Control Surface Nylocks

[Dbro172]

regarding the hardware securing the control surfaces it appears that only the flaps (-9 anyway) use castle nuts and cotter pins to secure the bolts. The ailerons, elevator and rudder use AN lock nuts. I recall that all control surfaces on a Cessna use castle nuts and cotter pins.

Are locknuts equally secure as the castelated nut and cotter pin? Is anyone substituting castle nuts w/ cotter pins in these locations; or even (presumably) better locking castle nuts w/ cotter pins?

It seems these lock nuts will be on/off numerous times before this thing flies. Do builders typically go through the whole plane and install all new locknuts nearing final inspection / first flight?

[Mel]

Aileron, elevators and rudder on RVs are secured with rod end bearings. The nuts on these are "torqued" down solid. The -9 flap hinges use castellated nuts because they are not "torqued" down and are subject to rotation.
Any time a bolt is subject to rotation, castellated nuts and cotter pins are required.

As far as reusing nylok nuts go, these nuts can be reused many times before replacement is necessary. The rule is, if you can turn them with your fingers, they must be replaced. Typically, many builders use standard nuts when they will be removed and replaced several times, then use the nylok for final assembly.

[jlfernan]

The difference is the flap's pivot is a bolt thru a bronze bushing, since it rotates it needs castle nut. The ailerons on the other hand pivot on rod end bearings. There is no turning of the bolts so you can get away with nylocs. Now, if it makes you feel better, use castle nuts.

Just saw that Mel's faster than me!

[Andrew M]

I to am building a -9 and work on C208B's to fund this project.
Generally speaking if the bolt turns in a hinged assembly, then it needs a cotter pin or saftey wire. The -9 rudder and elevator rotate on the rod end ball, not the bolt. The bolt is clamped tight, that's why there is no cotter pin. I see the same thing on the Caravan flap system (rod ends). Now as to why the 208 has saftied bolts on the other flight controls? I believe it's because the bearings installed are needle bearings, not rod ends. They are more likely to fail by seizing, causing the joint to rotate on the bolt. A rotating bolt risks loosening the nut. Rod ends just wear out.
When it comes to replacing hardware, it is usually corrosion issues or just plain dropped on the floor and lost. Replacing lock nuts because I can run the nut down all the way by hand is rare, but it does happen.

[Jeff A]

Originally Posted by Dbro172

Are locknuts equally secure as the castelated nut and cotter pin? Is anyone substituting castle nuts w/ cotter pins in these locations; or even (presumably) better locking castle nuts w/ cotter pins?

It seems these lock nuts will be on/off numerous times before this thing flies. Do builders typically go through the whole plane and install all new locknuts nearing final inspection / first flight?

Derek,

I had the same concerns while building. I used the Avery assembly tool and pins for most of the build so I wouldn't have to constantly take bolts and nuts in & out.



http://www.averytools.com/prodinfo.asp?number=445

After looking at hundreds of RVs and seeing none with castle nuts and cotters pins on the control surfaces, I decided the Van's way was probably best (and easiest). FWIW, yes, I DID replace every bolt and nylon lock nut on my controls surfaces when the the final assembly took place. On the -8, we are only talking 15 or so bolts and nuts....usually less than $1 a piece from ACS.

[rzbill]

Originally Posted by Mel

Typically, many builders use standard nuts when they will be removed and replaced several times, then use the nylok for final assembly.

True. Two comments.

One. It was a REAL RELIEF to actually put things together for the final time and use the real hardware and torque seal.

Two. I was almost to the point of losing sleep over the fact that the "wrong" hardware had been in place for SO LONG, that it LOOKED natural. I was scared stiff that I would overlook one. Get others to eyeball your plane. A LOT.

[Toobuilder]

Two quick points: concerning hardware subject to "rotation"...that means "relative to the surface"... Some people think that if it is on a hinge and rotates, it needs a mechanical locking device. But as Mel points out, if the fastener is smoked down tight on a bushing, a locknut is good to go.

Also, on all the military aircraft I have worked, nylon or fiber locknuts are one time use only, regardless of any residual run on torque remaining. Only the all metal, distorted thread locknuts can be reused. Personally, I only use nylon locknuts on go carts and lawn mowers.

[Flying Scotsman]

Originally Posted by Toobuilder

Two quick points: concerning hardware subject to "rotation"...that means "relative to the surface"... Some people think that if it is on a hinge and rotates, it needs a mechanical locking device. But as Mel points out, if the fastener is smoked down tight on a bushing, a locknut is good to go.

Also, on all the military aircraft I have worked, nylon or fiber locknuts are one time use only, regardless of any residual run on torque remaining. Only the all metal, distorted thread locknuts can be reused. Personally, I only use nylon locknuts on go carts and lawn mowers.

AC 43.13 says

"DO NOT reuse a fiber
or nylon locknut, if the nut cannot meet the
minimum prevailing torque values. (See table
7-2.)"

wherein said table lists no prevailing torque for anything less than a 7/16 nut

That aside, though...it does appear that nylon locknuts can be reused, at least for general aviation.

It may give someone a warm fuzzy to use all new hardware on everything, but it's not necessary and seems likely to add only cost (minimal, granted) with no improvement in safety or reliability.

[9GT]

The rudder and elevator on my C-152 use Nylon Lock-nuts straight from the factory, just like what is used for my RV-10. My C-152 has over 13,000 hours on her and climbing. No one has ever complained of the tail feathers ever falling off yet.

[Neal@F14]

Originally Posted by rzbill

I was almost to the point of losing sleep over the fact that the "wrong" hardware had been in place for SO LONG, that it LOOKED natural. I was scared stiff that I would overlook one. Get others to eyeball your plane. A LOT.

For non-locknuts, old used bolts, etc used as temporary assembly hardware, paint them a bright color with a rattle can before using them. That way they'll stand out like a sore thumb when it comes time to replace them with the correct final assembly hardware. I used a rattle can of Chevy Orange engine paint for that purpose.