I can normally fly F3C style quite well, but yesterday was very windy and gusting when I arrived at the field so I thought I'd just practise approaches and hovering in various orientations with my Raptor 50. All was fine - then I was doing nose in which I am quite competent in but the blustery wind was making it a challenge. The heli was facing into the wind at this time.

Using Glass rotors which were well tightened in the grips. Head speed was around 1700.

On one occasion, just as I was touching down (quite lightly - no impact) I had a sudden, and to me, inexplicable boom strike.

There are two possibilities that come to mind

1) A gust got under the rotor disk at the front, lifting it and causing the rotor to dip lower than normal at the rear. With the skids already on the ground, the body of the heli could not rotate backwards (pitch up) to match the rotor disk.

2) After picking up the pieces, I noted that the link to one blade grip had popped off. Turned out it was cracked, but this was on the rotor that did not impact the boom. Is it possible that this crack caused the incident? I tend to think this this was crash damage but I'm not sure.

Anyone got any other ideas?

Just as an aside - only one blade impacted, but the other was also destroyed. The sudden deceleration caused the lead weight to rip out through the glass skin - pretty impressive. Spindle shaft was surprisingly, not bent, stabilizer bar was of course bent but can be re-straightened.

Depending on the cg-cp relationship, if the pitch arm is liberated then the blade will either weathervane or else it will go to max plus or minus pitch, whichever is closer. After consulting my ashtray and coffee cup, I'm going to take a stab at guessing what happened. The cg-cp relationship is such that the pitch goes to max + or - (an assumption that the cg is farther from the leading edge than the cp, which may be wrong), and assuming there was some + pitch at the time when the link broke (which is probable since the heli just landed) that blade went to max + pitch, the closest limit, sending that blade up for all it's worth, the other blade down, and into the tail boom.

soft dampers did that to me

I am running the red dampers.

Actually, I did some closer checking of the trashed rotors. Previously I thought one did not contact anything , but then I noted that the underside of the rotor (the one with the cracked ball link) did in fact scuff the top of the horizontal fin. The other rotor (non broken link) was the one that really smacked into the tail boom, it actually struck the boom by getting under the horizontal fin.

Although it is still unlikely, it looks more and more like it was the cracked ball link that set off the chain of events

Those links, even the double links in the head that arent logo'd are unidirectional and if they are backwards, repeated snapping and unsnapping, say working on tracking or whatever, can fatigue them and crack them. Those things always break when you hit something though.

I've had a number of "unintended arrivals" over the last year, but this is the first time I have ever had a broken ball link on any of my helis.

I'll put it down to experience and make a habit of changing them once a season, even if there are not apparently worn.