[prkaye]

i'm assembling the control stick assembly as recommended during the assembly of the main carrry-through bulkhead. I'm confused about something.
There's AN4-27 bolt that goes through this brass bushing - the bolt is supposed to rotate freely in the bushing to allow the control sticks to move side to side. The problem is when I torque down the castlenut it clamps the clevis of the WD-610 agains the bushing, preventing it from rotating freely.
so i'm thinking... is the reason we use a castle nut and cotter pin here that we are NOT supposed to torque this nut? If i'm right about that, how tight do i put the castlenut on? finger tight?

 

[mgomez]

It's the bushing that rotates

My understanding is that the bolt should not rotate in the bushing, but that the bushing should rotate in the stick weldment. If it's all done perfectly (mine's not), when you torque down the bolt, it should grab the bushing between the ears of the control shaft weldment, not allowing it to rotate about the bolt. Then the stick will rotate about the bushing.

 

[prkaye]

really??

hmmm... that doesn't seem right to me... the brass bushing is a really snug fit inside the weldement. I though that the point of the bushing was that the brass provides a smooth surface for the shaft of the bolt to rotate against... the inside of the weldment is not very smooth. But maybe i have this wrong... was I supposed to ream out weldment to allow the bushing to rotate inside it? I guess in this case i should have left the brass bushings a bit longer than the weldment too...

 

[vlittle]

Phil, Martin is correct.

You need to ream out the control stick until the bushing freely rotates. A word of caution here-- don't use a drill for this. Beg or borrow a 1/4" reamer. You don't want a loose fit or you will get free play in the linkages. You also don't want any friction.

I know of someone (Andy Karmy, I think) that had to fabricate a new brass bushing on a lathe because the original was too sloppy.

This is a tricky part of the design, and I wish Van's would pre-bore the weldment so that problems are not introduced later on.

A tiny amount of freeplay is ok (some old salts will say desireable). I think mine is about 1/32" total which is probably the sum of all of the linkages plus the control stick bearing.

Too much freeplay leads to over-controlling fine adjustments, and in the worst case can exacerbate flutter. That being said, I've never heard of any serious problems in this area.

V

 

[prkaye]

yeah, now i remember this (reaming for bushing) from the bellcrank thing in the wing. Silly me.

Question 1 - it would have to be bigger than 1/4" reamer... the outside diameter of the bushing is 3/8. so do i get a 3/8" reamer, or a slightly oversized one?

Question 2 - how much longer should the bushing be than the weldment that it sits inside? in otherwords, how far should the bushing stick out either end of the weldment?

 

[chunt0]

Stick Bushings

My stick tubes rotate around the fixed brass bushings as smooth as silk. They certainly didn't start that way. The interiors of the tubes were very rough, causing serious friction.

I used a thin saw blade to cut about a 1.25 inch long slit (length not critical) length wise down a piece of 3/8 inch wood doweling. I then cut a small rectangle of 240 grit sandpaper, sized to fit in the slit and wrap in an S shape around the dowel. Only one leg of the S will be abrasive, but that's fine. I ran a 3/8 inch drill through the tubes to clean out any really rough stuff. Next I put a drop of light oil in the tube, chucked the dowel in my drill and proceeded to burnish the interior walls of the tubes. If you want a mirror finish, you can use progressively finer grades of sandpaper. If your dowel + sandpaper diameter is too large to insert in the tubes, using your drill again, you can just spin the dowel against another piece of sandpaper to quickly turn the relatively soft wood down.

Since I had the doweling and sandpaper on hand, total time to smooth, shiny tubes was about 10 minutes.

 

[Rivethead]

And a little bit of grease to keep things nice.

 

[vlittle]

yeah, now i remember this (reaming for bushing) from the bellcrank thing in the wing. Silly me.

Question 1 - it would have to be bigger than 1/4" reamer... the outside diameter of the bushing is 3/8. so do i get a 3/8" reamer, or a slightly oversized one?

Question 2 - how much longer should the bushing be than the weldment that it sits inside? in otherwords, how far should the bushing stick out either end of the weldment?

Yup, should be 3/8, not the 1/4 I cited from memory.

 

[briand]

Reamer Size

Next size past 3/8".

So a .377 or a 9.75 MM reamer.

However, mine just needed the powder coat cleaned off the edges. I then coated the OD of the bushing and the ID of the stick with moly powder worked in real good.

I would make the bushing .020-.030 (.010-.015 longer on each side) longer than the sticks bushing holder thingy. Remember you can always cut more off but you can't add material back.

 

[Michael Burbidge]

Van's tech support said

the following when I asked about torquing the castle nut on the control stick attach bolt:

"In this case, the torque value is meaningless, because we aren't using the bolt to "torque"
things together.

We're using the bolt another way, as a shaft, so just tighten the nut until you begin to feel
friction and no slop, then pin it in place with the cotter key."

 

[DanH]

Van's tech support said the following when I asked about torquing the castle nut on the control stick attach bolt: "In this case, the torque value is meaningless, because we aren't using the bolt to "torque" things together. We're using the bolt another way, as a shaft, so just tighten the nut until you begin to feel friction and no slop, then pin it in place with the cotter key."

The tech person was misinformed. As others have correctly explained, the brass bushing should be firmly clamped......which requires standard torque applied to the bolt.

Phil, the bushing should be .010-.020" longer than the tube in the stick.

 

[Michael Burbidge]

Why different nuts are used...

My intent was not to misinform people. I was simply relaying information that I got from Vans on this topic. Now I'm a little confused and worried that I would get bad information from Vans tech support.

The reason I pursued this question with tech support is because of the specific directions spelled out in the note on the plans. And these directions are different than the directions for the elevator bellcrank where it looks to a non-engineer like similar rigging.

Why does the bellcrank use a locknut, and the control column use a castle nut? To me the movements and connections look very similar, if not identical. And why the different directions on the plans?

 

[pierre smith]

I'll hazard a guess...

In the event of a bushing binding on the bottom end of the stick, with the bolt now rotating instead, a non- cotter keyed nut could be worked loose, so it may be for redundancy purposes.

Along those lines, why are the rear spars attached with a cotter-keyed bolt, even on my -10? There's no motion there either??

Best,

 

[RVG8tor]

Not Good

The tech person was misinformed. As others have correctly explained, the brass bushing should be firmly clamped......which requires standard torque applied to the bolt.

Phil, the bushing should be .010-.020" longer than the tube in the stick.

Now this has me concerned, if you can't trust Builder support at Van's then who can you trust! I had a slight buckle in the lower left side of my F807 bulkhead (came this way, QB Kit) I was told this happens sometimes and not to worry, now I wonder!

 

[bruceh]

I just fitted together these parts on my controls this weekend.
I reamed out the brass bushing to 1/4", and lightly sanded the interior of the steel tubing so that the bushing moved freely within. I had to reduce the length of the brass insert in order to fit between the steel ears on the WD-610 control column.
Once that was snug on both sides, the control sticks needed some grinding down in order to fit between. The triangular tabs that hold the tubes on the stick protruded a bit, so they also got some taken off.
On the passenger side controls, this all works smoothly and there is very little play fore/aft on the brass bushing. The pilot side is a different story here. There is about 1/16" play fore/aft on the steel tube around the brass bushing.

Can I put some sort of thin nylon washer or plastic insert in here to take up the slack and to keep the steel tubing from rubbing on the steel ears of the WD-610 control column?
There is definitely some play in the controls with the 1/16" gap and I'd like to minimize this without introducing any binding.

I have a similar issue with the F-665 pushrod that connects the pilot/copilot sticks. The rod end bearing has lots of play between the steel ears even with the requisite washers. Van's doesn't give any note on adding additional washers in the plans here.

 

[DanH]

Now this has me concerned, if you can't trust Builder support at Van's then who can you trust!

Well, the good news is that it doesn't make a huge difference....the tech person's advice doesn't result in an optimum setup, but it's not unsafe. There are lots of older aircraft with weldments pivoting directly on the bolt, with no bushing. They wear and get sloppy.

I have a similar issue with the F-665 pushrod that connects the pilot/copilot sticks. The rod end bearing has lots of play between the steel ears even with the requisite washers. Van's doesn't give any note on adding additional washers in the plans here.

"Play between the steel ears"? Sounds like the ball is not properly clamped between those ears. This is another bolt that gets normal torque.

 

[koda2]

bushing play

One of my control sticks was welded incorrectly and I threw it away and bought a replacement. Even then, I had to put the sticks in a mill to straighten things out. Also, the ears on the WD-610 were not parallel either so it took some work to get a functioning joint.
When I was done it took very thin steel shim washers to eliminate end play in the joint.

From a purely technical standpoint, the joint should be designed so that the wear occurs on replaceable parts, in this case the bushing and the bolt, not the bushing and the steel tubing welded on the control stick. And oil-impregnated bronze would be better than brass, but it would be more expensive.

In this design however, if you let the bushing or the bolt rotate, the bolt will almost surely elongate the holes in the WD-610 over time, and also wear the ends of the brass and eventually corrective measures will have to be taken.

The bottom line is that the stick move freely in all directions without any slop or end play. Once that is achieved, it will probably take years (many) before replacement is required.

Dave A.
6AQB

 

[bruceh]

"Play between the steel ears"? Sounds like the ball is not properly clamped between those ears. This is another bolt that gets normal torque.

DanH: You are right. I torqued down the bolt and you can see that the ears get pulled together. The steel here is thin enough to bend together.

You can see in this picture how I still have about 1/16" gap between the length of the brass bushing and the steel control tubing. It would seem to be a good idea to put some thin washers around the brass bushing at each end to keep the slop down to a minimum, and also to keep from wearing the steel parts on one another.

 

[Lars]

I just fitted together these parts on my controls this weekend.
I reamed out the brass bushing to 1/4", and lightly sanded the interior of the steel tubing so that the bushing moved freely within. I had to reduce the length of the brass insert in order to fit between the steel ears on the WD-610 control column.
Once that was snug on both sides, the control sticks needed some grinding down in order to fit between. The triangular tabs that hold the tubes on the stick protruded a bit, so they also got some taken off.
On the passenger side controls, this all works smoothly and there is very little play fore/aft on the brass bushing. The pilot side is a different story here. There is about 1/16" play fore/aft on the steel tube around the brass bushing.

Can I put some sort of thin nylon washer or plastic insert in here to take up the slack and to keep the steel tubing from rubbing on the steel ears of the WD-610 control column?
There is definitely some play in the controls with the 1/16" gap and I'd like to minimize this without introducing any binding.

I have a similar issue with the F-665 pushrod that connects the pilot/copilot sticks. The rod end bearing has lots of play between the steel ears even with the requisite washers. Van's doesn't give any note on adding additional washers in the plans here.

If you mean something like the below, where there is still a gap even after adding the number of washers called out on the print, then you need to add more washers to fill that gap. In my experience, some of the Vans weldments are not super accurate or consistent dimensionally. Ears on the clevises (the part of the weldment into which the rod end fits) may need to be bent parallel; sometimes they may be too far apart to close the gap with the number of washers specified; or both. The ears of the weldment have to be clamped to the flats on the ball with a properly torqued fastener in order for this to be assembled correctly. The idea is that the rod end pivots about its ball. Adding another washer or two to accomplish this, even if it's more than called for on the print, won't hurt anything.

OK, between the time I cranked out the pic above and the time I posted, you added informative photos. Looks like you have the first cased figured out. For the second, I would be inclined to take a 32nd off the brass bushing and pull the ears together a little further. 1/32" isn't much as far as bending the ears together, but it'll make a big difference in how sloppy (less) the control column feels.

 

[koda2]

Control stick fit

Bruce,
You have at least 3 choices.

1) you can bend in the ears of the WD-610. I would not bend them past 90 degrees. You want a nice even "parallel" slot otherwise the flat brace portion of the control stick may mate unevenly and bind up. Take a piece of aluminum, make it square, cut the corner off and use it as a gage to see if they are 90.

2)If the ends are at 90 and the brass fits real snug you can make washers that go over the brass on each end and center the control stick. If you are really OCD you can use feeler gages to get the thicknesses just like you want them. The washers can be either steel or brass or bronze. I would not use aluminum.

3) Alternatively you can cut the brass so it is just oversize as listed in the plans and then put washers on both side that have an AN4 ID and are pretty wide. This will allow the steel tubing to ride on them rather than the WD610. The brass should still "lock up" against the washers and not move.

I did method 3 but I think 2 is probably a better way. Would take more work though.
Dave A.

 

[Toobuilder]

In the event of a bushing binding on the bottom end of the stick, with the bolt now rotating instead, a non- cotter keyed nut could be worked loose, so it may be for redundancy purposes.

Along those lines, why are the rear spars attached with a cotter-keyed bolt, even on my -10? There's no motion there either??

Best,

Cotter keys are used if there is relative motion between parts (as you correctly point out) or if there is a need for the "extra" security a cotter key provides. Nylon self locking nuts are only good for one use, so some designers specify cotter keys at critical connections.

One thing I do see missing from this thread is pointing out the difference in torque between tension nuts (thick) and shear nuts (thin). Smoking a thin shear nut down to the values for a much stronger tension nut can damage it. Make sure you are using the right values.

 

[Lars]

Cotter keys are used if there is relative motion between parts (as you correctly point out) or if there is a need for the "extra" security a cotter key provides. Nylon self locking nuts are only good for one use, so some designers specify cotter keys at critical connections.

One thing I do see missing from this thread is pointing out the difference in torque between tension nuts (thick) and shear nuts (thin). Smoking a thin shear nut down to the values for a much stronger tension nut can damage it. Make sure you are using the right values.

Good point on the shear nut vs. tension nut, however there are very few shear nuts used on current RVs. As for nylon self-locking nuts and reusability, there are some on this forum (Mel, to name one) who would disagree with them being limited to a single use.

 

[Toobuilder]

Good point on the shear nut vs. tension nut, however there are very few shear nuts used on current RVs. As for nylon self-locking nuts and reusability, there are some on this forum (Mel, to name one) who would disagree with them being limited to a single use.

Most of the castle nuts on the RV-8 in my hangar are shear (thin), rather than tension, so my experience is limited to that type. Per general application however, the control stick nuts as described in this thread are almost certainly are in shear.

As for reusability of nylock nuts, notwithstanding Mel's substantial expertise, I still defer to military training, extensive personal experience, supplier data sheets, and the engineering direction of my employer - single use.

 

[Danny7]

Most of the castle nuts on the RV-8 in my hangar are shear (thin), rather than tension, so my experience is limited to that type. Per general application however, the control stick nuts as described in this thread are almost certainly are in shear.

As for reusability of nylock nuts, notwithstanding Mel's substantial expertise, I still defer to military training, extensive personal experience, supplier data sheets, and the engineering direction of my employer - single use.

don't the supplier data sheets mention torque values for fifth off use?

see this post, it isn't just Mel, Alan and Terry also say it is fine for 3-4 times usage.

i guess the question is how do you keep track if you want to use this method?

edit- this thread was the one i was trying to reference: http://www.vansairforce.com/community/showthread.php?t=12842&page=2

 

[Lars]

Most of the castle nuts on the RV-8 in my hangar are shear (thin), rather than tension, so my experience is limited to that type. Per general application however, the control stick nuts as described in this thread are almost certainly are in shear.

As for reusability of nylock nuts, notwithstanding Mel's substantial expertise, I still defer to military training, extensive personal experience, supplier data sheets, and the engineering direction of my employer - single use.

Fair enough. It was the absolute nature of the initial comment (Nylon self locking nuts are only good for one use...) to which I was responding. Everyone has to go with their comfort level, and I'm not necessarily inclined to re-use them on my own airplane (despite my own extensive experience with locking fasteners in a variety of technical disciplines) since they are vanishingly cheap compared to most of the stuff on the plane.

 

[Toobuilder]

Fair enough. It was the absolute nature of the initial comment (Nylon self locking nuts are only good for one use...) to which I was responding...

You are right; it was somewhat "too" absolute because there are a few examples when they can be reused (a few times). However, in the military, and again with my company, (and me) the edict is the same, overarching and absolute philosophy: Nylocks are cheaper and safer than keeping track of whether it has been on or off 3 or 4 times. Personally (again, "spoiled" by the military and my employer), I avoid nylocks for airplanes - and I have thousands of brand new surplus stashed all over the place. If it?s my airplane, it gets all metal ? I save the nylocks for my cars or holding metal shelving together.

Also, the minimum running torque value (testing the condition of the self locking feature) for all self locking types (deformed thread or nylock) has a specific minimum value; the "can/can't turn it by hand" method is only for fasteners smaller than .250 inch. Larger fasteners have a specific min/max value that must be considered not only for condition determination, but also to add to the torque value at final torque. In other words, if you are looking for 100 pound inches of "clamping" torque, but it takes 50 to overcome running torque, you are only "clamping" with 50 pound inches... Yes, this is generally more critical on an Air Force jet, but a good "general practice" to be aware of.

 

[Sam Buchanan]

In the event of a bushing binding on the bottom end of the stick, with the bolt now rotating instead, a non- cotter keyed nut could be worked loose, so it may be for redundancy purposes.

Along those lines, why are the rear spars attached with a cotter-keyed bolt, even on my -10? There's no motion there either??

Best,

Pierre,

It is my understanding that the rear spar attachment is a pivot point. As the wing develops lift, there is a pitching torque created which tends to rotate the aft spar attachment as the wing flexes.

In the real world, this is a tiny amount of motion, but enough for designers to consider this a rotation point and therefore subject to the castle nut and cotter pin.

 

[Lars]

You are right; it was somewhat "too" absolute because there are a few examples when they can be reused (a few times). However, in the military, and again with my company, (and me) the edict is the same, overarching and absolute philosophy: Nylocks are cheaper and safer than keeping track of whether it has been on or off 3 or 4 times. Personally (again, "spoiled" by the military and my employer), I avoid nylocks for airplanes - and I have thousands of brand new surplus stashed all over the place. If it?s my airplane, it gets all metal ? I save the nylocks for my cars or holding metal shelving together.

Also, the minimum running torque value (testing the condition of the self locking feature) for all self locking types (deformed thread or nylock) has a specific minimum value; the "can/can't turn it by hand" method is only for fasteners smaller than .250 inch. Larger fasteners have a specific min/max value that must be considered not only for condition determination, but also to add to the torque value at final torque. In other words, if you are looking for 100 pound inches of "clamping" torque, but it takes 50 to overcome running torque, you are only "clamping" with 50 pound inches... Yes, this is generally more critical on an Air Force jet, but a good "general practice" to be aware of.

That makes sense. This is probably getting a bit esoteric, but do you have tables of minimum running torque for deformed-thread nuts? I use them occasionally myself (in a really oddball earthquake engineering research lab) and I've encountered a fairly large variation in turning resistance (running torque). We are careful to specify US-made fasteners, but they are usually industrial grade rather than for aerospace. I've never tried to quantify it since safety of human life isn't a concern but it has surprised me.

 

[Toobuilder]

...This is probably getting a bit esoteric, but do you have tables of minimum running torque for deformed-thread nuts?...

I have a hard copy of the Technical Order 1-1A-8 at home. This manual provides more information about airplane hardware than you could ever want. The 1-1A-1 is also a good source of general repair info, but the -8 is where you will find the table for nuts.

Edit: I think I found what you're looking for. From the current 1-1A-8:

Table 5-7. Minimum Prevailing Torque Values for Reused Self-Locking Nuts

Fine Thread Series / Course Thread Series

Nut Size Minimum Prevailing Torque Nut Size Minimum Prevailing Torque

7/16-20 8 inch-pounds / 7/16 - 14 8 inch-pounds
1/2 - 20 10 inch-pounds / 1/2-13 10 inch-pounds
9/16 - 18 13 inch-pounds / 9/16 12 14 inch-pounds
5/8-18 18 inch-pounds / 5/8-11 20 inch-pounds
3/4 - 16 27 inch-pounds / 3/4 - 10 27 inch-pounds
7/8-14 40 inch-pounds / 7/8-9 40 inch-pounds
1-12 55 inch-pounds / 1-8 51 inch-pounds
1-1/8-12 73 inch-pounds / 1-1/8-7 68 inch-pounds
1-1/4 - 12 94 inch-pounds / 1-1/4 - 7 88 inch-pounds


5.3.2 To obtain the correct recommended torque value on self-locking nuts, the nut must be run down until it is one turn from the beginning of seating. At this point, the prevailing torque should be noted. If the prevailing torque is less than one-third of the recommended torque, it should be disregarded and the nut tightened to the recommended torque value. If the prevailing torque is one-third or more than one-third of the recommended torque, it should be added to the recommended torque. Example: The recommended torque is 50 to 70 inch-pounds. The prevailing torque at one turn from the beginning of seating is 30 inch pounds. The correct torque wrench reading would be 80 to 100 inch-pounds.

 

[Lars]

I have a hard copy of the Technical Order 1-1A-8 at home. This manual provides more information about airplane hardware than you could ever want. The 1-1A-1 is also a good source of general repair info, but the -8 is where you will find the table for nuts.

Edit: I think I found what you're looking for. From the current 1-1A-8:

Table 5-7. Minimum Prevailing Torque Values for Reused Self-Locking Nuts

Fine Thread Series / Course Thread Series

Nut Size Minimum Prevailing Torque Nut Size Minimum Prevailing Torque

7/16-20 8 inch-pounds / 7/16 - 14 8 inch-pounds
1/2 - 20 10 inch-pounds / 1/2-13 10 inch-pounds
9/16 - 18 13 inch-pounds / 9/16 12 14 inch-pounds
5/8-18 18 inch-pounds / 5/8-11 20 inch-pounds
3/4 - 16 27 inch-pounds / 3/4 - 10 27 inch-pounds
7/8-14 40 inch-pounds / 7/8-9 40 inch-pounds
1-12 55 inch-pounds / 1-8 51 inch-pounds
1-1/8-12 73 inch-pounds / 1-1/8-7 68 inch-pounds
1-1/4 - 12 94 inch-pounds / 1-1/4 - 7 88 inch-pounds


5.3.2 To obtain the correct recommended torque value on self-locking nuts, the nut must be run down until it is one turn from the beginning of seating. At this point, the prevailing torque should be noted. If the prevailing torque is less than one-third of the recommended torque, it should be disregarded and the nut tightened to the recommended torque value. If the prevailing torque is one-third or more than one-third of the recommended torque, it should be added to the recommended torque. Example: The recommended torque is 50 to 70 inch-pounds. The prevailing torque at one turn from the beginning of seating is 30 inch pounds. The correct torque wrench reading would be 80 to 100 inch-pounds.

Thanks for looking this up!

 

[DanH]

Nut Size Minimum Prevailing Torque

Got values for AN-3 and -4?

 

[Toobuilder]

Got values for AN-3 and -4?

From the -8:

Metal and non-metallic insert type locking nuts 3/8 inch and smaller may be checked by the ??finger tight?? method. If a nut can be run down with the fingers after the locking feature engages the bolt or stud, indicating the locking friction does not exist, it shall be replaced. The minimum prevailing torque values established for use with a standard torque wrench on used self-locking nuts over 3/8 inch are given in Table 5-7.

This corrects my prior assertion that the "finger tight" method was for .250 and smaller - according to the -8 it's .375.

They say the memory is the first thing to go...

 

[rvbuilder2002]

the following when I asked about torquing the castle nut on the control stick attach bolt:

"In this case, the torque value is meaningless, because we aren't using the bolt to "torque"
things together.

We're using the bolt another way, as a shaft, so just tighten the nut until you begin to feel
friction and no slop, then pin it in place with the cotter key."

The tech person was misinformed. As others have correctly explained, the brass bushing should be firmly clamped......which requires standard torque applied to the bolt.

Phil, the bushing should be .010-.020" longer than the tube in the stick.

Actually the tech. person was not misinformed but I think something got lost in translation.

It is true that the bushing is intended to be held stationary by the bolt with the control stick pivioting on it.

A lot of the reason that a cotter pin safetied bolt is used in this location is that in many installation instances, if you used a standard nylock nut and torqued to standard torque values, you would induce friction in the control system.
The reason is this... Often times the ears that the bushing is being bolted between are not exactly square to the end of the bushing (as designed the control weldment for the RV-4 and 8 are not). If you install a bolt at the full rated torque with even a slight mismatch between the welment and the end of the bushing it will usually cause the bushing to bow slightly and you have then added friction in the system (in roll on the side by side models, in pitch in the tandem models).

Using the cotter pin safetied nut and only tightening enough to prevent the bushing from rotating allows adjusting the installation so that no friction is induced.

Side note.........There are a lot of RV's flying around with this friction. Most people don't even realize it because they probably still have a rather low friction system. It means the difference between a good control feel or a great control feel. On the tandem seat airplanes, depending on how much friction is being induced, it can effect return-to-trim pitch stability (because of the slight friction, the elevators wont return to quite exactly the same position as when previously trimmed, after a turbulence upset, etc.)