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Rudder & elevator cables

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Mark,  I do not think it is as simple as many have replied.  No matter what you use,  the key question is whether it will fail under what load,  the number of cycles for failure, & its mass.  I'm sure the 10mm 304 1×19 stainless wire with 12.6mm 316 stainless turnbuckles which keep my yacht's mast upright with a breaking strain of around 30kN would work with your rudder cables, but it would be tad heavy. 


Stainless steel does work harden more than the steel alloy use in AN fittings.  Stainless fittings with thread are also more likely to gall.  Further,  stainless fittings immersed in seawater can also corrode leaving them looking good,  but very weak. 


Nevertheless,  many aircraft have wire cables of stainless, some have galvanised (same for yachts, though increasingly yachts have plastic such as dyneema replacing wire rigging. My 11m yacht has 5mm dyneema braid for the rudder circuit & it has loads easily 10 times of what you would get in a light aircraft ).


Both my aircraft have stainless cables and a mixture of AN turnbuckles and stainless ones. My scratch built Cygnet has stainless turnbuckles on the rudder circuit (20 years,  1000 hours).  Each one has a safe working load of 5kN. The ailerons and elevator circuit has AN cadmium plated steel turnbuckles.  All cables are terminated on a thimble with Nicopress sleeves. My Corby Starlet (40 years 300 hours),  previously VH registered, also has stainless cables. Turnbuckles are all AN steel ones (no turnbuckles on the rudder circuit). However the cables are all terminated by swaged stainless fittings and were supplied by a certified aircraft cable supplier.


Having built several aircraft (successfully) my advice would be to stick with what the aircraft designer specifies. If you want to change it,  discuss with the designer.  And remember the rule for assessing whether to add something or make it stronger than the designer specified.  Hold it in your hand & throw it up in the air. If it stays up,  it should be added. if it falls down it was never meant to fly and should be discarded. 


Cheers,  Mark



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Remember you pay over $100 / hr to have some apprentice change the oil on the wife's car.. Nev


Not in my lifetime.


Hi all,


I'm about to install rudder & elevator cables.


Firstly, turnbuckles.  Is it acceptable to use marine-style stainless steel turnbuckles?  Looking at various pictures of 701 builds, they look like brass fittings (obviously supplied in the hardware kits).


Secondly - cable shackles (see pic below)




These handy little things seem ideal for the control surfaces and elevator bellcrank (so 6 required).  Trouble is they seem to cost an arm and a leg.  Aircraft Spruce in US sell them for $10.85 each,  I logged on to an Australian supplier (AAE) who have them as something like $38 each.


So it looks like an Aircraft Spruce order (when the dollar gets higher perhaps...) unless anyone knows of a supplier here or has some spares they'd like to sell??


Thirdly - safety wire.  Is this a special grade or will any 0.032" S/S wire do the trick?  




Cheers, Marty


1/8 SS cable in 7 x 19 is fine used with nicopress swages and thimbles with the drilled plates as used by Zenith and Savannah. If you can make them to length, small adjustments can be made with the nosewheel steering rods.


A roll of 0.032 SS lockwire is cheap and you will use it for many things on your aircraft.




The pliers are useful too.



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If you want cables assembled in Australia that is good. I think we should support local, BUT when I replaced my cables I got quotes from a couple of Aussie suppliers. From memory they were x much per cable, plus x much per fitting plus a big number of dollars for the paperwork. I bought from Aircraft Spruce at about 20% of the Aussie price. The order was taken and delivered in about a week with delivery to the door.


Much as I would like to support Aussie businesses I cannot afford to provide their pension. Probably not their fault, no doubt CASA has a big say.



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