Upgrading the SR-30 Miniature Turbojet for Adaptable Exhaust

The California Polytechnic State University, San Luis Obispo (Cal Poly, SLO) Aerospace Department is requesting a variable nozzle adaptation for their SR-30 turbojet engine. The nozzle is intended for laboratory use in sophomore and junior level courses to supplement instruction on the effects that exhaust behavior has on the performance of propulsion technologies. Topics covered during a performance study of the SR-30 turbojet engine will include, but are not limited to: Brayton Cycle analysis, turbojet operation in ideal and non-ideal test conditions, instrumentation limitations, and basic nozzle operation. The SR-30 turbojet engine is similar in design and operation to engines used to power full-size jets, but is scaled down in size for practical use in educational laboratories. Current designs for variable area nozzles in the aeronautics industry are tailored for use on large jet engines, rather than small educational engines such as the SR-30 turbojet. Therefore, this senior project seeks to adapt existing technology designs to an appropriate scale, and manufacture a variable-area nozzle that will allow for controlled exhaust-flow restriction. The solution proposed in this document draws on existing fighter jet variable nozzles J85 and F119-PW-100 for inspiration in nozzle flap layout and uses common methods of robotic motion control, including linear electronic actuators and hydraulic actuators. Given the scale of the existing turbojet exhaust pipe, this senior project team, “TurboTRIO”, has determined that a circular nozzle would be difficult to actuate in an accurate, flexible, and durable manner. Similarly, design specifications such as thrust-vectoring capabilities and hydraulic control systems present themselves as unnecessarily complicated for the scope of this project. As such, these were likewise discarded. The proposed design is, consequently, a converging-diverging nozzle with a fixed-area converging duct and throat, and a variable-area diverging duct. The diverging duct will have a rectangular cross-section, and will be composed of two stationary flaps and two independently-actuated flaps controlled via mechanical linear actuation. This design will allow for educational demonstrations and performance analyses of a sonic converging nozzle, supersonic converging-diverging nozzle, and potentially engine thrust vectoring