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Dragon wings are hitting my torque tube, why?

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  • N447MR
    started a topic Dragon wings are hitting my torque tube, why?

    Dragon wings are hitting my torque tube, why?

    UPDATE below.
    Okay- So I finally got back to the airport yesterday and to my surprise, the teeter block was NOT in the top hole. This really surprised me because I thought that it had been there all along and so hadn't considered it further. Always humbling. None of the guys at the hangar thought of it in all this time either. I'm very grateful to have the additional online forum help, thank you.

    With the block now in the top hole, the teeter is as it should be.



    CLT Tandem Air Command, Subaru 2.2, Warp drive prop, 28or 29' dragon wings, electric prerotator. I've got over 100 hours on this machine. Sure does fly nice as best I can tell. More stick shake than I'd like since flying my friends MTO, but perhaps its as good as it gets.
    Problem is, if there's any kind of wind that gets under the rotor before or as I'm spinning them up, they can be at such an angle that the hub will hit the torque tube on the mast. Until I'm up over 50 rpm or so it can do this and it hits it enough to be really un-fun and it can stop the blades. It will even be on an extreme enough angle that it can scrape the ground if I'm taxiing out and don't have the rope on it. It doesn't matter if I have the stick forward or not because it is teetering so that it doesn't matter the angle of the whole head. I've attached pictures that I took in the hangar where you can see there where it can hit the tube. (though it would hit the other side when spinning, it was just to take a pic). some have suggested I need a rubber stop of some kind under the teeter block to act as a stop, but I don't know what that does when I need the stick forward, I don't know how the "teetering" looks when spinning at flight speeds.
    As it is now, I taxie down close to the end of the runway and pull the blades down with the tie rope so I can get hold of them. Then I give them a good heave-ho and try to engage the prerotator ASAP so they spin up before any wind can cause them to teeter too much. This has happened only a few times, but I don't like it and when I go out to have fun on a windy day it concerns me cause it can hit hard, then I have to go back and make sure nothing is messed up(and it hasn't been yet other than a couple small gouges out of the hub corner).

    Tried to be clear, but please let me know if I can be more clear. Just want to find out if this is either something to live with, fix, or could be dangerous beyond what I've already explained.

    Thank you very much for the help.

    Geoff
    Attached Files
    Last edited by N447MR; 05-26-2018, 06:10 AM. Reason: updated to include the answer found later in the discussion

  • Gyro28866
    replied
    I did not like what I saw. I am thinking this is not a RFD machined tower. Ernies towers have a roller bearing in them and the bushings are teetering in the roller bearings. If yours are just bushing to tower and they have wore the slop into it. That is likely the culprit for the odd stick shake. Instead of just flapping/teetering on a fixed position, it is also able to move out of center; and is flapping on a moving out of center position.
    I am no expert, by any stretch. But my gut feeling is excessive wear in bushings and towers.

    Leave a comment:


  • N447MR
    replied
    Originally posted by Gyro28866 View Post
    Normally , YES.
    However, if you have a heavy blade and the the rotor is following it, the stick will move in a circular motion; and you are shimming to migrate the rotating mass to center.
    I think I get the centering idea. The hat bearing moves in and out of the tower a tad so when it’s all tightened up it can move as much as that.
    I found a when I took the rotors off this time I found extra play in the left side bearing. The measurements of the hole in the tower seem off. 0.75” side to side 0.78” up and down. I took a video. What do you think?

    Leave a comment:


  • eddie
    replied
    looks like it might benefit from making sure the blades are centered between the towers.

    A few thousands will make a lot of difference.

    Leave a comment:


  • N447MR
    replied
    Originally posted by N447MR View Post

    Flew it with ONE shim on the Left side, where I left off, and I couldn't say it was any better, maybe a bit worse? Then I added two back to have a total of THREE on the left side. I feel like it had a strange feel to it, and was probably a bit worse, but I couldn't pin point it. So I put a FOURTH one in there and put it away. Hopefully I'll fly it tomorrow. Four seems like a lot looking at it. We'll see.
    Flew it with ONE shim on the Left side, where I left off, and I couldn't say it was any better, maybe a bit worse? Then I added two back to have a total of THREE on the left side. I feel like it had a strange feel to it, and was probably a bit worse, but I couldn't pin point it. So I put a FOURTH one in there and put it away. Hopefully I'll fly it tomorrow. Four seems like a lot looking at it. We'll see.

    Flew it with FOUR shims expecting obviously worsening condition, but didn't. Was kind of indecisive really.
    Went back down to TWO shims expecting it to be obviously smoother, but is wasn't. Probably better than when I started...I think maybe; but I wouldn't bet much on it.
    So, I gave up. Four shims was visually alot. I figured if there wasn't a change there then FIVE was just being silly. YES, NO?

    Took some video today using the SLO MO on the iphone. Kinda worked out. I may make a new thread sumamrizing all your input just to make anyone searching this topic again easier.
    Video link here.
    https://youtu.be/U64oam8WTS0

    Leave a comment:


  • N447MR
    replied
    Originally posted by N447MR View Post

    Put ONE shim under the Right side of the teeter block and hub bar and didn't notice anything I could be sure about. Put a second shim in the Right side and at first didn't seem to notice much, but then realized over 50-60 mph indicated it felt really bumpy on the stick. Looking at the blades there was still definite separation (two lines).

    Took both shims out of the Right side and installed BOTH (two shims) on the Left side. Definitely noticed a smoothing and certainly was nicer over 60mph. Fairly certain that the separation of the two blades was less too. It was a nice night so I just flew around for 45 minutes at that point.

    After putting the Gyro away, I took One shim OUT so there is now ONE shim in the left side instead of two. I will see how that feels next time and either go to three or leave it. I'll let you know!

    How many shims would you all think it would normally take? How many is too many?
    Flew it with ONE shim on the Left side, where I left off, and I couldn't say it was any better, maybe a bit worse? Then I added two back to have a total of THREE on the left side. I feel like it had a strange feel to it, and was probably a bit worse, but I couldn't pin point it. So I put a FOURTH one in there and put it away. Hopefully I'll fly it tomorrow. Four seems like a lot looking at it. We'll see.

    Leave a comment:


  • Gyro28866
    replied
    Thanks for getting back. Between the washer and the hat then. Are they put on both sides equally?
    Normally , YES.
    However, if you have a heavy blade and the the rotor is following it, the stick will move in a circular motion; and you are shimming to migrate the rotating mass to center.

    Leave a comment:


  • N447MR
    replied
    Originally posted by Gyro28866 View Post
    The shims are placed where in the drawing you have the washer.
    NOTHING goes where you have 1 and 2 indicated.
    Thanks for getting back. Between the washer and the hat then. Are they put on both sides equally?

    Leave a comment:


  • Gyro28866
    replied
    The shims are placed where in the drawing you have the washer.
    NOTHING goes where you have 1 and 2 indicated.

    Leave a comment:


  • N447MR
    replied
    Originally posted by N447MR View Post

    Perfect, I'll give it a try and report back. I thought I read someone saying they just loosened the teeter tower bolts and slipped shims in. Also, as note for future readers, Mr. Boyette emailed me back and told me that there are no torque specs of any consequence for the teeter block bolts that hold the tower to the hub. Just tighten it up real well.



    Put ONE shim under the Right side of the teeter block and hub bar and didn't notice anything I could be sure about. Put a second shim in the Right side and at first didn't seem to notice much, but then realized over 50-60 mph indicated it felt really bumpy on the stick. Looking at the blades there was still definite separation (two lines).

    Took both shims out of the Right side and installed BOTH (two shims) on the Left side. Definitely noticed a smoothing and certainly was nicer over 60mph. Fairly certain that the separation of the two blades was less too. It was a nice night so I just flew around for 45 minutes at that point.

    After putting the Gyro away, I took One shim OUT so there is now ONE shim in the left side instead of two. I will see how that feels next time and either go to three or leave it. I'll let you know!

    How many shims would you all think it would normally take? How many is too many?
    Last edited by N447MR; 06-07-2018, 05:58 AM.

    Leave a comment:


  • AirCommandPilot
    replied
    The teeter bolt, teeter block, and hat bushing should all move as one piece. That block assy should move together back and forth within the tower with the 4-8 thousands tolerance.

    Leave a comment:


  • N447MR
    replied
    Originally posted by Gyro28866 View Post
    Hello Geoff:
    Between the bushings and tower there is a plastic washer inserted. The aluminum SHIMS are placed between the plastic washer/shim and bushing top. You are shimming to close the gap to 4 to 8 thousands total.
    If you shim out all the gap/play and the teeter block and tower are being pushed together, you will have a pronounced stick shake (two per rev vibration) and probable galling and heat buildup at the tower and bushing area.
    I took the rotors off a couple days ago to check balance (seem pretty darn good still) and everything looks good to me visually. I didn't notice any plastic washers. There's no galling or apparent heat build up or wear. The only washers are on the outside of the teeter towers between the bolt head and on the other side between the nut and tower. I attached another crude drawing.
    Should the plastic washer you reference be on the inside of the teeter tower?
    Does the plastic washer contact the teeter block, or is it between the bushing and the teeter tower somehow?

    I numbered the options I tried to explain the second drawing, but I don't know if it is clear.


    Leave a comment:


  • N447MR
    replied
    Originally posted by gyromike View Post
    I think I made mine about 3/4" wide and as long as the side of the block, and punched a hole for the bolt.

    You will start noticing a difference from the first shim.
    Stick a shim under one side and it will either get better or worse.
    If it gets worse, move it to the other side and keep adding until the blades tips are in track.
    I kept adding shims until it went out of track again slightly, then removed shims until it was back in track.

    Perfect, I'll give it a try and report back. I thought I read someone saying they just loosened the teeter tower bolts and slipped shims in. Also, as note for future readers, Mr. Boyette emailed me back and told me that there are no torque specs of any consequence for the teeter block bolts that hold the tower to the hub. Just tighten it up real well.



    Leave a comment:


  • Gyro28866
    replied
    Hello Geoff:
    Let me see if I can explain this in a way that makes sense and you can visualize.
    The teeter bolt and Bushings/Majic hats and Teeter block are a rigid/solid component. If machined correctly, there will be several thousands clearance.; as much as 20 thousands clearance to the Teeter Towers. This will allow the teeter block and hub bar to move side to side within the tower. Between the bushings and tower there is a plastic washer inserted. The aluminum SHIMS are placed between the plastic washer/shim and bushing top. You are shimming to close the gap to 4 to 8 thousands total. You should be able to take a flathead screwdriver and move the teeter block back and forth between the towers and have a total of only 4 to 8 thousands play. And you are trying to get it shimmed to the exact rotational center.
    If you shim out all the gap/play and the teeter block and tower are being pushed together, you will have a pronounced stick shake (two per rev vibration) and probable galling and heat buildup at the tower and bushing area.
    Hope this helps and hope to see you at Mentone.
    Start making a list of questions to ask while you are there.

    Leave a comment:


  • gyromike
    replied
    I think I made mine about 3/4" wide and as long as the side of the block, and punched a hole for the bolt.

    You will start noticing a difference from the first shim.
    Stick a shim under one side and it will either get better or worse.
    If it gets worse, move it to the other side and keep adding until the blades tips are in track.
    I kept adding shims until it went out of track again slightly, then removed shims until it was back in track.

    Leave a comment:

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