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  • #31
    On my Patrol, I am using 5/32 ss wire with swaged ends. A fork on one end and stud with threaded fork on the other. I called Bob to get the wire diameter.

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    • #32
      Originally posted by Bcone1381 View Post
      A call to Univair and APR 2007 issue of Beartracks revealed some facts and allows truthful comparison between Bob's tail wires and what Univair can offer the Patrol and Four Place builders.

      Bob's design calls for round 4130 steel tail wires that are 42.5" and 48" long, .200" in diameter with .250 cut threaded ends.


      Univair's tail wires are all round, none are streamlined, made from 302W stainless steel. The longest that the offer is 42.5." All are .168" diameter with .125" rolled threaded ends. Univair has their wires made up. They cut the wire to length, then send out the wire to have the threads rolled by a subcontractor, 1000 wires at a time.

      Perhaps Univair has expanded their offerings since 2007 as not all of Uniair's wires are round(or perhaps they manufacture the round wires and resell the streamlined).

      Their Citabria upper wire ( http://www.univair.com/aeronca/contr...ailbrace-wire/ ) is streamlined and 48.56" long with 10-32 threads(3/16")so it might(and it is completely up to the builder to discuss this with Bob) work for the 48" wire.

      This non-streamlined Cub wire( ( http://www.univair.com/search.php?se...31-002&Search= ) is 41.5" long(again 10-32 threads, 3/16" diameter) so might work for the 42.5" wire(again, discuss it with Bob).

      Note the "Nominal dimension" of Brunton's wires refers to the diameter close to the threads and not the cross section of the center. Refer to second and third items in the "Tie Rod Notes" section here ( http://www.steenaero.com/Products/flying_wires.cfm? )

      I don't know how the wires fit on the four place or Patrol, but for my LSA I had to trim my "off the shelf wires" to length and Dave(refer to the "DavzLSA build thread" in the LSA Plans Build forum) also recently had to trim his "LSA Specific" Brunton wires to length.

      Also, not all "Certified" wires are/were rolled threads. Some interesting reading here( http://sbeaver.com/Bucker/index.php/...rt-mainmenu-82 ) highlights that the "long term producer, now defunct" McWhyte wires were cut threads as well as discussing other things of interest with regards to material selection.

      With regards to issues coming from "plans deviations" causing wire/wing failures, see here( http://www.bowersflybaby.com/safety/hinton.htm )

      And I certainly agree posters should be very careful to "identify" speculations/opinions or provide references for items presented as facts.
      Last edited by BTAZ; 01-09-2018, 01:24 PM.

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      • #33
        Consult with an engineer you trust before proceeding with weaker materials of a smaller diameter.

        I'm looking at other options.
        Dave B.
        Plane Grips Co.
        www.planegrips.com

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        • BTAZ
          BTAZ commented
          Editing a comment
          Exactly!

          Do your research, weigh the facts supported by references(not people's opinions) and make an informed decision you are happy with.

      • #34
        Regarding the 4130N option,Marcusofcotton in an earlier thread provided a number but I wanted to add a reference for the next time "Tail Wires" comes up.

        Yield strength(where the material permanently deforms) is given in lb/in^2 in this table ( https://www.engineersedge.com/materi...roperties1.htm )

        A .200" diameter round 4130N has a cross sectional area of Pi*R^2 or 3.14 *.100 in.*.100 in. which equals .0314 in^2.

        So the yield strength of a .2" diameter 4130N rod is ((63250 lb/in^2) * (.0314in^2)) which equals 1,986 lbs. This seems to be below any of the options discussed so far'. Quite frankly, I was surprised by that.

        Out of curiosity, I ran the same yield strength calculation for 3/16" round 316 stainless(http://www.hmwire.com/New%20PDFs/Sta...sion_Chart.pdf ) and got around 1625 lbs which is well below Bruntons "Min. strength Spec." (for 3/16 wires, 2100lbs for round, 2400 lbs for streamlined. (http://www.steenaero.com/products/flying_wires.cfm)

        It would be interesting to know if Bruntons "Min. Strength Spec." represents a breaking point spec(as defined by tensile strength, calculated as 2450 lbs for 3/16" round 316 stainless ) or a yield spec. If it's a yield spec,. than work hardening adds roughly 30% to the yield strength of annealed 316 stainless which I think is "Pretty cool!"..


        Last edited by BTAZ; 01-09-2018, 03:36 PM.

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        • #35
          If you use the ultimate tensile strength for 316 annealed you get ~2,200 lbs for 3/16" rod, which is consistent with the 2,100 lbs Steen lists for 3/16" round wire. This suggests they're using the ultimate breaking strength. But again that's just one part of the equation.

          If you're looking for equivalency with Bob's April 2007 Beartracks design you're going to want to use the yield strength as your guide, since we're not just interested in the ultimate strength but how much load the rod can bear before deforming plastically.

          Then there's the modulus of elasticity, in effect the "springieness" of the material, which will have an effect on the vibration and fatigue characteristics. The stainless steels we've discussed are close, but not identical to, 4130.

          Then there's the fatigue limits for each material...

          All these things need to be looked as as to how they will affect the strength and life of the part in its intended environment. Anyone can punch out numbers, but that's where Bob's experience as a designer of homebuilt aircraft should lead the discussion.

          But what I personally will not do is say "Well they have similar breaking strength" and call it good.

          Also Matweb is a good source for different material properties: http://www.matweb.com/index.aspx
          Last edited by Archer39J; 01-09-2018, 03:54 PM.
          Dave B.
          Plane Grips Co.
          www.planegrips.com

          Comment


          • BTAZ
            BTAZ commented
            Editing a comment
            The Matweb site is excellent and going into my bookmarks.

            And definitely, strength isn't everything. One link I provided earlier(http://sbeaver.com/Bucker/index.php/...rt-mainmenu-82) seemed to indicate Bruntons used 431 stainless (which per the Matweb link has a higher tensile strength than 316) but apparently also had cracking problems and subsequently changed to 316.

            But there is some "precedent for suitability" in that pretty much every typical light GA air frame that requires tail wires uses "stainless"(much too generic a term). It is unfortunate that suppliers provide undefined "strength specifications" and that the specific material isn't always stated in catalogs which adds to the challenge of identifying suitable "shelf items" to adapt,

          • Archer39J
            Archer39J commented
            Editing a comment
            Well that's true about the precedent. Just if your design calls for 4130 and you swap in SS you're coming close to halving the force it takes to permanently deform that part. But maybe it is just the breaking force that matters I don't know, I just engineer galleys, not small airplanes

        • #36
          I think a factor that can't be over stressed in this conversation, is that we're discussing properties of 4130 NORMALIZED to 316 ANNEALED. To be clear, 'Normalized' is heat treated to a specific strength and hardness. 'Annealed' is heat treated to achieve a soft condition. Because the 4130N is machined and used, without additional mechanical or heat treatment, discussion of it's properties is fine. The 316 Brunton's wires undergo significant mechanical working, which changes the mechanical properties. What we what we don't know, is details of the properties of the Brunton's wires, as worked and ready for installation. We know the alloy and and we know their strength claims. Tensile or yield? Elongation properties? We don't know.
          Don't get me wrong. I haven't given the subject enough thought to consider either one to be superior. I'm just reluctant to consider a comparison without full understanding of the Brunton's properties, which they just might not reveal.
          I gotta admit, though, after following this thread, I've been looking at my tail wires REAL HARD these last couple of days...

          Bill

          Comment


          • Archer39J
            Archer39J commented
            Editing a comment
            While not equivalent they both end up relieving stress in the metal. Regardless, from the breaking strength provided by Steen it seems we can infer they are using annealed 316 from what we calculated. The profiled wires having a higher breaking strength demonstrates the effect of work hardening when forming that shape. Rolling the threads will harden the 316 locally.

            ETA: Never mind, since they don't call it a breaking strength...
            Last edited by Archer39J; 01-09-2018, 07:57 PM.

        • #37
          I did a quick, but conservative, calculation and figure a pound of total downforce generates about 1/2 pound of tension in each top wire. If the wire is good for 2k pounds that translates to a total downforce of 4k pounds. I am guessing the failure mode has a lot more to do with the bending forces on the threads from vibration and handling. I just feel better with flexible wires vs solid.

          Comment


          • #38
            Originally posted by Archer39J View Post
            Well that's true about the precedent. Just if your design calls for 4130 and you swap in SS you're coming close to halving the force it takes to permanently deform that part. But maybe it is just the breaking force that matters I don't know, I just engineer galleys, not small airplanes
            Depends on what you are using for the calculation.

            Yield strength for 4130N at .2" diameter is 1,986 lbs

            Yield strength for 3/16" round 316 stainless in its annealed state is 1,625 lbs so "worst case" you are roughly 15% below the "lowest yield strength approved" 4130N solution.

            But oddly, the "Min. strength spec." for the Bruntons 3/16" wires is in the 2100 to 2400 lb range. If this is a breaking strength spec(note this number is close to the calculated Tensile strength of 3/16 diameter round annealed 316 stainless) then their yield spec is very likely lower than the 4130N option. If Bruntons "Min. Strength" spec is actually a yield strength that is increased because of the "cold working", then even the 3/16" Brunton wires are "stronger" than the 4130N option.

            I did find this table( http://hghouston.com/resources/mater...ing-properties ) that indicates both the yield and tensile strength of 316 stainless can double from the "annealed" to the "Full hard"(referenced to their Rockwell hardness number) condition. Interestingly, it follows that if one can determine whether the Brunton spec is a tensile strength or yield spec., one could then back out the required/desired Rockwell number and the amount of "work hardening" imparted during manufacture.

            What is also interesting is that there are currently three "approved" solutions that vary considerably in their "strength" properties, their aerodynamics, and their vibration behavior.

            1x19 5/32" round cable is pretty far in behavior/properties from machined round 4130N which is itself different than the "Cold worked" streamlined 316 stainless of the custom Brunton wires.

            Then add in that wire tension isn't carefully set(which means the resonant frequency is different from one plane to another), that the end fittings can be "rigid"(Bob terminals), offer flex in one direction(eye terminals to a tab) or a wide range of movement(some cable terminals and "production wire end terminals" akin to Cub parts) and either we are really lucky or the design is pretty tolerant.

            This has been a very interesting discussion and, like BDflies said, I am looking at my tail wires with a new level of awe and healthy respect.
            Last edited by BTAZ; 01-09-2018, 07:26 PM.

            Comment


            • Archer39J
              Archer39J commented
              Editing a comment
              Ah, I missed that they spec "cold drawn" bar too, which could mean anything. And I had it in my head they said "breaking" not "Min. Strength". So yeah, there's not really a way to tell. Though as work hardening increases your fatigue strength suffers, something to keep in mind.
              Last edited by Archer39J; 01-09-2018, 07:38 PM.

            • BTAZ
              BTAZ commented
              Editing a comment
              Interestingly enough the quote from this reference( http://hghouston.com/resources/mater...ing-properties ) states that "Cold working increases the fatigue strength of the austenitic stainless steels. However, the fatigue strength of these cold worked alloys is reduced by notches, as compared to notched fatigue strength in the annealed condition"

              So while actual fatigue performance goes up, susceptibility to a complete failure from a nick also goes up.

              Which explains the AD ( http://myplace.frontier.com/~air.bou...AD60-01-07.htm ) on Pipers requiring repetitive inspections of streamlined lower tail wires with the inspections eliminated for round lower tail wires

            • Archer39J
              Archer39J commented
              Editing a comment
              Susceptibility to complete failure then.

          • #39
            Also of consideration is the punishment for failure. I've read accounts that ranged from "didn't notice till I was on the ground" to "fell out of the sky"...
            Dave B.
            Plane Grips Co.
            www.planegrips.com

            Comment


            • BTAZ
              BTAZ commented
              Editing a comment
              Yep, I just read a thread on the ShortwingPipers forum relating several "no factor" experiences and one "dang near bought it" account.

              If nothing else, this thread changes my pre-flight for tail wires which will now include a "wipe them down with a rag and feel for nicks" instead of just a visual and pluck check.
              Last edited by BTAZ; 01-09-2018, 08:43 PM.

          • #40
            And now I've also learned that some cold worked stainless alloys can become magnetic (https://www.azom.com/article.aspx?ArticleID=1140 ) which might explain why my compass isn't happy. I mounted it with stainless screws(confident that the base material is naturally non-magnetic) but, if they happen to have rolled instead of cut threads......

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          • #41
            I would pay the $800. Those streamline wires are a thing of beauty. I bought round (bottom) and streamline (top). I will feel secure knowing they are back there protecting my tail. When you consider all the money you have to spend to complete a flying airplane, then consider the consequences of a component failure, I'd look elsewhere to save money.
            My .02
            Gerry
            Patrol #30 Wings

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            • #42
              Aren't there so many tempting rabbit holes that we pass on our building journey... So many times I have had the option of "spend the money and get it done" vs "spend lots of time researching and spend less money but then still end up spending the same money later." There is value in the education and in the fun of chasing the rabbits, but the tuition for these lessons is reflected in the build time.

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