HELICOPTER AERODYNAMICS WORKBOOK
the blade surface. This occurs where the relative wind shifts below the tip-path-plane sufficient
to produce enough driving force to overcome in-plane drag, but not enough to reach critical
AOA and reach the stall region.
Figure 4-7 shows the Blade Element diagram for each region of the blade at a given rotor
RPM. In the prop region, or anti-autorotative region, the high rotational speed combines with
little induced flow, shifting the relative wind toward the horizontal. In this region, in-plane drag
is greater than the driving force. In the stall region, AOA is exceeded, creating high profile drag.
If the pilot chooses minimum rate of descent, induced flow and rotational speed will increase,
thus providing greater lift and time aloft. Choosing max glide decreases induced flow and
rotational speed, therefore decreasing lift and time aloft.