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awesome effect from humidity in the air
thanks for sharing this one with us!
5 Stars*****

Belgium C-130H Serial Number 382-4479, Active Since Mar 1973

Note that all 4 props are at the same 'phase angle'[more or less]. This results from the 'prop synchrophase system' installed in Herc's. As an avionics systems design engineer in the Constellation Engineering Design Project at Lockheed Aircraft in Burbank CA in the 1950's - I was assigned to a special project - to design, install, and flight test a prototype Prop Synchrophasing System in a TWA Super Connie - 'bailed' from the production assembly line - for the exclusive use of TWA's President, Howard Hughes. We utilized a small magnet - placed in the rotating half of each prop hub. A magnetic sensor was placed in the stationary half - that sensed the phase angle of each prop. That signal was coordinated with the other 3 sensed signals - to 'fine tune' the rpm of each engine - to result in all 4 props becoming in mutual phase-angle synchronization. The flight testing was a success. The intended objective - to reduce vibration - particularly in the fuselage skin - was achieved. So a production version of the system was 'factory-installed' in all subsequent Super Connies built - and a service bulletin to retrofit the system in delivered aircraft was prepared. This system became SOP on subsequent Lockheed aircraft - such as the C-130 Hercules - and has become an industry standard. So look for the effect in high-speed photographs of prop-driven aircraft - as manifested in the accompanying photo.