BMA Viscount Spool-up Behaviour
As a lad standing at East Midlands perimeter in the 70’s, I used to be fascinated at how the engine note of a Viscount (813/4/5) on the takeoff roll would rise and then fall slightly before rising again for takeoff. This would appear to be the onset of prop speed governing (somewhere around 1100rpm?) – However: as a (slightly older) student doing turnround cleaning at the same airport in the late 80’s – watching the same aeroplanes (not so many Viscounts by then – but remnants of the same 70’s fleet) the engine note appeared to rise at takeoff – no dip as I recall .
Is this right? if so why .
Did I also notice a change from 4-engined taxying to 2-engined taxying over the same period. What would have driven this? fuel conservation? noise reduction? engine life stretching ? air-quality around airports? ...
Thanks