Control Cable Wear Limits

[jaredyates]

I'm doing part of my second condition inspection, and I see some wear on the up elevator cable. I've spent some time trying to decipher 43.13 (page 36 here) and I'm not sure of what it is saying. The seemingly applicable part says "Replace flexible and nonflexible cables when the individual wires in each strand appear to blend together (outer wires worn 40 to 50 percent) as depicted in figure 7-17." Can some of you who are more experienced at looking at cables tell me if it looks like I need to replace this one? Sections of the 19 strand sections are blending, but not sections of the 7 strands. I'm not sure which of the two 43.13 is referring to.

[marcusofcotton]

Time to replace it. Guessing you used stainless steel??? Galvanized will last longer.

[Battson]

The rule I was told to apply - if any of the sub-strands have worn through, then it's 100% definitely worn enough to make it worth replacing.

My rudder cables looked like those pictures when I replaced them. They were worn enough to alarm my IA, so I would definitely be replacing them.

Looks to me like some of your sub-strands have completely worn through or lost most of their section, which puts them well past AC 43 replacement criteria.

How many hours have those cables been in service, at what tension?

[jaredyates]

They are indeed stainless. The plans specify stainless(EDIT: No, they don't), though since the initial install I've read about why galvanized is better for this application. Those have about 175 Hobbs hours, and when the elevator is neutral, the tension is 30-35 pounds. mswain ordered a spool of cable direct from the manufacturer at a cost savings over the ACS price. Is anyone interested in getting together to order another spool? I think a spool provides 4 or 5 planes worth.

[LukeS]

Anyone know why stainless is specified?

[jaredyates]

It turns out it isn't specified in the plans, as best as I can tell. I did find a reference to it in another source, but not one of Bob's sources yet.

[whee]

How much savings? I'm not ready for cables yet but can buy in on a spool if the savings is worth it.

[jaredyates]

I'd have to call to ask for current pricing, but a full 500' spool of Loos GF12579 is around .66/foot vs .98 at ACS. ACS doesn't say who makes their cable. I suspect shipping would be a wash, but that's also not confirmed. Mike was figuring 150 feet per airplane.

[Bdflies]

Please help me, guys. Why is the cable wearing in this manner? Is the pulley not turning freely? Is the cable rubbing on something else? 175 hours?!? Am I the only one who thinks the worn cable is a symptom of another problem?

Bill

[DRLPatrol]

I was thinking the same thing. If I saw that kind of wear before several thousand hours, I would look for a reason.

Doug

[Mark Moyle]

Metal on metal contact? I'm about done restoring my 65 year old PA20. Didn't find any wear like that..... reinstalled the original galvanized rudder and aileron cables. The rudder cables use fairleads just like the Bearhawk.


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[JimParker256]

I'd have to call to ask for current pricing, but a full 500' spool of Loos GF12579 is around .66/foot vs .98 at ACS. ACS doesn't say who makes their cable. I suspect shipping would be a wash, but that's also not confirmed. Mike was figuring 150 feet per airplane.

Wicks sells their 3/16 galvenized 7x9 cable for $0.84 per foot, and gives a 20% discount if you tell them you're building a Bearhawk (tell them Mark Goldberg sent you their way). That brings the price down to $0.672 per foot, which is just about the same as the ACS price for 500' spools... Other sizes and types also available.

[dedgemon]

So... what does the pulley look like? Is it showing wear at the same point that the cable is? Sure seems like a short time frame.

This is for the 4 place right? It uses cable for the elevators???

[Battson]

So... what does the pulley look like? Is it showing wear at the same point that the cable is? Sure seems like a short time frame.

This is for the 4 place right? It uses cable for the elevators???

Usually the soft thing wears out the hard thing. Chances are the pulley is basically undamaged.

The same happens with fairleads, cable ties, etc. You have to watch cable ties on fuel lines, in that regard... unless you want a fuel leak.

[jaredyates]

The pulleys look fine, and there is no other rubbing that I can tell. The bearings are good. I appreciate the input about norms though. For the guys who are surprised by the wear, are you usually using galvanized cable instead of stainless?

[AZBearhawk272]

Jared,

3 thoughts.

1. An abrasive agent is being introduced into the area and becoming trapped in the lay and then essentially fretting.

2. The extension of #1, is the wear associated with elevator neutral position? Vibration of cable and structure, rubbing in place? Aerodynamic from the tail or engine vibe.

3. Rigging issue. It is very important that the angle of approach and departure of the cables at the stick bellcrank under the seat be at the same angle to the bellcrank.
If not, then as the bellcrank articulates, one stick direction will tighten the cable loop and the other stick direction will loosen the cable loop. This variation can create very high cable tensions as the bellcrank articulates thru the normal operating range.

I have just replaced all the control cables at about 550 hrs with the greatest wear at most cabin rudder fairleads ( parted strands) and aileron pulley at lower wing strut and flap cable.
All the excessive wear was located in the cabin area. The elevators were fine.........

Old cables were SS. new Galvanized.

Kevin Deutscher
Phx, AZ

[Battson]

I was thinking about this as I walked to work this morning Jared, and just out of curiosity, what led you to inspect these at 175 hrs?