Brief:
Hell Bent is a versatile 3FNC SPEV (spare parts equipment vehicle) that can fly on a wide range of motors: anything from a high thrust E or break Mach (according to simulations) on a 38mm high thrust I or J motor.

Construction:
I used the following components to build this rocket:

• 1 LOC/Precision 2.6" plastic nose cone
• 1 9" long x 2.6" diameter paper tubing
• 1 18" long x 2.6" diameter paper tubing
• 1 4" coupler tube
• 1 6" long x 38mm LOC MMT tubing
• 2 LOC/Precision 2.56-1.63 centering rings
• 3 1/8" thick birch plywood fins from U.S. Rockets Warp kit
• 1 1/8" thick birch plywood bulkhead
• 1 screw eye
• 1 elastic shock cord
• 1 paper tri-fold shock cord mount
• 9ft elastic shock cord, 3/8" thick
• 1 8-32 x 1/2" nylon screw
• 2 standard rail buttons from railbuttons.com

A significant portion of these parts I had laying around, and what I didn't have at the time was ordered from U.S. Rockets. I am a big fan of aliphatic resin (yellow wood glue) and have been trying different brands. Elmer's ProBond was used exclusively throughout the entire build except for polyurethane glue to bond the screw eye into the coupler bulkhead and CA to secure the rail buttons into the airframe. I picked up the ProBond after reading about its use in the EMRR Tips Library (click here). I do like that it's thicker and has a quicker tack than most yellow wood glues, although it does seem to take longer to dry when used in larger quantities.

The tubing was the last piece of several pieces of 2.6" tubing that I won in a couple of auctions on eBay. The couplers were acquired the same way except I have a bunch of them left over! I like for HPRs in my fleet to have a payload section, especially now that I have started getting into onboard electronics and would like for it to occasionally carry an altimeter (even though it will most likely not be used for recovery device deployment). That meant cutting the 27" piece of tubing into 9" and 18" pieces. I used a piece of heavy paper to wrap around the tube to draw an even line for marking the tube. I used several passes with a razor utility knife for cutting the tube. An orbital sander smoothed out the cut tubing to ensure that they would mount flush against each other when coupled together.

The motor mount is a 6" long piece of LOC 38mm MMT tubing. I used the same technique to cut it from the long piece in my parts box. I roughed up the tubing with 220 grit sandpaper before gluing and filleting the centering rings on 3/4" from each end. I then glued the MMT assembly into one end of the 18" long tube with about 1/4" sticking out the aft end (to make it easier to remove the motor post-flight).

I used the Fin Wrapper Generator tool in VCP to mark the fin placement. I then cut out the fin slots in multiple passes with a razor utility knife. I rounded the edges on the fins with an orbital sander, trimmed off about 1/8" from each end of the root edge to minimize the gap in the tube for the forward and trailing edges of the fins and then used the "double glue" method to mount the fins one at a time (I found this tip a long time ago in the EMRR Tips Library). After they were dry, I applied 2 layers of yellow glue fillets.

The bulkhead was glued and filleted into the coupler and then the coupler was glued into the payload tube. A dab of Gorilla Glue was put onto the threads of the screw eye before twisting it into the bulkhead.

Five holes were drilled into the tubing. Three were 5/32". Two of those were for the rail buttons in the main airframe and the third was in the payload tube for a nylon screw to hold the nose cone in place. The two remaining holes were 3/32" holes to act as pressure relief vents for both the payload and main tubes.

Coming down the home stretch, nine feet of heavy duty 3/8" flat elastic shock cord was tied onto the screw eye at one end and glued to a cardstock tri-fold paper mount several inches down inside the main airframe tube. A small loop was also tied in the shock cord about 3ft from the nose cone so that I could attach/remove the parachute with a quicklink as needed.

The final step of the build was to screw in the rail buttons, although I actually waited until after all of the painting was complete before doing this. A small dab of CA was put on the threads of the screw on each rail button before screwing them in.

Finishing:
Staying with my standard approach, I started by lightly sanding down the entire rocket with 320 grit sandpaper (actually the nose cone got hit with 150 grit first then 320). The fins received a treatment of diluted Elmer's Fill 'n' Finish, which I have continually improved my ability to spread it with an epoxy squeegee to reduce the amount of sanding I have to do afterwards yet press it down into the wood grain to ensure a smooth finish. With the fins sanded, then comes a couple layers of Krylon white primer. The primer was sanded with a scrub pad equivalent to '000' (fine grade) steel wool after each coat. Once happy with the primed finish, it was time for the final glossy coats.

I kept the paint scheme as simple as the rocket. Krylon Gloss Black was sprayed on the rocket, wet sanded, and sprayed again for a durable finish. Krylon Silver was sprayed on the payload tube and one fin for contrast.

To get the glossy black paint to really shine (but not the silver), I use 3M Rubbing Compound and a couple of pieces of an old T-shirt. Like Mr. Miyagi says, "Wax on. Wax off." Repeat until desired results are achieved. Lastly, I added some chrome automotive pinstriping as well as a West Coast Choppers sticker I had lying around. These highly reflective devices should make it easier to visually track the rocket during high altitude flights.

Flight:
Hell Bent's first flight was on an AeroTech 29/180 H238T-M. I used a 38-29mm motor adapter that came with my U.S. Rockets Sentra SRB 2.7 kit. The motor was inserted into the adapter and a couple wraps of masking tape were put on the forward end of the motor to retain it in the adapter. The adapter and motor were then inserted into the rocket and a hose clamp (found in the plumbing section of my local home improvement store) was tightened onto the aft end of the motor mount tube securing it in place.

The rocket was put on the rail and the countdown was started. Now, I knew it was going to leave the pad quickly but I was frankly stunned as the rocket absolutely vanished off the pad. The nearly smokeless Blue Thunder propellant had everyone in attendance looking in completely different directions attempting to see the rocket. It wasn't until we heard the squeal of my rocket beeper that we were able to hunt it down. The glare of the sun off the payload tube and fin aided greatly in visually tracking the rocket. Whew! That was fast!

My best friend, who is our club photographer, was amazed as anyone there that he managed to capture an in flight picture of Hell Bent.

Recovery:
I clipped on a Nomex heat shield that I move between a number of rockets in my fleet, one of my rocket beepers, and a small 18" nylon chute that came with a kit that I can't seem to remember right now. The chute was the right size for this rocket as it brought it down quickly and safely. Landing on a nice grassy section of the field, there wasn't a scratch on it!

Summary:
At its core, Hell Bent is a robust yet very lightweight 3FNC. The large fins may have a lot of stress on them if a high thrust I or J motor is used but they do guarantee that Hell Bent will be stable without any noseweight regardless of what size 38mm motor is used. That translates into a high performance rocket.