Brief:
This is an AeroTech Mustang fin can with longer carbon fiber body.

Modifications:
After an incident involving high speed soil mechanics, I had previously modified an AT Mustang by extending the body (see mod article "MOOSEtang"). After several successful flights, it again suffered a top soil overdose and provided me with yet another opportunity to improve it. I had been making carbon composite tubing and decided to rebuild it using this. I obtained a 34" piece of coupler stock for AT 1.88" tube to use as a mandrel and used 3 feet of 2" nominal diameter seamless carbon fiber sleeve from Aerosleeve to lay up a 30" AT size body tube.

The Mustang body was crushed down to the forward centering ring, leaving less than 2" of original body above the ring. This was clearly not enough surface area to anchor a coupler to. After the carbon tube was cured and finished, I removed it from the mandrel and cut 4" off of it to use as an internal coupler. At this point I replaced the shock cord with 8' of new 9/16" tubular nylon and a 2" diameter fiberglass mat ejection protector. With the coupler glued into place, I epoxied the carbon tube onto it and set it in a piece of angle iron to make sure it dried straight. I then took a 12" piece of regular AT 1.88" body tube, slit it down one side, and glued that over the fin can/carbon tube joint, with this external coupler extending down to the tops of the fins. This was clamped in place with several heavy rubber bands while curing. Due to the thickness of the external coupler causing the rocket to bind on a launch rod, the forward launch lug was removed and reattached at the top edge of the external coupler. The original Mustang nose cone, miraculously unaffected by multiple prangs, was tied in place on the end of the shock cord.

Construction:
Parts used:

• AeroTech Mustang fin can from forward centering ring down, including motor mount, baffle, and recovery
• 12" of 1.88" diameter AeroTech tube
• 30" of 1.88" diameter carbon-epoxy composite tube
• AeroTech Mustang nose cone
• 8' of 9/16" tubular nylon

Finishing:
The carbon tube was finished before construction. After the initial epoxy lay up was cured, it was given a second coat of epoxy. After curing, this was wet sanded (220 grit) and coated with urethane. This layer was wet sanded (320 grit) and a second coat of urethane put on. After drying, the tube was covered with Minwax Polycrylic clear acrylic coating, then wet sanded with 400 grit. This was repeated with 600 grit. Two final coats of acrylic were rubbed on with a lint-proof towel.

The fin can was repainted using Rustoleum appliance epoxy. The external coupler was painted with aluminum paint and covered with acrylic when dry. The nose cone was given two coats of acrylic to polish and protect it.

Flight:
Test flight was on an Ellis Mountain F20-8 24mm SU motor. Simulation showed apogee at 950' and coming 1.5 second before ejection. The boost was quick and initially straight. Due to high winds the rocket weathercocked upwind at around 30 degrees and the apogee was significantly lower and earlier than normal.

Recovery:
The rocket was more than half way back down before ejection. Despite deploying at high speed, no zipper occurred in the carbon tube. The High tech Chutes CR-3 parachute handled the deployment and brought the rocket down safely and gently the last 100 feet.

Summary:
Despite being lighter and thinner walled that the original body tube, the carbon tube seems to be far more zipper resistant. I have had carbon tube zipper in other applications but it was only single coated with epoxy and the shock cord was Kevlar® cord. Even so, the zipper was only 1/2" long. Properly treated, carbon composite is a superior body tube. Although the surface treatment of urethane plus acrylic requires more work than painting, the result is well worth it.