Tuesday, January 11, 2011

Review: Talk Radio

This rocket is made from a sports water bottle that was donated by a local talk radio station, hence the name. It has a 24mm mount, recovers by parachute, and uses 'plate fins'. 'High tech' features of this 'low tech' rocket include a Kevlar cord and positive motor retention.

A partial construction list consists of:

* 1 water bottle
* 1 piece of non-rocket junk tube ~1.25" diameter used as a parachute tube
* 24mm motor tube
* Hand-cut cardstock rings
* Kevlar® twine
* Foam backed tape to center the parachute tube
* Duct tape to press-fit the cap/nose cone
* One screw, chunk of BiC pen tube, and miscellaneous metal 'doohicky' for motor retention
* 1/8" and 3/16" lugs

The inner structure consists of a 24mm motor tube centered in a piece of junk tube by hand-cut cardboard rings. The motor tube extends below the end of the larger tube so that it could slip through the hole in the bottom of the bottle. The Kevlar® twine is attached to the motor mount. The top of the larger tube was centered in the neck of the bottle with foam-backed tape and the assembly was glued into the bottle using Liquid Nails.

The 'nose cone' is the bottle cap. After grinding off the threads, I found the cap was way too loose, so I built up the top of the bottle using black duct tape. The cap now fits fairly snuggly. To attach the Kevlar® to the cap, I merely popped up the top nipple, fed the line through the opening, knotted it, and pushed the nipple back down.

I had done some 'what-ifs' on various fin designs but in each case, RockSim said I'd need to add some nose weight. To avoid having to do so, I decided to move the fins well below the base of the bottle. I ended up mounting three chopsticks in the side of the bottle. On the tip of the sticks, I added cardboard triangles. These are bent slightly along their center line to help adhere to the sticks. This also looked a bit better in my opinion. The dowels were attached to the bottle with 5-minute epoxy and the cardboard 'plate fins' were attached to the chopsticks with carpenter's glue.

The motor retainer is simply screwed into the thick bottom of the bottle. This will eventually wear out and will have to be relocated. Finally, I added two sizes of lugs for flexibility.

I modeled the bottle in RockSim, simulating the plate fins with equivalent standard fins. Although I found the rocket to be stable, I still didn't trust that I had made a valid model, so to be sure I loaded it up and did a swing test, which was successful.

I loaded a wad of dog-barf wrapped in one square of Estes wadding and a 12" Rockethead mylar chute, and then wrapped a tape thrust ring on a D12-5 and positioned the retainer. The boost was a bit wobbly after burn out. Nevertheless, it was a cool flight, ejection was perfect, and it recovered 50' from the pad.

The Talk Radio has flown 6 additional times on D12-5's and twice on C11-3's.  The chopsticks have loosened a few times but are easily reinforced.

This was just a quick, goofy build. I love odd-rocs, what else can I say?