A High Useable Energy Density Flywheel System Making Solar-Powered Hale Uav a Realistic Technology

Document Number: 981276

Date Published: April 1998

Author(s):
Dwight Sweft - Optimal Energy Systems
Henry Ramirez - Optimal Energy Systems

Abstract:
Proposed high-altitude, long-endurance (HALE) unmanned aerial vehicle (UAV) concepts for solar-powered aircraft indicate that energy storage devices will be required that significantly improve power, energy density, efficiency, and depth-of-discharge over state-of-the-art electrochemical (NiH\d2) batteries, without which these aircraft systems cannot become a reality. Flywheel energy storage systems offer the potential for making these systems concepts practical. However, current concepts for flywheel energy storage systems rely on energy conversion and power generation approaches that limit the available energy for aircraft use to near 60% of the fully charged capacity of the flywheel, with efficiencies below 90%. With useable specific energy capacities below 50 Whr/kg, these systems are incapable of enabling solar-powered HALE UAV technology.

In this paper, the performance of a high-powered, ultra-low loss, "ironless" motor/generator design is outlined as part of a supercritical self-balancing flywheel energy storage module (FESM). The super high-speed "ironless" generator design enables a 99% energy conversion efficiency and a 90% depth-of-discharge (DOD). The design approach outlined combines th ironless stator design with a supersonic magnet array (\mg Mach 1.5) to achieve a cruise power output of 9 kW for 10 hours, and peak power output capability of 275 kW over the full range of the module. Analytical trade studies indicate stator power losses well below 10's of watts at cruising power, with maximum losses of 4 kW associated with 275 kW pulse output at minimum generator speed. Stress analyses indicate critical components affecting energy storage capacity are flywheel hub stress, hub-to-rotor interface stresses, and magnet contact stresses. Analysis indicates a low stress flywheel hub approach provides a flywheel specific energy of 120 Whr/kg, and unit specific energy of 84 Whr/kg. Electromagnetic analyses indicate useable specific energy of 75 Whr/kg, which is enabling for HALE UAV technology

Product Status: In Stock

See other papers presented at Aerospace Power Systems Conference, April 1998, Williamsburg, VA, USA, Session: UCAV/URAV Power Technologies II

Purchase more technical papers and save! With TechSelect, you decide what SAE Technical Papers you need, when you need them, and how much you want to pay. Learn more >