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Re: Acf-50?
I have to chime in here with a story that may be relevant.
Once upon a time, I bought a pretty little 150HP Grumman Yankee in Chicago. At the first Annual, a cranky old grizzled Huey pilot combat veteran IA mechanic looked up the AD's... one of which was a recurring inspection of six primary control cables in a very difficult location. He said for me to go down in there, all bent sideways and uncomfortable like, and look at the cables. I took a quick look with an inspection mirror, and was a little too quick to come out and say it was OK. Because I came out too hastily, he sent me back there again, which I was not appreciative of. Something about having control cables shot up and trying to maneuver through small arms fire over a jungle 40 years prior.
There's a stack of six small pulleys down on the floor of the Yankee, where both rudder cables, both aileron cables, and both elevator cables run through. Mr. Bede, or the engineers at Grumman, decided they could save 11 cents by mounting the pulleys so close to the honeycomb floor of the Yankee that the floor itself served as the cable guide (keeping the cables from jumping off the pulleys). It's in a very cramped place under the instrument panel, behind a center console, and in a minefield of obstructions and pointed objects. For a well-fed guy like me, it's very...very uncomfortable to get down in there and do anything.
The second time, I went back down there and ran my fingers back and forth where I could reach. Couldn't see anything wrong, so I resurfaced and asked for the next task on the annual. The IA asked if I had just ran my fingers on the cables where it was easy to reach, and if I had forgotten to move the controls so the part of the cable under the pulley came out where I could touch it. He had seen me not moving the controls, so I fought the temptation to lie. This time, I didn't even try to hide my irritation about having to go back down into that sweatbox. The IA left for the evening, only after I promised I'd check it a third time.
After a lot of cursing and grunting, I got back down in the sweatbox. In order to move the controls in that position, I had to allow some very uncomfortable objects to poke at my head, and the end of one particular AN bolt attempted to have sex with my ear. When I moved the controls, all seemed normal except for one single tiny strand of one cable, about 1/8 inch long. The problem was that the strand was sticking out perpendicular to the cable, not "un-wound" tangentially.
I had heard that one or two strands can be broken on a cable and it can still be used... but the perpendicular thing bothered me because it would have to be broken inside the cable to do that. So, with a rather significant amount of cursing, sweating, and a few threatening remarks to the Yankee itself, I loosened six very well-hidden turnbuckles, removed six pulleys, disconnected the cables from their attach points, and crawled out of the cockpit with six short cable assemblies.
I took a look at the cable with the little strand sticking out, and it looked not too bad. Until I flexed the cable into a loop that is. It "exploded" into a porcupine of broken strands. Only when looped (around a radius matching the small pulley) could it be seen that at LEAST 2/3 or 3/4 of the strands were broken. This was on BOTH rudder cables.
The next 2 or 3 weeks was spent "terminating" the AD by installing larger pulleys and new cables. Through the "Grumman Gang" online forum I learned the cause of the problem ... the dirt and debris that collects on the floor of any airplane would get swept up into the cables as they passed close to the floor. The lubricant inside the cable, with any extra grease, water, oil etc. would absorb this mixture and form an abrasive compound As the cables bent around the too-small pulleys, they would get eaten up, sometimes from the inside out.
Now the fun part. The Yankee uses an "open loop" rudder control system. There is a rudder pedal return spring from the pedal to the firewall, that keeps the cable taut. But no direct connection between the left and right rudder cables. So if the left rudder cable had broken, the right pedal return spring would create instant full right rudder deflection, and you would not be able to counteract it with left pedal. Because the Yankee is short coupled, low-wing, and very "sprightly" compared to most other light airplanes, it could have snap-rolled or spun rather quickly. The only hope of regaining any control would have been if I had figured it out very quickly and hooked my toe under the pedal and pulled the pedal back against the spring. But having all this happen on a climbout, being surprised by it and then a moment to react, then figure it out, then figure out the solution, while the airplane is rolling or yawing out of control - not very likely!
The purpose of this horrific rant is to add some color and Tabasco to make the (previously mentioned) concept of keeping control cables dry a little more memorable. Dirt can get swept and worked into a control cable where it flexes around a pulley. The damage may not be easily visible. Perhaps there are dry-lubes, dry graphite powders, etc. that can act as a barrier against dirt and not create this abrasive problem. or perhaps it is best to just keep the cables dry. There are probably volumes of data and test results on cables and "wire rope" as they are rightly known. Perhaps someone with specific technical knowledge can jump in and educate us on a technical level.
IF you ever run into an early (69, 70) Grumman Yankee, make sure to ask the owner if the control pulley AD has been terminated by upgrading to the large pulleys, NOT by repetitive inspection. I can guarantee you that a quick visual inspection is very very unlikely to be as thorough as it should be, and that a damaged cable is very difficult to spot in those circumstances. I will bet my ass in San Francisco that many many many Yankees have been annualled with damaged cables getting past the inspector.
I have to chime in here with a story that may be relevant.
Once upon a time, I bought a pretty little 150HP Grumman Yankee in Chicago. At the first Annual, a cranky old grizzled Huey pilot combat veteran IA mechanic looked up the AD's... one of which was a recurring inspection of six primary control cables in a very difficult location. He said for me to go down in there, all bent sideways and uncomfortable like, and look at the cables. I took a quick look with an inspection mirror, and was a little too quick to come out and say it was OK. Because I came out too hastily, he sent me back there again, which I was not appreciative of. Something about having control cables shot up and trying to maneuver through small arms fire over a jungle 40 years prior.
There's a stack of six small pulleys down on the floor of the Yankee, where both rudder cables, both aileron cables, and both elevator cables run through. Mr. Bede, or the engineers at Grumman, decided they could save 11 cents by mounting the pulleys so close to the honeycomb floor of the Yankee that the floor itself served as the cable guide (keeping the cables from jumping off the pulleys). It's in a very cramped place under the instrument panel, behind a center console, and in a minefield of obstructions and pointed objects. For a well-fed guy like me, it's very...very uncomfortable to get down in there and do anything.
The second time, I went back down there and ran my fingers back and forth where I could reach. Couldn't see anything wrong, so I resurfaced and asked for the next task on the annual. The IA asked if I had just ran my fingers on the cables where it was easy to reach, and if I had forgotten to move the controls so the part of the cable under the pulley came out where I could touch it. He had seen me not moving the controls, so I fought the temptation to lie. This time, I didn't even try to hide my irritation about having to go back down into that sweatbox. The IA left for the evening, only after I promised I'd check it a third time.
After a lot of cursing and grunting, I got back down in the sweatbox. In order to move the controls in that position, I had to allow some very uncomfortable objects to poke at my head, and the end of one particular AN bolt attempted to have sex with my ear. When I moved the controls, all seemed normal except for one single tiny strand of one cable, about 1/8 inch long. The problem was that the strand was sticking out perpendicular to the cable, not "un-wound" tangentially.
I had heard that one or two strands can be broken on a cable and it can still be used... but the perpendicular thing bothered me because it would have to be broken inside the cable to do that. So, with a rather significant amount of cursing, sweating, and a few threatening remarks to the Yankee itself, I loosened six very well-hidden turnbuckles, removed six pulleys, disconnected the cables from their attach points, and crawled out of the cockpit with six short cable assemblies.
I took a look at the cable with the little strand sticking out, and it looked not too bad. Until I flexed the cable into a loop that is. It "exploded" into a porcupine of broken strands. Only when looped (around a radius matching the small pulley) could it be seen that at LEAST 2/3 or 3/4 of the strands were broken. This was on BOTH rudder cables.
The next 2 or 3 weeks was spent "terminating" the AD by installing larger pulleys and new cables. Through the "Grumman Gang" online forum I learned the cause of the problem ... the dirt and debris that collects on the floor of any airplane would get swept up into the cables as they passed close to the floor. The lubricant inside the cable, with any extra grease, water, oil etc. would absorb this mixture and form an abrasive compound As the cables bent around the too-small pulleys, they would get eaten up, sometimes from the inside out.
Now the fun part. The Yankee uses an "open loop" rudder control system. There is a rudder pedal return spring from the pedal to the firewall, that keeps the cable taut. But no direct connection between the left and right rudder cables. So if the left rudder cable had broken, the right pedal return spring would create instant full right rudder deflection, and you would not be able to counteract it with left pedal. Because the Yankee is short coupled, low-wing, and very "sprightly" compared to most other light airplanes, it could have snap-rolled or spun rather quickly. The only hope of regaining any control would have been if I had figured it out very quickly and hooked my toe under the pedal and pulled the pedal back against the spring. But having all this happen on a climbout, being surprised by it and then a moment to react, then figure it out, then figure out the solution, while the airplane is rolling or yawing out of control - not very likely!
The purpose of this horrific rant is to add some color and Tabasco to make the (previously mentioned) concept of keeping control cables dry a little more memorable. Dirt can get swept and worked into a control cable where it flexes around a pulley. The damage may not be easily visible. Perhaps there are dry-lubes, dry graphite powders, etc. that can act as a barrier against dirt and not create this abrasive problem. or perhaps it is best to just keep the cables dry. There are probably volumes of data and test results on cables and "wire rope" as they are rightly known. Perhaps someone with specific technical knowledge can jump in and educate us on a technical level.
IF you ever run into an early (69, 70) Grumman Yankee, make sure to ask the owner if the control pulley AD has been terminated by upgrading to the large pulleys, NOT by repetitive inspection. I can guarantee you that a quick visual inspection is very very unlikely to be as thorough as it should be, and that a damaged cable is very difficult to spot in those circumstances. I will bet my ass in San Francisco that many many many Yankees have been annualled with damaged cables getting past the inspector.
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