As the aviation adage goes, all take-offs are optional but all landings are mandatory. Landings just became a little less mandatory, thanks to government research.
Scientists at the Naval Research Laboratory recently shattered their own UAV endurance record by flying an Ion Tiger UAV for 48 hours and 1 minute without landing.
The record-breaking UAV was powered using liquid hydrogen fuel in a new cryogenic fuel storage tank and delivery system.
The April 16-18 flight nearly doubled the previous record of 26 hours and 2 minutes, set by the same team with the same UAV four years ago.
“We have been able to drastically improve the endurance of an electric vehicle to multiple days through implementing hydrogen fuel cell technology in place of batteries,” said Karen Swider Lyons, head of the Chemistry Division in NRL’s Alternative Energy Section.
Lyons told Homeland1 the ability to achieve long endurance flight clearly shows the benefit of fuel cell technology.
A number of military and homeland protection applications could benefit. Any mission requiring long duration flight such as border surveillance, ship tracking, or communication chores could likely exploit this technology.
“For unmanned systems, the increase endurance is necessary to enable scenarios where UAVs are always on station, such as for persistence surveillance and communication relays,” Lyons said.
Increased UAV endurance also means fewer take off and landing cycles, which saves wear on the vehicle.
“Being unmanned also keeps the warfighter out of harm’s way,” Lyons said.
The craft achieved the new flight record by using a fuel cell to convert hydrogen into electricity. Lyons said the challenges were to make a high power-to-weight fuel cell, a storage tank with high hydrogen storage capacity, and an efficient air vehicle to carry the system.
In 2009, NRL demonstrated a fuel cell from Protonex Technology Corporation with a tank for carrying 5000-psi hydrogen with 12 percent hydrogen gas by weight.
For the recent two-day flight, NRL replaced the tank for high pressure hydrogen tank with a custom dewar for cryogenic, or liquid hydrogen. Lyons said the liquid hydrogen was stored at low pressure and 20 degrees Kelvin, so the tanks are built for maximal insulation, but not high pressure.
“The liquid hydrogen is also denser than the 5000-psi hydrogen, so more can be stored in a smaller space,” she said.