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R44 crashed Alps

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R44 crashed Alps

Old 1st Nov 2020, 23:35
  #41 (permalink)  
 
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Originally Posted by chopjock View Post
Arnie,
We use the offset pitch link system on model helicopters. It adds in negative feedback to the blade during gusty conditions. Imagine advancing blade flaps up but the pushrod from the swash plate holds the grip where it is, the result is the blade introduces momentary less pitch during the flapping (up) event and automatically twists the blade back down again at the same time. This happens for both teetering and flapping events when the pitch link is offset in this manner.
.

Thank you

Frank also incorporates some Delta-3 angle in the main rotor.
Now I wonder if that offset pitch location is how he accomplishes it

Of course 2 blade tail rotors have Delta-3 to retain the plane of rotation and prevent flapping into the boom
but as far as I know he is the only one who does it on the main rotor as well.

Through the years my suspicious mind has pondered whether his unique Delta-3 combined with his unique coning hinges can create an unknown gremlin in certain conditions

I have often wished some researcher would mount the R system on a test stand and put it through every conceivable
motion to see if the blades would divert from their proper plane of rotation (not including Zero-G of course)

It would not require a lot of funding and if they used measuring instruments on all 3 hinge points could determine
if the coning hinges sometimes pivot beyond the design intentions.
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Old 2nd Nov 2020, 04:46
  #42 (permalink)  
 
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Originally Posted by Robbiee View Post
I have flown an R22 in 35kts.

,...they can handle it just fine.
the discussion is about R44s.
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Old 2nd Nov 2020, 05:57
  #43 (permalink)  
 
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Anyway, I remember once during my commercial training back in '06, while in a hover the instructor jammed in the right pedal and I was to react by chopping the throttle. I did, the yaw stopped and we set down.
Robbiee, that will have been a poor attempt to simulate a TR failure not unintentional yaw - this is only safely and realistically done in a simulator.
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Old 2nd Nov 2020, 14:50
  #44 (permalink)  
 
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Originally Posted by Robbiee View Post
That video seemed less about disproving the existence of LTE and more about the pilots just not putting in enough left pedal to stop it. I think?,..I was having trouble following him.
That's not correct. The video is quite hard to follow given the English-as-second-language challenges. The paper suffers less from that. You are encouraged to read the paper at the link posted earlier in the thread.

Anyway, I remember once during my commercial training back in '06, while in a hover the instructor jammed in the right pedal and I was to react by chopping the throttle. I did, the yaw stopped and we set down.

I don't recall this guy mentioning that as an option?
The intent of his research was to show that LTE as many pilots currently understand it is, if not a myth, substantially misunderstood, and that under all conditions associated with certified designs sufficient tail rotor thrust can be developed to stop the rotation. While reducing torque is one way to assist the resolution of unanticipated yaw, it is not always an option available depending upon phase of flight, nor necessarily the best option. Also, one should not confuse responses to a stuck pedal or tail rotor failure with that suitable for unanticipated yaw.
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Old 2nd Nov 2020, 14:54
  #45 (permalink)  
 
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Originally Posted by Arnie Madsen View Post
.

Thank you

Frank also incorporates some Delta-3 angle in the main rotor.
Now I wonder if that offset pitch location is how he accomplishes it

Of course 2 blade tail rotors have Delta-3 to retain the plane of rotation and prevent flapping into the boom
but as far as I know he is the only one who does it on the main rotor as well.

Through the years my suspicious mind has pondered whether his unique Delta-3 combined with his unique coning hinges can create an unknown gremlin in certain conditions

I have often wished some researcher would mount the R system on a test stand and put it through every conceivable
motion to see if the blades would divert from their proper plane of rotation (not including Zero-G of course)

It would not require a lot of funding and if they used measuring instruments on all 3 hinge points could determine
if the coning hinges sometimes pivot beyond the design intentions.
Modeling and simulation of the design have been performed. The original GTRI modelling effort is documented here:

https://smartech.gatech.edu/handle/1853/52548

It's quite a large document. Chapter 5 is where the meat is, starting on PDF page 118 (not document page number).

There is also this, however I have not paid the $30 to download it and see if it is any good. It is quite recent:

https://vtol.org/store/product/mast-...tems-12593.cfm


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Old 2nd Nov 2020, 15:28
  #46 (permalink)  
 
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Originally Posted by aa777888 View Post
Modeling and simulation of the design have been performed. The original GTRI modelling effort is documented here:

https://smartech.gatech.edu/handle/1853/52548

It's quite a large document. Chapter 5 is where the meat is, starting on PDF page 118 (not document page number).

There is also this, however I have not paid the $30 to download it and see if it is any good. It is quite recent:

https://vtol.org/store/product/mast-...tems-12593.cfm
Thank you very much ..... this is exactly what I was looking for (wishing for) .... lots of reading so off I go to do it .... I may even pay the $30 and download the second one ...... will report back if I do.
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Old 2nd Nov 2020, 15:36
  #47 (permalink)  
 
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Originally Posted by aa777888 View Post
That's not correct. The video is quite hard to follow given the English-as-second-language challenges. The paper suffers less from that. You are encouraged to read the paper at the link posted earlier in the thread.

The intent of his research was to show that LTE as many pilots currently understand it is, if not a myth, substantially misunderstood, and that under all conditions associated with certified designs sufficient tail rotor thrust can be developed to stop the rotation. While reducing torque is one way to assist the resolution of unanticipated yaw, it is not always an option available depending upon phase of flight, nor necessarily the best option. Also, one should not confuse responses to a stuck pedal or tail rotor failure with that suitable for unanticipated yaw.
Ok then, what is LTE?
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Old 2nd Nov 2020, 16:07
  #48 (permalink)  
 
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Originally Posted by Robbiee View Post
Ok then, what is LTE?
Itís a phenomenon where an aircraft tries to punish the pilot for demonstrating his superior skills and inferior footwork.
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Old 2nd Nov 2020, 17:27
  #49 (permalink)  
 
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Originally Posted by Bell_ringer View Post
Itís a phenomenon where an aircraft tries to punish the pilot for demonstrating his superior skills and inferior footwork.
Hmm, already knew that.

,...but thanks for saving me from that excruciatingly long paper!
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Old 2nd Nov 2020, 17:51
  #50 (permalink)  

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Anyway, I remember once during my commercial training back in '06, while in a hover the instructor jammed in the right pedal and I was to react by chopping the throttle. I did, the yaw stopped and we set down.
But what would you have done for full left pedal?
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Old 2nd Nov 2020, 17:59
  #51 (permalink)  
 
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Originally Posted by Bell_ringer View Post
It’s a phenomenon where an aircraft tries to punish the pilot for demonstrating his superior skills and inferior footwork.
Ha ha, that's awesome, love it!

To answer your quesiton, Robbiee, per the paper, what everyone likes to call LTE is instead "unanticipated yaw", because at no point does the tail rotor demonstrate any ineffectiveness. It could be called "loss of pilot foot control" Per the paper, if the pilot lets significant yaw rates develop it can take quite a bit of time to get it stopped, but assuming full pedal deflection it will stop. If the pilot does everything else necessary, such as maintaining altitude and position, it should stop without the helicopter doing anything else untoward. You really should read the paper.

Edited to add: unanticipated yaw (incorrectly termed "LTE") is not the same as stuck pedal is not the same as tail rotor failure.
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Old 2nd Nov 2020, 18:39
  #52 (permalink)  
 
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There is also LTA - loss of tail rotor authority where you reach the pedal stop and still the unintended yaw continues. It is why some aircraft have a reducing crosswind limit with increasing density altitude.

As an example, the Wessex MAUM was 13,600Lbs but in Cyprus at the top of Troodos, the PA was 6,500 and the OAT often in excess of 20 deg C which could leave the DA in excess of 9000'.

The yaw envelope of the venerable old girl narrowed markedly up there and we were limited to 12,500 lbs for landing at the top and coming to a hover wasn't an option.

I took a visiting (Ex-84 Sqn) pilot up there and let him fly the approach as he had done it before when he had been in theatre but I reminded him about the yaw problem we might encounter.

We lost too much speed on short finals and reached the left pedal stop and started to yaw right - the only solution was to turn right, lower the collective slightly and try to get airspeed on. I succeeded but it taught me a lot about yaw control!
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Old 2nd Nov 2020, 18:49
  #53 (permalink)  
 
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Originally Posted by aa777888 View Post
Ha ha, that's awesome, love it!

To answer your quesiton, Robbiee, per the paper, what everyone likes to call LTE is instead "unanticipated yaw", because at no point does the tail rotor demonstrate any ineffectiveness. It could be called "loss of pilot foot control" Per the paper, if the pilot lets significant yaw rates develop it can take quite a bit of time to get it stopped, but assuming full pedal deflection it will stop. If the pilot does everything else necessary, such as maintaining altitude and position, it should stop without the helicopter doing anything else untoward. You really should read the paper.

Edited to add: unanticipated yaw (incorrectly termed "LTE") is not the same as stuck pedal is not the same as tail rotor failure.
Hmm, this sounds like the whole SWP thing all over again. You guys just don't like how the FAA names things.


By the way, if you understand what causes LTE, then you should be anticipating it. Therefore, the only "unanticipated" yaw should be from stuck pedal, loss of tailrotor thrust, or engine failure.

Last edited by Robbiee; 2nd Nov 2020 at 19:48.
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Old 2nd Nov 2020, 19:45
  #54 (permalink)  
 
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Originally Posted by ShyTorque View Post
But what would you have done for full left pedal?
Had that happen in training once too. It was at the end of the flight and we had just gotten back to our home airport. Assuming the training was over I was nice and relaxed (guard down) as I brought it to the pad. Just as I got the nose straight and was about to set it down, BAMN! the nose snapped left! I jammed in the right pedal, the yaw stopped (about 90į later) I raised the collective, we hit the ground, and had a good laugh.

Ah, how I miss surprise throttle chops..

,...'course if you're referring to stuck pedal, than well, I've only had about five minutes of stuck pedal training (none of it in a hover) so I'd probably crash before figuring out the correct course of action.
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Old 3rd Nov 2020, 00:10
  #55 (permalink)  
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Operating at 3,000 metres over mountainous terrain immediately puts you into a corner of the operating envelope where you had better have some options up your sleeve. Power margins, turbulence, down draught velocity, escape routes, visibility and control issues are all great things to cover on the pre-flight briefing. It's a very unforgiving environment when things don't go to plan, and a great place to have experience on your side.
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Old 3rd Nov 2020, 01:06
  #56 (permalink)  
 
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Originally Posted by Two's in View Post
Operating at 3,000 metres over mountainous terrain immediately puts you into a corner of the operating envelope where you had better have some options up your sleeve. Power margins, turbulence, down draught velocity, escape routes, visibility and control issues are all great things to cover on the pre-flight briefing. It's a very unforgiving environment when things don't go to plan, and a great place to have experience on your side.
No joke. The highest I've flown my trusty 44 is not quite 2000M, and I treated her like a delicate flower up there. Not at all like the tough old bird she is nearer to sea level. 3000M op's has got to be something else entirely.
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Old 3rd Nov 2020, 07:16
  #57 (permalink)  
 
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Hmm, this sounds like the whole SWP thing all over again. You guys just don't like how the FAA names things.


By the way, if you understand what causes LTE, then you should be anticipating it. Therefore, the only "unanticipated" yaw should be from stuck pedal, loss of tailrotor thrust, or engine failure.
I think you should learn a little bit more about helicopters before you make sweeping statements like that.

You could start by reading that 'excruciatingly long paper' !
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Old 3rd Nov 2020, 16:06
  #58 (permalink)  
 
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Originally Posted by [email protected] View Post
I think you should learn a little bit more about helicopters before you make sweeping statements like that.

You could start by reading that 'excruciatingly long paper' !
If its anything like that video, its just going to put me to sleep.
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Old 3rd Nov 2020, 16:53
  #59 (permalink)  
 
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If its anything like that video, its just going to put me to sleep.
well it sort of depends if you want to learn about something that might save your life or not!
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Old 3rd Nov 2020, 17:14
  #60 (permalink)  
 
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Originally Posted by [email protected] View Post
well it sort of depends if you want to learn about something that might save your life or not!
Well (as with SWP) what the FAA taught me about LTE has kept me alive for almost twenty years.

,...but if you think you've discovered something new in that article, please, feel free to share with the group.
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