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Thread: Changing out PA-12 bungee cords

  1. #1

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    Changing out PA-12 bungee cords

    I’m in the middle of an extended annual and need some help. I need to do my periodic replacement of my bungees and my normal source of expertise and tooling has retired and moved to Florida. Any ideas as to how to safely get them swapped out? Any help would be appreciated.

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Been decades maybe this tool. I had one. I bent it too. Not sure if it applies to yours. We always just put 18 gear on -12 s

    http://m.aircraftspruce.com/catalog/...clickkey=17935


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  3. #3
    cruiser's Avatar
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    Under the resources tab on Univair’s website you will find a link to service bulletins and other hints and tips pertaining to the PA-12. Look far enough and you can find instructions on shock cord replacement. Clyde has instructions in an old Cub Clues for building the tool. IMO building the tool to pivot on the bend and the hook for the new cord on the end works more conveniently. Support the airplane, sit in the back seat to pull down on the tool and the cord up on the hook in front of the truss. When you see the tool plans it may be somewhat clear.

  4. #4

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    I have the above mentioned cub clues tool I would gladly loan out if you pay freight, it doesn't make it easy but it works. The last set i did I used the tool and I tied the plane to the floor (or a ramp tie down hub), and stretched the bungles with a webbing strap on an engine puller and used the tool and some silicon lube to slip the bungles in place. If you don't anchor the plane to the ground the engine puller just lifts the plane
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.
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  5. #5
    cruiser's Avatar
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    I have used a modified version of Clyde’s tool on two bungee change outs. I thought it went well. Move the tool pivot point to the bend in the tool and the hook to the short end. Man A sits in the back seat and pivots the tool up and towards the panel with the hook on the front side of the truss. Hook the bungee on the back side, under and then to the hook. Pull down on the tool and Man B finagles the bungee in place. Fairly easy to hold down against the bungee when the geometry is correct. Not so easy to push up against the bungee as the tool is designed. IMO, Jim

  6. #6

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    I used a 1970's General Motors bumper jack modified for a stock PA12 according to an article in an old Club Clues. I used 3/8 rod to make a hook and it straightened out on the very first bungee. 1280HDs are tough! Switched to 1/4 inch rope instead of the hook and I thought I was dead when the rope broke on the third bungee but nothing got hurt. Double loops held up for the left three bungees but even that was near failing on the last one. You can't use enough lube on the third bungee on each side. We resorted to slipping strips of plastic bag material into critical spots to get more slippery effect. I have no desire to do this again.
    You can't get there from here. You have to go over yonder and start from there.

  7. #7
    Charlie Longley's Avatar
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    I’ve changed several by myself using a modified handyman jack. It’s a little cowboy!
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  8. #8
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    I tackled this project a couple of years ago. I couldn’t find the tool I was told was out there and even after, I really haven’t figured how it would work. I ended up using 2 engine hoists. One to support the wing, (it had a closed foam pad on a frame that would swivel both pitch and roll) and the other stuck through the door to the bungees. Ended up using a tape they use in pulling wire through conduit to lift with (2500# rated). We got it done, but don’t know if I would do it again. You can’t believe how much force it takes to stretch and position them. You could get hurt easily.
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  9. #9
    skywagon8a's Avatar
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    Quote Originally Posted by JCM View Post
    I tackled this project a couple of years ago. I couldn’t find the tool I was told was out there and even after, I really haven’t figured how it would work. I ended up using 2 engine hoists. One to support the wing, (it had a closed foam pad on a frame that would swivel both pitch and roll) and the other stuck through the door to the bungees. Ended up using a tape they use in pulling wire through conduit to lift with (2500# rated). We got it done, but don’t know if I would do it again. You can’t believe how much force it takes to stretch and position them. You could get hurt easily.
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    A very graphic reason for installing PA-18 gear on a -12.
    N1PA

  10. #10

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    I've never had to do this on my 12 however it makes me wonder.
    1. How much does it cost to have a mechanic perform the change and how often should it be done?
    2. I've heard switching to pa-18 gear kills speed. What is the fastest and lightest better great option for a certified pa-12?


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  11. #11
    Gordon Misch's Avatar
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    Yes, the -18 gear does cost some speed. I converted to -18 gear on my -12, and think if I had it to do over I'd probably stick with the stock -12 gear arrangement.

    I made a tool to change out bungees with the stock gear and it wasn't hard to use. Pull wheels together with rope and spanish windlass, cut bungees off of one side, and stretch new ones on. Then cut off and replace the other side. One man job. More time tying the wheels together and removing the gear fairings and seat than doing the bungees.

    I don't have the tool anymore though.
    Last edited by Gordon Misch; 08-14-2018 at 11:17 PM.
    Gordon

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  12. #12

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    It's a couple hour job for a couple people, not as bad as everyone makes it out to be. Especially since you only need to do it every 10 years or so, at least the way I fly.

    The only reason I can see to switch to 18 gear is if you are on floats or landing in places I don't go.

    I also prefer the way 12 gear lands compared to 18 gear, oh so smooth....
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.

  13. #13

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    Changing Bungees not so bad

    Quote Originally Posted by Gordon Misch View Post
    Yes, the -18 gear does cost some speed. I converted to -18 gear on my -12, and think if I had it to do over I'd probably stick with the stock -12 gear arrangement.

    I made a tool to change out bungees with the stock gear and it wasn't hard to use. Pull wheels together with rope and spanish windlass, cut bungees off of one side, and stretch new ones on. Then cut off and replace the other side. One man job. More time tying the wheels together and removing the gear fairings and seat than doing the bungees.

    I don't have the tool anymore though.
    I’d like to echo Gordon’s remarks. I bought my Super Cruiser three years ago, and was overly anxious about changing bungees. After talking with an old time IA who rebuilds Cubs for a living, he confirmed Gordon’s method is the simplest and safest. You don’t want to be messing with screwdrivers or anything that could turn into a projectile from a snapped or popped bungee. The same IA welded a bungee tool out of 1” square tubing that made it really simple to stretch the bungees over the upper keepers after feeding both ends up through the belly.

    The whole job took maybe two hours total, most of which was prep (removing front seat, access panels, ratchet strapping the wheels to relieve bungees, and cutting the old bungees - nothing to be afraid of, just take a box cutter or knife and gently slice - it may snap just a bit, depending on how worn it is, but nowhere near explosive as I expected - I wouldn’t suggest trying to hold a razor blade by your fingers and cutting one though!). We did have to spend about 20-30 min rewelding the tool a few times to get the correct angles needed to retain the bungee on the tool until over “top dead center,” so to speak. Here’s some photos showing the tool and how it was used. You can see where there are several holes drilled to obtain the right stretch for each bungee, depending on how many you use (I only installed two 1280HDs per gear, and think three would have been way too stiff for my purposes). Note that we also used vice grips to prevent the tool from moving left or right on the gear truss as it was rotated up and forward to gradually stretch the bungee up and sliding it over the keeper. I’ll make detailed measurements of lengths and angles of the tool and post them along with more photos. Next time will be a piece of cake after having done it under the tutelage of an experienced IA! Thanks again Gordon, for your advice and the other bungee tool you sent me.

    Shane
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  14. #14
    skywagon8a's Avatar
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    A modified old fashioned car bumper jack does a good job too.
    N1PA

  15. #15

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    This is a bungee too I got for installing bungees on a Pitts.
    no more holes in the ceiling, missing teeth etc..
    so easy it takes all the fun out of it.
    im thinking it would work on a PA18, not familiar with 12 set up but judging from photos think it would.
    ”T” handle can be replaced with a nut for more clearance if needed .

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    Last edited by Oliver; 04-01-2020 at 07:56 PM.

  16. #16
    NDRII's Avatar
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    Last month had to help a friend, new -12 owner, change bungees on standard -12 gear.

    We built the Piper tool based upon their instructions for a -12 tool, except you’ll see we used/had 2 inch flat stock, since he had it.

    Hoisted the airplane by the engine mount and installed all 3 bungees on each side. Took more effort on each of the last ones, but it was not bad at all.

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  17. #17

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    Recently replaced my 12 bungees with the ACS type tool. Was very easy. Lube with tire talc or bees wax where they slide over on the bottom. Less than an hour for the install with the access disassembly done. Do not sweat it.

    GM
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  18. #18

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    Great info on this thread guys. I am a little confused though about which cords and how many per side. My airplane has 3 per side currently, how do you know which cords were used? Is there a chart? Is the 1280HD the only acceptable cord?
    I found a chart in Spruce catalog, it lists 1280HD requirement as 4. Are regular 1280s not acceptable for PA-12's?

  19. #19
    NDRII's Avatar
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    When you cross reference the original Piper part number from the PA-12 parts manual to the Univair part number it is 6- 1280s (not 1280HD). 6 -1280s is what we installed on his -12 back in March, worked just fine.

    The PA-12 Parts Catalog can be found online on the Univair website.
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  20. #20

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    Quote Originally Posted by PA-12driver View Post
    Great info on this thread guys. I am a little confused though about which cords and how many per side. My airplane has 3 per side currently, how do you know which cords were used? Is there a chart? Is the 1280HD the only acceptable cord?
    I found a chart in Spruce catalog, it lists 1280HD requirement as 4. Are regular 1280s not acceptable for PA-12's?
    That chart shows 4 or 6 depending on how stiff you want your suspension. As far as I could find, the 1280HDs are the only ones authorized. I had 3 per side but since I’m not landing out in the boonies, I decided to install only 2 per side and I thinks that’s plenty! Suggest you try that as you can always add a another if you want.

    Good luck!
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  21. #21

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    Thank you both for your quick responses. So Univair says regular 1280's and Spruce says HDs, lol. Do you guys know how to determine what is on the airplane? How do you distinguish between regular and HD? I had no issue with how the airplane handles, so I'd like to jsut keep it the same. Here is a photo of what is on there now
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  22. #22

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    Quote Originally Posted by PA-12driver View Post
    Thank you both for your quick responses. So Univair says regular 1280's and Spruce says HDs, lol. Do you guys know how to determine what is on the airplane? How do you distinguish between regular and HD? I had no issue with how the airplane handles, so I'd like to jsut keep it the same. Here is a photo of what is on there now
    Should be identified in your logs, since they're both the same dimensions. How long have your current cords been on, and were they already installed when you bought your PA-12? Reason I ask is because mine were already on and I had no issues with how they felt either, and only realized how soft they were after changing them. You may be surprised how stiff 6 cords are, unless you’ve flown one with new cords?

  23. #23
    TurboBeaver's Avatar
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    At Lodge we have a saying " knowledge is the secret of the unscholered mind".
    It is very obvious from this thread, and all the other ones on this subject over the years. That very very few folks, actually know how to do these correctly.
    The amount of highly modified levers, contraptions, and gizzmos that have been
    tryed; is mind boggling. Quite interesting how many different ways it has actually been accomplished, from innovative minds! In late years it has become the accepted standard to simply cut brand new ones off instead of simply removing them.
    Or as Mike suggests to avoid changing them in Alaska, they usually throw the whole gear away! And replace it with 18 gear to the tune of $3/4000 bucks.
    Guess there will always be a hundred different ways to skin the same cat!
    Keep up the good work, it's always an interesting subject the old PA 12 bungee
    drama.
    E


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