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HTPB has also been used before. Literature suggests that it is more suited for high-G flights where case adhesion is paramount. HTPB used as a liner should be around 50% solids for strength, with carbon being the primary additive, with TiO2, fiber, zinc borate, and other additives potentially useful. A plasticizer is also strongly suggested for HTPB based liners to improve casting performance. Chemical etching can significantly improve liner adhesion to the aluminum case, as can other binding agents. A suggested etchant is Chemloc. Use IPDI as a curative to allow for a slower reaction and provide time for the propellant to cure into the liner matrix. The propellant is slightly mobile in the liner.
Discussion with Zach B. lead to the discovery of the industrial use of a 'primer' to improve chemical bonding between the 'insulator' (traditionally called the liner by the team) and the 'liner' (traditionally called 'casting tube' on the team). Note that the conflict between amateur and industry nomenclature can lead to confusion when reading literature.
Motor Design
Charlie G. designed the following motor profile.
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