This is a basic 29mm "el cheapo" tube fin rocket inspired by Larry Brand's BottleBat 3.0. Like the original, this one is made from a mailing tube and uses a bottle for the nose cone (an Aquapod, what else?)
The parts list:
* 3" mailing tube (~17.625) with liner (~26")
* one Aquapod bottle
* plywood centering rings (2) and bulkhead (1)
* Kevlar® twine and ¼" elastic
* 29mm motor tube
* buttons from railbuttons.com
* small nylon rivets (2) -- Giant Leap
* lead shot
* chute and protector to be selected on the field
I started running some sims, but as long as I had the bottle modeled using the cap as the nose cone and the exposed body as an ogive transition, I was getting results that I didn't believe. The CP was coming up very close the top of the rocket and appeared to be a bug in RockSim. After all, I keep hearing about how stable tube fin designs are. Later, when I modeled the cone as a simple ogive, the results were more in line with what I expected. Since I always believe in picking the answer that I like, I stuck with the latter. The sim showed I'd need some nose weight to fly on a G reload and the more I thought about he Aquapod sitting on the end of a weighted section, I envisioned some crunching going on. Long story short and two Aquapods later, I decided I'd screw the bottle to the bulkhead and fill it with 2 part foam. After this was complete, I weighed the rocket and found I still needed a little weight. So, I drilled the foam at the tip of the bottle and imbedded about 0.75oz of lead shot in epoxy.
I finished mine in a camo style using Model Master dark tan and medium green. I wasn't sure how this mix would look, but I am extremely satisfied with the results. I painted the cap fluorescent red--I guess this round is "live".
Flight and Recovery:
I use a chute protector and a 36" chute for recovery duties. I also toss in a little dog barf just for good measures. A small F39-4 powered the first flight. This required an adapter that I made form some tubing, pieces of a 29mm SU motor, and a clamp-on aluminum thrust ring. The boost was quick enough although the altitude was fairly low. Recovery was perfect.
The AquaBottlebat has logged four additional flights to date, on a G77-5, and two F35-4's.
I liked the BottleBat concept from the first time I saw it, and I love my version. I don't know the actual cost of materials, but the airframe, fins, and cone were all leftovers/scrap. I liked my approach to the fins, as it gives me a away to use up tubing that might otherwise gather dust--I see more tube fins in my future.