Figure 4-6

HELICOPTER AERODYNAMICS WORKBOOK

CHAPTER 4

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 4-6

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.

AUTOROTATION 4-7