Lockheed Martin has raised the flight endurance of its Stalker XE from 8h to nearly 13h by using larger propane tanks to supply fuel cells, which charge the battery that powers the aircraft.
"We're still using the same Ultra ANI-based fuel cell," says Lockheed programme manager Tom Coontz. "The change was we simply put in a larger tank, and the Stalker XE was designed from the beginning to hold a larger tank," he adds, referring to a 3.2L liquid propane tank, one liter larger than previous models.
"We're matching the endurance to the mission requirements of our customer."
The Stalker is used in an improvised explosive device detection capacity for the US Army and US Marine Corps in Afghanistan, especially by special operations forces. The battery-powered vehicle is known for its relative silence in flight.
"The feedback has been great," says Coontz. "They haven't asked for any changes to the airframe; they've just been putting hours on it. They're flying it two to three times per day, every single day."
The Stalker has also been used as a test bed for other power technologies, including notably using a laser to recharge its batteries, allowing the aircraft to fly 48h without landing.
Testing will continue once the LaserMotive-built "horse trailer-sized" laser apparatus has shrunk down to something suitably small for tactical operations, which Coontz describes ideally as the size of two travel suitcases put together. Though customers have not formally requested a smaller laser, Coontz says they clearly desire the capability, and that shrinking budgets have led to a "build it and they will come" business case.
Several potential sales abroad are under negotiation, and although Lockheed declines to disclose the potential customers or exact numbers of aircraft they may purchase, Coontz sees a robust market for the aircraft.