Unmanned air vehicles (UAV) utilize a wide variety of energy sources to power their flight, ranging from solar-powered ultralights to Flight of the Century’s use of flying UAV “battery pods” to recharge its electric aircraft during a trans-Atlantic journey. Researchers over at the U.S. Naval Research Laboratory (NRL) recently announced its results in using fuel-cells to keep its vehicles up the air.

The Ion Tiger UAV, in the NRL’s latest test, used liquid hydrogen (LH2) as fuel to power its 48 hours and 1 minute flight on April 16-18. That beat the plane’s previous record of 26 hours and 2 minutes back in 2009. At that time, the Ion Tiger used hydrogen as a fuel source as well, but in its gaseous state. Since liquid hydrogen is three times more dense than in its gas form, the UAV, not surprisingly, had more energy to draw upon.

States Dr. Karen Swider-Lyons, principal investigator over at the NRL: “Liquid hydrogen coupled with fuel-cell technology has the potential to expand the utility of small unmanned systems by greatly increasing endurance while still affording all the benefits of electric propulsion.”

ion tiger
Image courtesy of the Naval Research Laboratory

The Ion Tiger LH2 flight was developed by the NRL’s Tactical Electronic Warfare and Chemistry Divisions as well as sponsored by the Office of Naval Research. The Laboratory, as it’s also called, had to develop a high quality, lightweight and insulated flight dewar to deal with the Tiger’s cryogenic fuel tank. For future flights, the government organization has proposed building a LH2 generation facility on site.

The NRL has also looked into gas-powered UAVs and pure-electric aircrafts. It has found current gas systems too inefficient, nosy, and unreliable while electric-only UAVs suffer from limited range.

The Ion Tiger is not the only UAV using fuel-cells as a power source. In 2010, Horizon Energy Systems and Elbit Systems successfully completed their test flight of Elbit’s Sklark Unmanned Aircraft System. And we’re a bit surprised researchers aren’t looking for ways to combine the solar-powered techniques from companies like Silent Falcon UAS Technologies with the LH2-powered Tiger. Qinetiq’s Zephyr, for example, flew over 336 hours and 22 minutes (or two weeks) on one of its flights. Is it a weight issue? Technology? We won’t be surprised if the NRL finds solutions to all those issues.

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