I’ve had a small, partly-airborne, multirotor SuperTurbine™ operating here pretty-much continuously, and autonomously, for 9 years and counting. I’ve worn out and replaced one set of blades, and have recently noticed significant erosion on the leading edges of the newer blades, suggesting a second blade replacement might be a good idea, within a couple of years. The generator, however, has hung in there with no issues for the full 9 year operational stretch. No burnouts, no new bearings. I’ve been pleasantly surprised at the longevity, which is unusual in wind energy. Most new turbine models, let alone new types of turbine, don’t survive the first good storm, let alone run for almost a decade with no real issues. Well, you gotta get lucky once in a while. 
PS funny but if I see the word “heuristic” or sentences starting with phrases like “Doug overlooks”, I already know who is posting without having to check.
Might want to check with Joe on this, since he is an expert on hang gliders, but what I keep hearing regarding hang glider longevity is a sail is getting old and may be in need of replacement at 500 hours. Then again I know people who buy and fly used gliders with worn-out sails, applying lots of tape and repairs. Someone gave me one after it was really just getting too worn to fly - a WW T2 glider, considered high performance. “All it needs is a new sail”. Well, add it to the collection, since I have room indoors for them. At least it’s good for parts. Usually though, since a sail costs almost as much as a new glider (thousands of dollars), people just get a new glider, or so I am told.
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