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Safety cables and shoulder harnesses for an L-2?

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  • #16
    Originally posted by RyanShort1 View Post

    Can we agree to disagree??? This was about a decade ago and was why a certain aircraft I used to fly had them installed. I wasn't on board when this happened.
    I would wonder if the shock strut had been properly inspected to start with. bungees don't normally snap unless they was not changed routinely, or was improperly installed and were cut during the process. Saftey cable is a good backup, but should not be necessary on the L-2.

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    • #17
      I have seen bungees that are 15-20 years old on airplanes that were flying, not safe or wise...and the new pilot/owner had no clue...and the experienced owners were too cheap and bragged on how long they were able to get on a set of bungees...they were about half sheared through the rubber, but they saved $100 by waiting to change them. Same person spent $7k on ads-b though...
      Last edited by astjp2; 05-15-2019, 11:37.
      N29787
      '41 BC12-65

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      • #18
        Replace them every five years or per the manufacturer's recommendation. They are dated vis color threads imbedded during manufacture.

        Read this and decide how lucky you are today: https://www.univair.com/content/Shock-Cords.pdf

        Gary
        N36007 1941 BF12-65 STC'd as BC12D-4-85

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        • #19
          Originally posted by PA1195 View Post
          Replace them every five years or per the manufacturer's recommendation. They are dated vis color threads imbedded during manufacture.

          Read this and decide how lucky you are today: https://www.univair.com/content/Shock-Cords.pdf

          Gary
          Gary, they are technically an "on condition Item" the bungee manufacturer does not call out a shelf life or a service life, only a recommendation, and that has changed to a 3 year based on experience and changes to the rubber compounds used to make them for some people. There have been at least 2 discussions about that on here alone.


          https://www.univair.com/content/Shock-Cords.pdf

          N29787
          '41 BC12-65

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          • #20
            Thanks Tim. Local IA's have been tuned up to inspect bungees and at five years or visible wear sound the "on condition" alarm to owners. Taylorcraft is an easy changeout compared with Pipers. Like main landing gear bushings or tailwheel components it's often "out of sight out of mind".

            Gary
            N36007 1941 BF12-65 STC'd as BC12D-4-85

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            • #21
              Originally posted by PA1195 View Post
              Thanks Tim. Local IA's have been tuned up to inspect bungees and at five years or visible wear sound the "on condition" alarm to owners. Taylorcraft is an easy changeout compared with Pipers. Like main landing gear bushings or tailwheel components it's often "out of sight out of mind".

              Gary
              Nah, its easy on a cub, just call Burl and install an ASOS...problem solved!
              N29787
              '41 BC12-65

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              • #22
                The bungees were still good. Some hidden damage to the tubing came to light. All it took was a bit of a heavy landing. Either way, though, the group I was with became convinced that safety cables were cheap insurance compared to what that repair cost them.
                Ryan Short, CFI, Aerial Photographer
                Former Taylorcraft BC-12D owner - hopefully future owner as well.
                KRBD and KGPM - Dallas, TX
                TexasTailwheel.com

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                • #23
                  Tim, That link didn't work from the forum page because it is a pdf. Here it is as copy/paste.

                  Shock Cords Shock Cords.doc Identification, Dating, Damage and Wear, and Storage Life Identification: Shock cords, aka shock rings, are assigned their part number based on their diameter as measured in 1/16ths of an inch. A 1080 cord is 10/16 or 5/8 in diameter. The second set of numbers like 80 indicates the diameter of the ring in a perfect circle in 1/8ths. A 1080 cord is 10/16 or 5/8 in diameter with a circular diameter of 80/8 or 10 inches. A 1280HD cord is 12/16 or ¾ diameter and it is a Heavy Duty cord as compared to the straight 1280 cords. This means they are built to the high end of the specification range. There is also Cold Weather version of these cords. The cold weather cords are intended for very cold environments as you would have in Canada or Alaska. North Dakota can get very cold in the winter, but they are not likely to see -40 degrees for extended periods. Several years ago, Univair sought PMA approval for many of the commonly sold shock cords. To satisfy PMA requirements for approval, Piper part numbers were used. Most of our PMA’d cords begin with U31322. Not all shock cords are covered under PMA approval. They are however all manufactured to a military specification, MIL spec. Dating: Shock cords are made from a continuous winding of a rubber band. They are made in accordance to MIL-C-5651D. The military specifications also requires that a color code woven into the outer cotton braid to give an indication of the manufacture.

                  The code consists of colored yarns consisting three colored segments using five colors. Two of the colored segments are the same color and these indicate the year, while a single colored segment indicates the quarter of the year in which the bungee ring was manufactured. All bungee ring braided coverings are whipped with natural color whipping thread except for the HD rings which are whipped with a brown color whipping thread. Year Colors Year of Mfgr. Two black strands A year ending in 0 or 5 Two green strands A year ending in 1 or 6 Two red strands A year ending in 2 or 7 Two blue strands A year ending in 3 or 8 Two yellow strands A year ending in 4 or 9 UNIVAIR AIRCRAFT CORPORATION 2 Quarter Marking Quarter One red strand January thru March One blue strand April thru June One green strand July thru September One yellow strand October thru December

                  Damage and Wear: Damaged or worn bungee rings are pretty easy to spot. If the bungee has been over-stressed – because of a very hard landing or overloading – the rubber strands will break. When this happens, the cotton braid will neck down and look thinner at the point where the strands are broken. If the bungee rings have weathered and deteriorated because of exposure to sunlight, dirt or chemicals, they will lose strength. A loss of bungee strength is also easy to identify. It depends on how they are used, but in some airplanes a soft bungee will cause the main landing gear wheel track to widen and the airplane will look like it is squatting. If only one bungee has lost its strength or been damaged, the wing tip on the damaged bungee side will be closer to the ground than the wing tip on the other side.

                  Storage Life: There is no specified shelf life. SBC sent us correspondence in 2000 stating: There is no prescribed limit on shelf life. As long as the Superior Rings are kept in a controlled environment with low relative humidity and out of UV light, they should keep for periods longer than we could reasonably record data. An excessively dry condition of storage can eventually cause dry-rot of the rubber core. Conversely, an excessively damp condition can cause rot of the cover material. We have had rings in the field in place on an aircraft last greater than 20 years. It is therefore reasonable to assume that non-extreme conditions in a warehouse should yield a shelf life more than sufficient to inventory our product until resale.

                  Advisory Circular, AC 43.13-1B, 9-4 (a) states: a. Old aircraft landing gear that employs a rubber shock (bungee) cord for shock absorption must be inspected for age, fraying of the braided sheath, narrowing, (necking) of the cord, and wear at points of contact with the structure and stretch. If the age of the shock cord is near 5 years or more, it is advisable to replace it with a new cord. A cord that shows other defects should be replaced, regardless of age.
                  Cheers,
                  Marty


                  TF #596
                  1946 BC-12D N95258
                  Former owner of:
                  1946 BC-12D/N95275
                  1943 L-2B/N3113S

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                  • #24
                    Somewhere here Forrest recommended replacing just one of the used cords per side with a new one, then cycle out the old one at some point later. Gave better landing. Probably helps spread expense over time too.

                    Gary
                    N36007 1941 BF12-65 STC'd as BC12D-4-85

                    Comment


                    • #25
                      Originally posted by M Towsley View Post
                      Tim, That link didn't work from the forum page because it is a pdf. Here it is as copy/paste.

                      .
                      It works on my 3 different systems? Just like every .pdf I post in the tech section. Shrug.

                      N29787
                      '41 BC12-65

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