how this effect is possible???

[mixedgas]

I am assuming the video with the prop, that the engine is attached to a dehavilland dash 8. (it sure looks like one). With that in mind...

At cruise the dash 8's prop is spinning at ~900 rpm. 1450 rpm at takeoff and 1450 rpm near touchdown feathered for instant recovery if needed. Multiply the 900rpm prop shaft by 4 for the 4 blades attached and you get 3600 passes a minute. divide by 60 and you end up with 60. 60 passes per second. Not sure if this helps anyone explain the phenomenon with the propeller.

But, if the camers is shooting at 29.97 frames per second (typical NTSC scan frequency) then thats just under half the framerate of the prop. At 25FPS (PAL standard) its quite a bit less than the half prop framerate.

Thats perfect, fits exactly, 2 or 4X oversampling when you factor in fields, frames and compression, = the right amount of blur for the bending.

And I checked, the P3 is a 9600 to 10,000 constant output shaft RPM, not prop RPM, there is a "dual speed gearbox" between the prop and the output shaft. This puts the prop at ~1200 RPM, NOT THE 9600 RPM i QUOTED. Mea Culpa.

Thank you, Captain!

Steve

Steve

[hakzaw1]

de ja vu.....^^^

[dash8brj]

Nah - I think Steve was trying to edit his post and the forum interpreted it as a new post - look at the number about the P3 statement - they changed.

I'm as much a captain as I am a famous cricketer - i.e. not :P I just happen to know the Dash 8 and its pratt and wittney power plant quite well, its my favourite aircraft. Thanks for the compliment though Steve *salutes*