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  #1  
Old 12-07-2017, 07:51 AM
chris mitchell chris mitchell is offline
 
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Location: near Harrogate, England
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Default Control linkages and washers

I am trying to install the various control linkages from the sticks back to the elevator. There seems to be a shortage of information on the plans, though I might well be missing something. Not helped by these odd washer sizes that are called out in various places.

So, F-635 on drawing 38. The center bearing has two AN960-416 washers and two 5702-95-30 washers. Nice clear diagram and I understand that the 5702 95 30 washers capture the bearing if it fails. These funny washers are 0.25id and .75 od. Fair enough?

Drawing 30. Where F-441, the big pushrod, is attached to the elevator horns, there is an AN3 bolt and an AN365-1032 nut, plus enough washers between the elevator horns to fill the gap.

Drawing 28, F399 and F-440, are connected to the front stick base, the rear stick base and back to the bottom of the bell crank. Two of those locations (F-440 to back of rear stick and F-440 to bottom of bellcrank.) indicate to use the little 5702-75-60 spacers/washers. Should I use the same little washers on the other two locations (front stick to F-439 and F-439 to rear stick)? That would use up all 8 of the supplied 5702-75-60.

What about he top of the bell crank to the F441 big push rod? Can't find the details for that at all.

Finally, two possibly dopey questions:

Why do we not use the larger washers in all these locations as there are still rod end bearings that could, presumably, fail?

Why do we use nyloc nuts in these locations rather than AN - (non-A) bolts, castle nuts/split pins?

As ever, many thanks.

Chris
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  #2  
Old 12-07-2017, 08:48 AM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Here's the way I like to think of it - If I was a bearing in a rod end, and if I became separated from the rod end (either by failed bearing race or some defect), then what would happen next. If the answer is that the rod end and whatever it is connected to could fall outside of the safe operating area where it is supposed to be in - it could then jam the control - well then you have to have something to prevent that from happening. On your large elevator pushrod that is captured in the elevator bellcrank, you don't need a large diameter washer because if the rod end bearing fails it is held in the same relative position because it can't get outside the jaws of that bellcrank - as long as the bolt doesn't break. On your aileron inboard bracket where it connects to your aileron push pull tube rod end, you will need to have the large diameter washer on the bearing side of the approximately 1/2" spacer that's there. Even though the whole collection of spacers, and washers is inside of the aileron bracket, a failure of that rod end could allow the now liberated bearing to slide laterally a half inch or more, which would possibly jam the control tube in the aft spar opening. That large diameter washer prevents that from happening.

As far as those very small (and difficult to install) 5702-75-60 washers - I think the only place I've seen those used is in place where a normal size washer would contact and drag on the part that the ball is pressed in to - like the outboard aileron bracket on some models, or on a rod bearing where the rod pivots a lot. That small diameter washer gives a space between the ball and the normal washer or surface, so it can move freely without interference.
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  #3  
Old 12-07-2017, 12:33 PM
chris mitchell chris mitchell is offline
 
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Thank you Scott - that all makes perfect sense!

So if one imagines the F399 in use (the push rod within the stick mixer assembly) it just moves forward and back. The F440 has to deal with that assembly rolling with aileron input, and hence the bearing fitting could bind, if not for the little spacers 5702-75-60 at the base of the P2 stick and the bottom of the big bell crank F-635.

OK, then I surmise that the other points of assembly just need the requisite bolt washer and nut, with no need for capture washers or spacers unless specified eg at the aileron bell crank.

Excellent. Progress is happening again

Chris
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  #4  
Old 12-07-2017, 01:11 PM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by chris mitchell View Post
...

The F440 has to deal with that assembly rolling with aileron input, and hence the bearing fitting could bind, if not for the little spacers 5702-75-60 at the base of the P2 stick and the bottom of the big bell crank F-635.

....

Chris
There is another interesting twist here for owners of very early -4 and -6 kits.

Vans changed the vendor for the rod ends, and if you have the Heim rod ends that were supplied in the very early kits they had a different profile at the end of the ball portion. It looks sort of like the tiny Vans washer was actually built into the design.

I believe this explains why some early kits did not need the tiny washers while later kits did.

Nevertheless, the aileron pushrods should not bind in any position of the stick. If they do, add the tiny washers.

These two pictures show the difference -

https://static.summitracing.com/glob.../afc-10422.jpg

http://www.dansperformanceparts.com/...H3MSHEIM_5.JPG
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Last edited by az_gila : 12-07-2017 at 07:17 PM.
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  #5  
Old 12-07-2017, 07:15 PM
Scott Hersha Scott Hersha is offline
 
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Chris,
I think you have it figured out. Remember, any time you do something not in the plans, you'll need to apply this same standard in the parts you are assembling. If you install an autopilot, the servo actuator control rod is anchored by a rod bearing at each end. These rod ends are typically connected to the bell crank (roll or pitch) on one end, and the servo actuator on the other end by a bolt. The outboard end of the rod bearing attachment is nothing but the head of the bolt, so a large diameter capture washer is necessary here. Hardware isn't always specified in the auto pilot installation instructions - if you have them. Having a bearing fail on an autopilot actuator can have severe consequences. Having it slip off the end of the bolt head and rendering your autopilot unusable is inconvenient. Having that rod flopping around and jamming the bellcrank can be fatal.
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2001 RV-6 - sold 2005
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  #6  
Old 12-08-2017, 07:56 AM
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daddyman daddyman is offline
 
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Location: Fredericksburg, Virginia
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Default Castle nuts

Quote:
Originally Posted by chris mitchell View Post
I am trying to install the various control linkages from the sticks back to the elevator. There seems to be a shortage of information on the plans, though I might well be missing something. Not helped by these odd washer sizes that are called out in various places.

So, F-635 on drawing 38. The center bearing has two AN960-416 washers and two 5702-95-30 washers. Nice clear diagram and I understand that the 5702 95 30 washers capture the bearing if it fails. These funny washers are 0.25id and .75 od. Fair enough?

Drawing 30. Where F-441, the big pushrod, is attached to the elevator horns, there is an AN3 bolt and an AN365-1032 nut, plus enough washers between the elevator horns to fill the gap.

Drawing 28, F399 and F-440, are connected to the front stick base, the rear stick base and back to the bottom of the bell crank. Two of those locations (F-440 to back of rear stick and F-440 to bottom of bellcrank.) indicate to use the little 5702-75-60 spacers/washers. Should I use the same little washers on the other two locations (front stick to F-439 and F-439 to rear stick)? That would use up all 8 of the supplied 5702-75-60.

What about he top of the bell crank to the F441 big push rod? Can't find the details for that at all.

Finally, two possibly dopey questions:

Why do we not use the larger washers in all these locations as there are still rod end bearings that could, presumably, fail?

Why do we use nyloc nuts in these locations rather than AN - (non-A) bolts, castle nuts/split pins?

As ever, many thanks.

Chris
Chris,
This year I had the final (aft) to elevator nyloc nut fall off. The bold did not back out so I was able to land without disaster.
I immediately changed to castle nut + cotter pin.
I also removed the aft inspection plate and made one out of plexiglass so that I can examine it prior to every flight for integrity as part of my pre-flight.

Daddyman
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  #7  
Old 12-08-2017, 07:30 PM
Michael Henning Michael Henning is offline
 
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Daddyman,
How did you find out you lost the nut? After flying aerobatic aircraft, I put on a plexiglass inspection cover to be able to visually inspect before each flight.
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  #8  
Old 12-10-2017, 04:45 PM
chris mitchell chris mitchell is offline
 
Join Date: Jul 2006
Location: near Harrogate, England
Posts: 327
Default Castle nuts and cotter pins rather than nyloc nuts??

Daddyman, that's a nightmare.... its exactly what I worry about with fastenings in the control linkages that I cannot visually inspect before flight. I am now thinking of replacing the less accessible fastenings with non-A bolts/castlenuts/cotter (split) pins, particularly the ones in the elevator bellcrank assembly.

Guess that's tomorrows building session.

Chris
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Chris Mitchell

Repeat offender;
RV-8, QB, built, flown 150 hours, sold;
RV-4 - on-going repair, rebuild and remediation - abandoned and junked ;
RV-4 fuselage and wing kits - both at QB stage;
2015 and 2016 dues paid!
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  #9  
Old 12-10-2017, 09:47 PM
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Ironflight Ironflight is offline
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Location: Dayton, NV
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Default

Quote:
Originally Posted by chris mitchell View Post
Daddyman, that's a nightmare.... its exactly what I worry about with fastenings in the control linkages that I cannot visually inspect before flight. I am now thinking of replacing the less accessible fastenings with non-A bolts/castlenuts/cotter (split) pins, particularly the ones in the elevator bellcrank assembly.

Guess that's tomorrows building session.

Chris
You can replace all of the bolts and nuts if you like Chris, but remember - there are over 10,000 RV's flying out there in the world, the majority of which have been built to plans - which mean with fiber lock nuts on bolts that are not subject to rotation. I don't know of any crashes caused by disconnected controls. Yes, some people have found loose nuts - but they can't fall off if they were fastened properly, and the nuts were in good condition. The key to not being worried about it is understanding how it is designed - the fact that if it is torqued up tight, the rotation occurs in the ball joint, not the bolt.

That is how Van's designed it, and it works well. If you go with something else, you're going outside the design parameters. Remember - to line up a castle nut for a cotter pin, you have to over or under torque the bolt. Not use it as designed.It can lead to looseness between the two elevators.

I guess the point I want to make to others reading this thread is that if you don't understand how the design of the joint works, you might or might not have a better idea than the designer. If you build it per design, it is highly reliable. You've trusted Van's basic design for the entire aircraft....why not his hardware design?
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  #10  
Old 12-10-2017, 10:14 PM
gasman gasman is offline
 
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If a nyloc nut fell off, I would expect a frozen rod end to back off the bolt. But with the proper bolt thread exposure, I don't see how a first time used nyloc nut can ever fall off of the bolt.
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