Saturday, January 29, 2011

Scratch: Gone Batty

This is a Halloween-themed rocket with jack-o-lantern nose cone and bat wings. The original flew on two 24mm motors. After two flights, I decided it needed more power so I added two 24mm outboard pods. Four D12's are much better than two!

The parts list:

1. 1 ~6.5" diameter hollow pumpkin from Michael's craft store
2. Foamboard
3. 2" clear mailing tube from (The Container Store)
4. 2" cardboard mailing tube with telescoping inner tube (also from The Container Store)
5. 2 pieces of thick walled 24mm tubing (Totally Tubular)
6. ¼" lug (LOC)
7. Bamboo skewers
8. Scrap plywood
9. Eye bolt
10. 3/16" bungee
11. Car airbag material (optional)
12. 4 hex-head stand-offs (any small screws will work)
13. 10.5mm tube (Apogee)

I started by cutting a hole in the bottom of the pumpkin to fit a 2" tube. Because I wanted to make this night launch capable, I installed a piece of 2" clear mailing tube in the pumpkin. It hangs about 2" out of the bottom and is attached to the inside top surface with Gorilla Glue. A short section of cardboard tube telescopes over this plastic tube and is attached with 2 small screws. These are actually hex standoffs -- I thought this gave it a 'Frankenstein' head bolted-on look. I made the shoulder out of a piece of the telescoping cardboard tube, a plywood bulkhead, and an eye-bolt. This too is held together with standoffs, which make the inside accessible so a lighting device can be installed. In fact, here is the cone section with a laser pointer installed as a demo (see picture). Finally, to accommodate the launch rod, I inserted a piece of Apogee 10.5mm tubing through the pumpkin. I decided on the tubing instead of just open holes since I wanted all the photons to come out of the jack-o-lantern face.

The motor mount is two pieces of 24mm tubing glued together. This pair slips nicely into the mailing tube. I made foamboard centering rings to keep the ejection charge in. These are more like half-rings since the motor tubes touch the inner wall. The upper surface of the top ring, and the bottom of the lower ring were covered with a thick layer of carpenter's glue.

I recycled a section of bungee from my now resurrected Public Enemy 3" Ultra Fatboy. This was epoxied to the inside of the tube just above the motor mount. To provide some protection, I glued in a small piece of car airbag material to cover the bottom four inches or so. I've never done this before but have a lot of odd scraps of this stuff.

The fins were inspired by the Rocket Team Vatsaas' Halloweener. They are foamboard trimmed with bamboo skewers. The skewers were covered with light spackling and a little Elmer's Fill 'n' Finish.

I left the surface of the fins quite rough. A bat's wing isn't that smooth after all. The whole thing was covered with a coat of white primer and then painted with Rustoleum black paint.

Does carving the pumpkin count as 'finishing'? The carving was actually performed at the start of the build.

Flight Reports:
I friction fit the D12s, packed dog-barf wadding, and used the 18" nylon chute from my Semroc SLS Sky Hook. The winds were gusting to 15mph or so and there was a little weather cocking. Ejection was just a little late. I will probably try a three second delay on all but calm days. Unfortunately when it's that windy, the rocket is more likely to land on its fins, even if they are swept forward like the ones on Gone Batty. Two of the foam fins suffered some minor damage.

Flight number two D12-3's. It was another low flight with a slight zig-zag in the middle. Ejection was early and the large 42" chute ensured the foamboard fins sustained no damage.

More Power!
Take 2 tubes that hold the 2nd grain in the G64 reloads (which are conveniently 24mm). Find 2 matching cones. Mark and trim strips from the painted body. Epoxy cones in tubes and tubes on rocket. Since I didn't want all the motors in-line, I had to block the existing lug so I added another.

Well, I did some quick touch up with brush-on gloss black. I may overcoat the gloss with flat later. Meanwhile, I know I like the orange cones and think the plain white tubes are OK. The bungee shock cord has seen better days. What was I thinking mounting bungee near the motor mount? If it doesn't burn through this time, I'll add a Kevlar leader through the wall at the launch lug.

More Flight Reports
The augmented version flew on four D12-5's. Despite using Quest Q2G2 igniters, they insisted I use the Cluster Buck. This relay system provides something like 100A. Overkill maybe, but it worked. Great flight! Much better with the 'strap on' boosters.