Scratch - Fat-Ass-Tron Sprint {Scratch} Original Design / Scratch Built

Contributed by Jim Sekol

Manufacturer: Scratch


 

Fat-Ass-Tron  Sprint
The Fat-Ass-Tron Sprint:

The F-A-T Sprint is a combination of the Estes Fat Boy, and the Astron Sprint. It was originally created to address one of the Fat Boy's inherent design flaws, that being it's inability to contain a 38/720 motor casing. While flying the Fat Boy on 'I' motors is somewhat entertaining, shoving that NC-80B into and possibly beyond the transonic range requires just a little more effort. The extra 2" of length from the F-A-T Sprint's boat-tail is enough (along with all that wasted space in the nose cone) to contain a J-350, and it also provides a subtle improvement (along with the sleek and stylish elliptical fins) to the already outstanding aerodynamic qualities of the original Fat Boy.

While pondering just where the hell the CP of this vehicle might be, it was determined that it might be prudent to research the location with a lower powered model. While it would be simple to incorporate the fins and boat-tail into a stock Fat Boy kit, the version illustrated here is slightly more ambitious, intended for 29mm single use motors. 

F-A-T SPRINT LONGITUDINAL SECTION

The BT-80 supplied with the kit does not seem likely to withstand repeated applications of 'G' motor thrust, and the forces of high velocity 'chute deployments. Glassing might help, but would also build up the OD of the tube and create a mismatch with the nose cone. In this design, the base of the nose cone shoulder is removed, allowing a heavier internal tube to extend into it, providing additional room to contain the recovery system, improved resistance to zippering, and increased strength.
Exploded View
Diagram

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