How does the core shape influence the thrust-time curve? The thrust (and chamber pressure) that a rocket motor generates is proportional to the burning area at any particular instant in time. The core shape has a profound influence on the shape of the thrust-time profile, as shown in Figure 2.įigure 2 - Core shapes and influence on thrust curve The core may have a wide variety of cross-sections such as circular, star, cross, dog-bone, wagon-wheel, etc., however, for amateur motors, the most common shape is circular. Usually, a central core that extends the full length of the grain is introduced, in order to increase the propellant surface area initially exposed to combustion. The grain may consist of a single cylindrical segment (Figure 1), or may contain many segments. As a rule, propellant grains are cylindrical in shape to fit neatly into a rocket motor in order to maximize volumetric efficiency. Regardless of the composition, however, all propellants are processed into a similar basic geometric form, referred to as a propellant grain.
An opacifier may be added to absorb heat that may otherwise be transmitted through a translucent grain resulting in unpredictable burning. Curing agents, phase stabilizers, and solvents may be other additives included in small percentages.įor any propellant, additives may control the burnrate, either to accelerate or to slow the rate. Experimental composite propellants, on the other hand, may have a composition that is fairly complex, and may contain oxidizer of various mesh sizes, polymer binder, and even metals such as aluminum or magnesium. Such is the case with the "sugar" based propellants. The propellant utilized in amateur experimental rocket motors may be simple in composition, being comprised of two main constituents - fuel and an oxidizer.
Solid Rocket Motor Theory - Propellant Grain Richard Nakka's Experimental Rocketry Web Site Richard Nakka's Experimental Rocketry Site
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