The Sultan et al
I guess all these checks would have been made with a structurally sound airframe and rotor system. Can you get a destructive resonance in a tilt rotor if something bends, breaks or cracks and changes the harmonics of the beast.
A long time ago (1973??) the Navy sent a few of us QHI's on a five day helicopter design course at Bristol University. The lectures and demos were fascinating. I remember the structures guy giving us a demo of resonance. He had a wooden model of a building with (one or two - can't remember) vibrators attached to it. The vibrator was also attached to a digital readout of the vibration frequency. He showed us low and high amplitude vibrations and they had no effect but at one particular frequency the structure flew apart in a hundred pieces. This he said was the effects of resonance.
Putting this past lesson together with the safety blurb delivered on Tuesday (remember the video associated the Osprey with 'hard in-plane resonance') I am keen to understand it better. Maybe you can help.
G.