Aircraft Cables

Discussion in 'Workshop Tips and Secrets / Tools' started by Norman, Feb 20, 2004.

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  1. Feb 20, 2004 #1

    Norman

    Norman

    Norman

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    This showed up on another list this morning. I thought it might be of interest to some of you guys.


    ---- Original Message -----
    From: Michael Wallace
    To: ******@***.***
    Cc: mike_1
    Sent: Wednesday, February 11, 2004 4:51 AM
    Subject: Aircraft Cables


    Hello Sir:

    In the below statement you wrote that every commercial aircraft flying is equipped with nothing but SS cables and fittings. This statement is only partly true. Yes, the fittings are made from Stainless Steel Type 303SE but most of the cables are Zinc or Zinc & Tin Plated Carbon Steel.

    My name is Michael Wallace and I am Vice President of Sales for Loos & Co., Inc. and we are the OEM supplier to just about every commercial aircraft manufacturer in the Western Hemisphere. I'm here at home this morning browsing the internet and stumbled across your statement in the Beech Owners chat room. I realize your statement was from way back in May '03 but I thought I might set the record straight for you.

    Our customer list includes Boeing, Douglass, deHaviland, Cessna, Beech, Piper, Gulfstream, Lockheed, Embraer and many other smaller manufacturers. The only ones that use strictly Stainless Steel cables are Gulfstream and Cessna.

    The others use 1/8" 7x19 Carbon Steel cables in their primary flight controls. Carbon steel cables provide much greater fatigue life compared to stainless cables. Boeing uses practically no stainless steel cables. They use the Tin over Zinc variety of carbon steel cable in their primary flight control cables.

    As far as Aircraft Spruce is concerned, as KenV35A writes below, They pass off foreign manufactured cables as being made to the military specification MIL-W-83420. If you look at the fine print in their catalog, they state that their cables are not QPL certifiable. QPL means "Qualified Products List". It is the list of qualified manufacturers to MIL-W-83420 (The latest revision is titled MIL DTL 83420) that the U.S. Military maintains. There are only 5 companies in the whole world that are on the QPL list and they are all U.S. companies. I'll list them here for you:


    Continental Cable - Hinsdale, NH
    Loos & Co. - Pomfret, CT
    Strandcore - Milton, FL
    Strandflex - Oriskany, NY
    Wire Rope Corp. - St. Joseph, MO


    What Aircraft Spruce pawns off as being "just as good as" to the flying public is in no way representative of true Military Specification wire rope. When Spruces' cables are tested to the criteria in the Mil Spec, they fail miserably. Their intentional mis-representation should be stopped but the FAA has bigger fish to fry. They turn a blind eye to the Sport and Home-Built aviation industry.

    Below I've pasted an article from Aviation Today discussing flight control cables.





    AC43.13-1B, chpt.7, section 8, lists two types of corrosion-resistant steel for flexible cable use on civil aircraft. Type I, composition B cables, MIL-W-83420 and MIL-C-18375. Goes on to say "is equal
    in corrosion resistant and superior in non-magnetic and coefficient of thermal expansion properties. Aircraft Spruce lists MIL-W-83420 as stainless. KenV35A




    Inspection: Flight Controls Depend on Quality Cable

    By Vicki P. McConnell, Technology Editor

    When purchasing wire rope for use as flight-critical aircraft control cable that must meet MIL-DTL 83420, a certificate of conformance is not the same as a certificate of testing. For some years now, the former has been frequently passed off as the latter, according to Michael Wallace, vice president of sales and marketing for cable-manufacturer Loos & Co. This creates confusing or even bogus credentials for aircraft cable that doesn't offer the highest performance properties as manufactured, tested, and supplied by Qualified Producer List (QPL) companies such as Loos & Co. These companies have invested considerable funds to perform mil-spec verification testing of their cable, and go through the requalifying process every two years.

    Some large airplanes, such as certain Boeing models, require nearly half a mile of steel aircraft cable, Wallace said. Boeing specification BMS7-265 designates flight-control cable as a QPL item. "This means that replacement of this cable by an MRO facility must be made with cable that comes from a QPL company," he added. Aircraft cable qualified to this mil-spec features 7 X 7 or 7 X 19 construction (referring to 19 wires per strand, 7 strands per cable, or a total of 133 wires working together to deliver optimum performance characteristics). Diameters range from
    1/32nd inch up to 3/8ths inch, but typically 1/8th inch is common in flight controls.

    "You get what you pay for," Wallace said, "and non-QPL certified cable is always less expensive. In most cases, it is not lubricated and the performance tests have not been performed. Lubrication greatly extends the wear properties of aircraft cable, and all QPL-certified cable is lubricated." Loos & Co. has tested a number of lots of unlubricated non-QPL cable and found significant reductions in the cable's fatigue life. "These products may pass initial breaking strength tests," he said, "but rarely pass the criteria of retaining 50 to 60 percent of breaking strength beyond 30,000 endurance cycles." As a result, the non-QPL cable can fail in a much shorter lifetime.

    What tips does Wallace offer MRO facilities that may need to purchase replacement cable? "First, read the OEM's manual to find out if QPL-certified cable is required; most often, it is. Next, obtain the QPL of approved companies from the OEM of the aircraft on which you're installing cable, or use this website,

    http://astimage.daps.dla.mil/quicksearch

    and download document number 83420."

    When ordering from a distributor that doesn't wish to divulge the name of a cable supplier but states it is QPL approved, Wallace said, "beware, especially if the price is significantly lower. Further, if you order from a non-U.S. company directly and it claims to offer mil-spec conformance, realize that is not the same as meeting mil-spec testing requirements or of having QPL approval. To date, the only non-U.S. QPL-approved cable supplier is located in Germany. No matter whom you order cable from, absolutely insist upon seeing the cable manufacturer's certificate of QPL testing to the mil-spec."

    The "Rev level" should also be noted, referring to the alphabetical revision letter at the end of the mil-spec number. With regard to MIL-DTL 83420J, an earlier letter designation such as "D" or "E" means the supplier is working with older data. "This doesn't mean the cable isn't QPL-certified," Wallace said, "but it can be a tip-off to dig deeper into your cable supplier and quality verification."

    Each QPL certified cable manufacturer is assigned a two-color tracer filament that is embedded within their cable. In working with the Aircraft Cable Control Group, Wallace reported cases of "documentation of non-QPL manufacturers using colors assigned to QPL manufacturers." He advises cable users "to be sure to inspect and verify all the labels, lot numbers, and reel numbers on the cable." He also suggests nraveling a section of cable to verify the cable supplier's identifying tracer colors. "We've seen attempts to counterfeit these," he said. When a supplier is named on a purchase order, there's no harm in telephoning that company to verify that it supplied the cable. (Loos & Co. has been named on purchase orders when it wasn't in fact supplying the cable.)

    Wallace also cited

    http://www.faa.gov-/avr/spophoto.htm

    for providing photos of noted differences between approved and unapproved wire rope.

    This issue is relevant for replacement of both commercial and military aircraft cable, because in many cases the OEM specs are the same. Wallace isn't the only voice crying out in the cable quality-control wilderness. A number of investigations regarding bulk wire rope are underway by the U.S. Department of Transportation, U.S. Department of Defense, as well as the Federal Bureau of Investigation, and may eventually result, said Wallace, "in someone going to jail for misrepresenting flight-critical cable as meeting mil-specs."

    The term "aircraft cable" is actually a misnomer, in Wallace's opinion: "Very little of the so-called aircraft cable consumed in the United States on an annual basis is actually QPL wire rope. Most of it is what you would find in your local hardware store." It is estimated that less than 2 percent of all "aircraft cable" is in fact QPL material, which makes attention to available safeguards for aircraft cable all the more important.

    Pemco Wins Verdict

    Pemco Aviation Group has experienced the non-qualified cable problem with some U.S. Air Force KC-135s that it worked on at its Birmingham, Alabama facility. On September 25, Pemco announced that it won a $7.5 million verdict against Certex of Alabama (part of Bridon-American Corporation). Pemco had filed a lawsuit claiming that Certex provided non-conforming aircraft cable, resulting in the grounding of several KC-135s in April 2000. According to Pemco, the KC-135s were refitted with new conforming cable and returned to active service.


    _________________________________
     
  2. Feb 20, 2004 #2

    Midniteoyl

    Midniteoyl

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    Umm... wow!

    Aircraft Spruce huh? :rolleyes:
     
  3. Feb 21, 2004 #3

    Johnny luvs Biplanes

    Johnny luvs Biplanes

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    So how do you get the proper stuff, particularly if not in the USA?
    John :confused:
     
  4. Feb 21, 2004 #4

    Largeprime

    Largeprime

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    He advises cable users "to be sure to inspect and verify all the labels, lot numbers, and reel numbers on the cable.
     
  5. Mar 19, 2013 #5

    Alan Waters

    Alan Waters

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    Good old info.
     
  6. Apr 19, 2016 #6

    dougwanderson

    dougwanderson

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    update went to acs and now description and documentation

    The major difference between aircraft and commercial cable is the lubrication applied to aircraft cable, which provides substantially better fatigue life than non-lubricated commercial cable. Aircraft cable requires extensive extra testing, documentation and certification to meet military specifications. We obtain our aircraft cable from domestic sources and the cable is certified to MIL-DTL-83420 and QPL Certified. Unit of measure is feet.
     
    Norman likes this.
  7. Apr 19, 2016 #7

    choppergirl

    choppergirl

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    I lubricate my motorcycle cables to keep them from rusting stuck by spraying PB Blaster down in them. Seems to work, the excess comes out the other end. And since its penetrating oil it should get between the individual strands and spiral spring groves of the tube and stay there. It's just what I happened to have on hand. Good idea, or no? Something better? Lots of people give WD-40 a bad rap so I avoid it.

    Opinions on using Marine Teleflex cables for your primary Aileron/Rudder/Elevator/Throttle controls on like an Ultralight? Too expensive? Too heavy? I'm not crazy about the look of open bouncy bare naked sloppy cables on pulleys that were previously on my plane. All it would take would be one pulley to break or slack otherwise getting in the system and you lose control input.

    I'm wonderng if it also would be a good idea to put springs on all your control surfaces where they attach to the plane, to return them to neutral when you release pressure on the stick... in case a line going out or back there was to break, or the pilot was to become incapacitated, at least the control surface would return to neutral. Bad idea? Does anybody do that? Or would the springs just be superfluous extra dead weight?
     
    Last edited: Apr 19, 2016
  8. Apr 19, 2016 #8

    BoKu

    BoKu

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    I've seen such cables used as primary flight control connections on a couple of ultralights, but it's not something I'd do. The engineering guide for the brand of push-pull cable that I use says that unless the cable eliminates two or more bellcranks, then a tension-cable or rigid push-pull tube arrangement is probably lighter and more effective. Also, such cables get old and stiff and sticky, and the internal swages that hold them together cannot easily be inspected, both of which I consider to be disqualifying criteria for a primary control.

    That said, I do use a push-pull cable for the flaps on my sailplane. However, this is a glider you can safely land in almost any flap setting, and for which the flap drive is non-reversible and travel-limited right at the flap mixer. So if the cable breaks or sticks, the flaps will just stay where they were. But the primary controls are either tension cables (rudder) or good solid push-pull tubes with good rod ends and linear ball bearing guides (elevator, aileron).
     
  9. Apr 19, 2016 #9

    Rockiedog2

    Rockiedog2

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    To expand a little on doug's post...
    the opening statement concerning "update went to spruce and now description and documentation" wasn't clear to me.
    I went to the ACS catalog both paper and online and found this statement which is a repeat of Doug's for clarity(hopefully)

    >>>The major difference between aircraft and commercial cable is the lubrication applied to aircraft cable, which provides substantially better fatigue life than non-lubricated commercial cable. Aircraft cable requires extensive extra testing, documentation and certification to meet military specifications. We obtain our aircraft cable from domestic sources and the cable is certified to MIL-DTL-83420 and QPL Certified. Unit of measure is feet. <<<

    so the report saying Spruce's claim that their cable is QPL and mil spec is intentionally misleading; or words to that effect, was written in I believe it was 04. I'm wondering if the catalog statement then was the same as it is now and if this current claim is bogus as well. I looked for the fine print that says their cable isn't QPL certifiable and couldn't find any fine print. I'm not nieve(sp) enough to put anything past any company these days but that statement that it's domestic sourced/QPL/Mil Spec doesn't look to leave much wiggle room. Maybe they cleaned up their cable act in the last 12 years? (I have to wonder why they would have outright lied as most of us homebuilders don't know what QPL is)
    I looked up Wicks cable and you gotta request the info on theirs they don't volunteer any.

    It was an interesting and informative report I learned something again. Thx Norman.

    I been using whatever the stuff is that they sell for 50 years. Think I'll keep on...no worries.
     
    Last edited: Apr 20, 2016
  10. Apr 20, 2016 #10

    Dana

    Dana

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    Telesales cables have a lot more friction than open cables on pulleys, so the control feel isn't nearly as nice.

    Spring centering, not necessary, the airflow is sufficient.

    Dana
     
  11. Apr 20, 2016 #11

    BoKu

    BoKu

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    The latter.
     
  12. Apr 20, 2016 #12

    choppergirl

    choppergirl

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    I never thought of push pull tubes for my plane, though I've seen them on others, that sounds even better. Something I could fabricate myself with a bit of hardware. And they will never fray. And if one breaks, the other should get you home. Thanks! More challenging though I imagine to route the whole affair around multiple bends and corners. That's going to take some measuring, planning, and thought.

    As far as the springs were concerned, I was thinking along the lines if someone were to have a seizure, heart attack, epileptic fit, or get hit in the face with a bird, or some other insanely unexpected thing, the plane would have some kind of chance of landing itself at a sane angle with neutral controls, like a falling leaf. My motorglider doesn't have any dihedral so I guess the chance of that is nil anyway.
     
    Last edited: Apr 20, 2016
  13. Apr 20, 2016 #13

    Dana

    Dana

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    CG, you misunderstand... with push/pull tubes, there's only one, it pushes and pulls, instead of two cables, each pulling in the opposite direction. There's no redundancy with either system, but the pushrods have less friction than cables running over pulleys and through fairleads.

    Re springs, they're not necessary. Let go of the controls in a normal plane and the airplane keeps flying straight; the airflow holds the control surface straight absent any force (i.e. pilot input) trying to deflect it. Actually there are two different stability calculations: "stick fixed" (control surface locked in position) and "stick free" (control surface free to float). The airplane must be stable in both conditions. The only time springs are used (in some aircraft) are to increase the force required to deflect the controls when necessary to add some artificial "feel" when the control forces are too light. For standard category certificated aircraft, there are regulatory minimums for "stick force per g".

    Dana
     
  14. Apr 20, 2016 #14

    BBerson

    BBerson

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    It will continue straight hands off only if trimmed.
    Some planes have a trim system with springs on the stick to keep it centered. And for pilot adjustable trim a lever attached to the springs can change the tension up or down as needed.
     
  15. Apr 20, 2016 #15

    choppergirl

    choppergirl

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    Ok, so I'd just need 4 of them instead of 8. I imagine on the long stretches, run them through eyelets so they don't bend under "push". What sizes are these push rods typically made of, alluminum tube, or small diameter steel tube? I think I've seen both.

    Previous system used the aforementioned cables under tension (which I have), and I've seen it work just fine on Quicksilver's in video, but it sure does jump around a lot and I'm afraid a pulley would break or the wire jump up and then slip down between pully and whatever holds pulley on, add slack, get jammed, and or get frayed.
     
  16. Apr 20, 2016 #16

    BBerson

    BBerson

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    The pulley has a cable guard that should keep it from jumping off. Cables should have some tension. Airplanes are usually 10 to 40 pounds tension. (See service manual)
    Nothing wrong with cables if maintained.
    Push tubes are quicker to connect when assembling, so gliders use em more.
     
  17. Apr 20, 2016 #17

    Matt G.

    Matt G.

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    PB Blaster is for loosening rusty hardware. LPS 1 is is used by most aircraft mechanics I know for lubricating control cables.
     
  18. Apr 20, 2016 #18

    Turd Ferguson

    Turd Ferguson

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    If properly installed, the cable can not come off the pulley due to pulley guards, guides, etc. Phenolic pulleys rarely fail in a sudden manner and being very accessible, the entire installation should be easy to inspect on every flight. A cable actuating system has been proven safe and reliable 100x over. Why fix what isn't broken and possible introduce a lot of new flight safety issues?
     

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