Facebook's Aquila internet drone recently completed its second full-scale test flight, and this time the aircraft had a smooth landing.
The test flight took place on May 22, but Facebook only shared details on Thursday.
"The aircraft flew for 1 hour and 46 minutes, and landed perfectly on our prepared landing site," Facebook's Martin Luis Gomez wrote in a post on the company's engineering blog. Check out a video of the successful landing below.
This test was an improvement from the first flight, during which Aquila experienced a "structural failure" as it was coming in for a landing and crashed in the Arizona desert, causing the US National Transportation Safety Board to investigate the incident.
To prepare for this second test flight, the Aquila team made a number of modifications to the aircraft, taking into account the lessons they learned from that first trip, Gomez wrote. They added "spoilers" to the wings, for instance, to increase drag and reduce lift during the landing approach. They also modified the autopilot software, applied a smoother finish on the plane, added hundreds of sensors to gather new data, and installed a "horizontal propeller stopping mechanism to support a successful landing," he added.
The team also prepared a 500-foot circle of level gravel, about 6 inches deep on which Aquila would land.
"Aquila flies autonomously, with the exception of manual interventions in cases such as lining up with the wind," Gomez wrote. "Shortly before landing, the flight crew uploads a landing plan based on the wind direction."
A few seconds before landing, the plane's autopilot killed the propellers, as planned. This happens so the propellers can be locked in a horizontal position so they're not damaged when the aircraft touches down. In this test flight, "only one propeller [out of four] locked horizontally," as it should have, Gomez wrote. Still, he said, the "aircraft settled onto the landing surface very gently and came to a stop in about 10 meters."
Gomez called the landing "absolutely perfect," but admitted that Aquila suffered a "few minor, easily repairable dings" from the gravel.
The drone has the wingspan of a commercial airliner but only runs the power equivalent of three hair dryers. Facebook says it will eventually fly for weeks at a time, beaming internet signals up to 60 miles away.
"By design, Aquila does nothing fast: It climbs slowly, descends even slower, and when flying upwind moves only at 10-15 mph over the ground," Gomez wrote. "We designed Aquila this way because it is meant to stay in the same area for long periods of time to supply internet access."
Going forward, Facebook plans to use the data it collected from this flight to further refine the aircraft.