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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 9th Dec 2018, 11:34
  #1041 (permalink)  
 
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Hi sycamore,
No idea I am afraid. My reference to the para "The lever pivots around the connection at the control shaft end and creates a demand on the hydraulic system via the solenoid valve, which moves the hydraulic piston and control shaft of the actuator" is to highlight words that seem to me to be either; badly written, incorrect or confusing.

OAP
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Old 9th Dec 2018, 12:32
  #1042 (permalink)  
 
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Among my Laundry List of questions was this one......

The design must not be as "simple" as suggested due to the various discussions upon what role all the various components played in that event.
Are we seeing in the various posts before and after my question showing up....confirmation that understanding how this 168/189 Tail Rotor Control system operates is far more difficult than at first glance?

I appreciate all the posts as they come from knowledgeable people and that quality of discussion is very informative.

This is where having a Maintenance Manual for the 169 would be very useful....to read what the Manufacturer has to say about it all.


Oh....and by the way....Army BEAT Navy yesterday! Go Army-Beat Navy!
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Old 9th Dec 2018, 12:55
  #1043 (permalink)  
 
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Originally Posted by sycamore View Post
OAP,part of the yaw channel AFCS...?
Not current on any of this, far too old! But proportional solenoid valves are available, so it is possible but not shown on the drawing posted. Maybe a dual operated valve?
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Old 9th Dec 2018, 15:13
  #1044 (permalink)  
 
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Originally Posted by Onceapilot View Post
badly written, incorrect or confusing.
OAP
Forget the fact that I have type knowledge, from a maintenance engineer's point of view I found the report poorly written, with poor terminology, and confusing. This has been proven by the majority of the posts and questions in this thread since the report was published.
The use of the word 'solenoid', as quoted above, was incorrect and misleading. As has been pointed out, a solenoid is an electrical-mechanical component. I would refer to the item that the report is referring to as a servo valve, or spool valve. These are standard hydraulic servo component terms.
The AW169 tail rotor servo and pitch control system really is pretty straight forward and not particularly unique, compared to some I've seen over the years. It's not always easy though to visualise these things unless you have one in front of you, or a series of detailed photos. I still think that the report could have done a better job of clearly relaying the technical information to the industry and public.
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Old 9th Dec 2018, 20:17
  #1045 (permalink)  
 
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nodrama, perhaps you could elaborate on the `cable` arrangement to the tail ,from the pedals..? ..Is this a new terminology for a `teleflex` control,as cables are usually `pullers,not pushers`..?Why not carbon fibre rods ?
If one had a hyd failure,does the servo have a `bypass`loop,..?to allow manual inputs from the pedals..?
Can the controls be checked on the ground for `full,free and correct` operation prior to start,or only with an ext,hyd rig...?
Could you also confirm the spider pitch links go to the rear of the t/r blades,ie behind the feathering axis....?
thanks in advance...
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Old 10th Dec 2018, 03:00
  #1046 (permalink)  
 
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Oh....and by the way....Army BEAT Navy yesterday! Go Army-Beat Navy!
Having served in both I come out a winner either way SAS.
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Old 10th Dec 2018, 05:47
  #1047 (permalink)  
 
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Originally Posted by sycamore View Post
nodrama, perhaps you could elaborate on the `cable` arrangement to the tail ,from the pedals..? ..Is this a new terminology for a `teleflex` control,as cables are usually `pullers,not pushers`..?


A ‘flexiball cable’ is what it is called. They’ve been used successfully by several helicopter manufacturers for the last 20+ years (e.g Eurocopter/ Airbus, MD, Agusta), though a flexiball control was attributed to the cause of an EC135 crash in Japan in 2007. The last statement with reference to no maintenance and lubrication isn’t strictly true. They are subject to periodic friction force checks and the eye-end sliders sometimes get greased (depends on aircraft type).
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Old 10th Dec 2018, 07:32
  #1048 (permalink)  
 
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Originally Posted by sycamore View Post
If one had a hyd failure,does the servo have a `bypass`loop,..?to allow manual inputs from the pedals..?
Can the controls be checked on the ground for `full,free and correct` operation prior to start,or only with an ext,hyd rig...?
Could you also confirm the spider pitch links go to the rear of the t/r blades,ie behind the feathering axis....?
thanks in advance...
1. See previous posts
2. With one engine running in 'Acc Drive'
3. Yes
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Old 10th Dec 2018, 10:55
  #1049 (permalink)  
 
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nodrama. I would be interested in your thoughts on lubrication of the failed bearing, with the burned 'black grease' on the rod nearby. In my experience with classic cars, black graphite grease can 'dry out' if not used regularly - and this a/c was apparently not used all that frequently?
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Old 10th Dec 2018, 11:01
  #1050 (permalink)  
 
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Nodrama,thanks for that; assume `acc drive` is similar to WX,S-K,Lynx...
Leonardo (the Engineer),said `Friction keeps the World together,Lubrication (grease,oil, money ), allows it to spin``...pity his namesake didn`t take note......
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Old 10th Dec 2018, 12:28
  #1051 (permalink)  
 
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With my 28 yrs of aircraft maintenance involvement I can only agree with nodrama, that report is surprisingly ambiguous - AAIB was always a first-class source of information. Using term "solenoid valve" for a hydraulic system component is softly said, misleading. (except in case there is truly an electromagnetic valve involved - in that case I will have to bury myself )

nodrama, can you comment or confirm that torque applied to castellated nut, that holds duplex bearing in place on control rod, has no effect on the bearing itself i.e. that overtorquing it will not "squeeze" balls between inner and outer race, but "only" overload the rod-threads?
Is duplex bearing actually made of two completelly separate bearings, turned one against the other, or is it one component? From the Fig. 4 in AAIB S2/2018 it seems there are two inner races, but one outer race. Such design implies that nut torque could have an effect on bearing friction? (if there is a gap between inner races-depends on design) Please help clarifying this, if you can!

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Old 10th Dec 2018, 12:57
  #1052 (permalink)  
m25
 
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hoistop, I think this is a good question. The AAIB report on page 5 states that this nut was "found to have a torque load significantly higher than the required assembly value".

In addition, on page 7, paragraph 2 "the increased torque load on the castellated nut that remained on the spider end of the shaft is consistent with rotation of the tail rotor actuator control shaft"

Are they saying the jammed bearing would tighten the nut? If the rotor is turning anti-clockwise, the bearing jams and the thread is clockwise it does not seem to make sense. Or does it mean it could have tightened on impact?
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Old 10th Dec 2018, 15:22
  #1053 (permalink)  
 
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If one had a hyd failure,does the servo have a `bypass`loop,..?to allow manual inputs from the pedals..?
on an aircraft the size of a 169 there is no way you are going to move the TR without hydraulic assistance.

Aircraft like the Squirrel or Gazelle are enough of a handful with hyds switched off in yaw.
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Old 10th Dec 2018, 17:07
  #1054 (permalink)  
 
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Quote:
Originally Posted by [email protected]
on an aircraft the size of a 169 there is no way you are going to move the TR without hydraulic assistance.
Lots of Bell mediums, bigger than the 169, only had a single hydraulic on the tailrotor, and if you shut Hyd1 off, yes you could still move it slowly with a lot of foot pressure.

169 I don’t know, and there is no way for the average pilot to test without bypassing the lockout logic. Leonardo flight test pilots would know.
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Old 10th Dec 2018, 17:32
  #1055 (permalink)  
 
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In the nineties, at BHL Alister Gordon, introduced an amendment to the 212 flight test schedule to include a double hydraulic failure. His reasoning was that if an aircraft had a single failure on a rig, it could still be flown back, on the assumption that a second failure would be controllable. It wasn't, the aircraft each time went into a right hand dive and turn, and the pilot urgently said turn it back on, or words to that effect.
The amendment was withdrawn after Bell said ,"stop being so stupid, your going to kill yourselves".
With regard to the S76 tail control aft quadrant spring centring system, this was fitted to put the system to neutral in the event of a cable brake. It would have no effect on a servo runaway.
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Old 10th Dec 2018, 19:27
  #1056 (permalink)  

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My experience of flying various types from three major manufacturers is that helicopters with a single hydraulic system have the facility for the pilot to revert to manual control. Those with two separate hydraulic systems do not have manual reversion and the design is such that both systems cannot be simultaneously switched off.

I have been told by an engineer working on the type that there is no manual reversion on the 169 and it is not possible to switch off both systems at the same time.
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Old 10th Dec 2018, 20:03
  #1057 (permalink)  

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Originally Posted by m25 View Post
hoistop, I think this is a good question. The AAIB report on page 5 states that this nut was "found to have a torque load significantly higher than the required assembly value".

In addition, on page 7, paragraph 2 "the increased torque load on the castellated nut that remained on the spider end of the shaft is consistent with rotation of the tail rotor actuator control shaft"

Are they saying the jammed bearing would tighten the nut? If the rotor is turning anti-clockwise, the bearing jams and the thread is clockwise it does not seem to make sense. Or does it mean it could have tightened on impact?
I think it's likely that as the right hand duplex bearing began to seize, the nut on the left side came under a loosening torque but was initially held firm by the resistance of the split pin, as per the design intention and it began to rotate clockwise in the pin carrier. No doubt the locking wire would break at this point. The continued rotation of the shaft simultaneously caused a tightening torque on the starboard nut. When the starboard nut could be tightened no more, the port nut, still rapidly rotating as it was not designed to do, friction welded to the carrier, the split pin then came under sufficient torque to be sheared off, allowing the nut to instantly be unwound off the thread on the end of its shaft, at which point the controls no longer responded to the pilot's input.
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Old 10th Dec 2018, 20:28
  #1058 (permalink)  
 
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Lots of Bell mediums, bigger than the 169, only had a single hydraulic on the tailrotor, and if you shut Hyd1 off, yes you could still move it slowly with a lot of foot pressure.
malabo - which models? Ones with 2 bladed TRs? I think TR power in these modern aircraft is considerably higher - the 139 for example can deal with a 40 Kts crosswind - I stand by my assertion that manual control isn't possible.
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Old 10th Dec 2018, 20:36
  #1059 (permalink)  
m25
 
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Originally Posted by ShyTorque View Post


I think it's likely that as the right hand duplex bearing began to seize, the nut on the left side came under a loosening torque but was initially held firm by the resistance of the split pin, as per the design intention and it began to rotate clockwise in the pin carrier. No doubt the locking wire would break at this point. The continued rotation of the shaft simultaneously caused a tightening torque on the starboard nut. When the starboard nut could be tightened no more, the port nut, still rapidly rotating as it was not designed to do, friction welded to the carrier, the split pin then came under sufficient torque to be sheared off, allowing the nut to instantly be unwound off the thread on the end of its shaft, at which point the controls no longer responded to the pilot's input.
ShyTorque, thanks for your explanation and that's how I initially read the report as well. However if you pick up a bolt and a couple of nuts it would seem that in order to loosen the bolt which came off the torque you need to apply via the inside race of a bearing would tend to loosen the nut holding that bearing on also. I am lost as to how this can happen the other way around. Do the actual directions make sense to you? If so I must be misunderstanding the way it is assembled.
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Old 10th Dec 2018, 22:36
  #1060 (permalink)  

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Originally Posted by nodrama View Post
It wasn't you.
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