Brief:
For completion of her NARTREK Sliver cluster flight requirement, I suggested to my wife that we rebuild the stock 18mm engine Estes Bullpup with a cluster of four 13mm A3-4T motors. She had already built one Big Bertha and didn't feel like building another 3-motor version (Astron Ranger) that NAR recommends for this task. So we tried this.

Construction:
The stock Estes Bullpup kit was built according to the plans, except the stock 18mm motor mount and thrust rings were omitted entirely.

Modifications:

1. 5-minute epoxy was used, since sims predicted a 200 mph, 26G climb out
2. Recovery system: 9" nylon parachute on 18" of 3/8" elastic
3. Boattail was omitted to accommodate the 4 motor cluster
4. Four 3" lengths of 13mm Estes tubing glued together in a 2x2 square array were used instead and slid into the aft body tube after slathering with ample 5-minute epoxy.

Approximately 1/4" of the cluster array was left protruding. No motor stops or motor hooks were used; retention was by friction fit using bits of masking tape and by wrapping the protruding aft 1/4" of the motors and protruding aft 1/4" of the motor tubes with masking tape before launch.

It is important to seal the five open spaces between the motor tubes and the hull with bits of cotton soaked in wet epoxy to insure ejection charge pressurization. For balance, the nose cone had 25g of epoxy and fishing sinkers added as ballast at the tip--don't omit this step!!

Use plenty of extra wadding (or better yet, a small Nomex pad) when flying to protect that chute from the heat of 4 ejection charges!! Final flying weight is 85g.

If desired, both the scale and cluster requirements of the NARTREK Silver program can be satisfied with this rocket (separate flights needed) by finishing in scale colors and using the kit decals; for maximum scale points, the boattail can be loosely attached over the 4-13mm motor cluster for "judging". All in all, this is about the cheapest, simplest and fastest building 4-motor cluster model that I know of. It easily goes together in less than an hour with epoxy and including painting. Of course its main reason for being built is to fly the NARTREK Silver requirement (a cluster rocket having 3 or more motors). Besides, there just aren't any inexpensive kits of this type available nor few scratch cluster designs that qualify (a few are my "2BZ", "Funnel Vision" and "Cheap Dumb Rocket" on this website). Altitude performance is identical to the stock C6 powered Estes Bullpup, 700' or so, although the "C12-4" powered "Silver Bullpup" sure gets there a lot faster!!

Finishing:
Model was finished with a single coat of silver spray paint.

Flight:
The ship is designed exclusively for A3-4T motors and it should fly well even on only two of these. I don't recommend substitution of A10-3 motors (equivalent to a C40-3!) unless you want to see a shred. Ignition was done with a clip whip--it works every time and you can check continuity on each motor with this setup.

First flight was perfect: straight, incredibly fast boost to 600-700', and with ejection right at apogee.

Recovery:
Despite lots of extra wadding, my wife's brand-new, shocking pink 9" Top-Flite chute was scorched black and holed by the ejection blast.

Summary:
PROs:

• This is the fastest kit to build that can be used for the NARTREK Silver badge.
• Small 13mm motors make this good for junior flyers and/or small fields.
• Good flying qualities

CONs:

• Added complexity of cluster flight
• No real advantage over the great-flying stock Estes Bullpup (except you can toast a C6-powered Bullpup in a drag race)