ORIGINAL: stek79
...With mine, a FAIR intense yaw moment there will be, towards the left... in other words, my point is: the yaw moment due to spiraling slipstream is not so weak!
Yes, you would feel some yaw in addition to roll due to torque reaction. When I have done this with small airplanes, I sense primarily roll with some yaw.
I would not have expected to see more than about 3 degrees maximum of spiral, based on NACA research. In the absence of better knowlege, I would expect higher pitch props to generate more spiral than lower pitch props due to higher induced drag.
8178, I know what you wrote. If you were looking for something like 20 or 30 degrees, I can understand why it looked like zero, but are you sure there wasn't even a slight bias of something less than 3 degrees? It might be hard to see. To really measure it accurately might require carefully placed reference markings on the airframe.
To me, the most telling streamers are the left nose, and both sides of the the vertical stabilizer. You included two photos of the right side of the tail and in both cases the streamers are relatively slack compared to the one on the left side of the vertical stabilizer. That one is definitely being influenced strongly by the airflow. It is almost perfectly straight at the moment you captured it. Was it oscillating an equal amount below a line drawn on the fin parallel to the prop shaft?
Consider again the torque roll. That maneuver is indirect proof that there must be a spiral component to the slipstream (there must be a reaction to the left roll), though not overpoweringly strong. Consider that models generally require that the ailerons extend inward to very near the fuselage in order to be able to counter the left rolling effect and hover without torque rolling.
Maybe I'll do this experiment with my 35% Giles if I can get my three Yorkie pups settled long enough. It has a 26 x 10 prop.
8178, I don't mean in any way to disparage you, I am enjoying this discussion, and thanks for sharing your findings. Have you drawn any conclusions based on your experiment or do you think it's premature?
As far as a windsock spinning rapidly, that's definitely not in unison with slipstream rotation. It doesn't rotate that fast.