Manual elevator trim - what does this part do?

NM Doug · #1 12-13-2012, 10:31 AM

I was trying to find the source of a little noise when moving the elevator during preflight, and when inspecting the the manual elevator trim cable, I noticed that the rubber end on the metal sleeve (toward the left side of the photo) is starting to disintegrate. (This doesn't seem to be the source of the noise, but the sleeve caught my attention.)

The whole sleeve can be turned (and slid a little, IIRC). The rod attachment to the trim tab is itself secure, and I haven't had any issues with trim while flying.

What is the function of this sleeve, and should it move as I've described?

JonJay · #2 12-13-2012, 10:47 AM

I believe it is just a dust shield. They break down over time and get hard and brittle.

chaskuss · #3 12-13-2012, 10:55 AM

That seal keeps dirt and water out of the cable's interior. Debris and rust will cause a premature death of the cable. Small rips can be repaired by cleaning the area with aerosol brake parts cleaner [available at the local auto parts store]. Once the boot is clean and dry, fill the crack with black RTV and let it cure at least 24 hours before moving the cable again. If the boot is beyond repair, you will have to replace it. I'd suggest the manufacturer, McMaster-Carr or MSD as sources of a replacement boot.
Charlie

NM Doug · #4 12-13-2012, 11:50 AM

Thanks for the info.

There's a chunk of the rubber missing, so it's probably worth replacing. I took a look at McMaster-Carr and found a complete control cable that looks like it has the boot/sleeve on it (http://www.mcmaster.com/#throttle-cable/=kks5ra).

I welcome ideas on where I could find this particular part of the cable, if that's possible. I'm guessing the cable was the one in the Van's fuselage kit.

Water might not be an issue, but dust/dirt certainly is, here in NM!

JonJay · #5 12-13-2012, 12:46 PM

Quote:

Originally Posted by NM Doug

Thanks for the info.

I welcome ideas on where I could find this particular part of the cable, if that's possible. I'm guessing the cable was the one in the Van's fuselage kit.

Water might not be an issue, but dust/dirt certainly is, here in NM!

Me too. Last time I needed one I stole it from a surplus cable I had. It is good practice to replace it and it is easy to do. However, these cables are designed for severe industrial environments. I would bet the cable would last a lifetime with no seal at all in the environments we operate our airplanes in especially outside of the engine compartment, even in NM.
Still , I would change it. Hope someone has a good source.

chaskuss · #6 12-13-2012, 03:20 PM

Quote:

Originally Posted by NM Doug

Thanks for the info.

There's a chunk of the rubber missing, so it's probably worth replacing. I took a look at McMaster-Carr and found a complete control cable that looks like it has the boot/sleeve on it (http://www.mcmaster.com/#throttle-cable/=kks5ra).

I welcome ideas on where I could find this particular part of the cable, if that's possible. I'm guessing the cable was the one in the Van's fuselage kit.

Water might not be an issue, but dust/dirt certainly is, here in NM!

Vans cables are made by a company called Cablecraft. I just went to the web page I had bookmarked for them. It appears they were/are a division of Tuthill. My web link was broken and Tuthill has a new [crappy] web site. A Google search led me to:

http://cablecraft.com/products_control_cables.html

I hope this is the correct site. I'd suggest calling these folks. They have to buy those boots somewhere. I'm sure that you could get them to sell or give you a few [never hurts to have spares!]

Charlie
PS Is it just me, or does the VAF web server seem a bit overloaded this afternoon? Since around 4pm [eastern] I've had a lot of pages dropped and SITE TOOK TO LONG TO RESPOND error messages from the site. None of the other sites are affected, only VAF.

ccsmith51 · #7 12-13-2012, 03:43 PM

Quote:

Originally Posted by chaskuss

PS Is it just me, or does the VAF web server seem a bit overloaded this afternoon? Since around 4pm [eastern] I've had a lot of pages dropped and SITE TOOK TO LONG TO RESPOND error messages from the site. None of the other sites are affected, only VAF.

Not just you, I've been having the exact same issues....

Greg Arehart · #8 12-13-2012, 06:07 PM

If/when a part number becomes available, please post it here. I would like to have a couple extra of these around the shop just in case.

Thanks,
Greg

rockwoodrv9 · #9 12-13-2012, 06:53 PM

I thought this thread may be discussing the plastic piece that fits on the end and connects to the trim tab. Does anyone else wonder if the threads on the plastic are strong enough to hold the trim tab in place? I think it would be a real bad day if they stripped out and the trim tab started flapping in the wind. Has anyone changed to a metal connector? I haven't heard of it happening but it looked like a place that could be a problem.

chaskuss · #10 12-13-2012, 07:07 PM

Quote:

Originally Posted by rockwoodrv9

I thought this thread may be discussing the plastic piece that fits on the end and connects to the trim tab. Does anyone else wonder if the threads on the plastic are strong enough to hold the trim tab in place? I think it would be a real bad day if they stripped out and the trim tab started flapping in the wind. Has anyone changed to a metal connector? I haven't heard of it happening but it looked like a place that could be a problem.

You are not the first person to voice a concern regarding the plastic clevis used on both the MAC and now RAC trim servos [as well as the manual cable systems]. That plastic piece is called a clevis. See

http://en.wikipedia.org/wiki/Clevis

Charlie