Bellcrank fitting advice

[Nev]

I’m connecting cables to the forward elevator bellcrank. It looks to me like I’m missing something rather obvious but I’m just not seeing it.

Should there be a bushing in here ? Or washers ? The turnbuckle as it is, is free with a large amount of play.

Thanks and Merry Xmas !

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[Nev]

On closer inspection it looks like the turnbuckle end needs to be sleeved down to AN3 size, and washers placed either side.

[Nev]

Right I seem to have answered my own question. Discovered I had mis-labeled a small bag containing two bushings and washers for spacing.

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[Nev]

Yep you’re right, but the next size down the shank doesn’t clear the bellcrank. Actually the one in the pic is ok with just one washer under the nut. I’ll get my friendly LAME to check it. Thanks.

[Battson]

They step down in size by about the length of two standard washers at a time, the next size down should be perfect. Nevermind the shank, it's not a high stress application

[James]

Yep, as a rule, if you ever need more than 2x 0.063 (thick) washers on a flight control bolt, you can get the next bolt length shorter, and use 16 or 32 thou washers. I'd take the washer out from under the head, to give max clearance for the flap cable, though I'm not sure about the geometry on the Model B.

Actually, to save weight for the whole airframe, I got rid of all the 0.063" steel washers, and just changed them out for 32 thou and 16 thou washers where I could. Also changed aluminium D washers for all the bolts going through aluminium - not sure why my kit came with heavy steel washers throughout the wing.

James

[Nev]

Thanks to both you chaps. I thought I had to have a washer under the bolt. Once it was removed I was able to use a shorter bolt, less washers, and there’s now no interference with the flap cable. A win on all counts!

[Battson]

I understand using aluminium washers in steel to steel applications with a steel bolt isn't advisable. The washers will deform before the steel - which would then allow the parts to become loose, wobble, and elongate the holes in the parts.

Assuming you are bolting steel to aluminium parts, or aluminium to aluminium, and the washers are high grade aluminium to match the parts, then there shouldn't be any issue using aluminium washers assuming they don't gall...

As James said, you only need one thin washer under the nut as a minimum.

In high stress applications, a thick washer is advisable, especially landing gear and empennage assemblies where in my view they are required. NAS washers would be a good idea...

You should always use the minimum number of washers required by shortening the bolt, not exceeding three under normal applications.

For bonus points, bolt heads should face upwards or outboard unless there's a good reason they cannot.

All the above is from AC43.13-B and other best practice sources.

[JimParker256]

For bonus points, bolt heads should face upwards or outboard unless there's a good reason they cannot.

I would alter that to say "bolt heads should face upwards, into the airstream, or outboard, unless..." I cringe at the number of times I see bolts installed with the head at the aft position and nuts on the forward side. Just something that was drilled into me in the Army when I was training to maintain helicopters, and again during Army flight school, and yet again during Army maintenance test pilot school. It was considered a "grounding condition" if any bolt in the rotor system was installed other than "head-first" in the direction of rotation...

[Battson]

Good point, I forgot the third axis!

[Nev]

Great tips thanks chaps. One more I learned.....for extra bonus points, stops cut hands. Quick and easy to do too.

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[Battson]

This is what I do

(although I do it tidier, this is all I could find online at my desk):
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I like it because the bent parts of the pin don't stick out too far, and there's less chance of catching them with a sleeve or nearby part, bending the pin arms out again. Note the downward facing pin arm is always against the washer / part.