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Elevator Hinge Bolt Torque?

tx_jayhawk

Well Known Member
How tight must you torque the elevator hinge bolts? Everything was set up nice with proper travel and friction, but after I tightened done the hinge bolts, the elevator seemed to stick a little and not be a fluid as it could be. Should this be tightened like a normal locknut?

Thanks,
Scott
7A
 
Yes, those bolts should be torqued. They bear on the ball in the ball joint and should not interfere with the hinging action. At 20 in/lbs, they should also not distort the ball to create friction. If it was free before, then I suspect one of the ball joints was probably sticking and turning around the loose bolt. You can try lubricating the ball or replacing the joint. I know it's easy to mar the bearing seal around the ball if you use a wrench to put the bearings in; that can cause the ball to stick. There's a bearing tool you can buy to prevent this or you can make your own out of PVC (I've seen a thread here with directions; search 'bearing tool').
 
You need to adjust the spacers/shims in the center and hinge bearings to prevent any binding when all these bolts are torqued. It can be a time consuming chore to get it all right.
 
Ah, good point, I had forgotten that. Yes, it's easy to 'pinch' the weldments together and cause some binding.
 
I experienced this as well.

When I tightened the elevator pivot bolts I noticed a decrease in the free play. I removed the elevators and greased the rod end balls. They were a little stiff from several years of non-use. I reinstalled the elevators and still noticed the "friction". I deduced it was from a slight miss alignment with the pre-punched parts (brackets and rod end nutplate holes). Not much you can really do about it. You can shim with .002" shims but you really shouldn't have to. I just checked the free play and after a few hours of flight the free play of the elevator is substantially better then after I torqued the bolts.

And no the nuts haven't backed off the bolts.

Food for thought.
 
Thanks guys. By shims, are you referring to the washers between the horn and the bellcrank bearing? Hard to imagine hoe that effects it and how exact that needs to be.

FWIW, everything was fine with the hinge bolt torqued. It went south when the rod-end bolts were torqued.

Thanks,
Scott
 
Thanks guys. By shims, are you referring to the washers between the horn and the bellcrank bearing? Hard to imagine hoe that effects it and how exact that needs to be.

FWIW, everything was fine with the hinge bolt torqued. It went south when the rod-end bolts were torqued.

Thanks,
Scott

After tightening all the hinge bolts and adjusting the rod ends to maintian exact alignment with the center bearing, make the correct size spacer to snugly fit between the horn and bearing. When you tighten the center bearing there should be no change in drag.
 
Thanks Walt. I think I misspoke in my previous post. Everything was fine with the center bolt (that connects the two horns together) and pushrod bolt torqued.

Only when I torqued the nuts on the 4 rod end bolts (two per side) did things get sticky.
 
Thanks Walt. I think I misspoke in my previous post. Everything was fine with the center bolt (that connects the two horns together) and pushrod bolt torqued.

Only when I torqued the nuts on the 4 rod end bolts (two per side) did things get sticky.

Thats because when you tighten the hinge bolts last you are applying a side load to the rod end bearings as you pull the elevator into postion. By doing it the other way around you avoid this, but, you have to make the correct size center "shims" then to prevent doing the same thing when you tighten the center bolt (there are only 2 so not a big deal).
 
Try checking on elevator at a time by torqueing the outer two bolts with no bolt in the middle. If an elevator binds, find out why. If both elevators pivot freely without a bolt in the middle, then you know the issue is related to the middle bearing, shims, etc.
 
Fricition Saga

Well, I spent some more time on it tonight and it really isn't much better. This is what I did:

1) I removed both elevators and sprayed some LPS1 on the rod end bearings. They were pretty stiff, but that loosened them right up (I think this helped a little).
2) I rechecked the distant from the elevator spar to the center of the rod end to make sure there was no obvious misalignment. Best I could tell, they were right on.
3) I installed one elevator at a time, and torqued the two rod-end bolts that connect it to the HS. Things still seemed to swing quite freely at this time. I repeated for the other side.
4) I then installed the bolt holding the pushrod / elvator horns. Things were still swinging relatively freely at that point.
5) I thne put the AN4 bole through the horns / center bearing. I experimented with difference numbers of washers to try to precisely space it, but it did not seem to make much difference. When the AN4 bolt was torqued, it got somewat stiff again.

It seems as though everything I did through the assembly process added just more friction, and there was not one thing that significantly changed it.


I may be expecting too much. With everything torqued (and pushrod connected all the way to stick including AP servo) now it still swings relatively smoothly. The only "difference" vs the untorqued configuration is that the heavy (they are not trimmed yet) counterbalances won't automatically swing down when left untouched (as before). By grabbing the edge and moving it it swings smootly (but generally stops where you put it).

Am I expecting too much? Wouldn't be the first time I obssessed over a small detail.

Thanks,
Scott
 
Have you sighted through all of the hinge holes with the elevators off?

You should be able to look directly through all of the holes from one tip to the other, which will show any misalignment better than a ruler measurement...:)
 
I spent many, many hours (i.e. days) working on getting the elevators to move freely when all the bolts were tightened.

Not only is it a matter of getting all the spacers and washer combinations sized for the right fit but for me, I had to go back and re-align the rod end bearings in the elevators. Screwing the bearings in or out 1 or 2 threads makes a big difference.

It was a very frustrating exercise but well worth the effort.
 
Well, I spent some more time on it tonight and it really isn't much better. This is what I did:

5) I thne put the AN4 bole through the horns / center bearing. I experimented with difference numbers of washers to try to precisely space it, but it did not seem to make much difference. When the AN4 bolt was torqued, it got somewat stiff again.

Scott

Sott,
Using washers generally won't work here, like I mentioned in a previous post, make the correct size spacer for this location. Use tubing cut to the approx. length and then final fit by sanding a little at a time until you can just squeeze it in.
 
What is the criteria?

I am just about at the same place as Scott, no friction, smooth, but counterbalances won't automatically swing down when left untouched.

Scott asked an excellent question.

"..I may be expecting too much. With everything torqued (and pushrod connected all the way to stick including AP servo) now it still swings relatively smoothly. The only "difference" vs the untorqued configuration is that the heavy (they are not trimmed yet) counterbalances won't automatically swing down when left untouched (as before). By grabbing the edge and moving it it swings smootly (but generally stops where you put it).

Am I expecting too much?.."

What is the criteria for "done"?
 
With the autopilot servo connected into the system, you will get some drag casused by the servo. Check it without the servo connected.
 
My elevator will free float to it's neutral position with no assistance.
This is everything hooked up, flying airplane with AP sevo.
 
I am just about at the same place as Scott, no friction, smooth, but counterbalances won't automatically swing down when left untouched.

Scott asked an excellent question.

"..I may be expecting too much. With everything torqued (and pushrod connected all the way to stick including AP servo) now it still swings relatively smoothly. The only "difference" vs the untorqued configuration is that the heavy (they are not trimmed yet) counterbalances won't automatically swing down when left untouched (as before). By grabbing the edge and moving it it swings smootly (but generally stops where you put it).

Am I expecting too much?.."

What is the criteria for "done"?

I had the same slight binding when I first mounted my elevators and torqued the AN-4 bolt that connects the horns to the center bearing. As Walt indicates the fix is to make custom spacers or shims to make the fit around the center bearing as "perfect" as possible. It can be done, just takes some trial and error. After shimming my elevators swung completely freely with no binding at all.
 
Alan/Walt,

How did you measure to make the perfect spacer? With the tail fully assembled it is quite hard to get to, and given the lack of space and fact that you have to also account for the large washer over the bearing, it would seem like luck to get a fit more precise than the width of a single 416L washer (which I think I have right now)?

Did yours float to neatural after initial build?

Mine is smooth enough that I suspect it will be back to floating after some usage time (I had a experienced builder look at it and tell me I am obsessing).

Sorry for obsessing (I think there is a name for that), but I would like to make it perfect if there is a reasonable path.

Thanks again,
Scott
 
Alan/Walt,

How did you measure to make the perfect spacer? With the tail fully assembled it is quite hard to get to, and given the lack of space and fact that you have to also account for the large washer over the bearing, it would seem like luck to get a fit more precise than the width of a single 416L washer (which I think I have right now)?

Did yours float to neatural after initial build?

Mine is smooth enough that I suspect it will be back to floating after some usage time (I had a experienced builder look at it and tell me I am obsessing).

Sorry for obsessing (I think there is a name for that), but I would like to make it perfect if there is a reasonable path.

Thanks again,
Scott

Scott - in my case I used custom-made shims (ie, pieces of aluminum sheet), fit by trial and error. These can be thinner than a 416L washer (which is 1/32" if I recall correctly), and easier to slide into place if you make them a bit oversize. Once you know the overall thickness of shims it would be fairly easy to make a spacer of equivalent size from tubing.

My elevators did float to neutral during the initial build, after the shimming procedure. It was surprising how much difference the right shims made. Personally I did not want to settle for "good enough" but then again maybe I was being obsessive?
 
Do it before the tail is fully assembled. Remove the VS if you have to; it is not needed to rig the elevators. Here's one way to do it: with the upper holes aligned (pass a bolt through them), use calipers to determine the spacer size. This spacer prevents side load on the rod end bearings by preventing the bolt from squeezing the horns together when a nut is added and tightened. Now insert the bottom bolt (no nut) and tighten the top nut to torque on the spacer. There should be no binding on the elevator at this point. Use the calipers to determine the spread at the bottom bolt, this is what you want to maintain to prevent the horns from being 'pinched' which will misalign the horns and tend to 'bow' the hinge line slightly, causing friction. Subtract the width of the pushrod bearing from your caliper measurement and divide by two to get the spacer measurements for either side of the bearing. Round up slightly and do a test fit (torque the bolt). Polish the spacers if necessary to reduce them and repeat until you can torque the bottom bolt and it still moves freely.

Another poster mentioned their pitch servo imparted enough drag to keep the elevators centered against the counterweights. That should not happen. Either the servo is dragging (it should be free unless powered) or the attachment to the elevator controls has some drag that needs to be addressed. My system was free until the sticks were connected; they had enough weight to keep the elevators either full up or full down but the stick forces are still extremely light.
 
Control horn bolt friction

I just wanted to add my experience with my build into this conversation. I am having issues with the center bolt going through the bearing in the elevator control horns. I drilled holes and everything went in fine, but I torqued the bolts to 85 in lbs which is proper torque spec for an an4. I had some friction on the elevator movement. I loosened the locknut up and snugged it up and went a little past 50in lbs. Everything is perfectly fine now and all moves smoothly with no friction:)
 
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