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Aileron bellcrank washer

Tom Martin

Well Known Member
I am making a minor modification to the aileron bellcrank installation that I present for your consideration and dialogue.
The bellcrank is installed on a 3/8" O.D. brass bushing that is captured between and upper and lower bracket on the spar.
When the bolt is tightened properly the bellcrank is supposed to rotate freely on the brass bushing with a very slight up and down movement along the bushing.
My concern is that the metal bellcrank, although it rotates on the bushing, rests on the bottom aluminum bracket. Each time it turns there will be contact between the end of the metal 4130 tube and the face of the aluminium bracket.
The addition of a 960-616L washer will eliminate this contact. The washer goes over the bushing and is free to rotate around the bushing, this can be seen in the picture below

2po2kg8.jpg


This is one of those long term issues. I can see no problems with this addition and it has the potential to reduce or eliminate wear at this important location.
I was able to install this washer without any trimming of the bell crank or the supplied brass bushing, while maintaining the torque and "play" specified in the plans.
(maybe the engineers left the correct spacing for this washer and it somehow got omitted in the plans?)
 
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Same here

I did the same here a few months ago on that. Especially with having aluminum brackets that the steel bellcrank is going to rub against, I decided not to let them rub. The RV-10 had steel brackets.
Tim
 
"My concern is that the metal*bellcrank, although it rotates on the bushing, rests on the bottom aluminum bracket. Each time it turns there will be contact between the end of the metal 4130 tube and the face of the aluminium bracket.
The addition of a 960-616L washer will eliminate this contact. The washer goes over the bushing and is free to rotate around the bushing, this can be seen in the picture below"


Tom (and others):

I have just completed this stage on my wings (and actually moved on to the fuselage kit - finally!). *I didn't fully appreciate this issue until I saw it first hand, and then reviewed the issue and your proposed solution with two of my esteemed technical advisors. *They both shared your concern, coming from building planes utilizing steel brackets.

However, a question was raised about your fix - that being that it does not guarantee that the friction and wear occurs steel-on-steel with the Bellcrank rubbing on the washer. *It is possible the washer and Bellcrank move as one with the washer rubbing the aluminum bracket, though the washer certainly increases the bearing area.

Their proposed solution is to use 2 NAS1149F0463P (or 432P) washers, one on each end of the bushing/bellcrank, this washer having an inside diameter hole matching the bolt rather than the bushing. In this configuration the bushing would pinch the washers between it and the brackets (one at each end), preventing the washer(s) from turning. Dimensions now become more critical and therefore complicating installation over your proposal, as the bushing must be shaved/shortened enough to incorporate it plus 2 washers between the brackets, and the Bellcrank must be shaved/shortened enough to prevent binding between the washers on each end. *However, this would ensure that Bellcrank movement is steel on steel, with wear measured in decades vs years.*

You probably considered this - did you rule it out as too complicated?
 
".. *It is possible the washer and Bellcrank move as one with the washer rubbing the aluminum bracket,..."

The way I made my installation, the washer just fits over the bolt, not the bushing, so that
when the bolt is tightened properly, both the upper and lower flanges of the aluminum bracket, the bushing, and the proposed washer are all clamped together as a single unit.

The bellcrank is free to rotate about the bushing since the bellcrank tube is slightly shorter than the bushing inside it.

(Maybe Van's would like to weigh in on this)

Jerry #140158
 
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PS. I didn't see any need to trim either the bushing or the bellcrank at the time, since the slightly increased gap between the bracket flanges caused by the washer seemed insignificant and all other dimensions stayed the same. My understanding was that the concern was just the weight of the bellcrank and attached pushrods pressing down on the bracket flange, so I didn't think an upper washer was needed.
 
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