rudder trim tab

[Flyhound]

Arghhh! preflight yesterday revealed the cable going to the rudder trim tab was badly frayed on the right side of the plane. Any experience replacing these cables? Is this a straightforward part swap, or am I in for an adventure? There seems to be a "gooseneck" passthrough into the rudder that these cables run through. Is there a transition piece at the end of the gooseneck that is supposed to reduce friction and wear? Any other thoughts? The picture was taken from above the cable looking down at the tailwheel.

[andy]

I think you mean the rudder servo tab, which isn't rudder trim. It's connected to the aileron cables. Here's drawing 3011F Rev. M. If my memory serves me, the cables pass into the fabric through grommets and then through several sets of guides and fairleads attached to the tubing but there aren't any other connections until you get to the cable clamps where they attach to the aileron cables.

[Kirk]

Replacing the cable should just involve the inner cable and not the outer housing. Probably will thread in fairly easily and push through. I personally have not done one, so no secret tips here. I would expect it is all one continuous cable to the servo tab as the diagram Andy posted shows.

Looking at your pic, I would say the cable has been chafing on the outer cable housing by not being aligned with the line of travel. Adjusting that angle would require cutting fabric and realigning. Hopefully, you won’t have to do that.

Here’s a pic of how mine looks:

[Old Piper]

Hi Flyhound,

My concern is why the cable/wire broke within the sleeve housing into the fabric. Is a burr or something going on there?

Andy and Kirk got it right, it should be an easy repair other than what above mentioned.

I would take a fishing line or something similar that won’t break and back feed it from front to back. Replicate old cable/wire to size and feed it back forward. You may have to pull the headliner up to get at the cable/wire attach points near above the pilot/copilot rear door posts if zipper access is limited.
All doable though. Maule Factory should have those cable/wire sets in stock, unless you’re making them yourself.

Good luck, hope all goes smoothly.

[Andy Young]

As mentioned above, you do need to take a close look at the coiled-wire guide tubes that the cables run through in the rudder (they terminate just inside the fuselage, and the cables are bare from there forward). I believe these have a plastic sleeve in them to reduce friction and wear. Yours might be worn out, damaged, or not positioned properly. If you can get away with just doing the cables, it’s not too bad a job, especially if you do as suggested, and tie a string to them before you pull them out from the rear. If you have to replace the guide tubes, it will involve significant fabric work on the rudder.

A small number of planes came from the factory with no servo tab on the rudder. Others have removed theirs, though I’m not sure what the paperwork story was to do that. It’s possible that you could get Shirley (engineer at the factory) to add your serial number to the list of those approved to not have the servo tab, if you wanted to just eliminate it. Of course, that would also involve fabric (and steel) work at the rudder. Maybe there is even a mod kit already to do this? I don’t think so, but worth a look.

[Flyhound]

OK, I got some great guidance here, and more from an A&P/IA that was working on another Maule nearby. I was able to connect the old cable to a string and had the sting follow the old cable as it pulled out. Figuring out how to inspect the gooseneck passthrough inside the rudder for any fairing piece still has me baffled. I'll get back to it tomorrow. I'm afraid that inspection will involve cutting fabric and I hate to do that. The borescope I have available is too large to fit through the gooseneck for an internal inspection. The part was 23 years old, but the cable on the other side of the servo isn't showing any wear. I may replace it while I'm at it just to be sure. Here are some pics of the string connection I made to ensure the new cable could be pulled back through the fairing leads without disassembling the headliner and crawling back in the fuselage tailcone.

[Andy Young]

When you connect the new cable, keep in mind that rigging this properly is important to get the plane to fly straight. It should be streamlined to the rudder when the ailerons are neutral.

[Mog]

When you connect the new cable, keep in mind that rigging this properly is important to get the plane to fly straight. It should be streamlined to the rudder when the ailerons are neutral.

Or locked out to fly like a normal plane.

[Andy Young]

Nothing normal about a Maule….

[Flyhound]

Yeah, my mechanic recommended that I lash the yokes to hold the ailerons in a neutral position and then measure the offset (if any) of the rudder tab. The MX-7 plane he demonstrated this on had a slight offset to the left. That would impart a small amount of right rudder when the ailerons were neutral. My plane had no offset, so I adjusted the tension in the replaced cable to keep the rudder tab perfectly streamlined with the rudder when the ailerons were neutral. It's all back together, but the weather is LIFR, so I'll do my post maintenance test flight when the conditions improve. Hopefully tomorrow.

[Flyhound]

A full inspection of the failing rudder tab cable didn't show any scuff marks indicating localized wear, but there was a buildup of dirt and grime around the fabric passthrough. My guess is that the buildup of dirt acted as an abrasive and over 20+ years of flying that "abrasive" was pushed around as the cable moved in the fabric passthrough and that led to the failure of a couple of wire strands. I've added a maintenance task to move the ailerons all the way to one side and then to clean the most exposed cable of all dirt residue. Then flip the aileron deflection to the other side and repeat the cleaning effort on the other cable.

[PCH]

Thank you for taking the time to inform and educate us. Great information here.

[Flyhound]

We have 5 Maule aircraft at my home base. One was just completely rebuilt, so it is basically a new airplane. Of the other 3 (not including my plane) one other had a frayed rudder tab cable that hadn't been noted previously. A single strand of the cable was broken on this M5, and the broken strand and been cut off at the swaged fitting at some point. The current aircraft owner was unaware of the problem, and will be addressing it during his upcoming annual. So, the problem isn't unique to my plane, or my kind of flying. It's just another item to be sure you inspect regularly. Maybe add this to your pre-flight checklist.

[Kirk]

Cables are good on my rudder servo tab but some years back I did have an issue at annual with the rudder cables. My IA detected some slight fraying of the cables at the fairing where they pass through the fuselage fabric.

I believe I remember him not liking the small fairings installed and replaced them with some slightly larger and checked for chafing. That’s a whole different setup than the servo tab cable routing but thought I’d throw that out there.

His method for detecting the fraying was running the edge of his thumbnail along the cable. According to him, any roughness required replacement. He is quite particular and could be right. Most any other IA I know would have passed it. As for me, I’m all in favor of conservative judgement when it comes to flight controls.

Kirk

[Andy Young]

Due to the mounting angle of the rudder on the airframe, the rudder cables actually move up and down a fair bit as the rudder moves side-to-side. Most Maules have a very small hole where the rudder cables pass through the fuselage fabric, so they do indeed rub on the fabric as the rudder moves. When I re-covered mine, I made the holes large enough so that the cables never touched the fabric; the hole had to be surprisingly large (maybe 3/4” to 1” in diameter or so) to achieve this. I then made long, angled fairings (which also don’t touch the cables) to cover the holes. In the end it looks great, but making the large holes did get my attention.