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Highlights of recent developments on the DoubleSShot project
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- Louis Schreyer has completed fabrication of the multi-piece Star mandrel “fins”, and has shipped the parts to Rick Maschek. Craig Peterson has completed the mandrel core and will also be shipping the part to Rick. Once the parts have arrived, Rick will be doing a trial casting to determine if this technique provides a solution to the difficult mandrel extraction problem.
Ben Brockert performed an FE analysis to determine the effect of varying the radius of the star “tips”. Having a larger radius has two consequences: reducing stress concentration, and increasing the minimum web thickness. The objective of this exercise was to determine what tensile strength the propellant would require to withstand a pressure differential (between core and outside of grain) of 1000 psi (6.7 Mpa). The radii Ben considered were 0.125, 0.15, and 0.175 inches.
http://sugarshot.org/downloads/star_core_radiii.jpg
The results indicated that the tensile strength needed for 1x FOS (Factor of Safety) for 1000 psi differential are 5500, 4780, and 4230 psi, respectively. Or at 1.5 FOS, 8250, 7170, and 6350 psi, respectively. For reference, basic KNSB has a typical tensile strength of 1100 psi. Ben pointed out “This is really worst case; a motor built like this could have the nozzle bonded to one end, the other end capped, and could be fired with no casing”.
Ben also noted that “A case bonded motor would require lower strengths if the young's modulus of the casing is higher than that of the propellant”.
- Richard ordered the hardware for the Tensile Testing Rig, which is being shipped to Randy, who volunteered to fabricate parts and assemble the rig.
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-Sugar Shot to Space is on facebook. Check us out.
http://tinyurl.com/2exr92k
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