ETL

scottyboy75

scottyboy75

Well-Known Member
This question is for the guys flying big machines. When you are on an approach to a pinnacle, how long do you stretch ETL? It seems to me I milk it as long as I can and am wondering if this is a bad habit to get into. No instructor has said anything about it but they don't fly turbines.
 
Honestly... I don't think about it. Since it is an OGE maneuver and I'll know whether or not I'll have OGE power when I get up there... I bring it in slow and steady so I don't over-shoot the landing. I think a gradual slowdown to a hover is preferable over satying at or above ETL till the last second then cranking it back. What I usually do is when I'm on approach I'll set my hover power early and as I slow down I should come to a hover with that pre-set power setting right where I want it. The only time I worry about ETL is on a dust landing and a roll-on landing. On a dust landing I want to ride the shudder all the way till the aft wheels hit the ground to keep the dust behind me.... for a single engine roll-on, I just want to make sure I never go below ETL, and no faster than 60 knots.
 
Stretch ETL? Explain.

I don't think turbines have anything to do with it. It is a matter of rotor aerodynamics. The aircraft is transioning from outrunning its vortices into sustaining flight on its rotorwash.
 
UH60driver said:
Stretch ETL? Explain.

I don't think turbines have anything to do with it. It is a matter of rotor aerodynamics. The aircraft is transioning from outrunning its vortices into sustaining flight on its rotorwash.
Click to expand...

I think he means staying at or above ETL until the last moment.
 
Staying above ETL until the last moment for a pinnacle landing sounds to fast. Although, I think weight becomes a big factor. I am landing at above 13,000 LBS with just four members onboard.
 
I see that so far there have been 34 views on this thread and I wonder how many poeple are wondering WTF ETL is!!??
 
Yeah I am talking about in ETL but at about the bottom of it. In the Robbie we hit it at about 10 - 20 knots. My normal practice is to drop ETL then set down no hover really on the pinnacle.
 
ChinookDriver said:
I see that so far there have been 34 views on this thread and I wonder how many poeple are wondering WTF ETL is!!??
Click to expand...
I'm sure there will be lots of terms in this forum that most of them won't have a clue. I'm sure there are a few where I'll be looking in the glossary of the Rotorcraft Flying Handbook to figure out what you are talking about.
 
scottyboy75 said:
Yeah I am talking about in ETL but at about the bottom of it. In the Robbie we hit it at about 10 - 20 knots. My normal practice is to drop ETL then set down no hover really on the pinnacle.
Click to expand...

Seriously not trying to sharp-shoot here, just checking my memory... I thought the aerodynamic property of ETL was always 17-24 knts and transverse flow was 10-20 knts. I just don't remember anything being helicopter specific. Correct me if I'm wrong... it's been a long time since I studied helo aerodynamics.
 
ChinookDriver said:
Seriously not trying to sharp-shoot here, just checking my memory... I thought the aerodynamic property of ETL was always 17-24 knts and transverse flow was 10-20 knts. I just don't remember anything being helicopter specific. Correct me if I'm wrong... it's been a long time since I studied helo aerodynamics.
Click to expand...
I looked in the Rotor Flying Hbk, because I have that kind of time on my hands. It says the ETL occurs at approximately 16 to 24 knots (p. 3-5). Transverse flow occurs at approximately 20 knots (p. 3-6).
 
In the Robbies you can still feel the shudder down to about 12 knots. Feels like ETL still but I could be oversimplifing it. The Airspeed indicator isn't the most accurate.
 
scottyboy75 said:
In the Robbies you can still feel the shudder down to about 12 knots. So to keep it simple I oversimplify it to about 10.
Click to expand...
Does the light weight of the Robbie's rotor have anything to do with it?
 
Originally posted by Scottyboy75
In the Robbies you can still feel the shudder down to about 12 knots. So to keep it simple I oversimplify it to about 10.
Click to expand...

Well, everybody here is correct in their interpretation of effective translational lift (ETL) and transverse flow. To further go into it, what Scottyboy is experiencing at 10 knots is transverse flow which occurs from 10-20 knots. In simple terms, what is happening is that the front half of the rotor system is creating more lift due to a more horizontal flow and the aft half has less lift due to the more vertical induced airflow. That causes a difference in drag between the front half and the aft half which creates the vibrations. Those vibrations will continue until ETL is attained between 16-24 knots.

The airspeed indicator is not a good gauge to try to figure out the exact speed because it is unreliable at the lower speeds (below 20-30 knots). Additionally, you could be at a hover in a 10 knot headwind and you will be experiencing vibrations due to the characteristics describe above. Your actual groundspeed might be 6 knots by the time you experience ETL.

No, I am not a nerd. I just had to pull all my civ and mil books.
 
I went through an reread all that stuff. I have the Jeppesen helo book and the FAA book. It's funny the way you reinterpet stuff as time goes.
 
Jeppesen has a helicopter book? I have to own that. I love aviation books. The more one reads, the better understanding. Still, I am not a geek. ha ha ha.
 
UH60driver said:
Jeppesen has a helicopter book? I have to own that. I love aviation books. The more one reads, the better understanding. Still, I am not a geek. ha ha ha.
Click to expand...
Being a geek is not so bad if you surround yourself with other geeks.
 
Face it... we're ALL geeks. And I agree, if we surround ourselves with like-minded geeks, we'll... well, we'll at least fell normal.

And on the subject of geekiness, I'd like to point out that without looking at a book I was off by only one knot on ETL and dead on with transverse flow. And it's been two years since my last APART!
 
I fly almost everyday and couldn't keep the speeds straight. I did take the oppurtunity to reread the chapter in the Jepp book though. I did notice the FAA goes into more flight aerodynamics than the other one.
 
You must log in or register to reply here.
Back
Top