Likes Likes:  0
Page 1 of 4 123 ... LastLast
Results 1 to 40 of 137

Thread: Elevator Spring

  1. #1

    Join Date
    Nov 2003
    Location
    Jonesboro, Arkansas
    Posts
    108
    Post Thanks / Like

    Elevator bungee

    OK I'm a little stumped again or just maybe overconcerned. Had great help from John at Cubs Unlimited giving me the correct length for the cable connecting the bungee spring to the jackscrew tower. Now when the cables are hooked back up and the elevator raised the spring drops down and rubs or hitts the elevator turnbuckle. Just does not look right to have two cables hiting like this. Is this normal? Also, if horz attachment is in midway position, where do we want the elevator?

    One more...The old elevators cables were larger that 1/8".. I tried to find the part numbers on Northlands CD 13745-03 and 10870-07 but had no luck. Mine is a PA-18-150 1960 18-7402. thank you in advance for any help.

  2. #2
    Bugs66's Avatar
    Join Date
    Feb 2004
    Location
    Spokane WA
    Posts
    2,309
    Post Thanks / Like
    10870 is on my drawings viewer. Couldn't find 13745.

    www.supercubproject.com/drawings

    Not sure if that is what you are looking for.

  3. #3
    RMREBOB's Avatar
    Join Date
    Oct 2002
    Location
    Arlington, Texas
    Posts
    264
    Post Thanks / Like
    Bugs, Cool web site. Whose is it?

  4. #4
    cubunltd's Avatar
    Join Date
    Mar 2004
    Location
    Belle Vernon,PA
    Posts
    1,138
    Post Thanks / Like
    Glidertow,
    What you are describing is normal. with the horizontal stab. raised about 1 7/8" from the top of the upper longeron to the middle of the sat. tube, the elevator should be approximately even with the stab. These are approximate measurements and may vary a little.
    The cables should be 1/8" Lower cad. plated cable p/n is 13745-00 and the S.S. cable is 13745-03. Upper cad. plated cable p/n is 10870-07 and the S.S. one is 10870-16. Or you can fabricate your own.
    Look at the illustrated Parts book on the CD. page 144and 145

    John

  5. #5
    Bugs66's Avatar
    Join Date
    Feb 2004
    Location
    Spokane WA
    Posts
    2,309
    Post Thanks / Like
    Quote Originally Posted by RMREBOB
    Bugs, Cool web site. Whose is it?
    Mine but for everyone. Glad you like it.

  6. #6

    Join Date
    Jun 2002
    Posts
    1,343
    Post Thanks / Like
    delete

  7. #7

    Join Date
    Nov 2002
    Posts
    7
    Post Thanks / Like

    Elevator Spring

    Hey Guys, I bought a elevator bungee spring from Dan's A/C to put in my 75hp J-3. As I am putting on PA-18 elevators and floats. My question is..when you have full nose up trim the tension is very strong on that spring and the elevator is then full up. Now I don't have the bottom balance spring as there is not a place for it on the J-3. How will this fly in flight? Fuselage not covered yet so any tip would be appreciated.

  8. #8

    Join Date
    May 2003
    Posts
    127
    Post Thanks / Like
    My Cuby is set up that way. No problems with it in flight, but sometimes on a long taxi it can get a little tiring fighting the spring and holding back stick.
    Dumb me, just thought I should go to full up trim on taxi and let the spring hold the stick back for me, then full down when going down wind, Duh!

  9. #9
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,992
    Post Thanks / Like
    I like it better with no spring at all.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  10. #10

    Join Date
    Sep 2003
    Posts
    6,875
    Post Thanks / Like
    Me, too, and the best handling Super Cubs (up to 160 hp, at least) are the ones with very, very weak springs. Opinion. What is wrong with the little J3 tail suirfaces?

  11. #11
    Clyde and Susan's Avatar
    Join Date
    Dec 2005
    Posts
    602
    Post Thanks / Like
    Can the bungee be removed from a PA-11 legally? I can't see why it was needed in the first place. Anyone know the real reason it's there? ...Clyde Davis

  12. #12
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    The spring is for stability. I don't understand how a weak spring or no spring helps the flight characteristics, or makes the stick work easier. When you pull the stick back the spring and cable go's limp. Look at a cub with a few hours on it. The fabric will be cracked at the base of the vertical fin from the cable and spring bouncing around.

  13. #13

    Join Date
    Sep 2003
    Posts
    6,875
    Post Thanks / Like
    I am the world's worst when it comes to feeling stuff. But I can sure feel the difference between a really tight spring and no spring - the lighter the spring, the better the aircraft feels to me. I'll look tomorrow for the fabric cracks, but so far have not seen anything jump out at me.

    Tightly sprung elevators cannot tolerate going from zero flap to full flap without some winding on the trim - loose springs? I don't even bother trimming in the pattern. Stability? Never flew an unstable Cub.

  14. #14
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,992
    Post Thanks / Like
    Feels better to me when horsing around not have to push against the spring on the 90 hp SC I fly. Flew it a lot with and without. It is a pain to install on a covered fuselage too. After installing the balanced elevators I doubt it makes any difference.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  15. #15
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    Never flew an unstable Cub
    Pull the nose up 14 degrees and let go of the stick and see how many oscillations it takes to return to level flight. The military wanted it to return when in 3 oscillations and thats why they had 2 springs. Has more to do with certification than anything.

    I still don't understand how you fight the spring when your flying because when you pull the stick back it loses tension. Only time I feel the spring is on the initial take off roll when I push the stick forward.

    I think there's other factors as to why some cubs seem to need more trim than others. EWCG, tire configurations, bent tails, wing mods etc.

  16. #16

    Join Date
    Mar 2007
    Posts
    518
    Post Thanks / Like
    The spring in the tail of my 12 broke not too long ago and I considered flying without it, but Clyde Smith Jr recommended that I replace it ASAP. Can't remember if he said why, but he was pretty adamant about it. I thought the elevators were really heavy when I first started flying the airplane, but I've gotten used to it and don't think much about it anymore. Might be different if I had balanced surfaces.

  17. #17

    Join Date
    Jan 2003
    Location
    nd
    Posts
    3,354
    Post Thanks / Like
    I always thought that the bungees were installed depending on if you had the short pivot new style control in your airplane or the long pivot old style like in the j3s or 11s. Some even have them top and bottom. What is the real scoop? doug

  18. #18
    S2D's Avatar
    Join Date
    May 2002
    Location
    Montana
    Posts
    4,068
    Post Thanks / Like
    glad this came up.
    I was just installing mine in my rebuild and had two old worn out ones. both different lengths. Wanted to find out if anyone else thought there was a correlation between light elevator controls and this bungee before i bought a new one the right length

    Having flown a bunch that felt different, I'm almost ready to agree with Bob. I think there is some correlation, I just don't know what. my old 55 model with a worn out spring was real light on the elevator, my 75 is stiffer.
    I may be wrong but that probably won't stop me from arguing about it.

  19. #19

    Join Date
    Jul 2003
    Location
    Clovis, CA
    Posts
    232
    Post Thanks / Like
    I flew another SC that felt like it had power assisted up elevator in the flare compared to mine which felt hard in the flare. I did notice that I had a bushing type pulley up front on the floor where the cable makes a 180 return towards the tail.

    I bought another SC project and noticed that it had a ball bearing pulley instead of the bushing type. Haven't finished the project, so I can't make the judgement. I do know that if you replace the 4 bushing pulleys out in the wings where the cable makes a 90 degree turn with ball bearing type, it is a lot easier and worth the money.

    Also, I noticed that if you run a string line along the hinges on the horizonal you will find that the bell crank area is 3/16" forward of the line. This has to make for a harder operation of the elevator. Every SC I have checked has been this way.---------PALHAL

  20. #20

    Join Date
    Sep 2003
    Posts
    6,875
    Post Thanks / Like
    No, I don't think it makes any difference. The cables apply a force couple, acting on the hinge line. Makes no difference whether their bolt holes line up with the hinge line in some fashion.

    I delight in flying Cubs without winding on the trim. That's why I find the bungees objectionable. I absolutely love pattern work, and the Cubs I fly have two flap settings - zero and as much past 50 as I can get. One Cub I fly cannot make that transition without much re-trimming.

  21. #21
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    I delight in flying Cubs without winding on the trim. That's why I find the bungees objectionable
    Pretend I'm your student. Explain to me how that spring effects trim.

  22. #22
    dreamer's Avatar
    Join Date
    Feb 2007
    Location
    Somewhere over the Rainbow
    Posts
    286
    Post Thanks / Like
    Confused student here... I don't understand how adjusting the trim OTG could substitute for correct positioning of the elevator whilst taxiing (or have I just read it wrong??) Please 'splain!

  23. #23
    S2D's Avatar
    Join Date
    May 2002
    Location
    Montana
    Posts
    4,068
    Post Thanks / Like
    Quote Originally Posted by kase
    I delight in flying Cubs without winding on the trim. That's why I find the bungees objectionable
    Pretend I'm your student. Explain to me how that spring effects trim.
    with a stiff spring, your horizontal would be higher for level flight since you wouldn't need to crank the horizontal down as far to get as much up spring pressure to the elevator.

    would flying with your horizontal lower make the elevator lighter, or is the spring even relevant in most flight configurations?

    I realize pulling on the stick unloads the spring, but from hands off to pulling on the stick, different spring pressures should mean the horizontal stabilizer is set in a little different spot


    another question. i've heard If you have a supercub with a high angle of incidence, you need to run the jackscrew higher in cruise flight. would a weak spring help this??
    I may be wrong but that probably won't stop me from arguing about it.
    Thanks Jonnyo thanked for this post

  24. #24

    Join Date
    Sep 2003
    Posts
    6,875
    Post Thanks / Like
    Pretend you are my student? The elevators on a Cub are very light without a spring forcing them to be in a certain position. So, no matter what you do or how you load it, it takes a feather touch to move the elevator to compensate. Put a big fat spring in there and it takes more force to move the elevator plus spring. In fact, there may be places where a weak captain cannot overcome the spring - just so in the Cub I mention. Requires lots of forward trim on flap extension, because I simply do not have the strength to shove the elevator far enough forward. There may be more to it, but what's the point? If you can make an aircraft fly without regard to trim position, why would you want to modify it so that it couldn't be flown with a broken trim system? Some regulatory thing about recovering from a Vne dive?
    Thanks Jonnyo thanked for this post

  25. #25
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    Some regulatory thing about recovering from a Vne dive?
    Thats new to me, please explain?

    How big of spring are you using? If you need lots of forward trim at flap extension your going to fast.



    there may be places where a weak captain cannot overcome the spring
    I would say you got the wrong part then.


    I think you should take that spring out of that cub you cant fly and report back to us if it makes a difference or not.

  26. #26

    Join Date
    May 2003
    Posts
    127
    Post Thanks / Like
    Confused student here... I don't understand how adjusting the trim OTG could substitute for correct positioning of the elevator whilst taxiing (or have I just read it wrong??) Please 'splain!
    Dreamer, Sorry for the confusion. My Cuby is a homebuilt, and the original builder did not use the standard Cub trim. He installed a spring on the top elevator control horn with a cable to the trim wheel in the cockpit. Adjusting the trim stretches the spring and moves the elevator. So full up trim is also almost full up elevator, full down trim is full down elevator. So on the ground you can be fighting the spring, and it can get pretty tiring on a long taxi.

  27. #27
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    Brian, I dont know how much difference a new or a wore out spring would make in level flight as to where the jack screw would be or if it would have any effect on elevator pressure.

    Guy from Piper told me the spring is for stability. Look at this example. 2nd airplane down.

    http://selair.selkirk.bc.ca/aerodyna...ity/Page3.html

    When we rebuilt my cub we replaced the spring and cable with parts from univair and I dont have any problem or need to trim when landing. My 9 year old can land the plane with no problem.

    When he comes into the pattern and starts to reduce power the nose will start to lower. I just have him hold a little back pressure and then when he pulls 1 notch, 10 degrees, it levels the nose and needs no pressure. When he turns base it takes some back pressure, pull on the next notch and it helps the turn and if you aint going to fast you dont need any pressure. Turn final and full flaps it lands its self.

  28. #28

    Join Date
    Mar 2007
    Posts
    518
    Post Thanks / Like
    I'm beginning to see that the aforementioned spring in a SC is different from the spring in my 12. I think it's there on the 12 because I don't have balanced surfaces. It's there to help with feel or something -- ain't got nothing to do with the trim. I don't think there is but one and it's at the very top of the elevator bellcrank and I think it is held by a piece of cable to an airframe member and not part of the trim or control system. If this is so, then all it does is provide resistance -- feel. Any of you guys ever fly a Tripacer with the bungees removed? The controls are so very light and quick (and scary the first couple of times) it is almost unbelievable compared to a Tripe with the interconnecting bungees hooked up. Maybe that's why Piper put these things in our airplanes back in the day.

  29. #29
    SuperCub MD's Avatar
    Join Date
    Jan 2002
    Location
    Collins, Wisconsin
    Posts
    1,349
    Post Thanks / Like
    It's interesting that the spring appeared in the PA's, while the J series did not have them. The J's all had the engines mounted straight, while the PA's had the engined tipped down below the thrust line. I kind of suspect Piper may have put in the spring to increase the nose up/tail down trim to offset the down thrust of the engine. Down force on the nose and tail will increase stability, but at a loss of performance because the wings need to create more lift to off set the down force.

    I'm one who likes a SUPER CUB with a light, or no spring at all. You could assume that a PA18 with zero thrust may not even need a spring as long as the engine installed is not to heavy. (I edited this to only include the PA18, not applicable to other models.)

  30. #30
    SuperCub MD's Avatar
    Join Date
    Jan 2002
    Location
    Collins, Wisconsin
    Posts
    1,349
    Post Thanks / Like
    Quote Originally Posted by oldbaldguy
    ain't got nothing to do with the trim. I don't think there is but one and it's at the very top of the elevator bellcrank and I think it is held by a piece of cable to an airframe member and not part of the trim or control system.
    It's attached to the trim horn, and has everything to do with trim. Do not fly a 12 without the spring installed.

  31. #31

    Join Date
    Mar 2007
    Posts
    518
    Post Thanks / Like
    Well, that shows how much -- or little -- I know.

  32. #32

    Join Date
    Sep 2003
    Posts
    6,875
    Post Thanks / Like
    I am willing to admit that it has been a while since I studied the PA18 bungee system. There are pulley brackets back there that mystify me. The Thrustline discussion is currently one of my favorites, but here again all of us are waving our arms, and nobody (well, almost nobody) has rock-solid information. It has been said that nobody remembers why Piper canted the engine down, and that maybe it was only for visibility over the nose? We have one pilot here who is sure the zero thrustline has dramatically improved longitudinal stability. The recovery from a dive theory of bungee installation is likewise a rumor - I had heard the Feds made Piper do it. Rumors are worth next to nothing.

    What we probably should do is go in there and look - and publish a schematic of the bungee, and then theorize about what it should do. We probably should look for some concrete data on a lot of these neat STCs - I am about to decide that glowing reports of improved handling are often based on unreliable emotions. But I admit - it is fun to speculate without doing any of the hard work. Yours - nobody.

  33. #33
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like

  34. #34
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,992
    Post Thanks / Like
    Before the Top Cub was certified on it's on TC Jim Richmond explained the changes they had to make to the bungee system to meet the new requirements. I have slept to many times since then but it was along the same lines as the article Kase posted.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  35. #35
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,992
    Post Thanks / Like
    Maybe Todd can fill us in on the requirements.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  36. #36
    SuperCub MD's Avatar
    Join Date
    Jan 2002
    Location
    Collins, Wisconsin
    Posts
    1,349
    Post Thanks / Like
    Piper Service Letter 150 gives the reason for the lower bungee installation on the first 18's and 105's is that the military required it for stability. The SL also gives approval to remove the lower bungee to lighten the stick force. There are still some early 18's running around with the lower bungee, I'd get rid of it if I had one.

    The upper bungee installation is a spring connected to the upper elevator horn connected to a cable that runs forward, over a pulley, and down to the trim yoke where it is connected. When the trim is adjusted nose up, the trim yoke pushes the front of the stab down and pulls the cable/spring which pulls the trailing edge of the elevators up. The effect of this is the elevator providing additional down force making the nose up trim more effective. Cubs which are nose heavy (like PA12's) need more spring tension to help the nose up trim. If you reach inside a Super Cub and crank the trim while looking back at the tail feathers you can easily see what is going on, this ain't rocket science.

    I think this is the way the upper bungee would be installed on all the long wingers, I don't think any of this would apply to the short wingers. I haven't flown a PA15 for a lot of years, but I don't even think it had trim. The later short wingers have the trim yoke mounted upside down, springs, cables, and crap running everywhere, I've never messed with one enough to figure out what it all does.

  37. #37
    kase's Avatar
    Join Date
    Feb 2002
    Posts
    1,565
    Post Thanks / Like
    Apparently the J3 couldn't exceed 140% of its landing speed with forward CG and your hands off the stick. To much drag? PA11 probably could because its faster?


    with a stiff spring, your horizontal would be higher for level flight since you wouldn't need to crank the horizontal down as far to get as much up spring pressure to the elevator
    This is a picture of my tail after I landed. 2500 rpm, 98 mph trimmed for level flight. Didnt touch the trim to land. Assuming my elevators trail my stabilizers it would tell me the cable and spring are limp and doing nothing in cruise flight.


  38. #38
    Widebody's Avatar
    Join Date
    Oct 2006
    Location
    ND/AZ
    Posts
    747
    Post Thanks / Like
    I agree with Kase, here's a pic of mine today after landing. 2500 RPM/94 MPH trimmed for level flight. I never touch the trim to land. My spring has almost 500 hrs on it.

    My buddies 12 has a large surface square elevator that hangs ALL the way down and I never trim to land his either.



    Brad

  39. #39
    Widebody's Avatar
    Join Date
    Oct 2006
    Location
    ND/AZ
    Posts
    747
    Post Thanks / Like
    Hmmmm. No more posts.
    Looking at Kase's and my tail, I will assume that if we swapped springs, we would still be landing in the same trim configuration on our planes.
    And if we removed the spring completely the configuration would be the same also. So although the elevator moves in reference to the horizontal, it doesn't really effect the trim configuration but more so the stick pressure and stability. Is that what's been determined????

    Brad

  40. #40
    S2D's Avatar
    Join Date
    May 2002
    Location
    Montana
    Posts
    4,068
    Post Thanks / Like
    Brad & Kase:
    actually your pictures seem to contradict each other, Brads horiz is lower and the spring was working during cruise and Kase's is higher and doesn't seem to be working. Probably contradicted what I said about spring tension and horiz placement too, but I'm still trying to figure that part out.

    How were each of you loaded?
    I may be wrong but that probably won't stop me from arguing about it.

Similar Threads

  1. Elevator assist spring
    By eski in forum Cafe Supercub
    Replies: 1
    Last Post: 05-14-2009, 10:40 PM

Tags for this Thread

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
  •