[jacquesm]

If not on this flight then on one of the subsequent ones, experimental helicopters are not something for those not schooled in materials science. The good news is that nobody else got injured or killed, that could have easily happened.

When I built that windmill I spent hours planning individual welds, ensuring no inclusions, grinding the mating surfaces to get a perfect fit before welding, annealing them properly, magnafluxing them afterwards to make sure that it wouldn't come apart due to some weld inclusion. It had a safety factor of four because there was a house within throwing range of the blades, and a variable pitch windmill is essentially a helicopter in a different plane. Design speed was 600 RPM, the hub was spun to double that with some weights attached and the plane of rotation angled such that even if it came apart the debris would not cause any damage.

As soon as you start spinning large things fast you need to be really careful.

A windgust managed to overspeed it (it is very impressive to see your homemade windmill break the sound barrier at the tips) and the machine survived without any damage at all.

That was very briefly the most power that it ever made. When the storm died down we pulled it down and modified the governor to ensure that that would never happen again, better safe than sorry.

[bruce343434]

How much power did it generate?

[jacquesm]

Nominally 2500 Watts (design power), in practice about 1500 to 2000 Watts, during that gust it maxed out the meter at 5 KW, so no idea how much more but quite a bit more (I never expected that or I would have picked the range a bit different).