Tanks for the input guys......really fascinating info. Am getting closer to answering the question I raised at the beginning.
But..........
Was todays blade material allowed in service because it is better at absorbing bird strikes than the RR "hyfil" was? Or is it solely the test requirements,as described above,that have changed since the 70's?
Was'nt rain (or whatever prcipitation) erosion also a problem with the 70's composite fan?
I notice a metallic looking leading edge to the current fan blades. Is this metal and if so how on earth do they ensure good integrity with the composite part of the blade?