Control Cable Wear Limits

[jaredyates]

Kevin, can you elaborate on the bellcrank point? I didn't follow that.

Jonathan, I do the condition inspection yearly, so that's why I was looking at them.

[Bcone1381]

http://luscombe.org/technicaldocs/controlcables.pdf

This document provides good inform regarding cable wear, giving data on the flexibility and wear comparisons between galvanized and stainless steel cable.

Other stuff I read that was interesting...if the pulley does not typically rotate 360 degrees, periodically move the pulley to even out its surface wear. There is also evidence that suggest cable wear increases at pulls locations where the cable contacts a small portion (for example 15 degrees) of the pulley compared to a larger portion (say 90 degrees plus) of the pulley. It seems as though cable tension may be concentrating its forces on a smaller surface thereby increasing the pressure on the cable in these locations.

[sbmurphey]

[QUOTE=jaredyates;n19448]Kevin, can you elaborate on the bellcrank point? I didn't follow that.

If I am understanding Kevin correctly, a simple bell crank system should be installed perfectly parallel. If installed at an angle to each other, the arms will move at different rates. This could cause a change of tension in the cables throughout the range of motion in the control system.

[jaredyates]

So the key here is to have the two bellcranks parallel to each other?

[Zzz]

Here's a short video I shot after rigging my elevator cables. It's not super relevant but might help some visualize the system: https://www.youtube.com/watch?v=0AfQzb3oMzw

My elevator control bellcrank came from the factory welded a little out of wack such that it's slightly out of vertical axis. The bearing tube is not perfectly normal to the bellcrank. The unintended advantage though is that the cables are slightly more spread laterally giving a little straighter shot to the pulleys.

There are only 2 pulleys per cable and they're a pretty straight run.

Anyone ever thought about the wear characteristics of phenolic vs aluminum pulleys? Some of the aluminum ones Javron and some others make *look* cool but I wonder about the harsher wear. Would that be the case?

I bought galvanized cables after agonizing over the question. The only advantage to stainless IMO is corrosion protection. A light wipe down with ACF-50 on a rag at installation and inspection of the galvanized cables should take care of that.

[jaredyates]

Thanks Zane. After talking with Kevin and doing some tests with the tensiometer, I built the new galvanized cables to have the bellcranks parallel when the elevator is neutral. I measured the tension in both cables at the neutral, full up, and full down positions. The tension increases from about 30 to 40 when I go from neutral to an extreme. Before, it would go from 30 to 50 or 60. My new bellcrank position has the pushrod almost as short as it will go. I don't think this alone accounts for the wear, but I think it's a combination of that, along with the cable having been hanging in place in the dusty hangar for a few years, along with it being made from the soft stainless.

[jaredyates]

Interestingly, I can't find a place where Bob specified stainless cable over galvanized. He prefers galvanized too, it turns out. If anyone is able to find a reference to stainless, let me know so that we can have him address it.

[Battson]

I bought galvanized cables after agonizing over the question.

Everything I have learnt since buying my cables (first time around) suggest you have made the right decision.

[Wes Ragle]

I ran across this comment:

"The advantages of galvanized cable are its wear resistance and cost. Galvanized cables resists abrasion wear four or five times longer than stainless steel. Stainless steel wire is high in nickel and much softer than the carbon steel wire. Stainless steel cable will show signs of wire wear at pulleys and fairleads much quicker than the galvanized carbon steel wire. Stainless steel cable costs about 30% more than galvanized steel cable. We recommend using galvanized steel cables except in coastal geographical areas, agricultural aircraft, float planes, and other applications where the cable is exposed directly to water."

Here : http://www.mcfarlaneaviation.com/Products/?CategoryID=47&

Wes

[whee]

I'm working on making my elevator cables. I set my elevators even with the H-stab and positioned the control stick so the crank was parallel to the elevator crank. Doing so makes neutral stick too far forward. I've adjusted the pushrod as far as possible. Any ideas?

[whee]

Made my cables and will replace the push rod with a heim joint for the close fit.

[Zzz]

I was going to put my elevators on with my cables to see where I ended up when I rigged mine but it was too hot to keep the garage door open Maybe tomorrow morning.

[Pat Fagan]

Finishing up the condition inspection on Smokey today. I took extra time to inspect my cables due to this thread and find no wear on my original galvanized cables after 14 years and 850 or so hours. I am also finally replacing the original Odyssey PC925 battery I bought in 2002. Hope I get the same service out of its replacement.

[jaredyates]

I hope you do too! I seem to get about a year out of a PC680, but that may be because it's on the forward side of the firewall.

[Collin Campbell]

Been giving this some thought... on this cable/bellcrank thing. I think we are forgetting to consider the effect that the pulleys (between the two bellcranks) have on the equation. If there were no pulleys involved, (cables traveling straight from one bellcrank to the other) keeping the bellcranks parallel is the right idea. But when the pulley displaces the cables from not being in a straight line between the two bellcranks, it changes things. It seems to me that if you make the cable attach points (on the bellcranks) the same distance from the pulleys you will get the same movement and thus no cable tightening/loosening. Just my thoughts, someone smarter than me can disprove this whole idea. Got to make it to the hangar and look at the plans, but I believe this is how Bob has it drawn.

[Sebastian]

Ok the new guy at this building. After reading all the posts I am wondering if I should send my stainless cable back to Wicks and exchange it for galvanized since I haven't opened the package. What is the consensus here Stainless or galvanized? Is the consensus for all sizes of the cable we use?