AS355 TwinStar
The Veloceraptor of Lounge Lizards
Joined: Jan 2005
Posts: 339
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From: From here the view is lovely
Sasless;
You are absolutely right. Sorry, I meant no trouble about groundings or complex inspections. If it did break in flight it could cause a serious buttock clenching moment. I haven't heard if this fault has actually happened or whether someone has realised the possibilities and reacted accordingly, if so good on them.
VH
You are absolutely right. Sorry, I meant no trouble about groundings or complex inspections. If it did break in flight it could cause a serious buttock clenching moment. I haven't heard if this fault has actually happened or whether someone has realised the possibilities and reacted accordingly, if so good on them.
VH
Joined: May 2002
Aviation Qualifications: ATP+Mil
Posts: 18,633
Likes: 1,072
From: Downeast
If this slight irregularity is of enough concern to require a daily visual inspection....one would assume the FAA, et al....would be issuing an Emergency AD on the issue. Another argument for operators to buy bare bones helicoters....see what happens when you add fancy avionics...nothing but extra costs and inspections!!!
Joined: May 2002
Aviation Qualifications: ATP+Mil
Posts: 18,633
Likes: 1,072
From: Downeast
Nick,
Sorry old boy...that is not a gotcha....just another chorus of the same refrain.
I said....yet another excuse for operators to argue against buying the fancy kit....citing the increased costs of yet another inspection.
If the aircraft did not have the servo....and the chance of interference with it....would it be a "daily" visual inspection vice a periodic inspection as are a multitude of other things?
A question is begged here....did the engineers drop a clanger on this one by not anticipating the conflict?
Sorry old boy...that is not a gotcha....just another chorus of the same refrain.
I said....yet another excuse for operators to argue against buying the fancy kit....citing the increased costs of yet another inspection.
If the aircraft did not have the servo....and the chance of interference with it....would it be a "daily" visual inspection vice a periodic inspection as are a multitude of other things?
A question is begged here....did the engineers drop a clanger on this one by not anticipating the conflict?
Joined: Aug 2000
Posts: 2,055
Likes: 31
From: Liverpool based Geordie, so calm down, calm down kidda!!
Just revising for my 355 OPC next week and the anti vibration resonator is not part of the autopilot. It just reduces vibration around the cabin floor area. The aircraft has to be checked once a day by a qualified engineer (not the crew) and details are available from macs
Joined: Mar 2003
Posts: 814
Likes: 2
From: the hills of halton
I have been told that they reduce vibration substantially , they were not going to be installed on EC120 but after first flights they changed their mind , with a 20 to 30 lb weight penalty there must have been good reason.
Joined: Nov 2000
Posts: 2,018
Likes: 73
From: Pewsey, UK
A "node" is a stationary point in a vibrating system.
Visualise a skipping rope, or tail rotor drive shaft. Start shaking it at one end, keeping the other held firm. As it vibrates, one part of the rope/shaft won't move - that's the node. Shake it / turn it faster, the node moves.
The lead weights I assume move the nodes in the AS350 cabin to near the seat attachment points - less movement, less bounce in the pilots' step when they get out.
Visualise a skipping rope, or tail rotor drive shaft. Start shaking it at one end, keeping the other held firm. As it vibrates, one part of the rope/shaft won't move - that's the node. Shake it / turn it faster, the node moves.
The lead weights I assume move the nodes in the AS350 cabin to near the seat attachment points - less movement, less bounce in the pilots' step when they get out.
Guest
Posts: n/a
Thanks for the pics Chopperdr - know I can see what everyone is yappin about. I personally can't see how a dumb piece of lead can have any significant advantage - but I presume it acts as a counter-balance? I've glued it up if you don't mind - i'll remove it if you like - thanks again. Also, how can it fall onto an acutator?
TFS
TFS
Joined: Feb 2001
Posts: 542
Likes: 5
From: Europe
The relevant Eurocopter Alert Telex equires a visual inspection at the next, and each, ALF check (after last flight of day) until they introduce a modification to prevent any interference with the trim actuator rod in the event of failure of the vibration damper blade.
No mention of engineers needing to do it. Extension of Check A, so effectively daily.
Anyone ever come across such a damper blade crack/failure or know the TT/history of the incident that triggered this?
No mention of engineers needing to do it. Extension of Check A, so effectively daily.
Anyone ever come across such a damper blade crack/failure or know the TT/history of the incident that triggered this?
Joined: Feb 2001
Posts: 542
Likes: 5
From: Europe
Oldbeefer
Tend to agree it is OTT, which is why I'm interested to try and find just how many incidents anyone knows of. What worries me is the added risk of finger trouble on a pretty big cowling that I reckon could cause some serious damage if it came undone.
OK it's got 3 latches but it is not light and a bit awkward. History tends to prove that if pilots (and engineers) open cowlings, sooner or later they'll forget to close them properly.
Balance of risk then. And allocation of responsibility!
Tend to agree it is OTT, which is why I'm interested to try and find just how many incidents anyone knows of. What worries me is the added risk of finger trouble on a pretty big cowling that I reckon could cause some serious damage if it came undone.
OK it's got 3 latches but it is not light and a bit awkward. History tends to prove that if pilots (and engineers) open cowlings, sooner or later they'll forget to close them properly.
Balance of risk then. And allocation of responsibility!
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
TheFlyingSquirrel-
That thing is a vertical vibration absorber, designed to "twang" probably at 4 per revolution frequency, kind of like a person standing on a diving board can make the board bounce at its natural frequency. It is resonant at the frequency, and so it absorbs those vibrations from the surrounding structure. It is very effective, that kind of absorber is used in the industry quite a bit. If it is not tuned right, that area of the cabin will feel like a rocky road. Two absorbers like that are located in the UH-60L near the pilot's step. The stiffness of the diving board and the amount of lead are selected to make it "like" the 4 per rev (which is probably about 21 to 25 Hz).
The place near its mount that is to be inspected is where the vibration gets passed through, so it is subject to high stresses, and thus the crack inspection.
I think I see a place on the weight for a vibration pickup to be mounted (the circle with a hole). If so, this is probably used at the factory to fine tune the absorber by reading how much it shakes in flight, and adding or subtracting weight until it is peaked out.
That thing is a vertical vibration absorber, designed to "twang" probably at 4 per revolution frequency, kind of like a person standing on a diving board can make the board bounce at its natural frequency. It is resonant at the frequency, and so it absorbs those vibrations from the surrounding structure. It is very effective, that kind of absorber is used in the industry quite a bit. If it is not tuned right, that area of the cabin will feel like a rocky road. Two absorbers like that are located in the UH-60L near the pilot's step. The stiffness of the diving board and the amount of lead are selected to make it "like" the 4 per rev (which is probably about 21 to 25 Hz).
The place near its mount that is to be inspected is where the vibration gets passed through, so it is subject to high stresses, and thus the crack inspection.
I think I see a place on the weight for a vibration pickup to be mounted (the circle with a hole). If so, this is probably used at the factory to fine tune the absorber by reading how much it shakes in flight, and adding or subtracting weight until it is peaked out.
Joined: Apr 2002
Posts: 199
Likes: 0
From: oceanside
nicks correct, you can see the cross hairs where the 6 attach bolts p/u the airframe, that is the pickup point. also note the washer glued to the hammer weight, this is very common to see washers or various amounts of loose change glued on the hammer face to fine tune the airframe.
dr
dr