Effective Translational Lift (ETL) in Helicopters

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In this video I'll be explaining Effective Translational Lift in Helicopters. Prior to watching this video, I recommend watching some of my other videos that serve as building blocks to this one. These videos include:
Dissymmetry of Lift ( • Dissymmetry of Lift in... )
Gyroscopic Precession ( • Gyroscopic Precession ... )
Transverse Flow Effect ( • Transverse Flow Effect... )
and Airflow at a Hover ( • Airflow at a Hover in ... )
Effective Translational Lift (ETL) occurs in Helicopters between 16-24 knots of airspeed (dependent on rotor size, area, and RPM) and is defined as the point at which the rotor system completely outruns the recirculation of vortices. Thus, the rotor system begins operating in clean, undisturbed air and produces Lift more efficiently.
I use 3 diagrams to show how the helicopter transitions from a complete stop to forward flight. At 0 knots of airspeed, the rotor system is operating in its own recirculated air. Once the helicopter begins accelerating in any direction, it transitions into Translational Lift. This is noticed as a slight increase in rotor efficiency as the rotor vortices are pushed backwards. As the acceleration continues, the helicopter will effectively outrun these vortices and pass through the ETL threshold. This point will be noticed by a slight pitching up in attitude (also referred to as "blowback") due to Dissymmetry of Lift and Gyroscopic Precession. Keep in mind this differs from Transverse Flow Effect. Transverse flow refers to the difference in airflow over the disk in he form of horizontal on the front half and vertical on the aft half. ETL refers to the outrunning of vortices.
During this transition the main rotor becomes more efficient and requires less torque for lift. Since there is less torque required, there is less anti-torque required by the tail rotor to maintain heading. Also, the tail rotor begins to outrun its own vortices passing through ETL making it more efficient. Lastly, while in directional flight, some of torque requirement for anti-torque is compensated for by the vertical fin. For these 3 reasons, there is less left pedal required and therefore the pilot needs to add right pedal to maintain heading.
Last thing to consider here is that all of this happens in reverse when landing. While on approach when decelerating below 16-24 knots helicopters transition to a less efficient environment. Pilots need to increase collective to maintain approach angle and prevent under-arcing or "falling through" the approach. Also, pilots will need to put in more left pedal to maintain heading and prevent a yawing motion to the right.
That wraps up Effective Translational Lift. Thanks again for watching! Hit like below if you enjoyed the video and subscribe to see more.
If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook - amzn.to/2ifPlnZ
If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - amzn.to/2ifQGLx