Quote from Arthur Bellcrank:
"The 'flapping' noise on Dart aircraft came from the prop leading edge erosion strips, held on with evostick type adhesive, the strips would erode or tear, become unstuck.
Impossible to rectify on the line due to the long drying time of the adhesive."
That rings a bell, and perhaps the peeling strips flapped even harder with the slightly coarser blade-pitch when water-meth was being used.
Good point, oldchina. BTW, I recall that the total cruise fuel-flow was about 2200kg/hr with 119 pax at M0.70**, whereas the A320 with (say) 168 pax is about 2400kg/hr at M0.78. Not completely sure what you mean by "draggy slats", however?
** [Edit] Or was it M0.73?
Last edited by Chris Scott; 18th Feb 2017 at 21:28.