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Control Column Binding Investigation

HAL Pilot

Well Known Member
I have a QB Fuse that comes with the control column horizontal assembly preinstalled and conveniently Preset to binding. I am now at that part of the build and decided to investigate a little deeper as I was not understanding why the thing was binding.

I attempted to loosen one lock nut first. Binding went away. I thought great all I need to do is re shim this side and life is good. Not so much. Many iterations and attempts later I decided I need to investigate what exactly is behind the binding as it seems that the consensus was play around with it till its good but not actually finding the cause. I decided to stop playing around with washer sizes and dive into what was going on.

My first thought was maybe the washers were being pushed into the Bearing bracket assembly. See Figure 4 bellow. As It is impossible to see into this area with the control column assembly installed, I moved it out of the way and attached a short bolt with washers and lock nut torqued to specs. It moved easily but if I put a load on the bearing by either pushing on the bolt head or locknut in the direction the bolt was pointing then I would feel binding. the washers had very little clearance around the opening So initially I thought it might be the washers contacting the Bearing assembly bracket.

To test this hypothesis, I shaved down 4 washers by placing them on a bolt and spinning with a drill in contact with a hand file. The new narrow diameter washers were reinstalled with plenty of visible clearance. The new bolt and washer assembly also moved easily but if I put a load on the bearing by either pushing on the bolt head or locknut in the direction the bolt was pointing then I would still feel binding, so the culprit is not the bearing assembly bracket or interference with the washers.

Long story short the culprit is side load on the bearings themselves. As an example, if you place one extra larger size washer on the locknut side on each end of the control column assembly (Spot A in figure 4). Make it big enough for demonstration purposes that you have to force it between the tab and the bearing you would end up pushing each bearing outboard and causing binding in both the left and right bearings because they are both having a side load imparted.
The fix then is to have enough washers in all 4 places (inboard and outboard on both ends of the control column assembly) without being able to see gaps easily so that when the lock nut is torqued neither tab of the control column assembly is being pushed in either direction as that would impart a side load on the bearing.

The question for tomorrow is how does one do that without having to assemble torque and disassemble the part 25 times. ;-)

I will update hopefully with useful info.
 

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I

I attempted to loosen one lock nut first. Binding went away.

No 14 experience, so won't comment on binding. However, generally, a lock nut only locks if the bolt threads go all the way through the lock nut and protude just a bit (1 full thread si the recommendation). Your pics show that the locking feature of that nut is not active. Not a good idea on a critical rotating part necessary to keep the plane in the air. Reducing torque on the nut just makes it easier for the nut to back off on it's own, making the locking feature even more critical!

I have only limited experience with the deformed steel locknuts and it is possible that they lock well before the end on some versions, so suggest research before accepting my opinion. I believe some only lock on the last thread or two and others have fully deformed or undersized threads. In general, it is NEVER a good idea to only have a bolt 1/2 engaged through a nut, regardless of locking. Holding strength is greatly reduced.

Strongly recommend some guidance from an experienced builder to sort this out. This is one of the more critical fasteners on the plane and you want to get it right. If that nut backs off, you are going to have a REALLY bad day.

Larry
 
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Thanks for the advice on the lock nut threads. However as stated in the description that was a test to see what might be causing the binding. The control is not actually connected and that setup will not be used for flight. It was just to see what a torqued nut and washer was looking and acting like without the controls connected as I was trying to test whether the binding was coming from interference on the washers and the housing or something else. It turns out it was the side loading on the bearings. I apologize if I did not make that clear.
 
Vans has some tiny washers (really spacers) for the rod end balls to allow greater off axis motion. This will provide an engineered solution to your custom washers.

They are kinda hard to find when looking up in the drawings. I'll post when found.

OK, never mind - - side loading us understood, simply select correct stack of washer thicknesses.
 
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Side Load

For grins/giggles take it all apart and measure the thickness of the various washers.

Are they really .032" and .0625" or are they a little more/little less? This can happen with AN960 washers that "sneak in" to the mix...

That 100th or many 1000th of an inch can bind things up.
 
Vans has some tiny washers (really spacers) for the rod end balls to allow greater off axis motion. This will provide an engineered solution to your custom washers.

They are kinda hard to find when looking up in the drawings. I'll post when found.

OK, never mind - - side loading us understood, simply select correct stack of washer thicknesses.
Those small diameter washers are required for applications where the rod end bearing could move side to side (throttle, mixture rod end bearings) are good example of that.
In this case, there is no side to side motion once everything is locked in place.

Since this is a welded part, they are not quite as precise as one hope them to be so a good rule of thumb is to try different size (thickness) washers on each side of each bearing (pilot and co-pilot) to make sure there is no binding and also no free play. Then if you need to take it apart for whatever reason, you make a note of those washers and their position so you can put them back in the same manner. Another location that comes to mind that has this situation, is the center bearing on the HS for the L&R elevator.

Now that you have got to this part, get read for setting/fine tuning the up/down elevator stops at the control column. But you will be doing that after the elevator has been installed and max up/down on that has been set.
 
Just completed this last week. It took me about 3 hours all in to find the right stack for both sides. Started on one side and once preliminary washers were in place I grabbed CS-00006 and tried to shove it port/stbd quite forcefully. “Heard”movement so tried again. Wasn’t happy until I couldn’t hear anything, then installed washers on opposite side. It is tedious. I had to “push” washers into place, not just slide them in. Once complete, the CS-00006 will drop with no resistance. A washer wrench and small magnet are essential. See attached for what I ended up using. YMMV.
Shim stock are supplied with SB. .014 and .025 iirc.
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34C62A32-97A5-4D04-8E33-3245F04CC37D.jpg
 
I had a thought this morning that if one knows the inside measurements of the brackets on the control column assembly and the outside measurement of the FLAT end of the COM-3-5 bearings. In other words the distance between the two flat faces that the washers end up sitting on on the com-3-5. Than it should be simple to figure out the thickness of the washers required. Then measuring the bearing bracket distances and accounting for them it should take the guess work out of the process.

The COM-3-5 bearings are close tolerance so I assume the size should be consistent.

I would like to test this however I do not have a COM-3-5 bearing that is easy to measure. Can some one please give me a 0.000" measurement?
 
Should be able to stick tail of digital caliper through hole against something flat on other side. They are proud of bracket so should work.
 
I had a thought this morning that if one knows the inside measurements of the brackets on the control column assembly and the outside measurement of the FLAT end of the COM-3-5 bearings. In other words the distance between the two flat faces that the washers end up sitting on on the com-3-5. Than it should be simple to figure out the thickness of the washers required. Then measuring the bearing bracket distances and accounting for them it should take the guess work out of the process.

The COM-3-5 bearings are close tolerance so I assume the size should be consistent.

Because it is a welded component that is being installed, it can not be assumed that the COM bearing locates exactly centered between the tabs that make up the clevis on the control column.
So your idea will provide a clue to what the overall total dimension of the spacer washers needs to be, but not how much of that dimension is located on the left vs right side of the bearing. Though once washers are installed on one side, as long as you know the thickness dimension of those, it would help in selecting washers for the opposite side.
I don't think it is detailed in the build manual, but considering the low loads involved with this bolted joint, custom making specific thickness washers from scrap aluminum sheet is totally acceptable to help obtain a net fit and friction free movement of the control column (which is very important for best handling qualities and good dynamic pitch stability).
 
Final results

First a shout out to Scott McDaniels. THANKS SO MUCH FOR BEING A REGULAR CONTRIBUTOR ON VAF! Much appreciated.

I am convinced that any binding that anyone has been feeling is a result of side loads on the COM-3-5 bearings

After way too many measurements and head scratching because apparently making a mistake on one transposition throws one's math off everywhere else. I have figured out a simple solution on these washers. Once I had the math down the first test fit worked perfectly.

I am including 4 Pictures. The first 2 are for understanding the parts I will be referencing.
# 3 is the measurements you need.
# 4 is the math part (Its actually quite easy)

My fuselage was on its side for this work. I highly recommend the same for you as this way it is easier to place and maneuver the washers.

You need 4 measurements.
-The inside distance on #1 and #3 for comparison my numbers were 0.4875” on both.
-The width of your COM-3-5 bearings #2 and #4 for comparison mine were 0.2785
I recommend getting the COM-3-5 measurements BEFORE step 4 on page 25-04. Write these dimensions in your plans so as not to misplace them. My fuselage is a QB so I had to take the measurements with the control column assembly already installed. This is much harder to get a good reading as there is limited space. I just removed the bolts and washers and moved the control column assembly over where I could get the measurements with the back side or inside tongs on a caliper. You QB builders will need to do this any way to set up the correct washers.

Now comes the Math part

For Location A select an NAS1149F0363P and NAS1149F0332P per the plans Place them together on a used AN3 bolt add a very small drop of superglue between the 2 washers. Press and hold. This keeps glue off your hands and aligns the holes.

Remove the washers from the bolt and measure width with calipers record on your plans. Add this number and the width of the COM-3-5 bearing (dimension #2) together. This new number (#2 width+COM-3-5 width) is subtracted from Dimension 1 (bracket width) This final number is the new width for dimension B.

To test your work, place a feeler set with this width into space B while pushing the bracket and washer A set together. If it is a nice snug fit you now play around with washer sizes to get as close as you can get to dimension B. Select different washers from the same batch to go up or down a bit as they vary slightly. Use the Aluminum washers as required. I was able to get to .003 of the size required. Record the final size of washers you ended up with for your records.

It is much easier to insert the washers as a set that is super-glued together. Assemble washers, bolt, and locknut. Torque to final setting (28 inch lbs+drag). Check for free movement of the assembly. There should be no resistance at this time.


We are now moving to the other side of the Control column assembly. Take your feeler gauge set. Select 3 or 4 strips next to each other that come out to approximately .0800. Slide this into area D if the space is not snug fold the thinnest feeler gauge in and fold out the next thicker gauge in the set. Or vice versa for too thick. Test the fit. Once you have this dimension snug make a washer set as close as you can to the feeler gauge dimension (my gap was 0.0840 with the final washer thickness 0.0810).

Insert a used AN3 bolt and the new washer set in space D from the inboard side (opposite to how it is shown in the picture). This is to keep things straight and at the correct dimensions. Take the number you have for the GAP in position D record for your records then add the COM-3-5 width from #4 dimension. This number should be the size you are trying to get for Space C.

Take your feeler gauge set and create a width equal to this number and do a test fit. Pull the AN3 bolt down just far enough so that it is flush or slightly below the opening of the COM-3-5 bearing. Insert feeler gauges. Adjust until it’s a snug fit. Now try to get as close as you can to this number. (My gap was 0.1290 and my final washer size ended up 0.1270) Now assemble with the Correct AN 3 bolt, locknut, and washer in the orientation depicted in the manual. Torque to final torque. You should now have free movement of the assembly with no binding. On mine I feel a hair of resistance, but its very negligible. Most importantly I only had to assemble each side ONCE!
 

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Nice write up ! I totally agree that having the fuselage on its side makes this job a heck of a lot easier. I was able to accomplish this through trial and error. The bind up always happens as that AN3 bolt is tightened to its final spec. Hopefully this procedure will make somebody’s life easier :)
 
McMaster Carr Shims

Thankfully the tolerance’s on mine smiled on me and I didn’t have this same issue. I just wanted to point out that McMaster Carr does carry shims with an ID of 3/16 and in varying, precise thicknesses. One of the things that is critical to the final RV Grin is how smooth and fluid the entire control system is, getting this right is worth your time. Not to mention it might prevent having to replace the bearing later on a completed airplane! - Jason
 
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