February 2011 Navy
By Teng K. Ooi, Ph.D., LT, USN
Dr. Teng K. Ooi, an Office of Naval Research (ONR) Science and Technology (S&T) Unit 102 Reservist, in collaboration with The Pennsylvania State University’s Applied Research Laboratory (ARL), API Defense (formerly Kuchera Engineering), and Jadoo Power (Jadoo), recently conducted a post-flight analysis of the Naval Air Systems Command (NAVAIR) Mako Unmanned Aerial Vehicle (UAV) fuel cell bipolar plates. The new lightweight aerial fuel cell system was previously flight tested as the power source for the avionics and payload on a NAVAIR Mako UAV at the U.S. Army Yuma Proving Ground. This project is sponsored by ONR Code 31 for NAVAIR. The ONR Program Manager is Dr. Michael Duncan and the customer is Dr. Chyau Shen, Deputy Director, Special Surveillance Program, NAVAIR 4.5X.
The fuel cell was designed and built by Jadoo using commercially available hardware, a lightweight fuel cell stack, and associated packaging components. The fuel cell uses one of the most promising hydrogen fuel cell technologies, i.e., the Polymer Exchange Membrane Fuel Cell (PEMFC). With the aid of an electrolyte, the fuel cell converts hydrogen gas (fuel) and oxygen gas (oxidant) from the air to produce electricity. Water is the byproduct of the reaction without any production of air pollutants.
Intended as an alternative UAV energy source, the fuel cell was integrated into the Mako UAV. This UAV was manufactured by L3 Communications/Battlefield Air Interdiction (BAI) Aerosystems for NAVMAR Applied Science Corporation. The Mako UAV weighs approximately 110 pounds with a wing span of 12’ 11” and has a proven history of reconnaissance and surveillance flight missions during Operation Iraqi Freedom. The Mako UAV was selected as the test platform since it is low cost and highly respected by the U.S. Special Operations Command field personnel.
API Defense developed and executed the plan for fuel cell integration into the Mako UAV. Once the integration and ground tests were complete, a flight test was conducted at the U.S. Army Yuma Proving Ground in Yuma, Arizona, on 13 August 2009. The flight test successfully demonstrated the airworthiness of the fuel cell to withstand launch, trajectory accelerations, landing, and the effects of the operational environment while producing constant power to the payload and avionics.
After the successful flight test, additional post-flight analysis was necessary to validate the absence of any internal damage that may have occurred as well as to inspect the fuel cells for any signs of degradation or corrosion. Any signs of damage would result in a redesign of the system. The system consists of fuel cells combined to form a fuel cell stack. The metallic bipolar plates connect one fuel cell to another and are subjected to oxidizing, reducing conditions and potentials. Metallic bipolar plates are susceptible to corrosion which can decrease the fuel cell energy conversion efficiency. Due to this concern, a post-flight analysis was performed on the fuel cell plates. The system was disassembled for the subsequent inspection of its plates for the presence of any micro-structure defects by Scanning Electron Microscopy (SEM). The plates’ electrical and corrosion resistance were also measured to determine if there was any deterioration in the material properties.
“Post-flight test results proved the absence of any measurable degradation in material properties for these fuel cell plates,” according to Dr. Timothy J. Eden, Head of the Material Processing Division, Applied Research Laboratory, The Pennsylvania State University. “The test validated that the metallic bipolar plates have superior corrosion resistance compared to alternate systems. As a result, the fuel cell life will be significantly improved.”
The new fuel cell system offers greatly improved power density and is lighter in weight when compared to conventional battery systems with the same volume. Moreover, the fuel cell cartridges can be refueled or replaced at a much lower cost compared to the conventional battery systems.
“This results in substantial cost savings and also eliminates the cost and challenges associated with the disposal of conventional batteries,” said Dr. Eden. “The fuel cell with external fuel canisters has the potential to double the payload run time compared to a conventional battery system.”
Combined with high energy density and the use of hydrogen as its fuel, the fuel cell system is preferable to competing products due to its safety, reliability, increased energy-efficiency, and costeffectiveness. With regards to the functionality and ease of installation, the Mako UAV fuel cell system delivers a lightweight and globally-available power source that modern Sailors and Soldiers can easily use in the field.
“Additionally, this fuel cell technology supports the Navy’s green energy approach, where the fuel cell technology provides a route to clean and efficient energy that is environmentally friendly,” said LT Teng Ooi, Officer-in-Charge of this project. “Green energy minimizes any negative impact from energy use on the health of humans or the environment in the short or long term and governs systems whose byproducts can be reintegrated into the environment. The fuel cell is clean during use because the chemical reaction that takes place in the fuel cell generates electricity and produces water vapor without air pollutant byproducts. This technology may also reduce our reliance on fossil fuels for supporting future Navy operations and missions. Furthermore, this fuel cell technology serves as a tool for the Navy to build its fleet for the future.”