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Thread: Elevator Travel ??

  1. #1
    supercub's Avatar
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    Elevator Travel ??

    I have a friend that has a J-3 that has a O-200 PA-18-95 fwf. The fuselage from the upper longerons up has been converted to PA-18. Lower fuselage is J-3. It has PA-18 balanced elevators. We've checked the up elevator and it's 24.5 degrees, which is what spelled out for PA-18's. The trouble is, when making a 3 point landing you run out of elevator. I know the specs for J-3's and PA-11's call for 34 degrees up...........Do the specs call for 24 or 34 degrees for balanced elevators on a J-3, which it's still certified as. I use to own a similar Cub, except mine didn't have balanced controls, and the up trouble was set to the J-3/PA-11 specs and never had trouble making 3 point landings. Any suggestions. Thanks
    Last edited by supercub; 11-11-2019 at 11:01 PM.

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    What is the stabilizer travel when plane is level? How are you trimming for landing?
    DENNY

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    skywagon8a's Avatar
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    What is the loaded CG? It may not be the plane's fault.
    N1PA
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    supercub's Avatar
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    Not sure what you mean by stab travel when level. Have full stab travel on jack screw. typically trim for light stick pressure for landing, and have configured for different CG and problem exists in all ranges. Different pilots have flown the airplane all CFI's with lots of time as PIC and CFI in Cubs. All experience the same problem.
    Quote Originally Posted by DENNY View Post
    What is the stabilizer travel when plane is level? How are you trimming for landing?
    DENNY

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    Pick up the tail until firewall is vertical. Stabilizer travel should be 2.5 degrees up and 4 degrees down. If you are running out of trim you may have a bent fuselage or stabilizer could be off from previous repairs. How much nose up trim do you have left when you trim for light stick pressure? Have you simply tried full nose up trim when landing? Did you measure the elevators to make sure they came off a 18? Any paperwork in the logs on how to set the balanced elevator? Just things to think about.
    DENNY

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    I would think in this plane's case more than 24.5° is needed and would be a safety factor to have it. Clearly it does not appear to be a trim issue since the lack of elevator authority is over a wide range of loading.
    Not knowing just how the documentation shows the modifications I would say there must be the option of selecting the travel range needed for full flight operations. The plane might not need the full 34° but seems to need more than 24.

    When you look into this, just where is the travel limit set and is there room to increase it?

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    Since he says the airplane is in standard category, whoever provided “approved data” for the changes should have provided appropriate rigging instructions and travel limits. If those don’t exist, then I would question the legality of the alterations.


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    I have a J-3 that I installed PA-18 tail surfaces on I/A/W the Wilbur’s STC. Instructions were to remove old surfaces and install new surfaces. As I expected, elevator authority was improved. Elevator travel is per the J-3 TCDS.
    Mark
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    Steve Pierce's Avatar
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    Quote Originally Posted by mam90 View Post
    I have a J-3 that I installed PA-18 tail surfaces on I/A/W the Wilbur’s STC. Instructions were to remove old surfaces and install new surfaces. As I expected, elevator authority was improved. Elevator travel is per the J-3 TCDS.
    Yep, unless the STC says otherwise it is still a J3 under the J3 TCDS.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    I have a similar plane but it has flaps it has a pacer tail. I considered putting an 18 tail on it Initially I was trimming off stick pressure on landing At very slow speeds I found marginal elevator authority. I started landing it without trimming out stick pressure and found elevator authority significantly increased. With forward trim the leading edge of the horizontal would reduce elevator effectiveness it works well enough that I decided not to install 18 horizontals and elevators

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    Any update on progress with this problem. A photo of stabilizer location on landing might help.
    DENNY

  12. #12
    supercub's Avatar
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    Owner is out of town for a week or so. He's going to check paper work when he returns and we'll go from there. Thanks for all the input.
    Quote Originally Posted by DENNY View Post
    Any update on progress with this problem. A photo of stabilizer location on landing might help.
    DENNY

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