Development of a 2-Dimensional, Variable-Area Nozzle for Small Unmanned Aircraft Micro-Turbojets

This paper presents the design for a variable area nozzle for use on micro-turbojets which may produce between 20- and 500-lbf of thrust. Project motivation includes providing the ability for micro-turbojets to optimize nozzle area for all throttle settings, as well as spoiling thrust for rapid deceleration applications such as short field landings. Furthermore, there is a notable lack of variable nozzles suitable for small unmanned applications. This project aims to create a nozzle which can generate a thrust range independent from throttle control. This nozzle will be useful for reconnaissance or surveillance missions, or for aviation hobbyists. For this study, a JetCat P-100 was selected as a representative micro-turbojet, and a sized analytical model was developed to determine flow areas and design nozzle exit areas. The nozzle should be capable of producing a thrust range of 8-lbf at 80% throttle, while producing, at minimum, 19-lbf of thrust at 100% throttle, ensuring that the nozzle does not hinder stock engine performance. The nozzle is actuated with two servos, connected to two rotating flaps via 2:1 gear ratio. Nozzle thrust is measured via moment-arm loadcell test cell and recorded by Futek SENSIT software, and exhaust gas temperature is measured with a thermocouple. With success, this study provides a simple, affordable nozzle that can be easily implemented on existing micro turbojet engines.