Brief:
The Z7 is a 24mm dual stage sport rocket with sleek but simple design and a beautiful gold/white color scheme. Features a large payload bay and 18" parachute.

Construction:
Sustainer parts list:

• 1 Body Tube BT-60, 18"
• 1 Body Tube BT-60, 8"
• 1 Body Tube BT-50, 3.25"
• 2 Centering Rings, 1/16" Basswood
• 1 Bulkhead BT-60, Balsa 1.5"
• 1 Nose Cone (Estes PNC-60AH)
• 1 Engine Block, 24mm
• 1 Engine Hook (Estes standard size)
• 1 Eye Hook
• 1 Shock Cord 3/16" Wide Flat Elastic, 36"
• 1 Launch Lug 3/16" x 2"
• 1 Parachute, 18" plastic
• 1 Fin Set, 1/8" balsa

Booster parts list:

• 1 Body Tube BT-60, 4"
• 1 Body Tube BT-50, 3.25"
• 2 Centering Rings, 1/16" Basswood
• 1 Coupler BT-60 sized, 1.75"
• 1 Engine Block 24mm
• 1 Engine Hook (Estes standard size)
• 1 Fin Set, 1/8" Balsa

Building the Z7 is pretty straightforward using the RockSim file. Pay particular attention in the placement of the centering rings and motor mount tubes. Placement is critical for these as the booster and sustainer must mate properly. The tube coupler is glued to the booster section and three 1/8" holes are drilled 1/4" from the top of the booster tube equally around the tube (centered between the fins). Apply thin CA around the holes to strengthen them. These vent holes relieve the internal pressure from the booster's burn through and prevent premature separation of the booster from the sustainer. The ends of both motor mount tubes are flush with the rear of the main airframe tubes. The rear of the sustainer fins are flush with the rear of the body tube. The leading edge of the booster fins are 1/4" from the top of the booster body tube. Be sure to carefully measure and align the fins so that when the booster section is attached to the sustainer each set of fins lines up.

Yellow aliphatic glue was used throughout the construction. The double glue joint technique (EMRR fin tip #9) was used on all fins as well as the launch lug and glue fillets (fin fillets as per EMRR fin tip) were applied in two steps (a little bit each time) to provide ample strength and prevent air bubbles.

The shock cord was surface mounted about 2" from the top of the sustainer tube using the Estes tri-fold shock cord mount technique.

Finishing:
Two coats of white primer were applied lightly sanding after the second coat with 400 grit sandpaper. This was followed up with two coats of gloss white. The trim work was then applied by masking off the tube, nose cone and fin tips and spraying gold metallic paint. The trim pattern at the top of the sustainer was accomplished using Pactra Trim Tape. The Z7 decal was designed using Paint Shop Pro and printed on white bumper sticker paper. This paper is rather thick and does produce a raised edge. Papa Tango decal paper could be used to make a more pleasing application. When completed I applied Future Floor Polish for the final finish.

Flight:
The Z7 flies well on the D12-0/C11-7 combination, but for really cool flights use the D12-0/D12-7 motor combination. Since the Z7 was constructed with basswood rings and quality body tubes, she is rather heavy without a payload so I would not recommend using a C11-0 in the booster stage. Since engine hooks were used for both sections, prepping the Z7 is easy. Typical prep includes ample wadding for chute protection and making sure the nose cone fits tight on the payload bay. Once the motors are inserted in their respective motor tubes the booster section is simply slid on and twisted to make sure the fins align with each other.

The Z7 has only flown twice thus far but both flights were fantastic. The Z7 produces a clean staging of sustainer, straight and true.

Recovery:
The sustainer returns nice and slow with the 18" chute and the booster tumbles well. In windy weather, I would substitute a 12" chute, which I have used and seems to have worked well.

Summary:
The Z7 is a relatively easy rocket to build and looks great when finished as described. She flies well with very straight boosts and clean staging of the upper stage. The gap staging makes prep easy and foolproof. The only problem is that the Z7 is a bit heavy and so use of the payload bay is limited.