Checking the steel part number it is available. The stainless steel is out of stock but steel is available.

Herb; Do you know when they say "carbon steel" if that is by default a galvanized steel cable (like the article on wear differences discusses?). I found some early failure reports from a Canadian website that discuss failures on 336's (per what you mentioned to me before) and these were the carbon steel variety not the stainless steel, so it would seem that perhaps either one will fail? Here is one way to look at it, that if these are simply high wear items that have a known failure mode (apparently with either type of steel) then one might as well just replace them often and use the cheaper part! On that point, I seem to be getting odd price data, even on the carbon steel variety. I had one quote where the
"-8" variety were like $175 and the "-7" were multiples of that at $534 both apparently available. This doesn't make sense because perhaps other than length they have the same fittings on them etc. I can't imagine it costs hundreds of dollars more for 50 inches of longer carbon steel cable? When I spoke to Beechhurst, they claimed there was nothing wrong legally with using their replacement cables (and they had appropriate paperwork to verify proper mil-spec construction) and they are made to order in either carbon steel or stainless steel, but you can't order them directly they basically make them to match what you send them as replacements. If you end up ordering from Beechhurst let me know and I will order a carbon steel set alongside yours. Thanks. Bill

Flap Cable Inspection
 

While doing the inspection on the flap cables the idea came up to photograph the cable and then take the opportunity to zoom in on the photo for a closer detailed look. Anyone have any thoughts on this method?

I am having a very difficult time trying to find a visible issue that indicates the cables are compromised. I understand that it is difficult to detect the possible broken strand without removing the cable. I question if once the cable is removed and inspected could the strands break while inspecting? With the cable in such a tight bend for so many years does the opposite bending for inspection break the strands?

Did the known failures of these flap cables give any indication of problems before they failed? Was the maintenance documented and were the cables inspected to the degree that these photos reveal? Do the cable just fail or is there visible compromising of the material before it happens?

[quote=billsheila;18169]Herb; Do you know when they say "carbon steel" if that is by default a galvanized steel cable

Label "Carbon Steel" does not indicate that the material is galvanized. Galvanizing is a process of applying a coating not the type of steel.

Herb; Agreed galvanizing is applied. I wonder though if all aviation grade carbon steel cables are by default (or spec)' galvanized? The previous link I attached certainly seems to indicate that galvanizing reduces wear of the type that leads to failure.

Flap cables
 

Hi All, My guy Bob Evans at Eaglerock Aviation can make up these cables. He is an AMO (Aircraft Maintenance Organization) up here in Canada and he does all the work on my aircraft. He also has over 500 hours on Skymaster's and knows the a/c really well.
Bob has all the specialized equipment to make these cables up.
He can be reached at 905 684 4612.

I have removed and replaced the cables that connect inboard bell crank to the outboard bell crank. This is cable -8 or -308 for stainless. When the visual inspection was performed while the cables were still on the aircraft, there were no concerns found with the cables. Using a mirror, camera and q-tips the cables appeared to be in good shape with no indications of concern.

Removing the right wing side first and never have performing this task took about 2 hours. Being as careful as possible not to damage the cable during removal proved to be challenging. Although when the left side was removed it was much easier having done the right and knowing what to expect and what position the flaps should be in.

Upon inspecting the cable once it was on the bench the inboard side of the cable did not indicate any concerns but the outboard end did have a broken strand on the outside of the cable where the cable made the sharp bend around the bell crank. This broken strand was on the inside of the bend or the portion of the cable that touched the bell crank. It was detected by touch, as a finger glides along the cable in only one direction. Feeling the cable toward the fitting at the sharp bend there was a broken stand detected. See first photo.

Then on the inboard end of the same cable, where no detection of concern was felt or seen, the cable was twisted and opened to view inside. After vigorously bending and twisting a single strand was found broken. The question is, did the aggressive inspection cause the strand to break? See second photo.

Then the cable was cut and unraveled to reveal the broken strand inside on the inboard end. See third photo.

The cable on the left side once removed, revealed the same exterior strand broken on the outboard sharp bend. This strand could be felt by gliding a finger toward the fitting at the inside exterior of the sharp bend. No concerns were recognized from the inboard side of the left cable. The forth photo shows the left outboard end of the cable with the strand detectable by finger.

The last photo is the left cable, inboard end, that looks and feels clean with no worries. No other cables have been cut or twisted to inspect inside. More on that later.

The original (1968) cables that were removed appear to be stainless type. The only method of determination performed was using a magnet to detect the differences of the old cables vs. the new cables that were purchased stainless (-308). With this information would there have been concern that these cables could have had a catastrophic failure? This is the 6 million dollar question that really can't be answered but I have to believe that these cables removed would have provided many years of service without failure. This is my own opinion and only goes that far. This aircraft has 3000 hours total time and has spent the largest part of it's life in the desert west. It has no visible corrosion inside the wing areas. All other flap components look and work fine. If and when the cables are cut and there are any discrepancies found I will post them here.

Herb; Thanks for posting. This is great information for us all. Where did you end up getting the new cables, and which did you go with, regular steel (presumably galvanized) or stainless steel?

Bill

Stainless Steel (-308) I figure if the originals from 1968 were stainless then they can't be all bad......

Bill, I bought the cables from Don Nieser at Commodore Aerospace.

Another Data point
 

Airplane is t337g, 1973 with about 3200 hours. After reading this string we decided to remove and inspect the cables.
Balance cable had 4broken strands cable not cut yet to look at inside. Mid cable looked like it had been replaced already. None of the cables were stainless.
Sorry for the short response typing on iPad.

Sandy Loutitt
N81C, Cybw

Sandy

How did you determine that the cables were not stainless? Are the balance cables you replaced from the flap motor or going to the flap motor? I assume the mid cables are going from inboard bell crank to outboard bell crank?

Herb,
the Mechanic just told me they were not stainless, so not sure how he determined that other than visual inspection. Flap actuator inbd
1460100-7 is the part number and description, yes I think they go from motor to the first bell crank on each side. We sent the cables off to a local shop to see if they could make them and the old ones are not back yet so we have not cut them to determine if there are any more broken strands.
Regards,
Sandy

I just sent a set of cables to Mcfarland Aviation for duplication. Price is @ 70.00 ea. That is a ton better than Cessna's price.

Kim, galvanized or stainless? And why?

Ernie

cables
 

I went with stainless. I've changed out the cables in all 6 of our 337's and removed galvanized. I had broken stands in most cables with total times ranging from 1800 to 3000 hrs. should able to tell how stainless holds up.

Broken strand and minimum bend radius
 

One thing to keep in mind when you see one broken strand is not that you have all of the rest of the strands still there for strength, but that all of those strands have been subjected to the same stress as that broken strand indicating that their useful life is almost depleted. It would be interesting to find the manufacturer of the cable and ask what the minimum allowable bend radius is and see if the radius of the bell crank is under that. Depending on the cable manufacturer and the number/diameter of the strands, maybe there is one choice of cable that is better than the rest.

As far as handling of the cable, you should be able to bend a cable within its specified bend radius and it not break. If you take it and kink it, expect to see broken strands after repeated exercising.

Did anyone measure the diameter of a "bad" cable versus a new replacement cable?