I have looked and looked and the guidance I find from AC43-13 is don't use the clevis pin if it is continuously in use. To me that sound specious - If it was not being used it would not be in the airplane... which would rive me to clevis bolts and castellated shear nuts and cotter pins everywhere. Then for nuts on bolts, we have guidance to use self locking nuts where rotation is not an issue, whereupon we use castellated nuts and cotter pins. Why one or the other? Where do we go one way, where the other? It does not look like a big deal here, just the wait for some clevis bolts or change them if the DAR says too, but I am trying to figure out what sets to decision...
Tony Bingelis puts clevis pins and clevis bolts and regular AN bolts in his chapters on control systems, but gives no guidance on when to use what. And I see a lot of spherical bearings connected with a large washer and a Nylock nut. We are all concerned that the spherical bearing will come loose (and so the big washer that precludes the connection coming apart completely) but no one is concerned about a seized spherical bearing loosening the Nylock nut and the joint becoming sloppy and coming apart. Precautions against one failure mode and not about the other!
To my specifics;
Tony Bingelis puts clevis pins and clevis bolts and regular AN bolts in his chapters on control systems, but gives no guidance on when to use what. And I see a lot of spherical bearings connected with a large washer and a Nylock nut. We are all concerned that the spherical bearing will come loose (and so the big washer that precludes the connection coming apart completely) but no one is concerned about a seized spherical bearing loosening the Nylock nut and the joint becoming sloppy and coming apart. Precautions against one failure mode and not about the other!
To my specifics;
- I have turnbuckles for the rudder cables going to a built up steel mixer. The cables will have some load on them at all times, and I expect sometimes I will have some pressure on both pedals and thus tension on both cables at the same time. See picture of gray mixer with a 1/4" clevis pin. They will be moving quite a bit - they are rudders. Clevis bolts or clevis pins? And for bonus points, WHY?
- I have trim servos with custom blade end connecting to a little built up aluminum bellcrank with a fork integral to it actuating a pushrod using spherical joints:
- For the servo (black and brushed aluminum) to bellcrank (green epoxy primer), it sure looks like a 3/16 clevis pin, washers and cotter pin will work great. This joint has some load on it in flight and is moved frequently in flight. This seems to call for a clevis bolt with shear nut and cotter pin, but Tony B's book and other places seem to allow clevis pins. So which do I use and WHY?
- The spherical joints are very definitely AN-3 bolt, AN970 washer, and nuts. Lots of folks use self locking nuts, others use castellated nuts and cotter pins. Which nut type is actually required, and WHY?
