Page 1 of 2 12 LastLast
Results 1 to 40 of 44

Thread: Trim and Jack Screw

  1. #1

    Join Date
    Jul 2016
    Location
    Anchorage, AK
    Posts
    131
    Post Thanks / Like

    Trim and Jack Screw

    Hello,

    I have a couple questions regarding the stabilizer jack screw assembly on an experimental pa-18 build. Do Javron's and Dakota's jack screw have the same amount of trim adjustment or does one have more? Has anyone reversed/flipped the assembly to get more trim in the opposite direction? Does anyone have weights of the Javron and Dakota assembly?

  2. #2

    Join Date
    Jan 2007
    Posts
    2,171
    Post Thanks / Like
    The yoke of both look the same and should give you more nose down trim than stock. Someone posted the thread pitch on the Dakota was different than stock and it took a few more turns, not sure if Javron is the same. In the days before belly pods more nose down trim was required due to the heavy loads and rear CG. The loads are still big but CG is better with a belly pod. What are you looking to change, nose up, nose down, or total travel?
    DENNY

  3. #3
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Dakota Cub uses an Acme thread pitch which is a finer thread. I don't see where you can get any more trim adjustment with a different jack screw, the fuselage frame is the limiting factor. Found plenty of factory Super Cubs that would not meet the TCDS for nose up and down trim. Something to pay attention to at rebuild or build.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes DENNY, mike mcs repair, moneyburner liked this post

  4. #4

    Join Date
    Jan 2007
    Posts
    2,171
    Post Thanks / Like
    The original Yoke had a nubbin on top, not flat like the new ones. If it go's away good for 1 1/2 turns or so of trim.
    DENNY
    Last edited by DENNY; 12-19-2019 at 12:52 PM.

  5. #5

    Join Date
    Jul 2016
    Location
    Anchorage, AK
    Posts
    131
    Post Thanks / Like
    Im looking to at maximizing trim. I've heard several "rumors" that I asked above and was looking to substantiate it one way or another. Thank you

  6. #6

    Join Date
    Oct 2012
    Posts
    5,602
    Post Thanks / Like
    I could write a long post about trim, trim range, linear actuators, modified yokes, CG's relationship to trim, etc. But that's based on my plane. Your plane has a better empirical knowledge base to establish the required trim range. What's the motivation to change it? Are other planes running out of trim?

    One trim mod worth considering is electric trim. Adjusting trim with my thumb on the stick is handy. The mod of the century? Probably not, but I don't miss spinning the trim handle.
    Likes Bilair liked this post

  7. #7

    Join Date
    Apr 2003
    Location
    Clearwater,Fl
    Posts
    2,559
    Post Thanks / Like
    My airplane when loaded at gross requires almost all trim down. I would position the yoke to allow for max pitch down if that is at all possible. When flying lite the trim position is still beyond the forward center.
    What fuel qnt? All has an effect. I'm not sure if there are PA 18s which suffer from the opposite trim condition. Heavy power plant would have an effect I suppose. I recall when building it was a question as to which direction the yoke went. I've seen them installed both directions.

  8. #8

    Join Date
    Jan 2007
    Posts
    2,171
    Post Thanks / Like
    Like Steve said the key is to set the plane up and measure everything while you are doing your build. Unless you have some radical cub follow the TCDS. Where did you get your airframe? Are you planning on a belly pod?
    DENNY

  9. #9
    Marty57's Avatar
    Join Date
    Jan 2005
    Location
    Nipomo, Ca
    Posts
    1,409
    Post Thanks / Like
    I bought my yoke and jack screw from Javron; he also uses ACME thread pitch. Piper used a very different pitch and Jay liked using standard ACME threaded rod. He machines it to fit the adapter for his electric trim. Nicely done work by Jay.
    Marty
    N367PS
    Psalm 36:7 "High and low among men find refuge in the shadow of His wing"
    www.marty2plus2.com

  10. #10
    WhiskeyMike's Avatar
    Join Date
    Jun 2003
    Location
    West Boxford MA
    Posts
    941
    Post Thanks / Like
    As long as we're talking -- don't mix and match components. They might not be compatible. I found the Dakota trim gear and yoke, way better than stock, less shake and a nicer product. Every plane is different, most banner planes don't have enough nose up trim.

  11. #11

    Join Date
    Jul 2016
    Location
    Anchorage, AK
    Posts
    131
    Post Thanks / Like
    Experimental Airframes 4 place. No belly pod.

  12. #12

    Join Date
    Jan 2007
    Posts
    2,171
    Post Thanks / Like
    Go talk to Kirk Ellis, he is on the South Mountain side of birchwood. He has more experience than anyone with that airframe and can tell you if stock angles and dangles work.
    DENNY
    Likes Steve Pierce liked this post

  13. #13

    Join Date
    Nov 2002
    Location
    Fargo
    Posts
    737
    Post Thanks / Like
    I've used dakota Cubs jack screw on at least 4 rebuilds and have gone back to stock/Univair screw and yolk. Dakotas are to perfect and can make it difficult to get a smooth working trim at cruse power, then if you get any gunk in it it binds up.

  14. #14
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Quote Originally Posted by PA-22/20-160 View Post
    I've used dakota Cubs jack screw on at least 4 rebuilds and have gone back to stock/Univair screw and yolk. Dakotas are to perfect and can make it difficult to get a smooth working trim at cruse power, then if you get any gunk in it it binds up.
    I have had that issue when installing the Dakota Cub jack screw assembly on 2 flying Super Cubs. Turned out both were tweaked in the tail. Have used them on the last 4-5 rebuilds with no issues. Rebuilt a friends frame and it bound but seemed like it was rectified when the tail wires were rigged. I want the jack screw assembly to last till the next recover and have found the billet, through hardened DC yoke with Acme threads far superior the the cast yoke original style. Steve Conatster in Fairbanks was going through one a season until he switched, last I talked to him he had 4-5 season on his.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  15. #15

    Join Date
    Nov 2002
    Location
    Fargo
    Posts
    737
    Post Thanks / Like
    Quote Originally Posted by Steve Pierce View Post
    I have had that issue when installing the Dakota Cub jack screw assembly on 2 flying Super Cubs. Turned out both were tweaked in the tail. Have used them on the last 4-5 rebuilds with no issues. Rebuilt a friends frame and it bound but seemed like it was rectified when the tail wires were rigged. I want the jack screw assembly to last till the next recover and have found the billet, through hardened DC yoke with Acme threads far superior the the cast yoke original style. Steve Conatster in Fairbanks was going through one a season until he switched, last I talked to him he had 4-5 season on his.
    I definitely like the quality of the dakota jackscrew and I have no problem getting them to function fine on the ground or low power settings but the issue I've had is above 2300 rpm and It must move the tail enough to bind it up. I've got a couple new airframes Alaska fuselages here for the next 2 rebuilds maybe I'll try and see if a new fuselage makes a difference.

  16. #16
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    The bonding I had was noted on the ground so never made it in the air till rectified. Have had J3s and Pacers with issues in the air but never a Super Cub.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  17. #17
    RaisedByWolves's Avatar
    Join Date
    Feb 2005
    Posts
    4,200
    Post Thanks / Like
    I tried to swap out a Dakota on my cub when it was covered and it didnít work. The tail was twisted. Thatís the main reason I rebuilt it. The trim didnít go all the way. When I rebuilt it I put Dakota in, and the oil lite bearings up in the handle. It works really smoothly now. I donít put any grease on the jack screws. Any style. Dug old solid grease out of too many airplanes


    Sent from my iPhone using Tapatalk
    Likes mike mcs repair liked this post

  18. #18

    Join Date
    Nov 2002
    Location
    Fargo
    Posts
    737
    Post Thanks / Like
    Quote Originally Posted by RaisedByWolves View Post
    I tried to swap out a Dakota on my cub when it was covered and it didn’t work. The tail was twisted. That’s the main reason I rebuilt it. The trim didn’t go all the way. When I rebuilt it I put Dakota in, and the oil lite bearings up in the handle. It works really smoothly now. I don’t put any grease on the jack screws. Any style. Dug old solid grease out of too many airplanes


    Sent from my iPhone using Tapatalk
    I don't grease them ether only a dry lube/ graphite, Dakotas trim handle is also the only way to go.
    Likes mike mcs repair liked this post

  19. #19
    Binty's Avatar
    Join Date
    Jan 2005
    Location
    South Island, New Zealand
    Posts
    381
    Post Thanks / Like
    Dakota may have addressed this issue by now... But you should read this post before you chose a jack screw. Search "Dakota Trim Concern" https://www.supercub.org/forum/showt...a-Trim-Concern
    If you force it, it will fit

  20. #20
    www.SkupTech.com mike mcs repair's Avatar
    Join Date
    Aug 2004
    Location
    chugiak AK
    Posts
    11,491
    Post Thanks / Like
    Quote Originally Posted by PA-22/20-160 View Post
    I don't grease them ether only a dry lube/ graphite, Dakotas trim handle is also the only way to go.
    Me neither, just leave them dry or it just collects grit and wears out.


    Sent from my iPhone using SuperCub.Org mobile app

  21. #21
    wireweinie's Avatar
    Join Date
    Aug 2013
    Location
    Palmer, AK
    Posts
    3,491
    Post Thanks / Like
    Quote Originally Posted by DENNY View Post
    Go talk to Kirk Ellis, he is on the South Mountain side of birchwood. He has more experience than anyone with that airframe and can tell you if stock angles and dangles work.
    DENNY
    Kirk is the #1 guy for any questions on a four place.

    Web
    Life's tough . . . wear a cup.
    Likes Steve Pierce liked this post

  22. #22
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Quote Originally Posted by Binty View Post
    Dakota may have addressed this issue by now... But you should read this post before you chose a jack screw. Search "Dakota Trim Concern" https://www.supercub.org/forum/showt...a-Trim-Concern
    Yes, the bungee cable mount has been changed to the same position as stck and the forward face that was thicker is now the same size as the original. Mark has always been receptive to my comments and criticisms.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes mike mcs repair liked this post

  23. #23
    Binty's Avatar
    Join Date
    Jan 2005
    Location
    South Island, New Zealand
    Posts
    381
    Post Thanks / Like
    Quote Originally Posted by Steve Pierce View Post
    Yes, the bungee cable mount has been changed to the same position as stck and the forward face that was thicker is now the same size as the original. Mark has always been receptive to my comments and criticisms.
    Hi Steve.

    That is good to hear.
    If you force it, it will fit

  24. #24

    Join Date
    Jan 2017
    Location
    King Salmon, AK
    Posts
    52
    Post Thanks / Like
    So you can't get more trim with a new jackscrew assembly from Javron or Dakota? I run out of nose down trim even before I get to 2000lbs. PA-18 experimental. AOI changed to 1.84 I believe and tail was adjusted to proper angles but I'm still running out of nose down trim often.

  25. #25
    www.SkupTech.com mike mcs repair's Avatar
    Join Date
    Aug 2004
    Location
    chugiak AK
    Posts
    11,491
    Post Thanks / Like
    Quote Originally Posted by adamgrenda View Post
    So you can't get more trim with a new jackscrew assembly from Javron or Dakota? I run out of nose down trim even before I get to 2000lbs. PA-18 experimental. AOI changed to 1.84 I believe and tail was adjusted to proper angles but I'm still running out of nose down trim often.
    Picture of your jack screw installation please


    Sent from my iPhone using SuperCub.Org mobile app

  26. #26
    AkPA/18's Avatar
    Join Date
    Feb 2003
    Location
    Big Lake Ak
    Posts
    726
    Post Thanks / Like
    It would also be nice to know if the elevator is resting on the down stop When you have full nose down trim cranked in. Sometimes if the bungee is too short, it deflects the elevator up which requires more nose down trim. You can run out of nose down trim pretty easily if this is the situation.
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

  27. #27

    Join Date
    Jan 2017
    Location
    King Salmon, AK
    Posts
    52
    Post Thanks / Like
    Quote Originally Posted by mike mcs repair View Post
    Picture of your jack screw installation please


    Sent from my iPhone using SuperCub.Org mobile app
    Pictures are attached let me know what you guys think

    also have a pulley with no cable running through it. Not sure if thatís relevant to this topic or not.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	CF36A7BE-93DA-4B59-AD87-57EB2E3AFEE5.jpg 
Views:	67 
Size:	65.1 KB 
ID:	46845   Click image for larger version. 

Name:	D2304850-0F8A-4E23-84B3-46EC0FC12B6A.jpg 
Views:	73 
Size:	59.7 KB 
ID:	46846   Click image for larger version. 

Name:	D21845F4-7281-469C-BFEE-70B2BA64BD0B.jpg 
Views:	91 
Size:	46.6 KB 
ID:	46847  

  28. #28

    Join Date
    Jan 2017
    Location
    King Salmon, AK
    Posts
    52
    Post Thanks / Like
    Mark, I think it is. Let me know what you think off the pictures?

  29. #29
    AkPA/18's Avatar
    Join Date
    Feb 2003
    Location
    Big Lake Ak
    Posts
    726
    Post Thanks / Like
    Adam, easy to tell. Just start cranking nose down Trim in, when the stick stops moving forward the elevator should be on its stop. Then you go back to the tail And physically see if the elevator is on the down stop. Should hit the stop when you still have 4 to 6 Turns left nose down.
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory
    Likes mike mcs repair, flylowslow liked this post

  30. #30

    Join Date
    Jan 2007
    Posts
    2,171
    Post Thanks / Like
    Is the pulley on the right pic broken?
    DENNY

  31. #31
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    2,516
    Post Thanks / Like
    That cable runs below the brown pulley guard? Is that what you noted? It's been some time but isn't that for another trim spring on floats or?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	D21845F4-7281-469C-BFEE-70B2BA64BD0B.jpeg 
Views:	67 
Size:	115.4 KB 
ID:	46850  
    Last edited by BC12D-4-85; 02-05-2020 at 12:22 AM.

  32. #32
    www.SkupTech.com mike mcs repair's Avatar
    Join Date
    Aug 2004
    Location
    chugiak AK
    Posts
    11,491
    Post Thanks / Like
    Quote Originally Posted by BC12D-4-85 View Post
    That cable runs below the brown pulley guard? Is that what you noted? It's been some time but isn't that for another trim spring on floats or?
    Lower elevator cable missrun there. I fell for that also at first glance


    Sent from my iPhone using SuperCub.Org mobile app

  33. #33

    Join Date
    Jan 2017
    Location
    King Salmon, AK
    Posts
    52
    Post Thanks / Like
    Quote Originally Posted by mike mcs repair View Post
    Lower elevator cable missrun there. I fell for that also at first glance


    Sent from my iPhone using SuperCub.Org mobile app
    Denny,
    no pulleys are broken.

    mike,

    ill reroute cable through pulley. Also do I just pull the elevator spring or is there something else I need to do? Does this count as the issues for lack of trim?

  34. #34

    Join Date
    Oct 2008
    Posts
    134
    Post Thanks / Like
    Quote Originally Posted by Steve Pierce View Post
    I have had that issue when installing the Dakota Cub jack screw assembly on 2 flying Super Cubs. Turned out both were tweaked in the tail. Have used them on the last 4-5 rebuilds with no issues. Rebuilt a friends frame and it bound but seemed like it was rectified when the tail wires were rigged. I want the jack screw assembly to last till the next recover and have found the billet, through hardened DC yoke with Acme threads far superior the the cast yoke original style. Steve Conatster in Fairbanks was going through one a season until he switched, last I talked to him he had 4-5 season on his.
    This is correct doing three to six min takeoffs and landings a day from May 10th till Sept 23 I would wear out a univair yoke in one season installed a Dakota and this year I think will be 7 seasons still good shape I Had to shorten the bungie assist cable 1” it attaches in a Different spot than original piper
    Likes Steve Pierce liked this post

  35. #35
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    2,516
    Post Thanks / Like
    Threaded jackscrews take lube beyond oil or even none. Alaska Airlines discovered that to some sadness 20 yrs ago. It's a source of fretting and moly (MoS2) based lubes can help defer that wear.

    Gary
    Thanks boarfish thanked for this post

  36. #36
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Quote Originally Posted by adamgrenda View Post
    Denny,
    no pulleys are broken.

    mike,

    ill reroute cable through pulley. Also do I just pull the elevator spring or is there something else I need to do? Does this count as the issues for lack of trim?
    That pulley is for the bottom bungee cable that is not needed on your airplane. DO NOT run the elevator cable through that pulley.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes mike mcs repair liked this post

  37. #37
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Quote Originally Posted by supercub24a View Post
    This is correct doing three to six min takeoffs and landings a day from May 10th till Sept 23 I would wear out a univair yoke in one season installed a Dakota and this year I think will be 7 seasons still good shape I Had to shorten the bungie assist cable 1” it attaches in a Different spot than original piper
    Dakota Cub rectified the trim cable mount so you can now use your stock trim cable.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  38. #38

    Join Date
    Jan 2017
    Location
    King Salmon, AK
    Posts
    52
    Post Thanks / Like
    Ok. Thanks for the clarification. I do have one spring it may be the top. This doesn't sound like the out of trim issues explained tho.

  39. #39

    Join Date
    Nov 2020
    Posts
    6
    Post Thanks / Like
    What is the deal with the dakota cub pulley, seems like its always bigger than original one and 2 groove vs 1 ?
    Thanks barrow pilot thanked for this post

  40. #40
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    20,153
    Post Thanks / Like
    Quote Originally Posted by cubpilot2020 View Post
    What is the deal with the dakota cub pulley, seems like its always bigger than original one and 2 groove vs 1 ?
    Same diameter and number of grooves. Only the very early Super Cubs had a single groove trim system.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

Similar Threads

  1. Jack Screw Trim Pulley
    By fisher.garrett in forum Super Cub Sick Bay
    Replies: 2
    Last Post: 06-01-2011, 08:44 AM
  2. Trim Jack Screw Fairing
    By Darrel Starr in forum Modifications
    Replies: 8
    Last Post: 02-06-2008, 10:04 PM
  3. Jack Screw
    By Henry Baker in forum Cafe Supercub
    Replies: 15
    Last Post: 04-24-2005, 08:26 PM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •