Control Stick Slop

[Bcone1381]

https://bearhawkforums.com/forum/tools-technics-and-best-practices/86831-control-stick-deadband

This is a link to a topic on Control Stick slop previously reported on other aircraft. I am in the midst of fixing slop in my stick and at the end of this post I will share why I think it's important.

When my control stick its move L to R slop is seen at the red arrow hinge point on both sticks. This is the fulcrum of the slop and the bottom of the stick wiggles inside the torque tube like a teeter totter. I described my slop to Bob and it was deemed excessive, and a fix was concieved. Ream out the hinge tubing and insert an oversize bolt to remove slop.

The sticks are attached inside the toque tube via the interconnect tube. The 1/2" interconnect tube moves for/aft inside the larger torque tube. The yellow arrow points at the connection between the stick and the interconnect tubes. The two tubes have ample space but not excess space. Tight clearances of the design makes slop an issue.

My reamning of the rear stick went well, but the front did not. I admitted defeat early, and aborted the task before things got out of hand. Part of the issue was I reamed the control stick assembly in place instead of removing it from the airframe.

It only took me :40 minutes to remove the entire assembly after my fiasco. Right now the assembly is removed and at my Fabricator in Mason Michigan. They will be boring out the hinge tubing and pressing in a 4130 steel bearing that will give a slop free fit with a 1/4 - 28 bolt iaw the plans.

Why this fix is important. The clearance inside the torque tube is not generous. I had contact between parts inside the torque tube. I dismissed this problem for 5 years and never felt good about it. I trust my problem was a one off issue and the rest of the fleet is kosher. But contact inside there is the a precurser to a jammed elevator. And I just cant get that off my mind. A jammed elevator. So my advice is check your stick for slop, send it to a fabricator if you need to. You can get it out without removing belly fabric, and don't use castle nuts with cotter pins inside there. I see them gettiing hooked up on something. Add checking the stick for slop on your annual inspection checklist too.

[Pbruce]

“and don’t use castle nuts with cotter pins in there”. Hmm. Isn’t that the exact case (nut subject to rotation) for which use of a castle nut and cotter pin is mandated? Are you depending on the inner diameter of the tube to prevent the nut from coming off or do you have a different solution? Thanks. My bolt, castle and cotter seem ok in there (no contact) and not much slop. Maybe I’m missing something? The bearing sounds like a great idea. I’ll do it if it gets sloppy in future. Still fiddling with the fork at the idler though, so I have more than a passing interest in the whole assembly.

[TimTall]

There's lots of talk about the control stick slop. I have it. Maybe a 1/4" deadband in pitch and roll. I was thinking about how much of a non-issue it is while flying yesterday. I've never noticed it without looking for it in flight. If there is something wrong, and getting jammed, of course deal with it, but the design is fine.

[DBeaulieu]

Similar on my previous build of a Zenith 750...never noticed the slop with flight loads on the controls, regardless of being on wheels, skis or floats

[noema]

I fixed this L/R slop by TIG welding a donut onto the hinge tube, under-drilling and reaming it. The bottom of the sticks I secured with low profile castle nuts that also have nylocs in it (ACS has them). The bolt I cut and hand-drilled to allow for maximum L/R clearance.

While I generally like the simplicity and effectivness of the Patrol design, the torque tube and stick assembly is a bit finicky to get right. From a weight perspective it probably hard to beat though.

Screenshot 2024-07-26 at 11.57.15 AM.png

Screenshot 2024-07-26 at 12.27.36 PM.png

[noema]

Castellated Nylon Inserted Hex Nut: MS17826
(there is also a similar one: MS17825)

[Bcone1381]

“and don’t use castle nuts with cotter pins in there”. Hmm. Isn’t that the exact case (nut subject to rotation) for which use of a castle nut and cotter pin is mandated? Are you depending on the inner diameter of the tube to prevent the nut from coming off or do you have a different solution? Thanks. My bolt, castle and cotter seem ok in there (no contact) and not much slop. Maybe I’m missing something? The bearing sounds like a great idea. I’ll do it if it gets sloppy in future. Still fiddling with the fork at the idler though, so I have more than a passing interest in the whole assembly.

Here is some data. You make the call. I think a good argument to make is the designer trumps AC43.13. But I will be making my build so these nuts are easy to inspect on the preflight.

The text below (in bold and italics) and the attached drawing is cut and pasted from bearhawksafety.com. Its Title is Call out for bolts and nuts at bottom of the control stick. It was issued for the Patrol and LSA December 2013.

Hardware nomenclature.
-AN3-5a bolts are undrilled standard AN3 bolts. (letter "a" at the end is undrilled. absent letter "a" is drilled)
-AN364 nut is a standard low profile elastic stop nut. They are not castleated. The Castle nut is AN310, The thinner shear casatle nut is AN320.


Control stick hardware on Bearhawk LSA Drawing #26 and Patrol Drawing #29.

The bolts and nuts at the bottom of the control sticks are being called out to insure no interference with the torque tube throughout the travel range (see drawing below).

Install the nuts on the side of the control stick that has the most clearance with the inside diameter of the torque tube.

Screenshot 2024-07-26 at 9.53.39 AM.png

[Bcone1381]

Slop and rubbing. I no longer have either.

I think the two problems are common with installing this stick. Rubbing of the Push/Pull tube as it enters the torque tube (green Arrow) and stick slop that results in rubbing of nuts on the bottom of the stick (red arrow) Look for and remove all slop from the stick and all rubbing.

Here is the drawing. Below is "How to install/avoid common error" text.
Screenshot 2024-11-07 at 3.12.02 AM.png
Slop: Removing L to R Stick Slop
Don't accept stick L to R slop at the upper stick hinge 1/4-28 bolt. and Torque that bolt down tight to 60 in. lbs.

Look at the drawing and visualize the stick moving Forward and Aft. See the Interconnect Tube gently rise and fall inside of the Torque Tube. See the clearances of the Control Stick bolt (RED ARROW....AN3-5A bolt with AN364 shear nut...see drawing in post 5) as it rises and falls inside the torque tube. If there is slop in the stick's 1/4-28 hinge bolt above then these three bolts wiggle inside the torque tube and may contact and rub inside the torque tube as the descend at the bottom of the arc. The front bolt looks like a turtle head as its head moves in and out of its shell. Can you see how L-R slop at the hinge bolt creates a hazard down at the entryway of the tube? If a cotter pin catches here in flight it would be when the stick is being pushed forward. The serious failure mode of this happening can not be overemphasized.

The stick hinge bolt above is 1/4-28. Torque it to 60 +/- 10 in lbs. (AC43.13) My stick had L-R slop until I tightened this bolt to specs. That Castle nut tight to 60 in. lbs. squeezes the tower bushings against the stick bushing and stops the slop. The slight increase friction in the system is negligible. Backing off the nut's torque one flat results in slop returning to the stick. So, the design depends on the Nut being torqued down.

Common error is to...

1) Accept slop as normal.
2) rely on the cotter pin to safely hold the nut on (it will, but...)
3) Believe the torque chart only applies to non-castlated nuts.
4) Think a tight bolt unacceptable because it will increase stick friction.


Rubbing of Push/Pull Tube

To rig the Push/Pull Tube system, Neutralize the elevator. Adjust the aft Torque Tube so the Idler Arm is and the bottom of the arc like Bob shows in his Plans. Then adjust the front torque tube with the Heim Joint threads so the position matches the plans.

The Elevator has three tubes. Bob calls them (starting from the front) The Interconnect tube and one forward & one aft Push/Pull Tube.

Look at the green arrows. Again visualize moving the stick for and aft and See the tube rise and fall inside the torques tube. Widen your sight picture and see the Idler Arm at Station F. Can you see it swing back and forth, and see the arc the Heim Joint makes as the stick is moved? It also moves up and down. If you have the elevator system all assembled and functioning, the system stops when the elevator reaches full travel by the Elevator Horn in the tail hitting a tube welded to the fuselage. Thats key.

Adjustment of the three Heim Joints does nothing to adjust the elevator stop.

The ONLY thing the three Heim Joint adjust are the position the Idler Arm at Station F and the stick. IF the rigging of the system is correct the rise and fall of the Push/Pull tube will be perfect. If not expect rubbing at the entrance of the torque tube when stick is back and at the left and right stop.

To see why look at the drawing's front Push/Pull tube. Now, visualize pulling the stick aft so the elevator hits the stop, then mentally make the Heim Joint adjustment longer and see the stick move aft and also see more of the Push/Pull tube enter the Torque Tube. Do you see T6 - T7 welded joint just aft of the Entryway? That joint begins to enter the torque tube! Make sure that joint does not contact the torque tube with full left and right aileron.

So, The Push/Pull Tube may rub when joint enters the torque tube if things are not adjusted right. Secondly, When The Tube Lengths are off then the the Idler Arm may be off too. The Idler's arc lifts the Heim Joint up, thus it lifts the entire tube up, thus the position of the tube as it enters into the Torque Tube is higher. When Full left/right stick is held then for/aft stick movement is made, you will have that T7 tube rubbing again at the entrance of the torque tube.

Conclusion: Accept no slop in the stick and tighten that 1/4-28 bolt. Accept no rubbing of the Push/Pull tube as it enters the Torque Tube. Rubbing should be prevented by Adjusting the Push/Pull tubes three Heim joints to position the Idler iaw Bob's Plans with neutral stick. This will place push/pull tube entry into the Torque Tube vertically and longitudinally to avoid rubbing at the T6-T7 welded joint.

Hardware
Also, I keep thinking about Pbruce's strong argument from post #2.

“and don’t use castle nuts with cotter pins in there”. Hmm. Isn’t that the exact case (nut subject to rotation) for which use of a castle nut and cotter pin is mandated? Are you depending on the inner diameter of the tube to prevent the nut from coming off or do you have a different solution? Thanks. My bolt, castle and cotter seem ok in there (no contact) and not much slop. Maybe I’m missing something? The bearing sounds like a great idea. I’ll do it if it gets sloppy in future. Still fiddling with the fork at the idler though, so I have more than a passing interest in the whole assembly.

I've got shear (thin) castle nuts on the way and still have caution of a failure mode if a cotter pin catches on the torque tube. I Absolute respect his quote above. We have data (post #5) that conflicts with AC43.13 and will experiment with a locking method that has a gentler failure mode than a cotter pin catching. It's a bit creative and will not jive with AC43.13.

[spinningwrench]

The last week talked you were using AN363 or MS21042 nuts on the lower end of the sticks. Have you rethought that approach?

[Bcone1381]

The last week talked you were using AN363 or MS21042 nuts on the lower end of the sticks. Have you rethought that approach?

Yes.

I'm away right now from the hangar. I had my airframe inspected by an IA. But the inspection was Very thorough. VERY! it changed how I look at things. It made me better and changed what I see and how I think.

That and This thread and the input given comes together to some new things. Giving away the 1.5 thread exposure standard plus the washer, plus the hinging action drives me be creative to remove doubt about fastener security. The nut and cotter like Pbruce and Neoma show does that. I'll shortned the AN3-5A bolt like Bob says adn give up the thread exposre but will lock it in place. I see a risk of stick slop maybe returning. I want to experiment with the safety wire of the bolts instead of cotter pins to make the failure mode of a sloppy stick tolerable to to me and maybe please the crusty old OCD mechanic.

[spinningwrench]

What nut are you using then?

[Bcone1381]

I'll try the AN320 shear castle nut.

[spinningwrench]

After many iterations on control stick hardware and discussions with Brooks I am going with a shortened AN3-6A bolt and a MS21042-3 nut. This satisfies Bob's safety note and also provides adequate clearance to the inside of the torque tube. As designed this is a very tight fit and this is the only combination that gives me good clearance. I tried several combinations of shortened bolts and castle nuts with cotter pins and none of those worked to where I had good clearance. I would recommend not tightening the nut to the point of pinching the fork ends. I tightened mine to just eliminate any play of the washer and backed it up slightly to where the washer could be turned freely. There is no point in overtightening this hardware you just want to eliminate slop. The attached drawing shows my modified AN3-6A bolt which results in 1 thread showing past the nut.

[spinningwrench]

David see corrected drawing

[David Swartzendruber]

I used the MS21042-3 nut in my LSA control stick assy as well.

[Steve W]

In regards to the following:

""I would recommend not tightening the nut to the point of pinching the fork ends""

From what I understand the purpose of the bushing in the three pivot points at the ends of the push-pull rods is to have a wear point for movement in the control stick ends. The bolt is to be properly torqued so there isn't any movement of the bushing in the push-pull fork ends. The bushings are suppose to be of a sufficient length to be "pinched" to prevent movement. And the bushings are suppose to be of sufficient length so that the push-pull rod fork ends cannot be pinched against the blades at the ends of the control sticks. Movement is suppose to be between the bushing and the control stick ends. This is my understanding and please correct me if I'm seeing this wrong.
For extra clearance I used drilled clevis bolts and low profile castle nuts.

[Bcone1381]

I feel like a dog named "Blackey" from my youth. I could show Blackey his tail, and he would start chasing it around and around. If he caught it he'd bite it, yelp and stop.

Like Spinningwrench and Dave I settled with the MS21042-3 nut earlier this week. I wont go thru everything I tried and rejected. Arborite I collaborate at our local airport. I look up to him as he is an LSA builder, retired automotive engineer with sound advice on failure mode analysis. We tried a shear castle nut with a trimmed cotter pin, but Arborite suggested I paint the inside of my torque tube black to serve as a witness for rubbing inside of the tube. The black paint worked fabulous. A tiny scrape exposed the shear castle nut contact when the point of its hex shape was in the right orientation to the torque tube in certain scenarios.

So yes, I'm back with the MS21042 nut.

Also, I put a stick boot at the junction where the stick penetrates the floor. I velcro the boots to the floor to make inspection of these nuts quick and easy.

We think that every installation may be slightly different as clearance may vary on each stick assembly. The take away is to inspect and check carefully the mechanism and adjust hardware to eliminate any rubbing.