Facebook crossed yet another milestone with its massive, solar-powered Internet drone, Aquila, completing its second test flight and landing perfectly in May. The social media giant detailed the aircraft's latest flight in a blog post and outlined the modifications they made following its inaugural flight in June 2016 during which it suffered a "structural failure" due to a powerful gust of wind and crash-landed in Yuma, Arizona.
Based on the lessons learned during Aquila's first test flight in June last year, Facebook said the crew added hundreds of sensors to collect new data, "spoilers" to the wings to increase drag and reduce lift during the landing approach, modified the autopilot software and included new radios for the communication subsystem.
The team also installed a horizontal propeller stopping mechanism to support a better landing as well.
During its second test flight early on 22 May, the aircraft flew for 1 hour 46 minutes over the desert and rose to a flight ceiling of over 3,000 feet. The crew noted that its climb rate the second time around was 180 ft/min, nearly twice as fast as on its first flight.
"We attribute this to the numerous refinements to Aquila — especially a smoother finish — that were based on learnings from our first flight", Facebook's director of aeronautical platforms Martin Luis Gomez wrote.
He notes that the second flight was "all about the data" for the team, particularly to help the crew tweak their aerodynamic models used to predict energy usage and optimise for battery and solar array size.
The solar-powered drone flies autonomously except in cases where manual intervention is needed such as lining up with the wind.
Just a few seconds before landing, the aircraft's autopilot stopped the propellers as planned to lock them horizontally and prevent them from getting damaged while touching down.
"In this flight, the motors all stopped, but only one propeller locked horizontally," Gomez said. "The aircraft settled onto the landing surface very gently and came to a stop in about 10 meters. It was absolutely perfect. Similar to driving a car on a gravel surface, landing a plane on gravel causes a few minor, easily-repairable dings, but otherwise, Aquila landed in great shape."
The team plans on using the lessons learned in the second flight to continue tweaking the nearly 900 pound (408 kg), carbon fiber aircraft. Facebook aims to eventually fly Aquila drones for up to 90 days at a time and provide internet access within a 60-mile area on the ground.
"No one has ever built an unmanned airplane that will fly for months at a time, so we need to tune every detail to get this right," CEO Mark Zuckerberg said in a Facebook post.
"When Aquila is ready, it will be a fleet of solar-powered planes that will beam internet connectivity across the world. Today, more than half the world's population - 4 billion people - still can't access the internet. One day, Aquila will help change that.