Control column bearings binding?

Hello you all,

Now that I still have good access, while the side skins are off, I am installing the control column. The note on the drawing says not to use to many washers, so the control column moves freely. But no matter how many washers (normal or small ones) I use, after I tighten the F-633 control column mounts to the main bulkhead, there is some friction in the back- and forward movement. It?s not much, but the control column does not fall back on its own weight. Unlike the left and right movement, which is really free of any friction. When I have the AN3 bolts of the F-633 control column mounts undone, everything is fine and the controls move freely. However, after I tighten those bolts the bearings seam to ?bind?. I undid the AN3 bolts several times, pushing left, or right while tightening, reamed the holes a bit, put some oil on the bearings, but all this made no difference.

I masked the bearings while painting so there is no primer on the bearings.

Has anybody experienced this also? Is it just the bearings that are a bit tight and it goes away after its been used for a while? Maybe when the pushrods and elevators are connected-up you do not feel it anymore? Maybe I am just paranoid about it?

Any input would be appreciated, I still have good access to the whole thing now.

Actually, I think it was a good idea of some other builder, who made all four seat ribs with the removable part, so he could install and remove the complete control column assembly.

Regards, PilotTonny.

I seem to recall that there wasn't a lot of clearance on some of the moving parts. Is the friction at only one part of the movement, or throughout the full range? Perhaps something is just touching. I would keep at it, however, as any friction will add to whatever friction you add as you add more components. The control system is one of the most critical areas, so it would pay to get it right.

Bob Kelly

Pilottonny said:

Hello you all,

Now that I still have good access, while the side skins are off, I am installing the control column. The note on the drawing says not to use to many washers, so the control column moves freely. But no matter how many washers (normal or small ones) I use, after I tighten the F-633 control column mounts to the main bulkhead, there is some friction in the back- and forward movement. It?s not much, but the control column does not fall back on its own weight. Unlike the left and right movement, which is really free of any friction. When I have the AN3 bolts of the F-633 control column mounts undone, everything is fine and the controls move freely. However, after I tighten those bolts the bearings seam to ?bind?. I undid the AN3 bolts several times, pushing left, or right while tightening, reamed the holes a bit, put some oil on the bearings, but all this made no difference.

I masked the bearings while painting so there is no primer on the bearings.

Has anybody experienced this also? Is it just the bearings that are a bit tight and it goes away after its been used for a while? Maybe when the pushrods and elevators are connected-up you do not feel it anymore? Maybe I am just paranoid about it?

Any input would be appreciated, I still have good access to the whole thing now.

Actually, I think it was a good idea of some other builder, who made all four seat ribs with the removable part, so he could install and remove the complete control column assembly.

Regards, PilotTonny.

Click to expand...

This is a common cause of pitch system friction in any of the side/side RV's.
To have the minimum amount of friction (desirable for good handling qualities and hands off trim stability) it is important to shim carefully with washers and/or bend (very slightly) the ears on the control column so that there is no side load on the bearings.

Sometimes using other than AN washers (its no big deal, they are only shims) can give you more options on different thicknesses to get it all to fit just right. You can cause the same problem by forcing in washers that do not quite fit.

Taking the time to do it now will pay you back with a better flying airplane. Adding the rest of the control system will not make it better. Each part has it's own amount of friction to add to the system as a whole. You need to do all you can to minimize the amount of friction added as you install each part.

First, don't worry about not having good access later. I opened up forward seat floors so many times after I thought I was done. Whenever you need to make adjustment under there, just open the floor up. I hate to do it, but it is not a big deal.

I don't recall how much friction I had before mounting the elevator pushrod. But, I do know that the friction on the forward/backward motion and the left/right motion are not the same. Small friction should not be a problem. If you don't see any mis-alignment nor bending, add a little lubricate might help.

I had two issues on my control column. The first one was obvious during the build process and it is critical. When I pull the stick back, WD-610 cotnrol column jammed into the top of the seat ribs. I ground off the front upper part of the access hole quite a bit to clear them. It is important that the stick has full motion without any interference.

The second issue is the free play on elevator control. I could move the control stick fore and aft slightly without moving the elevator. I found the same kind of free play on my friend's RV. To solve the problem, I inserted a thin AN washer between the stick bushing and the WD-610 end opening and tighten the castle nut a little more before inserting the cotter pin (see Detail B on Drawing 38). Now there is no free play on my stick. It allows more precise control of the elevator.

Good luck on your project.

Another note on forward stick binding.

After installing the seat pans, I had a lot of binding at full forward (down pitch) stick position. I needed to shorten the floor pan attach screws that were positioned over the stick cross link weldment tube. There are about 6 or 7 of these shorter screws.

Kent

No Firction

After reading these threads and having some success installing the WD-610, I'm wondering how much friction is too much. After playing with combinations of washers, the 610 will fall from the upper, forward position, downward on it's own. However, it's still not as free as when I slightly loosen the top bolt on either of the F-633's. I don't believe there's any side pressure on the bearings, though that's really hard to tell for sure. It's like there's a little binding when the 633's are torqued down.

Like I started this, the 610 does fall on its own, and I'm just wondering if that's acceptable.

Thanks

PaulR said:

After reading these threads and having some success installing the WD-610, I'm wondering how much friction is too much. After playing with combinations of washers, the 610 will fall from the upper, forward position, downward on it's own. However, it's still not as free as when I slightly loosen the top bolt on either of the F-633's. I don't believe there's any side pressure on the bearings, though that's really hard to tell for sure. It's like there's a little binding when the 633's are torqued down.

Like I started this, the 610 does fall on its own, and I'm just wondering if that's acceptable.

Thanks

Click to expand...

Paul,
It's hard to tell just from your description.
Others will tell you that a little friction is ok and that it will fly fine. It will, but it wont be as good as it could be.
Pitch stability and the ability for the airplane to return to its trim speed is directly effected by control system friction. If in flight, the airplane is upset by a small turbulance bump and the control system moves slightly, if there is much friction in the system the trim tab will not be able to return the elevator to its priviously trimmed position. The same situation applys if you move the stick for manuvering and then release it for the airplane to return to its trim condition. The elevators may stop in a slightly different position, depending on which way they were deflected away from the trim point. If this happens, you are no longer in trim.

I have been working on RV's for 19 years and have seen this problem caused by many things (even dry elevator hinge rod end bearings, just needed some lube sprayed on them). When working on any RV control system, I strive for no change in the friction on any part of the system when I tighten fasteners.

- - I assure you there are RV owners (who already rave about the handling qualitys of there airplane) who have no idea how much better it could be! - -

Friction

Pilottonny said:

Hello you all,

Now that I still have good access, while the side skins are off, I am installing the control column. The note on the drawing says not to use to many washers, so the control column moves freely. But no matter how many washers (normal or small ones) I use, after I tighten the F-633 control column mounts to the main bulkhead, there is some friction in the back- and forward movement. It?s not much, but the control column does not fall back on its own weight. Unlike the left and right movement, which is really free of any friction. When I have the AN3 bolts of the F-633 control column mounts undone, everything is fine and the controls move freely. However, after I tighten those bolts the bearings seam to ?bind?. I undid the AN3 bolts several times, pushing left, or right while tightening, reamed the holes a bit, put some oil on the bearings, but all this made no difference.

I masked the bearings while painting so there is no primer on the bearings.

Has anybody experienced this also? Is it just the bearings that are a bit tight and it goes away after its been used for a while? Maybe when the pushrods and elevators are connected-up you do not feel it anymore? Maybe I am just paranoid about it?

Any input would be appreciated, I still have good access to the whole thing now.

Actually, I think it was a good idea of some other builder, who made all four seat ribs with the removable part, so he could install and remove the complete control column assembly.

Regards, PilotTonny.

Click to expand...

Tonny,
1. lube the bearings-should move freely, you may still have a bit of paint inside.
2. ream the control mount holes at one time so you know that they are straight.
3. add washers as necessary to prevent side movement-if you have to force a thin washer between the weldment and bearings it's one washer too many.
4. try to have same amount of washers each side of bearings and on each stick weldment if possible.
5. lightly grease-not oil-the bolt that goes through the bearing.
6. add washers as necessary to bring castlenut to hole in bolt without having to force the cotter pin in.
7. if stick movement is easy Before tightening the nut, but friction After tightening the nut, then the nut is too tight. Loosen it by one ear on the castle nut and see if friction stops, if not, loosen by another ear till it does. When you have no friction that is where you should leave the nut, washer as necessary between the castlenut and the weldment, install cotter pin. I believe I am correct that it is a castlenut on the main bearing mount and NOT an elastic stop nut, so torque on the nut is not the issue. Proper washer placement prevents side movement, not torquing the nut down.
Keep working on it, you will get it.
Mike H 9A/8A

mike109g6 said:

I believe I am correct that it is a castlenut on the main bearing mount and NOT an elastic stop nut, so torque on the nut is not the issue. Proper washer placement prevents side movement, not torquing the nut down.
Keep working on it, you will get it.
Mike H 9A/8A

Click to expand...

Actually you are not correct.
The main control stick assembly pivots on bearings (does not rotate on the bolt).
Because of this, I see no reason to grease the bolt (nothing pivots/rotates on the bolt) or to deviate from the plans and use a castellated nut and drilled bolt.
Because it is a self locking nut it requires proper torque value which is why careful shimming is required.

effect of auto pilot servo on "friction"

How does the installation of an autopilot servo in the elevator control system affect "friction"? I have a friend who is a locally very well respected pilot who rants about how much the TruTrak stepping servo and associated hardward adds to the friction, but everyone else loves the TT autopilots.

If it's a choice, I lean towards the safety of the auto pilot over choosing "perfect" handling rather than simply "really good". Can I have both "perfect" and an auto pilot?

Jeremy Constant

jjconstant said:

How does the installation of an autopilot servo in the elevator control system affect "friction"? I have a friend who is a locally very well respected pilot who rants about how much the TruTrak stepping servo and associated hardward adds to the friction, but everyone else loves the TT autopilots.

If it's a choice, I lean towards the safety of the auto pilot over choosing "perfect" handling rather than simply "really good". Can I have both "perfect" and an auto pilot?

Click to expand...

The step servo friction is very light, but you can feel it on the ground. In flight, the airloads on the flight surface is more than the "ground bound" servo friction. You won't feel it; and it isn't worth ranting about.............IMO.

L.Adamson

L.Adamson said:

The step servo friction is very light, but you can feel it on the ground. In flight, the airloads on the flight surface is more than the "ground bound" servo friction. You won't feel it; and it isn't worth ranting about.............IMO.

L.Adamson

Click to expand...

It does add some friction but I agree with L.Adamson.
If the control system is rigged properly and is low in friction
you wont feel it much (if any) in flight and it doesn't seem to have an effect on pitch trim stability.

Control Column Bearings Binding

I fly a 9A with the Tru-Track Digi-Flight II autopilot. You can feel a small amount of friction from the servos on the ground and none in flight. The normal flight loads are higher than the friction from the servos. Even with the autopilot servo, my elevator, for example, will return from a displaced position to a neutral position on the ground.

You shouldn't have any binding of the controls forward-aft, side-side. Keep at it until you find where it is binding.

Go after that friction. It's worth it.

I can attest to the fact that just a small gap can create significant friction loads on the control column. I installed my WD 610 today, lubing the bearings before installing the then inserted the washers and bolts through the F-633 control column mounts. I fitted as many AN960-10 and AN960-10L washers as I could, spacing things evenly on both sides, then put the bolts through and torqued to spec. This resulted in 8in lb of friction. I immediately jumped on the forum and found this post and clearly this was unacceptable. Thus before I pulled the assembly apart, I measured that a 16thou extra washer on one side to fill a gap on one side, so I fabricated it accordingly out of some sheet AL and sandwiched that between two of the existing washers. Prior to this I also cleaned the bearings where I could see some primer had got on the side, so now they would spin freely in all directions, then re-lubed accordingly with ATB (Absolutely The Best - best bike lubricant I've ever run). After torquing the bolts to spec, I re-ran my friction measurements, and sure enough it was zero. Incredible to think that this 16 thou gap could cause such a high friction level on the bearings, but looking closely you can could see the flange pulling in and feel the friction increasing as you progressively increased the bolt torque. I guess I'm just posting this as a point that going after this friction is the best 30 minutes you'll spend all week.
Tom.

Difficult and fiddly area. I put the bolt in first then carefully measured (feeler gauge) the gap for spacer and washers required. Worked out well. Having the fuselage on the rotisserie helped.
Either way it's a game of patience.

tgmillso said:

Thus before I pulled the assembly apart, I measured that a 16thou extra washer on one side to fill a gap on one side, so I fabricated it accordingly out of some sheet AL and sandwiched that between two of the existing washers.
Tom.

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I installed WD-610 today, and came up with the same results. I need to try a .016 thick washer. Is it acceptable to make one out of aluminum, or does it need to be another material? I can't seem to find a washer that will fit a -3 bolt that's only .016 thick. Ideas?

If you are asking me, then AL should be fine. Where AL is not good is where it is moving (oxidization causing aluminum oxide which acts as an abrasive), however in this application, IIRC, the bearing should take all the rotation and the washers should be static to one another. If you are asking this question from an intermetallic corrosion perspective, then AL and cad plated steel are fine, as this is a common setup all over your aircraft (basically at every bolt/screw location). Hope this helps.
Tom.

tgmillso said:

If you are asking me, then AL should be fine. Where AL is not good is where it is moving (oxidization causing aluminum oxide which acts as an abrasive), however in this application, IIRC, the bearing should take all the rotation and the washers should be static to one another. If you are asking this question from an intermetallic corrosion perspective, then AL and cad plated steel are fine, as this is a common setup all over your aircraft (basically at every bolt/screw location). Hope this helps.
Tom.

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Thanks, Tom. So did you make a shim/washer out of some .016 aluminum?

Yes, pretty sure I did.
T.

Where you don't want to use aluminium spacers is at the bushing where the WD-611 control stick fits into the ears of the WD-610 control column mount. I didn't want steel against powdercoat at this location, so I purchased some brass washers from McMaster to fit at each end. Aluminium is no good here, as there will be relative motion between the washer/spacer and the corresponding surfaces.
Tom.

tgmillso said:

Where you don't want to use aluminium spacers is at the bushing where the WD-611 control stick fits into the ears of the WD-610 control column mount. I didn't want steel against powdercoat at this location, so I purchased some brass washers from McMaster to fit at each end. Aluminium is no good here, as there will be relative motion between the washer/spacer and the corresponding surfaces.
Tom.

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Yeah, I think I'm good there. Headed out to the garage to give this a try! Been trying all different washer combos today with no luck! Frustrating

I'm in this mode at the moment. Spent a few hours finding the best combo of washers on the WD-633, torqued it down and had no resistance to falling under its own weight. Added the WD-611 & 612 & WD-665 and still perfect on all four directions. I came back after dinner to put my torque paint on and 633 won't fall under its own weight and 611/612 slightly bind when going full right. WTH??