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Lightweight Turbogenerator for Vertical Take-off and Landing Unmanned Aerial Systems- in Marine Environments


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Trusted AI and Autonomy;Integrated Network Systems-of-Systems OBJECTIVE: Develop a lightweight (prioritizing weight above efficiency) integral turbogenerator in a compact package intended for embedded integration into a Vertical Take-off and Landing Unmanned Aerial System (VTOL UAS) for support of high-power conditions on takeoff and landing. DESCRIPTION: Current VTOL UASs in development, and concepts being pursued by both commercial and military operators, require high-power delivery on takeoff and landing segments that can be delivered by small turbogenerators also in development. At small scales, around 50 shaft horsepower (shp) output, turbines with centrifugal compressors can provide high specific power but are typically less efficient than equivalent power reciprocating engines. Fabrication of turbines without the need to couple to a low-spool shaft for thrust generation, and instead coupling to a high-speed generator, can provide a path toward delivering high power levels during VTOL mission segments. New hybrid power architectures and electrical components can then support a serial or parallel propulsion system that could leverage the very low Brake Specific Fuel Consumption (BSFC) of the primary reciprocating engine, and provide additional power via a small lightweight turbogenerator that could generate sufficient power for the short-segment VTOL maneuvers, with much lower requirements on specific fuel consumption due to the short (on the order of one minute) durations involved. Modifying the cycle of a turbogenerator to optimize the design for high power output without concern for SFC could simplify the design as well as reduce the cost of the unit by lowering aerodynamic design tolerance requirements, and reducing the thermal cycle requirements in terms of pressures and temperatures, as well as simplifying the mechanical design without the need to couple a low-speed turbine to generate thrust. KEY SMALL AUXILIARY LIGHTWEIGHT TURBOGENERATOR ENGINE (SALT-E) PARAMETERS • Multi fuel operation on F-24, JP-8, JP-5, Diesel • Specific fuel consumption not to exceed 3.0 lb / hp-hr while operating at maximum design power level at 15,000 ft MSL STD day • High specific power > 2.0 shp/lb turbine output (Threshold), 4.0 shp/lb (Objective) including the generator system (does not include power control unit or fuel system) • System must include integral generator operating at peak efficiency of > 90% • Cold, electric remote start capability (-20°C) without ground support • Capable of operating in marine environments for sea-based operations • System should include air bearings to allow for oil-free operation and that include material systems that are marinized and capable of operation in sea-based environments with a time between overhaul (TBO) target for the design of >1500 hrs • Recuperators should be included in the design to increase BSFC (lbm/hr/kW-electric output) at an appropriate effectiveness (target minimum of 70% effectiveness) and weight • Recuperator temperatures that can support turndown to power level angles (PLA’s) with an objective of 30% • Capability of high specific temperature materials for the turbine wheel should be included • Multi-orientation capability: 10 minutes continuous operation at maximum power with a change in orientation of 90 degrees from about a horizontal axis without degradations to operability, durability or shaft power output. • Demonstrate a minimum of 150 hr durability for initial test articles • Must be capable of continuous operation at peak load for 24 hours • Unit must be capable of a minimum of 14 shp output (at the turbine shaft) and not more than 60 shp at sea level standard day conditions PHASE I: Develop a test unit turbine section with a measured output of 14 - 60 shp continuous power output with a specific power of >2.0 shp/lb for the turbine system. System should include design and consideration of air bearing material systems and designs compatible with marinization requirements for operations in salt spray environments. PHASE II: Integrate the turbine with the generator and demonstrate a fully integrated electrical machine capable of operations with simulated load profiles with controlled power output for supporting a VTOL hybrid power system. The combined unit should demonstrate continuous performance for up to 12 hours with logistical fuels. PHASE III DUAL USE APPLICATIONS: Demonstrate the unit in a VTOL UAS flight test asset in a hybrid power system demonstration. Ground testing in an altitude cell will confirm altitude capability up to 15k ft MSL altitude. Flight testing will demonstrate the controllability of the unit and the viability of the hybrid power architecture. Multiple commercial entities are developing, and have interest in small VTOL UAS for delivery of medical and other supplies to remote areas. Several capabilities exist that are less robust, and less capable than what a power turbine could enable in terms of payload and range capabilities, and in inclement weather. Likely there would be significant commercial interest in the technologies and capabilities developed in this type of power unit for both UAS and portable ground power applications. REFERENCES: 1. Cinar, G.,Markov, A., Gladin, J., Garcia, E., Marvis, D., Patnaik, S. (2020). Feasibility assessments of a hybrid turboelectric medium altitude long endurance unmanned aerial vehicle. AIAA Propulsion and Energy 2020 Forum. 2. Pamireddy, S. R. (2020). Comparison of power sources with scalability effects for rotorcrafts (Order No. 28149981). Available from ProQuest Dissertations & Theses Global. (2503638599). Retrieved from 3. Avera, M., & Singh, R. (2019, October). Scalability of Hybrid-Electric Propulsion for VTOL UAS. In Proceedings of the NATO Research Symposium on Hybrid/Electric Aero-Propulsion Systems for Military Applications, Trondheim, Norway (pp. 7-9). KEYWORDS: Turbogenerator; turbine; generator; recuperator; vertical take-off and landing; VTOL; hybrid; propulsion; hybrid-electric; hybrid propulsion; unmanned aerial system; UAS
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