Facebook's Solar-Powered Drone Under Investigation After 'Accident' (theguardian.com)

Facebook has hit a hitch in its plans to use a solar-powered unmanned drone to provide internet access to developing nations, after it was revealed the American National Transportation Safety Board (NTSB) has opened an investigation into an accident on the drone's first test flight in June. From a report on The Guardian:At the time, Facebook described the flight as "successful": the drone, called Aquila, stayed aloft for 96 minutes, three times the planned duration. "We have a lot of work ahead of us," Jay Parikh, Facebook's head of engineering and infrastructure, wrote when Facebook revealed the test flight, in late July. "In our next tests, we will fly Aquila faster, higher and longer, eventually taking it above 60,000 feet." In a second, more technical, blogpost published that same day, Facebook's Martin Luis Gomez and Andrew Cox acknowledged the failure in passing. "Our first flight lasted three times longer than the minimum mission length, so we were able to gather data on how the structure and autopilot responded under a range of real-world conditions to help verify these predictions," they wrote.Reporter Casey Newton mentioned on The Verge that at the time, Facebook had led them believe that everything was alright, and there were no hiccups.

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missing quote

[sacrilicious]

In a second, more technical, blogpost published that same day, Facebook's Martin Luis Gomez and Andrew Cox acknowledged the failure in passing. "Our first flight lasted three times longer than the minimum mission length, so we were able to gather data on how the structure and autopilot responded under a range of real-world conditions to help verify these predictions," they wrote.

I read that three times trying to figure out whether the "in passing" mention of failure was so subtle that I was missing it. Nope, the editors simply left out the actually relevant quote:

“We are still analysing the results of the extended test, including a structural failure we experienced just before landing. We hope to share more details on this and other structural tests in the future,” Cox and Gomez added.

Re:missing quote

[LenE]

OK, Internet super-engineer. You clearly do not know anything about aircraft or spacecraft structures.

Materials used for small drones have a very difficult time scaling up to very large lightweight structures. Care to expound on the loads and stresses experienced by a 144 foot wingspan wing, that weighs only 900 lbs? This drone was built to be light and barely strong enough. That was its design point. Have you shown the world that you can do better and can credibly criticize their design?

Extremely high aspect ratio wings, like this one, just don't want to quit flying. It is a real challenge to bring it down onto the ground. The pilots possibly exceeded design Vne trying to get it down. This exponentially increases drag forces on the airframe. Ground-effect makes landing even more difficult, and with a 144 foot wingspan, ground-effect starts at ~72 feet above ground.

Add to this the non-homogeneous nature of gusting winds in proximity to the ground, and it is not inconceivable that design limits were exceeded by a fluke of nature. There is not enough public information of what weather conditions existed during landing, but sudden adverse conditions during landing are not unprecedented. Did Lockheed's engineers under-design the structure on the L-1011?

Disclaimer - I work for an aerospace prototyping firm (not related to Facebook), and have worked on things that cover the conceivable gamut of Reynolds numbers that can be "flown". Although I have not worked on Facebook's drone, I have an intimate knowledge of the modern materials used in this air vehicle. My opinions expressed here are my own.

Re:Sturctural Failure

[tsqr]

Are you fucking shitting me? No aircraft designed since 1990 should ever have a structural failure unless the pilot deliberately took it over structural mach. The FAA was grossly negligent to throw away a century's worth of aviation safety experience and just let any fucking idiot put anything in the sky and call it a drone.

Actually, aircraft structural failures, while not common occurrences, aren't all that rare. They sometimes result from, and nearly always end with, an unplanned encounter with the ground. Sometimes they result from a control failure that causes the departure controlled flight. Sometimes they occur due to fatigue. And they happen a lot with uncertified, experimental, developmental aircraft.