Brief:
Part of the Shrox/Apogee Global Defense Series, this 2-stage missile is designed to protect our nation's capitol from hostile aircraft, missiles, (or alien craft?). It's small, light, and incredibly fast when flying on both stages, though works quite well on a single stage also.

Construction:Parts List

• 24mm nose cone
• BT-50 body tube 9.75" long (sustainer)
• BT-50 body tube 2.75" long (booster)
• BT-50 tube coupler
• (2) 18mm motor tubes (2.75")
• 13-18mm centering ring (engine block)
• (4) 18-24mm centering rings
• 1/8" launch lug
• 3/32 balsa or basswood fin stock
• 2 x 36 Mylar streamer
• 36" Kevlar shock cord (plan calls for 300#, I used 110#)
• Clay nose weight (about 0.5 oz)
• Decal sheet (can be downloaded from E-zine archives #83)

After downloading the Rocksim file (and looking at the pictures in the E-zine), you're on your own figuring out how to build this, since there are no instructions (RockSim is also available here on EMRR). Fortunately, that's not too daunting a task, as the design is comparable to most skill level 2 modrocs. I started with the motor mount assemblies, gluing the engine block in one tube, and mounting centering rings on each 18mm tube. Since this is a 2-stage, joined with a BT50 coupler, pay careful attention to the location of the centering rings in Rocksim so that the two stages will join well. After the motor mounts have set, they are glued into the body tubes along with the tube coupler.

I printed out the fin templates from Rocksim, and cut them from basswood, figuring the thrust from a 2-stage might put a bit of strain on balsa (though FinsSim, an add-on to Rocksim, indicates this would be no problem). Tack the fins on at 120 degree angles (I've found the Estes tube marking tool set to be the best $8 I've spent on this hobby), and apply fillets of wood glue. Install the shock cord/streamer, and the rocket is nearly finished.

Note: the clay nose weight - it was not referenced on the parts list in the E-zine, though is included in the Rocksim file. Without this nose weight, this rocket is probably not stable, and this could be an easily overlooked detail.

Finishing:
Two coats of primer and two coats of glossy white, followed by a coat of light gray on the booster, and you're ready for decals. I printed the decals with my inkjet on Avery clear decal stock, though this is a fairly opaque finish, and I'd recommend finding a better printer source, possibly going to the expense of water-slide decals. Also, depending on your field conditions, you might consider painting the booster a bright red or orange, to stand out more in taller grass.

Construction Rating: 4 out of 5

Flight:
There were no recommended motors in the E-zine or Rocksim file, so I tried a few combinations in Rocksim and decided to go with a C6-0 booster and A8-3 sustainer (I would have preferred a B boost, but didn't have any at the time). Field conditions were favorable for high altitude - 85 degrees and 5 mph winds, and our club uses a field large enough to handle most HPR motors.

I used the full 0.75 ounce of nose weight called out in Rocksim, and the rocket was a bit over-stable, angling into the light winds. Both stages lit, and ejection on a 3-second delay was at least a couple seconds early, even factoring in the weathercock. The nose cone separated, though this was from a weak shock cord mount, not due to the fact that I went with 110# Kevlar® instead of 300#.

I recovered all components, and after some minor repairs and removal of about 0.25 ounces of clay, flew again on C6-0/B6-6. The flight was much better, screaming out of sight on a straight trajectory. Apogee was beyond my eyesight, though the 6-second delay was a much better choice.

Recovery:
Pro's

• Terrific altitude from the 2-stage design

Con's

• A little tricky to get the right amount of nose weight

Flight Rating: 4 out of 5

Summary:
Overall, this is a very nice 2-stage design, especially given the price (free download). If you're new to Rocksim, it's also a good design to work with to learn to choose the proper motor(s) and fine-tune the CG/CP relationship.

Overall Rating: 4 out of 5