[AX-O]

I have been trying to install my left aileron bellcrank for the past 6 weeks. The right one fits properly however the left one is being a pain in the you know what. The inside of the bellcrank was reamed to 0.376 inches. The outer diameter of the brass bushing is 3/8 of an inch. I have plenty of room on the bellcrank as to when everything is torque, the bellcrank can move up and down on the brass bushing a small amount prior to touching the brackets. As soon as I torque the bolt down, the bellcrank binds and is no longer free to move. If I decrease the torque value, the bellcrank can freely turn around the brass bushing (brass bushing does not turn) but the torque is not correct. Seems that the brass bushing is deforming when torqued. I have tried everything that I could think to do. The assembly has come off 6 times and I am afraid that the nutplates that attach the bellcrank brackets will give out soon. Should I order a new bellcrank (I heard they deform when welded), should I buy a different bolt and use a cotter pin. Any advice would be welcomed.

 

[N908RV]

Axel,

You are correct, I'd avoid removing the brackets at all as you will start to wear out the crimp (i.e. locking feature) of the nutplate. Also, IIRC, I don't believe you need to remove the brackets to get the bellcrank assembly out.

Here's what I would suggest:

• make sure the bellcrank ends are square and that you have removd the powdercoating off of the bellcrank (where the bushing goes) tubing ends. If you already have done this, then file or sand a tiny amount off just to give yourself some additional clearance. If they are not square, then they can partially drag or bind.
• you can also bevel the ends of the brass bushing at the ends so if they mushroom out a tiny amount that will help alleviate that.
• if that doesn't seem to work, then can you back off just a TINY amount from your torque and have it work OK? If so, then that may be the simple answer. Remember this part is in shear and not tension so actual torque on this part is less critical and if your torque is causing the brass to mushroom out at the ends then maybe it is just a bit too much. Basically all that you are asking of this nut is to stay on the bolt, not hold anything in tension. But it better be secure or we all know the potential consequences. If you have to back off more than an insignificant amount, then I would recommend replacing the plain bolt with a cottered one and use a castle nut/cotter and you can have it as loose as needed without worrying how close to torque you are.

Good luck,

Rob

 

[az_gila]

No need to replace

...... The assembly has come off 6 times and I am afraid that the nutplates that attach the bellcrank brackets will give out soon.......

Axel... do not worry about the nutplates....

This statement comes from AC 65-9A - A&P Mechanics General Handbook - available at the FAA web site.

"Normally, elastic stop nut can be used many times with complete safety and without detriment to their locking efficiency. When reusing elastic stop nuts, be sure the fiber has not lost its locking frictions or become brittle. If a nut can be turned with the fingers, replace it."

Rob's comments do not seem to be backed by the FAA...

Six times is no sweat... look at the 30+ year old planes flying with the same nutplates on. The ones I have replaced on my Tiger have been for corrosion and holding the screws too tight! I have yet to find a loose one...

Do fix your general problem with the bellcrank though....

gil A

 

[az_gila]

Washers?

Axel,

[*]if that doesn't seem to work, then can you back off just a TINY amount from your torque and have it work OK? If so, then that may be the simple answer. Remember this part is in shear and not tension so actual torque on this part is less critical and if your torque is causing the brass to mushroom out at the ends then maybe it is just a bit too much. Basically all that you are asking of this nut is to stay on the bolt, not hold anything in tension. But it better be secure or we all know the potential consequences. If you have to back off more than an insignificant amount, then I would recommend replacing the plain bolt with a cottered one and use a castle nut/cotter and you can have it as loose as needed without worrying how close to torque you areGood luck,

Rob

Rob... this would seem to allow the bolt and the bushing to be the bearing surface and not the bushing within the bell crank. Van designed this part to have the larger diameter be the actual bearing surface and the bolt not to rotate.

Perhaps the angles are getting slightly "pulled in" when the bolt is torqued, preventing square ends of all the parts sitting nicely.

Measure the bushing and the distance between the angles, and see if they are the same, and square. You could shorten either or both a little, and insert a washer in there (inside the angles) in such a way that the washer sits against the bushing and not the bell crank. This would give you another shot at making your existing parts work...

gil A

 

[briand]

AX-O, can you take a caliper to the bellcrank and the bushing and tell us the length of each? Maybe there is not enough material on the bushing. I don't believe there is any mushrooming goin on.

I lockwired my bellcrank bolts.

 

[G-force]

FYI, I machined and reamed the bushings for AX-O's belcaranks in my lathe so we know they are perfectaly flat and of proper length. The plans called out for the bushings to be 1/64-1/32" longer then the weldment, so I split the difference and set them at .022-.023" . Axel, one thing to check is that you didnt mix the bushing up, the weldements and thus the bushings were different lengths, perhaps you got the short one in the long weldment?

 

[N908RV]

Rob... this would seem to allow the bolt and the bushing to be the bearing surface and not the bushing within the bell crank. Van designed this part to have the larger diameter be the actual bearing surface and the bolt not to rotate.

Perhaps the angles are getting slightly "pulled in" when the bolt is torqued, preventing square ends of all the parts sitting nicely.

Sorry Gil, I should have specified, yes agreed, absolutely the bearing surface is intended to be the outside of the bushing and you do not want to rotate the bushing around the bolt - that is definitely the intention of the design. The bellcrank should rotate around the bushing. I was just making a point that if he had to back off to achieve that due to mushrooming of the bushing that the torque may be too high and it he had to back off and it worried him then he could cotter the assembly just as a precaution.

You bring up a good point that perhaps the bushing itself is cut short and he may be squeezing the angles down onto the bushing. Hadn't considered that possibility.

I'm sure the nutplates are just fine and will continue to be, but I try to discourage folks from taking critical parts that are nutplated on and off over and over again if they can avoid it. It is just unnecessary wear. I wasn't even sure why he was taking the brackets on and off 'cause you shouldn't need to.

Potato Potata...

 

[AX-O]

Axel, one thing to check is that you didnt mix the bushing up, the weldements and thus the bushings were different lengths, perhaps you got the short one in the long weldment?

That was the first thing I checked. Both bushings are longer than the lenght of the bellcrank. I interchanged the bushings and the bellcrank being discussed kept binding once the bolt was torqued regarless of the bushing.

 

[Ironflight]

Just a thought.....

Take the bell crank, bushing, bolt, and nut out of the wing. Find two washers the size of the bolt and use them to "simulate" the brackets on the workbench. Torque the thing up the same way you are doing in the wing. If it binds, then you know it has nothing to do with the brackets, and everything to do with the bushing or bellcrank. It's one way to get eyeballs on the assembly as you torque it up. You might not learn anything, but it wouldn't be hard to do.

Paul

 

[AX-O]

I wasn't even sure why he was taking the brackets on and off 'cause you shouldn't need to.

Unfortunately you have to take the upper bracket off in order to install or remove the AN4-32A bolt (holds the bellcrank assembly). The bolt will not come out freely due to interference from the wing spar flange. If there is a better way to remove that bolt, I would love to hear it.

From Dan Checkoway's website
"Then I went to mount the bellcrank on the spar and I realized that it was a no-go. For some reason, the instructions tell you to bolt the bellcrank attach brackets to the spar early in construction. Or maybe I imagined that or something. In any case, you can't get the AN4 bolt into the top bracket without removing it! Duh. So I ended up removing the brackets and tossing the AN3-6A bolts that were in there and replacing them with fresh bolts. "

 

[AX-O]

Just a thought.....

Take the bell crank, bushing, bolt, and nut out of the wing. Find two washers the size of the bolt and use them to "simulate" the brackets on the workbench. Torque the thing up the same way you are doing in the wing. If it binds, then you know it has nothing to do with the brackets, and everything to do with the bushing or bellcrank. It's one way to get eyeballs on the assembly as you torque it up. You might not learn anything, but it wouldn't be hard to do.

Paul

Great idea Paul. I will try that tomorrow.