Elevator Hinge Pin Issue - Savannah S

[BC0979]

I am working on fitting all the ABS wing tips so I can paint them.

 

During the trial fit of the Stab and Elevator, I discovered that the elevator hinge pin will not accept both the brass bushing and the castle nut.

 

 

Chapter 23 page 4/10

I cannot slide the brass bushing SC210 completely over the hinge pin so to expose the hole for the cotter pin.

In addition, the AN3 castle nut will not thread onto this hinge pin.

I cleaned the threads, tried several different AN3 nuts without success, cuz the last thing I want to do is cross thread it.

 

*** Am I supposed to use the AN3 nut?????

Or is there a metric nut instead???

I searched through ALL the remaining hardware bags for an alternative to the bushing and the castle nut, nothing.

 

Any insight would be greatly appreciated.

 

Bryan

 

[IBob]

Hi Bryan,

1. The bushes sometimes have a slightly raised inner lip at one end, where they were parted off during manufacture. This needs taking off, I used a small deburring tool.

2. The pin is AN3, and should take an AN3 nut (all the bolts in the kit are AN, except perhaps the little ones in the trim linkage, and the big SS ones that hold the main undercarriage). I would look at the pin very closely to check there is no damage or weld spatter (since the pin is welded to a backing plate.) I would then try more than one nut, in case you have a damaged nut. If no nut/s would start, I would then clean up the tip of the pin, where the thread starts, with a fine file: once the nut is on, the thread at the tip does nothing.

[IBob]

PS There's a layer of black paint on the pin too: some careful smoothing of that with fine emery may be required if the bush is still tight.

[BC0979]

IBOB

Thanks for the reply.

I really needed to confirm that it is A3.

I will get a 10-32 die tomorrow morning and clean up the threads.

Both sides are an issue.

As far as the bushing, the grip/body of the hinge stud is about 0.005 larger than the AN3 bolts which is why the bushing will not slide over it. 

 

Thanks again for the help 

 

 

[IBob]

Hi again Bryan. That 0.005 surprises me a bit: I would have thought the stud was a standard AN3 bolt, welded to the backing plate, unless they have changed how they are doing it. Have you been able to clean the paint back from that part?

[onetrack]

FWIW - the shank diameter of bolts can vary by quite a few thou, as the manufacturing processes do not allow for very precise diameters.

 

There are dimension variation allowances for all bolts in the manufacturing processes, but I'm having trouble finding them, though.

[IBob]

Looks to be plus and minus 1.5thou for the AN3, Onetrack?
http://www.zenithair.com/kit-data/ra/an.html

[onetrack]

Yes, that's good, useful AN3 bolt information. Perhaps the bushing has not been machined accurately, and is a few thou undersize. I'd be miking the bushing.

[IBob]

My money is on the paint they apply to all the fabricated steel assemblies: the bush will be greased inside during final assembly, the paint needs to come off.
If the bush or the bolt are wrong, ICP need to be told.

[facthunter]

Those parts should be "masked" to prevent Powdercoat or paint causing 'fit" problems. You should NEVER sandblast threads or wearing surfaces either.. You can't adjust a tap but the dies you use should be adjustable at all times. Loose threads are weak threads. Not the sort of thing that belongs in an aircraft anywhere.  Threads in wrong places  (Bending loads) can be crack starters . Nev

[Blueadventures]

maybe drill a 3/16 nut with 3/16" and see if that fits over or cleans off any paint goop off the pin.  also see if 3/16" drill shank will fit bush.  could be under size i.d.  Also think about it, sleep on it; just don't rush a fix as may regret a rushed decision.

Edited March 27, 2023 by Blueadventures

[IBob]

8 minutes ago, Blueadventures said:

Also think about it, sleep on it; just don't rush a fix as may regret a rushed decision.

I think that's excellent advice any time you get stuck in a build.

[BC0979]

Update:

Got a Irwin brand 10-32 die and hand traced the threads.

Castle nuts now go on as they should.

 

Remeasured the hinge pins on both sides, 0.190 - 0.191

Outer diameter of the bushing 0.235

AN3 bolt grip measured 0.185

Used #12 drill bit then #11 then #10 to ream out the bushings.

Thank goodness it was brass. LoL

Fits like it should now except now I noticed that the center mount holes are off quit a lot. Will need to study this more before I am tempted to drill 

 

 

 

 

 

[BC0979]

Assembled the elevator on the end hinges.

The center mounting flange hole definitely has issues

#1 the hole in the Stab flange is 3/16 and the hole in the elevator flange is 0.235 for the bushing.

#2 the holes do not line up, about 1/3 of a hole(the 0.235 hole)off. 

 

Construction manual shows the bushing going through both flanges

 

*** Did you guys need to drill out the Stab flange like I need to?

 

[IBob]

17 minutes ago, BC0979 said:

*** Did you guys need to drill out the Stab flange like I need to?

 

Yes.

As I recall, with the tip pivots in, I used a fine marker to mark through the 0.235 hole onto the stab flange. I then disassembled and clamped a piece of thick scrap (steel?) with a 0.235 hole in it, over my marking on the stab flange. This held the drill centered so I could drill the stab flange.
I also took a bit off the tip of the stab flange so that it cleared the elevator skin at that point.

[facthunter]

Brass is not much of a bearing metal. It's copper-zinc. Bronze is copper-tin.. Nev

[old man emu]

20 hours ago, IBob said:

Looks to be plus and minus 1.5thou for the AN3, Onetrack?
http://www.zenithair.com/kit-data/ra/an.html

Here's the correct gen on bolt dimensions:

 

 

[facthunter]

All threads measure smaller than nominal size due a flat or radius in their form. AN -SAE has flats. Smaller  AN  sizes are GAUGE used on spokes also. The top one there is 10-32. 10 gauge 32 tpi. 11 gauge is Smaller just to make life interesting. AN is a GOOD system for aircraft. Most High tensile bolt threads are rolled hot.  Nev

[onetrack]

OME - But your document clearly states at the bottom, "Documents in this book for REFERENCE ONLY, not intended for design. Not guaranteed for accuracy". So there still could be errors in that chart.

[facthunter]

To ERR is human. To forgive Divine. There now you can sort it out. .  Nev

[IBob]

3 hours ago, IBob said:

Yes.

As I recall, with the tip pivots in, I used a fine marker to mark through the 0.235 hole onto the stab flange. I then disassembled and clamped a piece of thick scrap (steel?) with a 0.235 hole in it, over my marking on the stab flange. This held the drill centered so I could drill the stab flange.
 

PS and to state the obvious: the hole you drill must take in the existing (offset) pilot hole.

[facthunter]

It's not good practice to get alignment by drilling a bush  out of true. What if it then moves at some later time? Nev

[IBob]

That's not what is happening, Nev:
One part has the full sized hole in it, the other part has just a pilot hole (which is not exactly centered, it would be better if there were no pilot hole).
So it's a matter of marking up then holding the drill centered to drill on that mark (rather than on the pilot hole).
The bush (which not drilled out of true) is then inserted through those two parts, and secured with the ubiquitous AN3 bolt etc.

Given the shape of the elevator, which narrows to a box section at the centre LE, it would be surprising if the (pilot) holes were perfectly aligned.

Also this: that centre section (and bearing) takes all the load of the elevator control cables pulling forward. So, even if the holes were perfectly aligned initially, they wouldn't stay that way (without the bearing) once the cables were tensioned.

Edited March 28, 2023 by IBob

[facthunter]

In applications/ linkages such as this often rose joints are used but have threads, are bulky and weigh a lot.  Nev

[old man emu]

5 hours ago, onetrack said:

OME - But your document clearly states at the bottom, "Documents in this book for REFERENCE ONLY, not intended for design. Not guaranteed for accuracy". So there still could be errors in that chart.

That's there in response to the Americans' love of litigation. The producer of the handbook has obtained the data from the original specification sheets issued by the US Military in WWII to standardize hardware across industry. 

 

By World War II (1939–1945), virtually all national militaries and trans-national alliances of the same (Allied Forces, Axis powers) were busy standardizing and cataloguing. The U.S. AN- cataloguing system (Army-Navy) and the British Defence Standards (DEF-STAN) provide examples. For example, due to differences in dimensional tolerances, in World War II American screws, bolts, and nuts did not fit British equipment properly and were not fully interchangeable. 

 

National Aerospace Standards since 1941, have served as the foundation for aircraft, spacecraft, watercraft, ground vehicles, machinery, and electronics NAS parts are most well-known for state-of-the-art, high-strength, precision fasteners, electrical connectors, splices and terminations, rod end bearings, and many other types of hardware and components. Most parts are available as 3D CAD models.

 

MS- Military standard started around the 1950s and for the most part replaced the AN hardware series.  

 

Quick explanation: https://www.flywithspa.com/docs/pbm/toc453317738.html