Hi Tracy,  I assume that the 15 degree limit is anywhere along the blade rather than anyone radius.  Is that correct?  Best Guesses are accepted :-)

TJ
Tracy Crook wrote:

That conclusion was based on measurements of the blade angle, prop rpm & airspeed and calculating angle to airflow along with the assumption that stall would occur when angle exceeded 15 deg.  Then this SWAG was boiled in a pot with observations of how adversely the cooling was affected by the IVO (stalled air blocking inlets).