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Thread: Sb00020

  1. #21
    Administrator Pete D's Avatar
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    Default Re: Sb00020

    Quote Originally Posted by turbopilot View Post
    Thanks Pete. So the need for a heavier torque tube comes from some other decision on structural analysis and the caution about loose sticks as per SB15, still applies? What I am trying to understand is whether the torque tube wall thickness is some how related to loose sticks or was the inclusion to replace the torque tube in SB15 because the rivet holes became elongated in the original torque tube?
    The decision to make sure all aircraft had the heavier torque tube came about from additional analysis/testing that was done as part of an internal audit. Again, no failures or issues in the field other than the looseness that drove SB15 originally. The thicker tube helped keep the rivets tighter but was not required at the time if the rivets were not loose. It is now required.
    Pete Dougherty
    Customer Support Manager
    Cub Crafters Inc

  2. #22
    Senior Member turbopilot's Avatar
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    Default Re: Sb00020

    Quote Originally Posted by Pete D View Post
    The decision to make sure all aircraft had the heavier torque tube came about from additional analysis/testing that was done as part of an internal audit. Again, no failures or issues in the field other than the looseness that drove SB15 originally. The thicker tube helped keep the rivets tighter but was not required at the time if the rivets were not loose. It is now required.
    Ok, as you might guess I am looking for good information to make a decision about preceding with the torque tube replacement or just wait to see if my rivets get loose, then replace the tube. I understand the CC position about do it now.
    Bob Anderson, CC11-00435, N94RA

  3. #23
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    Default Re: Sb00020

    I just started SB20/15. Prior to starting I checked for lateral play as described in SB15 and noted no play. After removing the elevator control system we noted significant play between the torque tube and aft stick mast in the longitudinal direction. The rivet holes had wallowed out along the axis of the torque tube. With the controls off there was still no lateral movement but significant longitudinal. I have just purchase my airplane S2 S/N 77 with 240 hours.

    I am posting this because I was concerned that the SB might have done more damage than good. I stand corrected.

    Pat Anderson

  4. #24
    Senior Member turbopilot's Avatar
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    Default Re: Sb00020

    First, I want to thank CubCrafters for working on continuous improvement in the cub. Clearly as soon as they identify a weakness in the design they are moving forward with recommended fixes. This is good news.

    I still have the feeling we are missing something on the excess play issue involving the torque tube and the mast. Reading the documentation for SB15/20, it would appear the "thicker wall" torque tube was introduced into production beginning with SN147. I draw this conclusion because SB20 specifically excludes torque tube replacement on serial number greater than 146.

    However, I understand that several aircraft with serial numbers above 146 have experienced a loose torque tube/mast condition. If this is true then the SB15 solution of installing a thicker wall torque tube would seem to be insufficient to deal with the problem first identified in SB15.

    I had the opportunity to closely inspect my aircraft (SN121) today. The mast and torque tube are attached using 4 Cherry Max Rivets (5/32 x 1/4). Here is a picture of my rear stick assembly with one of the rivets in clear view.

    IMG2344-L.jpg

    With an inspection mirror I can visualize the rivet heads on each end of the torque tube.

    IMG2347-L.jpg

    Currently in my airplane with the "thin walled" torque tube my rivets seem fully secure with absolutely no play in the torque tube mast connection for either sick in any axis.

    Each stick represents a significant lever arm which can apply a significant force to the mast torque tube connection. Given the difficulty getting into the seats of the cub (particularly the rear seat) I have personally seen passengers putting significant stress on the control stick in a fully deflected position usually with a foot as they try to get into the rear seat. I would also wonder about the impact of the common practice of using a seat belt to secure the stick against wind thrashing at the control surfaces when the aircraft is parked.

    So I have a concern that the rivet junction between the mast and the torque tube is going to be susceptible to damage with a thin or a thick walled torque tube. It would probably be less susceptible with a thicker walled torque tube but evidently not immune to damage as we have seen in the field.

    So if all above is true, I would submit the SB15 should caution against "control stick abuse" and require torque tube replacement "on condition" when play is found to exist between the mast and the torque tube. Upgrading to the thicker torque tube, may reduce the chance of damage but will not eliminate that possibility.

    Just my two cents.
    Last edited by turbopilot; 03-01-2012 at 09:30 PM.
    Bob Anderson, CC11-00435, N94RA

  5. #25
    Administrator Pete D's Avatar
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    Default Re: Sb00020

    The two SBs came about because of two different reasons.

    SB15 was due to the possibility of play in the rivets on some aircraft. The thicker torque tube at that time was to give more for the rivets to grip.

    SB20 is due to further testing of the design it was decided that all existing aircraft should be upgraded to the heavy duty torque tube.

    Again, there have been no failures in service. The only issues in the field have been the loose rivets that originally triggered the issuance of SB15.
    Pete Dougherty
    Customer Support Manager
    Cub Crafters Inc

  6. #26
    Member rlinford's Avatar
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    Default Re: Sb00020

    I understand the frustration but to put some perspective on this I bought a 2003 CessnaT206H from the factory. You would think after making them for 40 years Cessna would have it figured out but no, it was a constant litany of SB's and AD's. It's just goes with owning an aircraft. Unfortunately fear of litigation has increased the frequency of them and it is smart to think about what your being asked to do because sometimes they are a bit silly. Cessna had problems with their seatback caused by "gravitationally challenged" people breaking them. I ignored the first SB (GASP!) because I thought the fix made no sense and sure enough 5 iterations later they got it right and I did it.

    In the case of anything to do with controls my opinion is to be extremely conservative and do what the factory recommends. If there is any chance of the stick breaking off in my hands, even if it's a small chance, I want to spend the money and fix the problem. Especially where I may have some innocent person sitting behind me that trusts I take care of things. Especially in a plane with no backup to the electric trim, meaning someday I may be making a landing with a lot of stick force.

    I dont like the hassle and expense but I'm really glad they went back and found a potential deficiency and let me know about it before I put my 10 year old in the back seat and took off. I would hate for them to sit around the conference room debating whether to issue a SB only because they were concerned about an angry backlash.
    Last edited by rlinford; 03-02-2012 at 11:59 AM. Reason: Keeps removing spaces between words!

  7. #27
    Senior Member turbopilot's Avatar
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    Default Re: Sb00020

    Quote Originally Posted by rlinford View Post


    I dont like the hassle and expense but I'm really glad they went back and found a potential deficiency and let me know about it before I put my 10 year old in the back seat and took off. I would hate for them to sit around the conference room debating whether to issue a SB only because they were concerned about an angry backlash.
    I agree with all you said. I have owned several Bonanza's and Cirrus aircraft over the years. Some of the SB's on those aircraft must have been written by the legal department not the engineering department.

    We have Service Bulletin 15C before us now with Service Bulletin 20"A" telling us to now do SB15C, no matter the serial number. Before I tear the airplane apart I was just trying do determine if there might be the need for an SB20B, in the near future telling us to do SB15D, because SB15C was not full answer. Been there several times with my Cirrus aircraft.

    Looking at the fix before us, I am just not convinced that a slightly thicker walled torque tube is the full answer to loose sticks. But what do I know, I am just an owner.
    Bob Anderson, CC11-00435, N94RA

  8. #28
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    Default Re: Sb00020

    I wrote the last email about the longitudinal play prior to removing the rivets that connect the torque tube to the aft mast. Upon further inspection of the inside of the mast, there was grease wicking through the rivet hole to the inside of the mast. No grease was noted on the outside. This was a clue to what we found next. After carefully removing the rivets, it was discovered that the wallowing that was creating the play was in the mast not the torque tube. The holes in the torque tube were round and the holes in the machined mast were slotted. In addition, there was grease saturating the junction between the torque tube and the mast.

    Pat Anderson

  9. #29
    Member rlinford's Avatar
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    Default Re: Sb00020

    Quote Originally Posted by andersop View Post
    The holes in the torque tube were round and the holes in the machined mast were slotted. In addition, there was grease saturating the junction between the torque tube and the mast.

    Pat Anderson
    That's interesting, can you post a picture?

  10. #30
    Senior Member Springloaded's Avatar
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    Default Re: Sb00020

    Figured I would just make a new stick out of 4130 instead of reinforcing Aluminum one. Saw one similar to this on a SS.
    Chuck
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