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Hughes friction dampers

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HI all,


I have a question to all hughes th55,A,B mechanics and owners.

Is there any cheap way for re-adjust/overhaul the m/r friction dampers?

I've asked some repair stations, which told me costs between $1,000 - $1,200 for each damper. :huh:

Is the re-adjusting for the friction dampers so complex?





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Pokey can answer that ? for ya.



Yip 67 i can


Fabian, how did you make out w/ that blade? Paul stopped by yesterday & said that you didnt get back to him. If ya lost his number i still have it.


As far as those dampers go? $1,200 apiece is pretty steep. I have done many sets & altho it is not a fun job, & very time consuming--it is not all that difficult. On the other hand those dampers are NOT to be taken lightly & if you suspect a problem, overhaul ALL 3 at the same time. The plates are becoming harder & harder to come by, but usually can find used dampers cheep if you need plates. There is no cheep way to overhaul/adjust them if they are acting up, other than complete dis-assembly & resurface the plates, replace the spring, site glasses & 'O'-Rings. You want to be very careful that you dont "mix & match" different dash numbers also,,,, some are 3 stage some are 4, but? definately DO NOT intermix them on the same ship.


I would suggest that you make sure that they are properly phased & the torque adjustment is correct B4 proceeding w/ overhaul tho. ( the torque check is required every 100 hours per HMI appx B ) I have never tried the "tip pull" method of checking torque ( even in the book i have never found a pound reading--only that all 3 must be w/in a 1/4 pound of each other)-- i always use the wrench adapter & dial type inch pound torque wrench to check reading of 200-230 in-lb. Read up in your HMI in section 8, & if you have any questions--just ask. BTW? as part of every pre-flight, i hold the T/R & with M/R blade in hand also, i move the M/R blade fore/aft against the 1st phase stops & kinda "get a general feel" of the drag between all 3 blades & also set them to the forward stop & take note that all 3 blades are at the same lead position (4 3/4 to 5) on the damper housing scale,,the number "5" should be painted yellow too BTW. They all seem to like to run at about 4 5/8 in actual flight i notice.


DO NOT ! take these dampers lightly, they are a very serious and important link between a safe flight and ground resonance, they work in harmony w/ their partners--- the landing gear dampers, & if either is not quite right, ground resonance will occur.


I had a TH-55 i was putting together for a friend, the dampers were kinda "cruddy" inside AND the HMI (paragraph 8-28) allows field cleaning. So? we had them on the bench, drained the dirty fluid out, flushed a few times w/ new hydraulic fluid, (didnt use solvent as HMI suggested----were worried about contamination of the hyd fluid), set torque to 230 & felt smooth, put them on, tracked & balance it & felt ok for the most part. I had always felt that they were acting up tho, as sometimes in a steep climbing left turn & auto rotations it would develop vibrations--NOT all the time tho. ( this guy was reallly cheep & i wasnt gonna overhaul the dampers for free) One day upon landing (on pavement) just as i had collective almost full down, i felt it,,,,,one hop, & just as the second hop ( which i could feel was going to be quite a bit more violent than the 1st) was beginning i lifted off immediately & landed on the grass. The soft grass allowed the vibrations to be dampened out enough to be able to land-----We immediately removed & overhauled the dampers ! ( i think i charged the guy $1,000 for all 3) Learned 2 lessons that day 1) have a verrry healthy respect for ground resonance & the parts that control it 2) dont work for friends

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Another option, although more expensive in the short term, would be to get an STC for elastomeric dampers. As pokey said, the friction plates are getting harder to find, and the elastomeric are a great improvement. Elastomeric shouldn't need to be overhauled very often, and are better dampers than the friction type.

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Yes, the elastomeric dampers are much less maintenance, altho i have never seen a set that make their life limit of 6,000 hours. I have seen ships that have scrapped them at less than 1,000 hrs.


The elastomeric's replaced the friction dampers in the 70's early 80's ? ( exact date i dont know), so no STC is required. Altho, they will only work w/ the 1190 or 1185 blades, as they never made the end that adapts to the old 1145 style trailing link bearing.


So? unless you have the newer style blades? yer gonna haftah buy them to make the elastomerics work, here is a quick cost estimate:


269A1291 fitting: 800

269A1290 damper: 3,000

269A1190 blade: 13,000


You're looking at around $17,000 conversion--not ALL that bad,, but? ya need 3 of 'em !! :o


oh, & yer still gonna need hardware & a track & balance :rolleyes:

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Hmm, I had answered Paul and wrote a 2nd email two weeks later.

So I thought he was on holiday or something.

I will try to contact him by email again.



We tracked and balanced my B model last week and had light vibrations at 70mph and 1 IPS on the scale.

Hovering on ground was stable 0,3 IPS. :unsure:

The SAC service center for germany advised me, that the dampers needs an overhaul.

But its hard to find someone in europe, who has experience with this friction dampers.

I think, I will check first the condition of each friction plate.

I'll come back with news.


thank you very much for the informations...

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those IPS readings? are they vertical OR lateral?


0.3 in a hover for lateral is not acceptable, less thatn 0.2 is

Vertical IPS in a hover is useless info, the track of the blades is the key here


Of all the track & balance work i have done w/ the 269's, unless you have trim tabs ( 1190 or1185 blades) and spend ALOT of flying time OR get "lucky" the vertical at Vne is tuff to get much below 0.3 or 0.4 IPS


It is not recommend to take a lateral reading, other than at hover speed.


Remember: lateral w/ friction dampers is w/tip weights, elastomeric is sweeping the blade ( altho i use tip weights too---to get the "stick-shake" out

Vertical is pitch link OR trim tabs ( trim tabs NOT in hover--but hi-speed flite)


ALSO remember: Track has a LARGE effect on balance,,,, balance has a small effect on track----you need to keep working the 2 simultaniously to get a smooth flying ship---along w/ properly functioning components.


BTW? when i do track & balance work? i always carry a pencil (not a pen) for 3 reasons:

1) to sketch the track targets as i see them & write the IPS reading & clock angle(erasable on the charts for "do-overs")

2) if ya hold it just right between yer fore & middle fingers? it gives you a "real world" example of the vertical bounce

3) in case a purdy girl walks bye ya can write down her number :rolleyes:

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I thought point 3 is reserved for certified mechanic only B) :D



I mean 0.3 lateral.

Vertical it looks great. There only problems with lateral.


Lateral should be measured only at hover speed ?

Is the hi-speed value not so important ?



I've found someone here, who will overhaul the dampers.

But at this moment i don't know, if he need plates.

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Great you found some one to overhaul them! Check the phasing & torque B4 you pull them off tho, as that may be your problem & you will then have a starting point to determin what to do next.


Not that the lateral balance souldnt be "checked" at flight speed,,but to make any corrections at that speed will thro off your hover balance. You will find youself "chasing your tail". I have had ships that in order to get the vertical bounce to an acceptable level, i had to bend the trim tabs to make the blades NOT track in the same plane, (or in case of no trim tabs-move pitch link to throw system out of track), which will throw off your lateral balance. ALL of the ships i have done? I find they have their own "personality", and each want to be treated a bit differently to fly smooth---some never do !


If the drag on the blades is not the same in flight ( which there will always be differences to to manufacture of the blade, pitch link adjustment, trim tab angle) then you can imagine what is happening to the lateral balance at varying airspeeds--it is constantly changing. As long as its below 0.2 in a hover & in flight it feels ok, i wouldnt worry too much about it ( unless its like 0.5-o.6 or higher)


Here is the procedure that we have found works well over the years.


track @ 2000 rpm flat pitch on ground, adjust w/pitch link, if ok:

track @ MAX rpm flat pitch on ground, adjust w/pitch link, if ok:

hover track, adjust w/ pitch link, if ok:

take lateral balance reading, adjust by either sweeping blades (elastomerics) OR tip weights till less than 0.2 (stick shake may occur when sweeping blades-if so, add tip weights)

fly ship @ 40, 60, 80 & Vne & observe track and vertical IPS, if ok: yer done ! ( hardly ever the case tho, so? NOW the fun begins) Its a simple matter now of trading this for that ( ie: out of track to get vertical bounce out)


The bottom line that i shoot for is hover lateral less than 0.2, cruise speed vertical as low as i can get it (usually 0.3-0.4 is best it will get- but every now & then ya get lucky) while still keeping blades in "resonable" track.


I have had some ships that we spent days, even weeks trying to get them as smooth as some others--only to find we couldnt. Some i spent an hour or afternoon with & fly really smooth, why? beats the heck outtah me !


Dont forget to check your auto rotation RPM when track & balance is all done too !


Let me know if you need any plates, i think i have a pile of them somewhere.


ps: i have been to the Schweizer factory & watched them track & balance new ships,,,,,,if they have problems w/ a blade not wanting to fly w/ the others? it goes "back in the pile" & another goes on, untill they find 3 that like to fly together,,,,must be nice huh?

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A questions for you, I am a Airframe Engine Helicopter mech in Australia working on Bell Jet rangers and S-70 BlackHawks, and came across this forum and noted you starting to talk about vibs in helicopters, in which have a great intrest in and I would like to ask you some questions and please excuse my ignorance if any when it come to the Huges family of helicopter as I haven't had any exposure to them so I stand corrected on anything I maight say in regards to them.


1. What type of vibe analysis gear do you use? Here we use Chadwick and Helmuith 8500.


2. Is it actually nessesary to run the blade in the same path reference the hughes? As we here inconjuction with the box as we call it will let the blades run in what ever plane they will run to get the best vibes for the aircraft that being anything under 0.2 ips, so for eg the best vibes are made with the blades runing 1ft apart then we will leave them there as that gives us the smoothest flight and therefore less wear and tear on the airframe and subsquentlyall the other parts.


If we can't achive below 0.2 ips within 4 flights then we use the info the box has given us to then to find what part of the airframe is us and then look at replacing it.


again I would to say that I stand corrected on the subject when it come to the huges type aircraft :unsure:

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Hi Gonzo,


I use a Chadwick 177M-6A.


No, its not necessary to run the blades in perfect track if out of track gives you a lower ips reading ( as i said in my previous post)----but it gives you a "starting point"

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  • 7 years later...

I'm in the damper rebuild/re-adjust mode now.


My A&P is studying this. I have found used replacements (low time?) for $750 each, but who knows if they don't need to be rebuilt too.


Anybody willing to re-build these for me?





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  • 3 years later...
  • 3 weeks later...

Shame you have the 1145 blades

Agree Pokey regarding the elastrometrics a lot do not reach life, our feeling is because of Phasing not really a good way to go.

New plates scarcer than rocking horse s**t,

We talked to Seaside & Edd a week ago they rang around.

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Guest pokey

Shame you have the 1145 blades

Agree Pokey regarding the elastrometrics a lot do not reach life, our feeling is because of Phasing not really a good way to go.

New plates scarcer than rocking horse s**t,

We talked to Seaside & Edd a week ago they rang around.


Nothing wrong with the 1145 blades, what i find amazing about them tho? The life limit of "1366" hours. That figure in itself is not all that strange (i guess), but what is amazing is there are still tons of them out there with time left on them. When did they stop making that blade? 1970? 1969?


Most of the elastomerics that i reject are because they fail the "stretch test", some have acceptable cracks, some don't. But? try this ! Save those that have failed the test by only a small margin, set them on the shelf for a month or 2 & test 'em again---9 times out of ten? they will pass now ! Beware of used elastomerics that are 'pro-rated' $/hour. Should we destroy these that fail the test the 1st time? YOU TELL ME?! I'v flown ships with dampers that flew smooth, took them off, tested them and scrapped them, only to have my customer tell me i'm nuts! (that may be the case, but? according to the book today, they failed the test and i cannot re-install them)


There was some guy? i think in Texas that claimed to have a ton of brand new plates. (look on barnstormers for him)


i do have a ton of used plates, housings. Some new springs & site glasses.

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