OneGuyFromBarlick

I had an idea that the 'scimitar' blades were a distortion of the camera lens Peter. Never seen vapour trails like that. I suppose they're related to the vapour trails you see from the wig tips of low flying aircraft sometimes.....

This web page is from 2005 when the first pics were released of the scimitar bladed prop for the A400M: Scimitar blades

This shows Airbus A400M prop blades on an aircraft taxiing where the outer set is feathered, and the inner applying thrust.

The blades of propellers on ships like submarines were modified to scimitar shapes as well.....

Thanks for pointing that out - there's plenty of info on the web about those, although some secrecy too.

I know that the big problem in water is cavitation, the forming and subsequent collapse of bubbles that are actually vacuums as they are a product of the propeller tips moving faster than water can move. You get the same phenomenon in centrifugal pumps. One of the things I found out about corrosion is that a corrosion cell in the metal of the pump impeller or body can be triggered by the collapse of these bubbles (in a centrifugal pump it is evidenced by a crackling sound.). This can result in erosion of the impellers and worm holes in the body of the pump. In marine propellers it evidences itself by erosion of the tips of the blades which get bad enough to spoil the efficiency of the propellers and become a source of sound by which the submarines can be detected. I suspect that in the case of the aircraft propellers the impairment is the formation of vacuums and vortices at the tips of the blades and this is what causes that distinctive screw pattern of condensation. But what the hell do I know about it.....

This really is a winged heroes story...
`World War Two: When 600 US planes crashed in Himalayas' LINK

The Curtiss C-46 Commando plane was new to me but I found this web site useful: Air Vectors

First I have ever heard of it Peter. Thank you!