Effective Translational Lift (ETL) in Helicopters
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- เผยแพร่เมื่อ 6 พ.ย. 2024
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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
I now understand translational lift, ETL, and transverse flow effect all in six and a half minutes…beautiful…
dude thank you so much for your videos, im an ex fixed wing pilot learning helicopters on the flight sim and using your videos to feed my hunger for learning about these truly beautiful machines
I wish you worked at my pilot school. I feel you explain everything so clearly, thank you for your videos
Hello there I'm Saul from Peru even though my mother language is not English but I understand I little bit , thanks 4 ur videos , it helps me to understand better how alot of thing works in rotary wings, I'm helicopter mechanic here fixing Huey II and EC145.
We are waiting for more videos since a long time. Your content is so clean and easily understandable. Please upload more
Watching your videos is helping me understand what I’m reading in the FAA handbook so much!!
Taking the AFOQT tmrw! Feeling confident about rotor systems because of these videos, thank you!
Great information! helped me a lot in IERW for the UH72A
Best description of helicopter flight I've ever heard. Great video!
These videos are just awesome dude. Thank you!
Thank you. Your instruction is concise and understandable. Although I only fly simulated helicopters in X-Plane (at least during this non-lotto winning period of my golden years) if I've paid proper attention to your tutorials they should be instrumental in my more effectively avoiding vertical ring states and settling with power during simulated attempted landings. I seem to be aces at crash landing. Getting something up in the air is one thing but getting that same something back to earth safely is the real trick shot.
Such great content, taught simply and well explained. Thanks for putting the time into creating this channel. Drawings are progressing haha.
I love your vids! As an IP I find them very useful! The only thing I’ll disagree with is that translational lift essentially“begins” at 16kts. From that moment the airflow is totally horizontal and continues to become more and more until climb airspeed. Until then at 10-20 kts (as you know of course) only the fore half sees horizontal airflow etc…
Please add more videos as your videos are greatly helpful
At, 3:55, you go into the dissymmetry of lift, and explain that with Gyroscopic procession, the advancing blades create lift that translate to a NOSE-UP tendency. However, in your video explaining the Compensation for Dissymmetry of Lift, at 1:00 you explain "if dissymmetry of lift were allowed to continue without compensation, there would be no way to maintain forward flight. The advancing side would continue to produce more lift than the retreating side, causing a constant roll to the LEFT." I don't know if this is a mistake or if I'm just missing something. TLDR: In one video you say dissymmetry of lift creates a left-rolling tendency, while in this you say it's creates a nose-up tendency.
Christian Cattell. Good catch! If left uncompensated for, Dissymmetry of Lift would cause a nose-up tendency due to gyroscopic precession.
Great stuff! In relationship to transitioning to forward flight & the T/R, it may be worthwhile to also mention dissymmetry of lift is increasing T/R effectiveness and reducing the left pedal/overall torque requirement. Thanks again.
thanks for the lesson please keep doing more content like this
Excellent explanation
Only video I have watched where I got it in one, thanks for the simple to the point expl.
Thank you for these videos 🙏
your videos are the best!!!
Nice videos. One suggestion....use different color markers for airflow.
My friend. Thank you.
Great lesson
Excellent video thanks
Great videos! Please keep them coming
These military intros are awesome.
Excellent!!! Great review before check ride.
What is blowback? Is it just the gyroscopic precession causing a nose up?
Thanks for your videos. Does dissymmetry of lift cause a left roll or a blowback? In your previous video on DL its states that it produces a left roll and is compensated with blade flapping and cyclic feathering but in this one it's compensating for a blowback. Just trying to understand how GP applies even to DL.
Good vídeo ! 👍🏾🚁
Great for me Just. Become interested in helicopters and the technical side
Great video mate, can you do one where you explain the aerodynamics in an auto rotation - comparing the TAF on the way down
Is it “to” ETL or “through” ETL?
Good one again! Thanks
just amazing
Are the effects of dissymmetry of lift felt before the effects of transverse flow?
Well explained. The slight difference I recommend is the drawing from top down should have had forward flight in the same direction as the drawings above (if you get my meaning).
Tray Wilson. I understand what you're saying but for my videos I try to keep all top-down diagrams in the same direction for continuity. You can see in my Aerodynamics in a Takeoff video where I combine multiple aerodynamic forces from my other videos. I reasoned that having changing directions would muddy the water and make it harder to put everything together. I do appreciate the feedback though.
Okay, but why would it pitch up/blowback if there is flapping to compensate? Wouldnt the flapping take out the effect?
thank you very much for these wonderful videos. if you allow me I have a question. why do you say that the lift on the advancing blade is higher than that on the receding blade? even if it is already compensated by the beat articulation, so they must be equal
Dissymmetry of lift
@@shamalkhan8551 yes dissymmetry of lift
I'm not a pilot but i understood your explanation. Very good.
Is it ETL happened btwn 16-24 kts for all helicopters? Nice video btw. Thanks Jacob!
be a ahmad. The airspeed varies slightly but that range generally covers the range most helicopters pass through ETL.
Lemme guess: the variations in speed depend more on the diameter of the rotor disk than anything else?
Great videos sir! Thanks a lot. A small question though: in the concept introduced at 3:40, don't the effects of gyroscopic precession and dissymetry of lift get compensated by cyclic feathering and blade flapping? Or they're greater than what can be compensated by these and a forward cyclic is necessarily required? I believe I am missing something, would appreciate if you could help.
Gandharv Mahajan. We compensate for Dissymmetry of Lift with blade flapping and cyclic feathering. Gyroscopic Precession is compensated for in the control rigging. I expanded on these more in my videos (Compensation for Dissymmetry of Lift th-cam.com/video/culBbvszRpk/w-d-xo.html) and (Gyroscopic Precession th-cam.com/video/MH1emIx5Ubs/w-d-xo.html). I hope these help.
Thanks a lot for your prompt reply, appreciated. So to clarify, the blade flapping (for DL)and control rigging (for GP) do not compensate for the effects of the blow back (4:00) and forward cyclic must be applied to prevent the helicopter from pitching up?
Gandharv Mahajan. Both blade flapping and cyclic feathering (forward cyclic) work together to offset that blowback effect.
Helicopter Lessons In 10 Minutes or Less: I understand now. Thanks a lot and again, you're doing a great job with the videos. I'm watching them all multiple times before i begin training. Any tips for a person who's gonna start training for CPL(helicopter) soon?
Gandharv Mahajan. The biggest advice would be to have an understanding of the basics before you get started. By understanding the importance of ETL or IGE when flying can keep you out of a lot of trouble.
Thank you 😊
Nice one. One question ...At ETL level of flight is it more efficient than case one i.e in zero speed ground effect ?
Rashmi Ranjan Nayak. That's correct. After passing through ETL, the rotor system outruns all of its vortices and operates in cleaner air. This means it is more efficient.
But wont the tip vortices always be present at the tip of rotors blades? Since the pressure difference is always present which produces lift, how can tip vortices disappear from tips?
And as per the video, do airplanes too 'outrun' their tip vortices? Or they are always present, which I think they are?
The vortices primarily refer to the overall churning of air underneath the rotor system and are not limited to tip vortices. Once the helicopter outruns these, it is operating in a cleaner air environment. The tips will still spin of vortices but the helicopter should be outrunning most of the negative effects.
Is EFL a threshold or a envelope? Meaning, do I still experience EFL above and beyond 25+ knots or is it only at 16-24?
Generally a threshold. The speed varies by aircraft. But once you’re through it, the helicopter is outrunning it’s vortices and is efficient. Below it, the helicopter is churning in its own wake.
Very fascinating video! I recently read about Translational Lift in Mark Garrison’s book, “Guts N’ Gunships” where he describes the role of Translational Lift in getting their fully loaded Charlie Model Gunships into the air. This video really helped me visualize it
Lol this is all pretty awesome. Though I bet it would take a bit extra to explain what a pilot must do to combat these effects if they dont have a mixing unit like the larger helicopters.
Why the helicopter is buftting during ETL ?
Thank you Sir! Just passed my SIFT yesterday, I can finally ask you the name of the intro song, I can't find it anywhere, also love all your intros, they make me very excited to become an Army aviator!
Most of the music is from the app Splice in its free music section.
@Aaron Rubinstein 58, I bombed the Spatial Apperception, was a very weird portion. These videos definitely help, I'd suggest reading the Federal Aviation handbook for helicopters
Hows the journey coming along?
@@cascadianapplications7124 I graduated as a 154F (CH47-F) pilot last month! Was a long journey, feel free to reach out with any questions!
does this have anything todo with the ETL switch in an r22?
im trying to find out what that switch does in a sim
Hi, I think the switch you’re talking about is an ELT (Emergency Locator Transponder) it’s used of you need to alert the coastguard or similar that you’ve had an accident. ETL is a form of aerodynamics.
@@hangtenhelicopters4498 thanks
3:58 ah so that's why my helicopters flip backwards like pancakes!
You could add that on approach after you leave ETL that the blowback goes away and the nose drops back into a hovering attitude.
Ray Blevins. Good point. Thanks for the feedback!
Thank you 😊 #HLI10OL #SkyBaum
Speed of translation lift occurs at 12-14 knts according to my reference. Is it so??
Mbuyi-Gereon Lopa. All the references I’ve seen say 16-24. Which reference are you looking at?
muito bom
great
nice videos ,i really want to know how the AOA change when a vortex ring state at first until totally in . i know the basic thing i want more detail .if you have time ,please make a new video .please.
siyu guan. Thanks for the feedback. I do plan on making a video covering Vortex Ring States / Settling with Power for this channel. Stay tuned!
Roger
After airborn th3n freefall gravity dif😂ferent than on ground and that is top secret in aerodynamics... Normally expect around 9.8 m/s^2
Let her fly
ETL is a goofy theory like the downwind stall. Its a wives tale.
Use more colors.
When do we get a face reveal ? 😶🌫️