Lateral rolling aka "Dutch Roll"

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Lateral rolling aka "Dutch Roll"

Postby seneca2e » Sat Dec 15, 2012 7:20 pm

Well we finally got to test fly the Brantly. At first we were elated but have since run into a aggravating issue. The thing flies good solo but when loaded to gross with two people it has a pronounced Dutch Roll in hover as well as cruise(made worse in turns when g force is increased it seems). Several people have said they've not seen the Dutch Roll in a hover just in cruise. Dutch Roll actually as applied to an airplane is not what it does but I think that is the term most use to describe this movement. It is a lateral up and down movement(more like if you moved the cyclic left and right say as opposed to the yaw type movement you would get if you worked the anti torque pedals).The Dampers only have a few hours on them time wise but are 11 or 12 years old calendar wise and they look great-like new in fact. It has aluminum damper brackets. We put in a new set of blade thrust bearings which did absolutely no good at all. If anything I think it's slightly worse with the new bearings. It was so windy on this second test it was hard to gauge but the problem is still there big time.

What is weird is how it is weight dependent, somewhat g load dependent, and also seems to get worse after it's flown a little while. I took my lightweight daughter for about an hour's flight yesterday and it didn't do much at all for about 30 minutes then it did it. You can put a heavier passenger in there and bring it to gross weight and it does it after just a few minutes. So weight dependent and somewhat time dependent. It usually will come out of it(had to set it down a couple times to get it to quit) but then it'll come back. The longer you fly the more it wants to do it. If anyone can help please weigh in with whatever ideas you have. Has anyone ever seen this "Dutch Roll" or whatever my lateral up and down movement is called in the hover before?
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Re: Lateral rolling aka "Dutch Roll"

Postby 9121u » Sat Dec 15, 2012 7:56 pm

HI you might want to check the clevis bearings or the blades where the dampener fork goes on the blade holes might me oblong in the fork or blade check this for now. have some other idea's if this is not it. hope this helps...
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Sat Dec 15, 2012 8:13 pm

Thanks Tom please throw any other ideas you have out there. It is very appreciated! The damper bolt holes look surprisingly good. Clevis bearings-you're talking about the main inboard flapping hinge bearings? They seem okay but have not actually removed bolts to feel them by hand. Man I feel like somebody busted my balloon and stole my candy to get this close and have another issue :-). I was looking forward to racking up a bunch of time after waiting 30 years to fly my own Brantly.
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Re: Lateral rolling aka "Dutch Roll"

Postby Ron Spiker » Sat Dec 15, 2012 8:35 pm

A dutch roll almost always comes from the outboard hinge general area. Here's a few areas to check, besides what Tom already suggested:
- Take the dampers off, out of the cage, and check for any separation between the steel and rubber. Don't put too much force on it, so you don't separate them by hand.
- I've heard of some problems with the aluminum cages, and that the steel cages are better and alieviate some problems. [I have some new ones if you need them, BTW.]
- Are the outer blades 100% in line with the inner blades?
- Are the pylon shafts completely/exactly in phase (120° apart)?
- If the hole where the damper fork bolt goes through is not oblonged, does the damper fork make a tight connection to the blade?
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Re: Lateral rolling aka "Dutch Roll"

Postby 9121u » Sun Dec 16, 2012 7:57 am

HI ED RON just finished the rest on what to look for.. that is the only thing left has to be.. one of them. that is the only that causes dutch roll......hope you get her going
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Sun Dec 16, 2012 11:43 am

Thanks very much for the comments and suggestions Ron and Tom. I really thought it would be in those areas as well and I'll go back and check those even more carefully. I know one thing I'm going to look at is the rubber bushing 342-5 in the elongated hole that allows the blade to lead and lag. I think the rubber is slight protruding there. Even though we left the bolts pretty lightly torqued to minimize this I think trimming them slightly so there's absolutely no friction at the top and bottom against the 342-16 washer might be in order. I'm going to double check the exact length of the damper as well-book calls for 2.850 inches from the inside of the fork to the back of the damper housing-I suppose that can change slightly after putting the blades exactly in line but shouldn't be much different I'm thinking. I'm pretty sure I checked that 2 years ago but at this point I'm going to have to really be precise and eliminate some stuff for sure. Aggravating problem to be sure. I wound up selling my old Enstrom when I could never get it to stay smooth(even had the factory guys come and work on it at the time)so I hope to get this resolved before I get too aggravated with it.
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Re: Lateral rolling aka "Dutch Roll"

Postby 9121u » Sun Dec 16, 2012 4:37 pm

ED there is a easy quick way to check what's going on with the outer blades. is to grab hold of one blade by hand with rotor brake on.. lift up and move fore and aft to See how much movement you have. do this to all 3 blades some times can fill extra movement if this is the case have some one else do it for you and look at the dampener area for play or whats moving in components you should find it. if then nothing there then go up buy the clevis and hub check for movement a few thousands up there is a half inch at tip of blade that means bearings is worn.. I do this check before every flight to get a fill how there supposed to be. I am positive you'll find excessive movement . the blade should only move slightly on the dampener.... helicopters take time.. remember the old saying fly for 1 hr work on it 10 hrs...
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Re: Lateral rolling aka "Dutch Roll"

Postby bryancobb » Sun Dec 16, 2012 5:59 pm

Ed,

If you haven't done a track & balance yet, you may find that playing "swap-er-roo" with the outer blades may magically solve it?

The piece of 3/4 diameter rubber hose gets trimmed off flush on top and bottom of the hinge block. The two thick steel washers slide fore/aft as the blade leads/lags. The steel sleeve fits very tightly inside the hose and needs to be wet to slide in. I made a tool to install/remove them and it was a pretty hard pull. The AN-4 bolt/washers/ doesn't have to be very tight because it only tightens against both ends of the sleeve.

I have talked to very few folks who had their damper forks fit well to the blade root. You cannot tighten the AN-3 bolts tight enough to expect the fork to
not slide in/out on the skin. Most everyone puts some type shim between the fork and root to make sure the tiniest bit of lead/lag is immediately working the dampers. It's not really allowed but there's just not much way around it unless you have brand new dampers and you machine the lengths of the threaded ends exactly to length so you don't need shims. There needs to be NO slop between the fork and the blade after the AN-3 is installed with no nut.
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Sun Dec 16, 2012 10:00 pm

Thanks Bryan. Excellent points all! That's why this board is so valuable. This info will all be there for the next guy with this problem. I'll post what fixes it when I get it resolved for sure.
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Tue Dec 18, 2012 6:34 pm

Okay I THINK we have it fixed. Kind of windy today and it was getting dark so only got to fly it a few minutes. Here's what we did. Unfortunately we did not have time to do one thing at a time and then try it to see what actually fixed it but here's how it played out. To start with we replaced the thrust bearings as I stated earlier(total waste don't go there first EVER on a dutch roll hover or cruise). The next things were all done before the next flight-one inboard blade had a minuscule amount of play where the yoke is riveted on with the double row of steel rivets so those were reriveted. Next the rubber bushings that have the steel bushings that go thru them and allow the blade to lead and lag was trimmed flush to allow the washers to slide easily on the flat surface. The steel bushing should always be the limiting factor and when the bolt is tightened it should be against the steel bushings and you should not have any binding of the big flat steel spacer washers against extruded rubber from the rubber bushings against the universal joint assembly. Next we removed all the dampers(they were the -3 dampers) and took them apart and inspected them. They were very, very tight in the housings. We sanded the dampers- mainly the steel washers which are part of the damper sandwich-which had rubber on them and other extruded rubber was removed if it was binding(the book actually mentions this) and their housings. Also please note that there are at least two lengths of damper housings-mine were the shorter ones with the -3 dampers. I saw some longer ones that had longer black dampers that we did not use. The net effect I guess would be the same but if you put a short rubber damper in a long housing or a long damper in a short housing the damping would have to be effected.

We also replaced the aluminum damper brackets with steel ones(which both pieces had to be changed the old aluminum piece the newer steel brackets mated to wouldn't mesh correctly. We did reuse my old dampers and housings as I previously said. We then lined up the blades with the string method from the inboard blade row of rivets to the outboard blade trailing edge-be careful if the threaded damper rod protrudes thru the fork. If it does it must be sanded(belt sander works best) or it will contact the root of the blade. If machined or sanded smooth this might actually be good. It would be the same as shimming except the contact area with the blade root would be much smaller so shimming would still be preferred if you want to get that clearance to zero. We did not shim ours as they were fairly close and the bolt holes were not elongated. Now it's time to fly after a quick check of the track.

It won't crank. ^&*^^&^( The new Lamar lightweight starter has issues. We got it fixed miraculously-brush blocks loose inside and overheated. By the way be careful if you take one of these apart since if you rotate the permanent magnet housing incorrectly the starter will work but turn backwards.

Finally time to fly and the Dutch Roll in hover is gone. Only got up to 80 in cruise but it seemed okay.

I'm not ready to 100% call it fixed but it just might be. Gonna fly it more tomorrow.
Last edited by seneca2e on Tue Dec 18, 2012 10:27 pm, edited 2 times in total.
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Re: Lateral rolling aka "Dutch Roll"

Postby Ron Spiker » Tue Dec 18, 2012 6:47 pm

Good news! Let us know after the flight tests.

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Re: Lateral rolling aka "Dutch Roll"

Postby bryancobb » Wed Dec 19, 2012 4:44 am

My Bet would be...

Tightening up the loose rivets, loosening up the dampers inside the housing so they were free to work, and the steel brackets, all 3 contributed to the fix. My guess is that you are done.
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Wed Dec 19, 2012 9:56 pm

Okay I flew it 3 hours today! I flew it solo and with three different weight passengers-135 pound passenger, 160 pound passenger, and a 225 pound passenger(all family members). There was no dutch roll in hover in any of the flights. However with the heavy passenger I did get a little dutch roll at cruise especially in turns. So this might be as good as it gets. I'll continue to strive for zero-maybe I'll shim the last bit of clearance out of the damper clevis fork to blade root junction and try that(doesn't cost anything-I like that kind of maintenance). Short of putting some brand new dampers and housings on(and remember mine only have a few hours but are 11 calendar years old) I don't know what else to try. It's definitely good enough but of course perfection is always the goal.

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Re: Lateral rolling aka "Dutch Roll"

Postby bryancobb » Thu Dec 20, 2012 5:52 am

My My! That's a good looking ship there!

Reeeeally makes me miss mine. I talked to Cy Russum several years ago and even brand new ships had these "come and go" occurrences of the rocks.
Ed, this has nothing to do with Dutch Roll, but let me tell you something to check for safety.

I have found 3 ships that had cracked "ears" on the 2 mixing levers, right behind the pilot's left ear, where the right/left cyclic pushrods connect to the levers.
The rod ends require a conical washer on each side. Many times, mechanics put in ones that are too thin (or leave them out). Then when the AN-4 bolts are tightened, it squeezes the 2 ears together and brakes one almost all the way off. It is very hard to see the crack.
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Re: Lateral rolling aka "Dutch Roll"

Postby seneca2e » Thu Dec 20, 2012 8:58 am

I actually found one of those conical washers down on the floor beneath the oil screen. They get dropped quite often and are hard to come by. All mine are in there though so I guess I have a "spare" lol. Bryan you need to hunt you down another Brantly-you have too much knowledge of the machine not to own one!
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