Rear Ejection Bomb Rocket

There is a newer version: https://www.thingiverse.com/thing:3920822
The new version uses an Estes BT-60 body tube in place of the paper towel tube used in this design, which makes for a slightly better rocket.

After showing my kids my Pringles F-Bomb model rocket (https://www.thingiverse.com/thing:3123333) my eldest said "Wouldn't it be cool if the parachute came out of the bottom so it came down like a real bomb?"

I thought "Why yes, that WOULD be cool". Then I looked around and noticed I still had a pringles can and the tube from a roll of paper towels on my desk. And of course I still had access to Tinkercad and some time on my hands.

So here is my rear ejection bomb rocket, based once again on a Pringles Can and other found items.

The main motor tube is a BT-50 equivalent. I didn't have a BT-50 handy so I made my own by rolling 110lb card stock around my 24mm motor plugs (https://www.thingiverse.com/thing:3113386) wrapped in wax paper.

This rocket is designed to use Estes engines up to the E size (95mm) or Aerotech engines up to F size. Mind you I don't know if it will survive motors that size, but it should.

The "ScrewtopInner" and "ScrewtopOuter" parts are glued to the inner nosecone bottom and top of the Centering RIng to allow you to unscrew the nose cone as opposed to gluing it in place. These parts are OPTIONAL, but I added them because I like to put an altimeter in my rockets. The "Inner" part has four holes at an angle. Once you've glued it in, drill through these holes to create the vent the altimeter will need.

Some build notes:

1) The parachute attaches to a screw eye threaded through the center of the "Centering Ring" part, which goes on top of the paper towel tube. Tie kevlar line to this and run it through the tube. This line WILL be exposed to exhaust gasses. I also used a piece of nomex cloth against the inside of this centering ring to protect the plastic.

2) The kevlar line runs between the paper towel tube and the "motor top" ring. I sanded a little part of this ring flat so it would fit easily. It's important that the entire motor tube assembly slide easily in and out of the paper towel tube, but not be so loose as to fall out when assembled. UPDATE: I modified this part with a notch for the kevlar line. Depending on the line you use you may have to widen this notch. The part has an arrow on it you can paint (or use a marker on) to highlight where the line is to go.

3) I only used enough Kevlar to get beyond the bottom of the rocket, then tied elastic to it. You can see in the build photo that I had a lot more kevlar line, but I found it was prone to tangling when bunched up in the rocket. The elastic is a lot less prone to this, so I used several feet of that.

4) UPDATE: I added another centering ring for the middle of the motor pod. This ring has a raised nub for screwing in a screw eye that the parachute for the pod can connect to. This nub should be facing the BOTTOM of the rocket. The intent is for the "Bomb" chute and shock cord to be isolated in the upper part of the motor bay by this ring and the pod chute to be isolated in the lower part of the motor bay. ALL RINGS SHOULD BE SANDED TO ALLOW THE MOTOR TUBE TO SLIDE EASILY OUT OF THE MOTOR BAY, but not so loose that it falls out.

5) I used an 18" chute for the bomb and a 12" chute for the motor pod.

6) The decals on this rocket are authentic...ly made up based on stuff I saw in the internet. This rocket is not a true scale of any known bombs.

7) I don't know if it works, I just finished it. I'll update this thing after flying it. UPDATE: YES, IT WORKS! Twice already anyway!

UPDATE:

Flew this on a D12-3 today. EVERYTHING WORKED!! Nice straight flight and the pod came out as planned and came down by streamer. One of the strings broke on the chute, but it still came down slow enough. More importantly it came down "Bomb first" and looked very good! I had a lot of rocket casualties this day but this rocket flying good made them all worth while!

FLIGHT REPORT 7/5/2019: Flew this again on a D12-5. Another amazing flight. This rocket looks so good both in flight and in recovery it's just fun to watch. Here is a (poor) video of the flight: https://www.youtube.com/watch?v=K6Uq97BGkHQ

The Bomb Cradle for this is found at: https://www.thingiverse.com/thing:4622791

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