Aquila in flight over Arizona. Image: Facebook
Facebook’s giant drone takes to the skies, heralding a future of affordable broadband for potentially millions of people.
About a year after its maiden flight, Facebook’s broadband-emitting Aquila drone, which has the wingspan of a Boeing 737, recently undertook its second successful journey.
Facebook said that the drone completed the flight on 22 May at Yuma Proving Ground in Arizona.
‘Connecting people through high-altitude, solar-powered aircraft is an audacious goal, but milestones like this flight make the months of hard work worth it’
– MARTIN LUIS GOMEZ
Made in an industrial estate in Bridgwater, UK by a company Facebook acquired called Ascenta, the plan is to serve the world with broadband and Wi-Fi using aerial drones that stay airborne at around 60,000ft.
Aquila has been modified considerably since its first flight last year.
The Facebook team added spoilers to the wings to help increase drag and reduce lift during landing. It now has a smoother finish and a horizontal propeller-stopping mechanism to support a successful landing. The updated Aquila also incorporates hundreds of sensors to gather data as well as new autopilot software and radios for the communications subsystems.
On a wing and a prayer
At 5.27am on 22 May, as the sun crept over the horizon, Aquila took off and flew for one hour and 46 minutes before making a perfect landing.
“Take-off was normal,” recalled Martin Luis Gomez. “It also quickly became apparent that all the systems were functioning normally: the motor current, the airspeed tracking, the heading tracking, the radio links and the differential GPS all showed nominal behaviour.
“The only surprise was a happy one: the climb rate – at 180ft per minute – was nearly twice as fast as on our first flight. We attribute this to the numerous refinements to Aquila (especially a smoother finish) that were based on learnings from our first flight.”
The solar-powered plane climbed to 3,000ft and moved at 10-15 miles per hour – the recommended speed to keep it hovering in an area to supply broadband to the ground for long periods of time. The efficient plane runs at the power equivalent of three blowdryers.
Gomez said that the second flight was all about data.
“We flew lengthy test points at constant speed, heading and altitude to measure the aeroplane’s drag,” he explained.
“The data from these ‘trim shots’, as they’re called, will be used to refine our aerodynamic models, which help us predict the energy usage and thus optimise for battery and solar array size.
“We also undertook extensive instrumentation of the aeroplane’s structure, adding hundreds of sensors to the aircraft to understand how Aquila’s shape responds to flight in real time. These included hundreds of strain gauges and three-axis inertial measurement units. These tools serve to verify and refine our structural model, which predicts both the static shape of the aeroplane – designed to be very flexible to respond to wind gusts and manoeuvres.
“Throughout the flight, we also continued to verify the drag created by new ‘spoilers’ that we added to Aquila at various angles. Spoilers are movable surfaces on the wing of an aircraft that help create drag to reduce speed and decrease lift. We also tested the two radio links’ signal strength from various aspect angles. After testing the landing algorithm with an elevated landing, we committed the aeroplane to a complete, successful landing on the designated site.”
Posted by Facebook Engineering on Thursday, June 29, 2017
A bird never flew on one wing
Interestingly, the Aquila aircraft has no landing gear. Instead, it lands on Kevlar pads bonded to the bottom of motor pods.
When landing, the Aquila follows a three-degree path – or glide slope – and it comes to a stop in about 10 metres, taking advantage of drag, the staunch ally of landing.
“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,” Gomez said.
The graceful landing is in contrast to last year’s first flight where the drone’s right wing snapped off.
“Connecting people through high-altitude, solar-powered aircraft is an audacious goal, but milestones like this flight make the months of hard work worth it,” Gomez said.
“And what is particularly gratifying is that the improvements we implemented based on Aquila’s performance during its first test flight made a significant difference in this flight.
“In the coming months, we’re excited to take the lessons from our successful second flight to continue the Aquila programme’s progress to help bring the world closer together through connectivity.”
