RE: found this interesting discussion on Spiral Slipstream
The air does change direction as it passes thru a prop-
the angle causes that - obvious stuff
The rate at which it straightens out is another thing all together.
It is far too easy to confuse motor torque reaction with the airflow.
On a pusher you can demonstrate the the true action quite easily- dun it
The flow quickly becomes a fading column of higher pressure -
Air which flows from a heavy jet wing tip is a different thing -
A ducted fan -yet another thing .