One of the most difficult challenges in pintle-controlled rocket design is configuring the nozzle so the gas pressure at the nozzle exit is equal to the outside air pressure in order to maximize thrust. Engineers at Stone Engineering Company (SEC) in Huntsville, Alabama, are reducing design time and cost by using computational fluid dynamics (CFD) rather than physical testing to determine the optimum configuration. CFD allows us to look inside our design to gain a far greater understanding than we were ever able to achieve with physical testing results alone in the past. The result is that we can see exactly where flow separation occurs for various nozzle geometries and fine-tune our design to maximize thrust under a wide range of flow conditions.

SEC provides technical support to the U.S. Army Missile Command and Space and Strategic Defense Command in the areas of propulsion and structures. The company has extensive "hands-on" experience in the analysis, design, development, and testing of solid, liquid, hybrid, and gel propulsion systems, metallic and composite structures, and gas generators. Extensive capabilities in structural analysis, ballistic prediction, combustion instability analysis, as well as an in-depth understanding of the requirements for today's systems place SEC in a position to move forward in our fields of expertise. One of our most interesting current projects is a bipropellant gel rocket engine that uses an axial pintle to control the throat area and hence the motor thrust. The use of the movable pintle to control the throat area provides the potential to promote higher efficiency in the lower-thrust sustain phase of the motor burn, and provides a flexible response to the requirements of the application.