More damper refinement

Service and maintenance tips, questions, and issues.

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More damper refinement

Postby seneca2e » Fri Apr 19, 2013 6:01 pm

Well I'm still searching for as near to ZERO dutch roll as I can achieve. I took all my dampers off and blueprinted them and their cages so they slide easily in and out of their cages. I then lined them up in the cage so that the wide fork slot was aligned with the cage "flat" and adjusted it to a nominal length of 2.85" but had to adjust from there. This gives you some adjustability if you need it. You probably will have to disassemble the damper a few times to get it close enough as the adjustability is very limited since the damper cage hits the bracket unless it's very close to right to start with(see aligning the blades below).

I further-as the factory guys recommended in the last school they taught on the Brantly-shimmed any play out between the root of the fork on the damper and the blade butt. One took .021 thousands and one .018 and one took none at all. This takes out any eccentricity you might have(oblong hole) in your blade hole and keeps it from working and continuing the damage. Of course it makes your damper work from the get go as well. My dampers while low time show some mild delamination but within the book(SI16)specs(SI16 says a "normal" paper clip should not go in more than 1/8". Also says not to force the paper clip in as that will cause it to delaminate further. It also says that "delamination may not affect significantly the function of the damper. As long as the helicopter is flying correctly then the damper is doing its job". I took a lot of time to painstakingly line up the trailing edge of the outboard blade with the inboard blade row of rivets via the "string method" and a laser pointer as well.

Did it do any good? I don't know-too darn windy to fly it. Tomorrow I should know if it helped any at all. I should roll past 40 hours on it tomorrow since its rebirth. Anybody else flying their Brantlys any?
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Re: More damper refinement

Postby seneca2e » Sat Apr 27, 2013 8:42 am

Well that didn't help the dutch roll but it definitely will reduce wear on the blade root bolt. We replaced the inboard blade rain seals and that took a lot of play out of the inboard blade assembly and that did help quite a bit. Still not exactly perfect but pretty darn good for now.

From an old post Bryan shimmed his damper (not at the damper fork-main blade intersection this time but inside the damper cage between the damper and cage) and had good success almost eliminating the dutch roll from his old machine. The theory was that the rubber needed to be of a slightly higher durometer(?stiffness). If anyone else has tried that it would be interesting to know if you had the same outcome.

I have over 52 hours on it since it was "reborn".
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Re: More damper refinement

Postby Brad Bowles » Sat Apr 27, 2013 7:28 pm

Be careful shimming the dampers.This has been discussed as one of the possibilities of the cause of problems that lead to the blade issue bringing out the SB and possible AD
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Re: More damper refinement

Postby 9121u » Mon Apr 29, 2013 2:59 pm

ED you do not want to shim tho-es dampeners.that will take out the dutch roll.. but you just masked the real problem and you will most likely end up with a cracked blade.but that's up to you i think i told you before to check the bearings at the hub clevis most likely there brindled or you have a bad damper or dampener's its hard to fix this type of problem over the web.. this is all i am going to say...be careful be safe abought it
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Re: More damper refinement

Postby seneca2e » Tue Apr 30, 2013 12:05 pm

Okay thanks Tom and and Brad. I would like to just throw a new set of dampers at it but that's $2400 and mine have less than a hundred hours on them. However they have some very minor delamination but they just don't look like they would be the problem. I'd love to have a set to try before I bought them but they're hard to come by. Gary has new ones but they have to be trimmed and he understandably doesn't want to make used ones out of new ones. As to the clevis bearings we checked the phase of the blades and had the inboard and outboard blades off with just the pylon tube on and they felt smooth. Dutch roll the vast majority of the time resides in the damper area. But throwing parts at it sure gets expensive :-)
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Re: More damper refinement

Postby Brad Bowles » Wed May 01, 2013 12:55 pm

The bearings will need a load on them to see if they are bad. This still may not show a bad bearing though.
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