Control Stick Deadband

[rodsmith]

I know there have been other posts about this. My control sticks had quite a bit of slop in the fore/aft direction. The top of the control sticks would move 1/4" before the elevators moved. I know it is the bolt hole/bolt tolerance that causes this. I ordered AN174 close tolerance bolts in an attempt to correct this. I installed them and it reduced the deadband to 1/8", better but still annoying. I miked the bolts and discovered that the AN174 bolts are only .0001 larger than the AN4 bolts, .249 vs .248. When I built the control sticks I used my 1/4" reamer which measures an actual .250 for final sizing of the bushings in the control stick and the control stick mount. I may have used a hand drill with the reamer so maybe the holes ended up a bit larger. I took some similar sized bushing material and reamed it with a drill press to .250 as a test, inserting an AN174 bolt I could still feel some play. Not sure if there is a way to fix this. The bolt has to be somewhat smaller than the hole or the control stick will bind. Has anyone found a solution to this?

[alaskabearhawk]

Do you have Russ Erb's CD? If you do, in the main directory under "Fuselage" look for "Control Stick Assembly Details". On page two of that hyperlink he did a mod on the control stick using Heim LSS-4 bearings. I have four MRC R4FF bearings that I was going to use to do the same thing, but haven't messed with it...yet.

[spinningwrench]

You can purchase reamers that are undersized. A 1/4” reamer makes a hole that is sloppy for a 1/4” bolt. A possible fix is to add braze material to the hole and re-ream it or if you have a lathe make a custom cotter pin from 4130 that is oversize.

[Nev]

There's a few different variations of oversized NAS bolts. I found one that was a very snug fit and effectively removed all the slop (dead-band). No complaints any more

Photos etc for other builders in the BH maintenance files HERE.

[Bcone1381]

I'm curious. Where do you find the Aerospace oversize shank bolts? I cant find a document with specifications on the internet.

[rodsmith]

I'm curious also, my web search didn't turn anything up.

[Nev]

NAS= National Aerospace Standard

A bit more info HERE.
Aircraft Spruce stock them HERE.

[rodsmith]

Turns out my diagnosis of the problem was only partially correct. I noticed after I installed the close tolerance bolts in the sticks that the whole stick assembly was moving before getting elevator movement. The link between the stick assembly and the bellcrank has two bearings. The specs say the bore of the bearings is .190. I miked the AN3 bolts that attach them at .186. The AN173 close tolerance bolts are supposed to be .190. I am going to order some. I think that will really tighten things up.

[jaredyates]

If we are thinking of the same parts, I believe I fully tightened the bolts on the rod end bearings. The pivot point is the bearing and not the bolt, right?

[rodsmith]

Correct on the pivot point. The undersized bolts through the bore of the bearings in my case would allow .008 movement of the link before actuating the bellcrank, which is magnified at the top of the control sticks.

[Battson]

How disappointing - I wrote a detailed response to this yesterday morning, but it hasn't posted.

Rod - I have the same issue and have been searching for solutions without any job. Unfortunately, the bad news is it only gets worse over time. Although I didn't measure my deadband back when we started with a 0-time airframe, I am sure my deadband is much larger now than it was ten years ago. Perhaps almost twice as large.

I think the main causes are, in order:

Aileron

1. Control stick assembly - the greased bushings. This gets worse over time.
2. Control stick main bolts - gets a little worse over time
3. Aurora bearings in the aileron pushrods (minor)
4. Cable tension (minor)

Elevator

1. Control stick main bolts - gets a little worse over time
2. Aurora bearings on the pushrod to the elevator bellcrank - this is more significant in this axis, as there are two bearings in series.
3. Worsening fit of the control stick assembly's greased bushings - gets worse over time.
4. Cable tension (minor)
5. Worsening fit of the bellcrank bushing assembly (minor)

General wear and tear appears to be the main issue. That said, my aircraft has had three situations where it was exposed to wind "flogging" the controls against the stops, in a minor way. I always fit primary control locks, but sometimes they work loose over time. As we know, some of the control stops are not direct stops. Naturally this creates wear in the system. I am sure this hasn't helped.

Tightening the control cables can give the illusion of progress, as the whole thing feels tighter and less wobbly. But ultimately, doing that just wears out the phenolic pullies and the control cables wear out against the fairleads. Eventually all require premature replacement, which is not a small job. I can say that increasing cable tension isn't worth trying, and suggest sticking at or below the cable tension values Bob recommends. In the end, I have gone lower to reduce wear - which does increase the deadband slightly.

I will be following this thread with interest, as I hope to one day find a solution which doesn't involve replacing all the parts!

[Mark Goldberg]

For me - replacing whole parts is not needed if you want to take some action. Replacing the metal bushings with smaller ID and then carefully reaming them out would provide the desired result. And in other places - just filling the hole with weld bead, and then drilling small and then reaming to size would take out most play that developed over time.

These steps obviously require the ability to weld. Mark

[Bcone1381]

McMaster Carr has shoulder screws. Machining stuff is easier for me that welding. I wonder about turning the shoulder down in a lathe to a clearance with a nice fit..
Screenshot 2023-12-11 at 2.03.34 PM.png

[rodsmith]

I received the close tolerance #10 bolts for the control assembly linkage and installed them. Deadband measured at the top of the stick is now only 1/16th inch. Barely noticeable compared to what it was, just by changing out 4 bolts. As Battson related it will get worse with time, but I am starting in a better place now.

[AZBearhawk272]

I have encountered this stick bolt slop and play where the torque tube is bolted down to the airframe with the u clamps.
Have found that it is beneficial to put a little wrap of teflon pipe tape on the bolt shank and the torque tube.
It will noticeably remove the slop and provide a nice smooth feel. Also will keep the bolt from galling in the assembly.

Kevin D
#272
KCHD

[Bcone1381]

Yesterday I talked with Genuine Aircraft Hardware. The oversized bolts are special order, and are oversized .0156” or .0312”. It seems an order or request for a quote would be made, then GAH would go to their suppliers and get a quote, and then price it with markup. Each GAH supplier has a minimum special order something like $50 -$100 for example.

Two oversized bolts will be pricey. Without a group buy I won’t go this route but if we have group interest I’d pursue it. I’d wants ten bolts and I’d hope the Patrol and four place use the same bolt.

I put the specific bolt down below and if you can scout the web and find them please pass along the info.

My (undersize) Patrol control stick bolt is an AN4-23 which has about 2” grip.

Details…..
My plans call for the tube to be 3/8 x 1/4. Standard 4130 tube stock that a factory likely would install is 3/8 x .058 giving an inside diameter of 0.259”. AN4 bolt’s minimum diameter is .246.

NAS6204-32x bolt has 2 inch grip, .2510 max and .2500 min diameter, and .370” thread length. The -32y diameter is about .015 larger.

NAS6604-32x and y is the same bolt but has about .500 long thread length.

each dash number shifts the grip length 1/16”.

For reference go to your 2021 GAH handbook ( I know everyone has one) p.13. Read all the small notes. Smarter builders don’t need guidance from there patient customer service.

[rodsmith]

The AN4-23 is what I used in my 4-place control sticks

[Nev]

Brooks - definitely worth shopping around for this. I managed to get one here in Christchurch for several dollars. That's NZ dollars ( aka - the South Pacific Peso). It might have been a one off, but I expect that some industries might be using them routinely.