The main motor tube is equivalent to a BT-50. Since I didn't have one on hand, I created my own by wrapping 110lb cardstock around my 24mm motor plugs (https://www.thingiverse.com/thing:3113386), securing it with wax paper. This rocket design accommodates Estes engines up to E size (95mm) or Aerotech engines up to F size. While I'm unsure if it can withstand motors that large, it should be capable. The "ScrewtopInner" and "ScrewtopOuter" parts are optional but useful for attaching an altimeter. These components allow you to remove the nose cone without gluing it in place. The inner part features four angled holes, which you'll drill through after gluing it in place to create a vent for the altimeter. Some essential build notes: 1) Tie kevlar line to the screw eye in the center of the "Centering Ring" part and run it through the paper towel tube. This line will be exposed to exhaust gases, so I recommend using nomex cloth against the inner ring's surface for protection. 2) The kevlar line runs between the paper towel tube and the "motor top" ring. Sand a small portion of this ring flat to ensure easy assembly. Make sure the motor tube assembly slides in and out smoothly but doesn't fall out when assembled. UPDATE: I modified this part with a notch for the kevlar line, which may require widening depending on your line choice. 3) Use just enough Kevlar to reach beyond the bottom of the rocket and tie elastic to it. In my build photo, you can see that I initially used more kevlar but found it prone to tangling when bunched up in the rocket. The elastic is less likely to tangle, so I recommend using several feet of it. 4) UPDATE: I added a centering ring for the middle of the motor pod, featuring a raised nub for screwing in a parachute attachment point facing the bottom of the rocket. This isolates the "Bomb" chute and shock cord in the upper part of the motor bay from the pod chute in the lower part. 5) Use an 18-inch chute for the bomb and a 12-inch chute for the motor pod. 6) The decals on this rocket are created based on internet research, not actual scale models. 7) I'm unsure if it works as intended since I just completed it. I'll update this thing after flying it. UPDATE: Flew this on a D12-3 today and everything worked perfectly! It had a nice straight flight, with the pod coming out as planned and descending via streamer. One string broke on the chute but it still came down slowly enough. More importantly, it came down "Bomb first" and looked great! FLIGHT REPORT 7/5/2019: Flew this again on a D12-5 for another amazing flight. This rocket looks fantastic both in flight and recovery, making it enjoyable to watch. Here's a poor video of the flight: https://www.youtube.com/watch?v=K6Uq97BGkHQ