AS350 Astar/Squirrel
Joined: Jul 2000
Posts: 794
Likes: 8
From: Wiltshire
Goose boy - we operate 27 AS350s with 2 axis autopilots, and that's what my chief engineer told me a couple of days ago.
TheFlyingSquirrel - as I understand it, the Squirrel was found to have numerous vibe problems. Some were removed/reduced by the antivibrator on the rotor head - some ground resonance (or something similar) difficulties were reduced by adding the springs on the back of the skids and dampers to the skid mountings. The anti vibration units under the floor are lumps of lead on flat springs and are mounted one under each pilot's seat. They are tuned in the factory to reduce the vibration levels felt by the front crew (engineers speak of 'nodes' whatever they are). It's probably the size and weight of the lead that makes them a problem if the spring or mounting fractures in flight!
TheFlyingSquirrel - as I understand it, the Squirrel was found to have numerous vibe problems. Some were removed/reduced by the antivibrator on the rotor head - some ground resonance (or something similar) difficulties were reduced by adding the springs on the back of the skids and dampers to the skid mountings. The anti vibration units under the floor are lumps of lead on flat springs and are mounted one under each pilot's seat. They are tuned in the factory to reduce the vibration levels felt by the front crew (engineers speak of 'nodes' whatever they are). It's probably the size and weight of the lead that makes them a problem if the spring or mounting fractures in flight!
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
Heliport
Yes, at least seems clear to me.
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!
Yes, at least seems clear to me.
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!
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
Joined: May 2002
Aviation Qualifications: ATP+Mil
Posts: 18,633
Likes: 1,072
From: Downeast
Nick,
Please do provide us a topic for some vibrant discussion....hopefully the frequency of posts in reply will vary with the source. Maybe that bit of information will dampen any misunderstandings and smooth any inconsistencies.
Please do provide us a topic for some vibrant discussion....hopefully the frequency of posts in reply will vary with the source. Maybe that bit of information will dampen any misunderstandings and smooth any inconsistencies.
Joined: Apr 2002
Posts: 199
Likes: 0
From: oceanside
hilico: for that a/c hose your okay, in stock, ready to ship, reasonable price, call platinum aviation.
now if i can just figure out how to finance an stc installation of PW207E engine we would really be cooking with gas.
dr
now if i can just figure out how to finance an stc installation of PW207E engine we would really be cooking with gas.
dr
Joined: Mar 2003
Posts: 814
Likes: 2
From: the hills of halton
CD I thought first plan was a RR250 in EC120 , surely with all the disposable income on this site we could raise enuff capital !!! As350b207E is a bit long , any shorter names ? Is Jack K still around talking of platinium ?.