Brief:
This is a fatter Fat Boy. It has the same body tube length but 42% more diameter.

Construction:
The nose cone is a resin covered Styrofoam egg from Hobby Lobby. The body tubes are Bristol paper printed with an ink jet printer and then rolled to shape. The fins are 3/32" balsa. Finally, there is a 1/4 inch elastic shock cord and mylar parachute.

This rocket has an egg-based nosecone. Hobby Lobby has 3.875" diameter Styrofoam eggs. They're open cell Styrofoam so they don't totally dissolve when you pour resin on them. In this case, I hand-rotisseried 20 minute marine resin on an egg, followed by a half-and-half mix of auto body filler and marine resin to build up the thickness. It wound up being 0.125" to 0.25" thick. As it cured, the Styrofoam inside pulled away from the resin allowing it to be easily removed. The inside is very rough, but that's good because it allows plenty of space to epoxy a bent paper clip for shock cord and parachute attachment. After much careful sanding, I had a fairly nice nose cone. I didn't have to add any more weight for stability.

The body tube was rolled with Bristol paper printed on a 13" x 19" ink jet printer. There are fin slots printed on it for the through the body fin roots. It has a BT-60 sized rolled Bristol inner parachute body tube (also on the PDF) that juts almost all the way up into the nose cone. (I couldn't figure out how to do this in RockSim so I left it out.) This inner tube adds needed extra space for the parachute while at the same time reducing the need for wadding. Inside the parachute tube is the 24mm engine tube. The 4 bulkheads are foamboard. The forward-most bulkhead is positioned just past where the nosecone shoulder stops in order to have a rigid platform for the heavy nose cone to rest against during high acceleration.

The nozzle end of a mounted E9 motor is recessed 1.75 inches from the end of the outermost body tube in order to achieve stability. Two more compromises to the god of stability were made with the fins. First, birch plywood would be the most obvious material choice, but the weight then shifts the CG so far back that the added nose cone weight makes for too slow of a liftoff with a reasonable length of launch rod, so they had to be made with balsa. Second, they had to be visually swept back and longer than the fins on the Fat Boy.

The swept fins and the proportional nosecone gives in an overall increased length of 3.35 inches over the Fat Boy, but rocketheads still get it immediately. (If you kept the exact Fat Boy nose cone length, it would look awfully flat... Flat Boy maybe would be a better name.)

Gotchas: The hardest part of this project was getting a good nose cone shoulder. I wound up making a tube in which the nose cone fit tightly to mark a shoulder step down. Next, I ground a shallow slot along the line with a cutoff wheel on my Dremel tool, then carefully used a sanding cylinder to sand away the shoulder up to the slot. It turned out pretty good. The through-the-body fin tabs straddle the rearmost bulkhead, which makes for a strong joint but requires careful measuring and gluing. Also, the Bristol paper really sucks up clear enamel. Mine has three coats and is still a couple of coats from being glossy.

Finishing:
With the printed Bristol paper, only the fins needed any sealing or finishing.

Flight:
Recommended engines are D12-3, E9-4, and F21W-6. Engine retention is by friction fit. Prep is straightforward with wadding and a 21 inch chute. Flight with an E9-4 is beautiful, slow, and straight with no spin. Apogee appears to be close to the RockSim prediction of 700 feet.

Recovery:
On the first flight all but a couple of the shroud lines on the parachute broke (at a fairly high velocity into the wind) but there was just a little wrinkling of the fore end of the inner parachute tube upon landing.

Summary:
This is a fun rocket with presence that flies slow and gets some chuckles. I love through the body fin mounts with pre-printed body tubes... They almost totally eliminate spin. Nose cone fabrication takes some time.