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I am looking into push-pull cables for flight control. This is new to me. What are the major categories of push-pull cables? If a push-pull cable needs to go around a corner, what is the minimum practical radius? What other cautions should I follow for push-pull cables? Thanks for reading!
I believe that most of what you want to know can be found in the Aircraft Spruce catalog. The cables are rated for tension and compression. Usually compression is what limits its use in applications.
Push pull cables in housings have a lot more drag than open cables routed around pulleys. And the control feel is often not as good as you want. And they are much heavier.
Engine controls do not have the "feel" requirements that flight controls do, so that is where push-pull cables are found.
Best of luck,
Wes
I have used push-pull cables on all the primary flight controls on my own-design. They have advantages and disadvantages, and depending on what you want to do with them they can solve some tricky installation issues. Bend radius will depend on the type of cable and its diameter - the limiting factor is the number of internal strands and therefore each strands diameter, also the type of casing etc. Most major cable manufacturers have data sheets and it is best to refer to those. I used "cablecraft" 3/16 and 1/4" cables on my aircraft, manufactured locally. I have decided to make my cables limited life items, and will replace them all at 1000hr because it is impossible to internally inspect the inner strands - considering the industrial cycle life of these cables this is very conservative, but should still give me 10 years or so usage. As the two 3/16 rudder cables work against one another, this gives minimum backlash and provides excellent feedback when flying. There is no need to use rudder cable tension springs with push-pull cables. There is a slight amount of backlash in the elevator cable, which exhibits as a slight dead spot - in normal flight it isn't an issue, but it is something to be aware of in the landing flare - you need to be positive with the movements as timidly hunting with the stick can induce "PIO". not a lot, and being aware of it, I don't have a problem with it. The big advantage of Push-pull cables is the ease of routing cables around the aircraft - my aileron cables run tidily inside my wing struts, and the tail controls sneak underneath the baggage bay very easily. They are extremely easy to rig and adjust - the threaded inner and out give a lot of adjustment options. even my flap cables, which operate in the less-ideal compression mode, and curl around in a large radius under the floor work extremely positively. make sure the brackets the outers attach to are good and solid - the working loads all transfer through there, not necessarily down the inner cable.
As far as care goes, keep the exposed ends clean and lubricate from time to time - lithium grease is good. Listen to them when you move them in your preflight - they should be almost silent, but if anything is out of rig, it will creak.
hope that helps,
Bruce.
As Bruce said, the manufacturer's data sheets will tell you the minimum bend radius and other parameters. Regardless of the minimum, use the largest possible radius you can fit for best control feel.