Effect of blade airspeed on lift on advancing and retreating side.
Caption: The blade tip speed of this helicopter is approximately 400 knots. If the helicopter is moving forward at 100 knots, the relative windspeed on the advancing side is 400 knots. On the retreating side, it is only 200 knots. This difference in speed causes a dissymmetry of lift.
United States Department of Transportation, Federal Aviation Administration
2012-01-01
<a rel="nofollow" class="external free" href="http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/">http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/</a> Chapter 02, page 2-19, Figure 2-34