Helicopter Flight Information
|
Helicopter Flight Information |
|
|
Translational Lift vs Effective Translational Lift This has been a confusing topic with many students, instructors and experienced pilots alike; often confused with Transverse Flow Effect and Effective Translational Lift. Translational lift occurs with any wind or movement of the helicopter in any direction. Translational lift also improves the aerodynamic efficiency of the rotor progressively and continuously as speed increases. While at slow speeds near the ground this can be demonstrated as less power is necessary to accomplish a given altitude over the ground. When translational lift improves to the point of Effective Translational Lift (ETL) significantly less power is required to maintain a given altitude. Many pilots incorrectly think this is maximum translational lift. The speed at which ETL occurs varies from aircraft to aircraft but usually occurs at about 12-15 knots. It is important to understand that the rotor does not know direction of movement therefore translational lift will result regardless of the direction of flight or wind. The fuselage and/or airframe does on the other hand, care about the direction of flight or wind since it is designed to fly in one direction. Translational lift continues to improve with speed infinitely however the negative effects of drag overcome any noticeable increase in performance beyond about 45-knots. The only sensation the pilot will notice relative to translational lift is the tendency of the helicopter to climb as ETL is reached and conversely the tendency of the helicopter to sink as ETL is slowed through on the approach. Translational lift does not cause any vibrations however it is often confused with the vibration caused by Transverse Flow Effect which occurs at an airspeed slightly below ETL.
|
Send email to
rb@helicopterflight.net with
questions or comments about this web site.
|