Nick,
Not discounting your piezo-electrics but I think the metal type of the leading edge protection does play a part in the effect. Perhaps there are two different effects / causes.
The S-76, the S-70 Blackhawk and the CH-53 all do it, especially in dusty conditions. Certainly on the S-76 you can see little white sparks bouncing off the underside of the blades with the naked eye even ground taxying at an airport but other types I have flown with stainless steel protection as opposed to titanium (flown into the same locations) don't seem to do it, even when shrouded in dust.
BTW, Have you seen the titanium studded knee-sliders that motorcyclists use to deliberately throw up a shower of white sparks on corners? Oh, sorry, you don't have corners in Florida do you?
Anyone know what type of LE protection the Chinook has?
Can't wait till dark, got my 14lb lump hammer and box of cubes at the ready, not to forget the steel / titanium toecaps and eye protection.
