Modification - Fat-Ass-Tron Sprint {Modification} Modification

Contributed by Kevin Johnson

Manufacturer: Modification

My own version of the DESCON 5 2nd place winner.

Rocket PicConstruction:
Standard Fat Boy kit contents with a 2 inch paper boat-tail and a long BT-50 motor tube to handle the Estes E9 motors. Made 3 Sprint-like elliptical fins with TTW tabs to take advantage of the Fat Boy's fin slots.

I wanted to fly the F-A-T Sprint at my local field so I modified the design as posted to use a 24mm motor mount. The schematics in Joe's post made it easy to make the new rear centering ring and I used VCP to print my templates. I printed 2 templates on 20lb bond paper then laminated them together with a liberal coating of CA for stiffness.

I also made some custom wire launch lugs by bending some solid core electrical wire around a BIC pen in a long U shape. Then I bent the last 1/4" of the legs 90 degrees. I poked holes in the tube wall and fed the legs through and then used CA to hold them in place.

I had to add about 4 oz of nose weight to make the rocket stable, and the CG is just behind the nose cone.

I had a small gap in-between the BT and the boat-tail and I used Elmers Fill'n Finish to fill it in. I also soaked the fins with CA and sanded them down to a streamlined shape. I probably won't use the CA soaking again as sanding the fins afterwards was a pain in the rear.

I painted the model with flat white spray paint (Painter's Choice brand by Rustoleum) and then sprayed the nose and 1 fin with fluorescent yellow. I copied the logo from the DECSON 5 entry and printed it our as a 1.5" circle, then colored in the white areas with a yellow highliter to match the fin. I glued the logos on with a glue stick then gave the rocket a coat of clear gloss.

I flew my F-A-T Sprint at the Feb Fat Boy launch held by NARHAMS. The 1st flight was on a C11-5 and since I didn't use a motor hook, retention was accomplished by friction fit. I used a motor block, but it was positioned for the E9. The model took off and flew a stable flight path. Ejection was after apogee and the model was pointed straight down. No damage occurred on landing. For the second flight I loaded an E9-6 and friction fit the motor. The boost was fast and high, the rocket arching over a bit before ejection. Because the rocket was so small compared to the altitude, I thought it was going to fly outside of our launch site, but the streamer brought the rocket down quickly and safely within our park's boundaries.

Both flights were made using 1/4" elastic shock cords with standard Estes paper mounts. The streamers made for quick descents, but with no damage. A good match for the E powered flights. Can't wait to get my hands on an Aerotech F21 for this rocket!

A fun rocket. Definitely turned heads as I was building it at club building sessions. Easily adapted to other motor mounts.

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