Piston engines of propeller driven aircrafts need to be cooled. There are engine cowlings which accomodate the inflow of air to "wash" over the engines within them and which is then exhausted out into the freestream.
The model in question here would be a single block engine in the cowling of a tracktor configuration propeller aircraft. The airflow enters the cowling, washes over the engine, and then exits into the freestream.
The question is:
What would be a good estimate for the velocity of this air stream exhausted into the freestream?