torque the castle nut for the control stick?

prkaye · #1 09-30-2007, 10:21 AM

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 · #2 09-30-2007, 10:55 AM

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 · #3 09-30-2007, 11:08 AM

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 · #4 09-30-2007, 11:43 AM

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 · #5 09-30-2007, 11:56 AM

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 · #6 09-30-2007, 01:55 PM

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 · #7 09-30-2007, 04:43 PM

And a little bit of grease to keep things nice.

vlittle · #8 09-30-2007, 06:53 PM

Quote:

Originally Posted by 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?

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

briand · #9 09-30-2007, 10:47 PM

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 · #10 04-26-2010, 05:31 PM

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."