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Thread: Trim Actuator

  1. #11
    Senior Member efwd's Avatar
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    Default Re: Trim Actuator

    One thing concerning me here. If you have not flown your aircraft yet, then you might consider the words in the manual. It is suggested that the 7/16inch is established as a safe place to initiate first flight as this is purposefully establishing a slight nose heavy situation as apposed to a nose high on lift off and possible stall. You can make adjustments after first flight to improve trim. Everyones Wt. & Balance will be different.
    Eddie

  2. #12
    Senior Member jiott's Avatar
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    Default Re: Trim Actuator

    Good point Eddie. It can't hurt to go by the book to start with, even knowing you will probably change it later.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #13
    Senior Member Flybyjim's Avatar
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    Default Re: Trim Actuator

    Eddie,
    I am a long way away from flight, just setting the stab on for the first time and setting up the actuator. In a couple of other builds the minimum of turns into a receiver for an end rod was stated as 10 turns so when I could only have 6 turns for the 7/16 distance I became concerned and wondered how others set up. Thanks for your reply.

  4. #14
    Senior Member jtpitkin06's Avatar
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    Default Re: Trim Actuator

    Quote Originally Posted by Flybyjim View Post
    I am very frustrated with adjusting the trim actuator and trying to get this to work. I have searched past posts and found John P. post from 2014 but my situation and his resolve do not seem to match.
    My actuator stroke is 4 inches, with the rod end all the way in at full stroke I have 3/4 inch between tubes. If I turn the rod end out (you can not turn the actuator rod to try to lengthen the rod end even if you remove the jam nut) to get the 7/16" called for in the instructions my rod end is only turned in 6 turns leaving 12 turns out of the actuator, this can not be correct. What am I doing wrong? Is 4 inches correct for the stroke of the piston.

    Jim
    Jim,
    I'm going back to your original question.

    Let's suppose you elect to use the recommended 1.5 times the diameter for thread engagement. The rod end ( ball joint, Heim joint... Whatever you call it), is AN3 threads; or, if you like, call it a 3/16-32 screw.

    So 1.5 times 3/16 is 9/32 or 9 turns.

    Now, you say you get only 6 turns engagement when the starting clearance of the stab is set to 7/16. Remember that dimension is plus or minus 1/16. To be comfortable turn the rod end in another 3 turns and you are only off by 1/32 in the nose up direction.

    Also note that most pilots are opting for a little more nose up trim which would screw your rod end inward even more.

    I'd say your trim actuator is not a sleep loss item. The important part is the horizontal stab does not hit the fuselage in either the full up or full down position.

    To answer your other question, the travel of the actuator is 4 inches and is not adjustable. Only the total length is adjustable by turning the rod end in or out.

    John Pitkin
    Greenville, TX

  5. #15
    Senior Member Maverick's Avatar
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    Default Re: Trim Actuator

    Hello. I have a question about the trim actuator that doesn't necessarily go along with this message string but I didn't see another string that would be more appropriate so, I'm going to add it here.

    I have a series 5 kit. The actuator that I have can be seen in the diagram below. The instructions call for there to be a bearing (P/N-93027.000). To put that in you are instructed to ream out the housing. Then you are to use a bushing, (P/N-11002.00). It seems to me if you ream out the housing it weakens the part. And, the bushing fits nicely in the housing so, what is the need to put in the bearing? It seems that the load will be on the AN3 bolt and the bushing. And, the amount of rotation on the bolt is really very limited so is the bearing really necessary. What do you think about this? Ream with bearing and bushing? Or no ream and bushing only?

    Thanks.
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  6. #16
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    Default Re: Trim Actuator

    This configuration of bearing-bushing-bolt is common practice. The whole point is to have the bearing a snug fit so that it doesn’t rotate. The bushing does the rotating. I wouldn’t just put the bushing in with no bearing and allow that to rotate in the actuator. You’ll oversize the hole over time. Reaming of the hole to get the bearing in has already been considered by the designer when determining the strength.
    David
    SS7 Builder

  7. #17
    Senior Member jrevens's Avatar
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    Default Re: Trim Actuator

    David’s right. Even though the arc of rotation is very small on this assembly, it is poor practice in general to use the surface of a bolt as a rotating bearing surface. The enlargement of the hole for insertion of the “bearing” is also relatively minor in this instance.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  8. #18
    Senior Member jrevens's Avatar
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    Default Re: Trim Actuator

    Quote Originally Posted by jrevens View Post
    David’s right. Even though the arc of rotation is very small on this assembly, it is poor practice in general to use the surface of a bolt as a rotating bearing surface. The enlargement of the hole for insertion of the “bearing” is also relatively minor in this instance.
    Hey Maverick,

    I just re-read what you posted, and my reply didn’t really address what you were asking about... sorry about that. I must have been tired! David’s reply is more accurately to the point.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

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