Editing Hybrid-propellant rocket (section)

====Cast====
Hybrid rocket fuel grains can be manufactured via casting techniques, since they are typically a plastic or a rubber. Complex geometries, which are driven by the need for higher fuel mass flow rates, makes casting fuel grains for hybrid rockets expensive and time-consuming due in part to equipment costs. On a larger scale, cast grains must be supported by internal webbing, so that large chunks of fuel do not impact or even potentially block the nozzle. Grain defects are also an issue in larger grains. Traditional fuels that are cast are [[hydroxyl-terminated polybutadiene]] (HTPB) and paraffin waxes.<ref name="stratasys">{{cite web |title=Hybrid rocket engines use additive manufacturing to combine the advantages of solid and liquid propellants |website=Stratasys |url=http://www.stratasys.com/resources/case-studies/aerospace/rocket-crafters |access-date=December 19, 2016 |archive-date=July 5, 2017 |archive-url=https://web.archive.org/web/20170705085309/http://www.stratasys.com/resources/case-studies/aerospace/rocket-crafters |url-status=dead }}</ref>