cjensen

cjensen

Well Known Member
Control surface rod end bearing torque??

i can't find anything that says there is or isn't a specified torque for the eyebolt nuts for the control surface connections. i would assume not, since there is really no way to get a socket around the eye to the nut.

so, is it just tightened, or is there some sort of guidance for tightness? :confused:

know what i'm talkin' about?
 
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thread clearance

if you are speaking of the rod end bearings for the control surfaces on the veritcal and horizontal stabilizers, I think that spacing and thread clearance are the issues. You don't have to worry about torque. I can't remember the number of threads, but the drawings or building manual should give you some direction. If not in the empennage section of the manual it may be in one of the general sections in the front of your building manual. Also check FAA aircraft standards and practices. You can find it online for free if you don't have a copy. Disregard this post if you are talking about something other than the rod end bearings. jack
 
that's what i'm talking about, thanks jack. i don't have my plans in front of me, and i couldn't remember what they were called.

i'll check the plans again for that info. i didn't look in the general section.

thanks!
 
If you look on the plans, you'll find measurements from the back of the spar to the center of the bearing. Be careful on the rudder as the bottom bearing is different than all the rest (it's a little bigger).

Do yourself a favor and order the Avery rod end bearing tool. I ended up making a tool out of a 14mm socket, but

a) it took forever to get it just right
b) the Avery tool is better and not too expensive.

I have the Avery tool now.

Don't crank them down with a wrench....you'll just end up mashing the bearings.
 
Chad,

If you're referring to the jam nuts that hold the rod ends in place, there is a specifed torque. I found it in the Standard Aircraft Handbook. I think it's half the torque called out for a normal AN365 nut, but please double-check that before you start tightening things down.

Hope this helps...

Dave
 
yeah, i knew there was a measurement callout, but i just wasn't sure about the torque on the nut. i've heard from a few people now that there is a specified torque here, and i will double check that.

i'm gonna get the tool from avery. if it's easier, then i want it!

thanks!!! :)
 
Non of my rod ends are adjusted so I hadn't even thought about torquing the nuts yet. Anybody have any ideas how to torque those things down? You could use one of those offset box end ratchet thingies, but it would offset things by and inch or so. That would probably put the torque at the wrench well below the 20in-lbs my wrench goes down to.

I'm sure someone's got some clever whiz-bang solution to this one.
 
Buy a cheap box/open-end wrench. Heat that sucker until she glows and put two 90 degree bends in it to create a big ol' "C" shape. The open end goes on the nut. Glue/weld a bolt with a nut into the box end so that you can use a ratchet to drive it. It's not pretty, but it works well for this kind of thing.

Steve Zicree
RV4 with wires and wires and ...
 
Both wiz AND bang! Thanks for the tip :)

The reason I like the bent wrench idea is that it keeps the bolt inline with the centerline of the wrench. The problem with doing the compensation for an offset with these nuts is that all the torques are so low to begin with, it would only take 1/2 inch of offset to knock it out of my torque wrench's range (20 in/lbs suddenly because 15in/lbs.....woops, I'm hosed!).
 
You can calculate the torque to use when you extend the arm (as that link shows), or you can turn the crowfoot 90 degrees to the wrench and use the specified torque, since the length of the arm (center of nut to wrench handle) hasn't changed.
 
??

Dan,
The wrench length is automatically considered when you set the torque wrench setting.

A 6" wrench or a 24" wrench set on 35 inch pounds should have the same results.

What am I missing here?

Mark
 
Using an extension

What you're missing is that sometimes you are forced to use an extension. A crowfoot adapter is considered an extension, albeit short. For example, here's the extension I used to torque my prop bolts:

20030913_prop_torque_adapter.jpg


)_( Dan
RV-7 N714D (680 hours)
http://www.rvproject.com
 
I got the extension part

Dan,
I can't believe how fast you can reply, with a photo no less.

Yea, ok I was screwed up. I was just trying to figure out why it made a difference how long the torque wrench is. I knew that 35 inch pounds is the same from a 12" torque wrench or an 18" torque wrench. BUT, the formula that figures in the extension DOES have to know the length of the torque wrench. Apparently you can't get there by just knowing how long the extension is.


I use your web site all the time for guidance, Thanks!
 
It's all about the arm

Put it this way -- the torque wrench is designed to "click" when a given force is applied at the fixed distance (length of the torque wrench). The torque wrench clicking is just an indication that you've applied that given amount of force.

Let's say you have a 20" torque wrench and a 10" extension, and you need to apply 300 in-lbs to the fastener in question. At a 30" arm, you need 10 lbs of force to supply 300 in-lbs at the fastener.

With a 20" torque wrench, 10 pounds of force, that's 200 inch pounds...the setting at the torque wrench.

Now let's say we still use the 10" extension but we're dealing with a shorter 10" torque wrench. To supply 300 in-lbs at the fastener, since we now have a 20" arm, you'd need 15 lbs of force at the end of the torque wrench.

So with a 10" torque wrench, 15 pounds of force, you'd set your torque wrench up for 150 in-lbs.

Assume:
X = torque wrench length
Y = extension length
F = force applied to the end of the torque wrench
T1 = torque setting on the torque wrench
T2 = torque applied to the fastener

T2 = F * (X + Y)
F = T2 / (X + Y)
T1 = F * X
T1 = (T2 * X) / (X + Y)

That last equation mathematically illustrates how the torque setting on the wrench varies with the length of the torque wrench.

Do you see now how the length of the torque wrench affects the torque setting you need to use?

)_( Dan
RV-7 N714D
http://www.rvproject.com
 
This is all very useful info, but it is worth noting that such formulas only work when the wrench and extension are in line. As was previously noted, no such conversion is required if you simply turn the extension at 90 degrees to the wrench.

Steve Zicree
RV4
 
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