On 8 Nov 2005 16:23:06 -0800, wrote:

When ground testing my auto engine with an old style 3 blade IVO prop, I
took several still photos. Some of the photos appeared to show the blades
advancing or retreating much like that of a helicopter.....not sure if this
was a trick of the camera or actually happening. After about 10 hours of
ground time I found damage to the base of the blades. Now that the engine
is flying with an MT prop I have been unable to duplicate that effect in any
of my photos.

The focal plane shutters used in many good cameras would give
that bent-prop effect. As the shutter gap moved across the plane,
either side-to-side or top-to-bottom, one side or edge of the film was
exposed before the other, so a rotating prop or rotor would be caught
over a rather long time, spread across the film, and would appear bent
or out of phase.

A rather extreme example:

http://www.bowersflybaby.com/takeoff.mpg

(Cheap digital video camera).

Ron Wanttaja