N1478D wrote:Hi Jim,
Would there be a good way to break the cable/pulley issue up so that the cost and effort could be spread over multiple annuals? If so, which systems would you do first and what would be the groups? Or, is it the type of project that's best done all at once, inspect/replace all pulleys and cables that need it?
I think that in the case of my 170 that I just do not have a good feeling about any of the systems cables. So far every cable has passed inspection except the rudder cable. The areas of most concern are those not easily accessible. For example either area inboard and out board of the wing root and the tail cone area aft of the bell crank. I still have to inspect my flap & aileron cables.
I would recommend breaking it down like this and in this order.
· Rudder System: Remove enough to get the forward end of the cables disconnected and the first two pulleys attached to the forward side of the main gear bulkhead. Disconnect it at the rudder and pull enough out to get the aft end of the cable toughly inspected. Crawl down the tail, remove the remaining pulleys clean and lubricate them. Note that except for the fairleads in the system two of which are under the stabilizer the rudder cable is now almost completely removed.
· Aileron System: Disconnect the aileron cables at the outer end. If you measure the tension on the system before the cables are disconnected and only disconnect the turn barrel on the follow through cable it makes re-rigging much easier. Pull enough of the cable out of the wing into the fuselage to thoroughly inspect the areas that pass through the wing root and upper cabin.
· Elevator System: This is the easiest system to get to, the cables start in the cabin and end in the tail forward of the Stabilizer. Disconnect the cables at the forward end at the elevator drive bell crank. Crawl down the tail and disconnect the elevator cables at the rear bulkhead bell crank. While in the tail took a good look at the top end of the elevator bell crank brackets where they are riveted to the bulkhead. They are prone to cracking in this area. Crawl out of the tail and pull the cables out into the passenger compartment. Now the cables can be pulled back and forth through the cabin area thoroughly inspected. If time and expenses allow remove all pulleys clean and inspect.
· Elevator Trim System Cables: The most difficult system to deal with. Mostly because once the cables are taken off of the sprockets it takes a lot of running back and forth from the tail to the cabin to get everything set up again. Disconnect the cable at the turn barrel and attach a string to one each end so it is easy to pull back to the cabin. Before you completely remove the turn barrel put a plastic tie wrap over the chain at the front trim wheel as close to the drive sprocket as possible and tighten it so that the cables will not com off of the sprocket. Remove the cover over the sprocket at the stabilizer on the trim actuator and pull the chain off of the sprocket. Depending on the condition of the screws in the bracket cover this can be a lot of work. If the screws are rusted in either the clamp are on the actuator you may end up spending hours here just getting this sprocket chain thing accomplished. Most likely you will end up having to remove the trim actuator completely and servicing it. Once the cables are lose you can pull them far enough forward and aft to inspect them enough by crawling into the tail and cabin. Unlike their 172 brethren the 170 only has a small access hole in the top of the stabilizer where the trim cables make 90 degree turn. The cables can be pulled inboard from this access hole and inspected. Be careful when re-installing the cables from here back to the trim actuator. It is easy to get the chain on up side down and get the trim moving the wrong direction. I put a piece of triple wrapped masking tape on the top cable only to identify it as the one on the top of the sprocket before I remove it.
· Flap System: I save the flap system for last but it probably makes sense to do this system at the same time as the ailerons.
o 170 *170A: Remove the cover on the top of the wing root. Disconnect the flap cable from the end at the flap handle. Pull enough of the cable out to inspect the area in the cabin. Pull enough out at the flap drive at the wing to inspect those areas of the cable that pass through the wing root. While the cable is loose pull the cable out at each section where it passes through the cabin overhead to allow physical inspection of each section of the cable.
o 170B: Remove the turn barrel on the two drive cable connections closest to the flap handle. Disconnect the cables at the flap bell cranks in the wing. Pull enough cable inboard and out board and through the floor to inspect the cable thoroughly.
In all cases follow the rigging instructions in the 100 series maintenance manual for re-rigging the systems. In the case of the 170 & 170A the aileron, elevator, and flap control systems run through a pulley set that has a common axel at the back of the passenger cabin that will not allow you to take cable tension off of one system and remove those pulleys with out affecting the other system. So it makes it difficult to service those pulleys during any one systems work. The 170B’s aileron and flap cables run through the rear doorpost, which is not the case with the 170 & 170A.
I hope this helps. I know it is rather brief and most likely will open a bigger can of worms but it is a beginning.
Jim
A&P, IA, New owner C170A N1208D, Have rebuilt some 50 aircraft. So many airplanes, So little time!