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Vertical Stab to front spar attach - 11-08 step 2

RV6-KPTW

Well Known Member
The strangest things wake you up at 3 in the morning...

I am putting the airplane back together after painting and put my hand on the attachment bolt and castle nut. I tried to turn this thinking it should be in a finger tight state. It is not. Now I question what I originally did during construction. Did I overtighten?

Is there a best practice for this attachment? Should there be a torque value applied to this bolt / castle nut?

Thanks
 
Thanks. All good on the anti-seize.

Wracking my brain to remember. I think I finger tighten the castle nut and then rotated it tighter to line up the hole. Would it have been better to rotate the castle nut to the adjacent looser slot?
 
I called Vans specifically on this bolt during my build and was told to fully torque it and all castle nuts to specification, in most cases. There is a old thread about torque ranges and the discussion for castle nuts stated to torque to the lower range value and tighten if necessary to align the hole but not to exceed the high torque limit. If this cannot be achieved try a thin washer or different bolt as there are tolerances for bolt length so a different one just might work.

Why is it castellated then? The only reason I can think of for a castellated nut is if the torque is not adequate to retain the nut. Also - why bother with anti-seize here if the nut is locking the structure into place. Not disagreeing with you, but confused as to the "whys"...

Van's section 5 says (regarding castle nuts for bolts used as pivot points): "In specific cases, bolts are intended to be used as axis of rotation. The most common example is the attachment of control system cables. Here, it is intended that the cable end fitting pivot on the bolt. In these instances, the nut must not be torqued to the standard torque value. Instead a castellated nut, safetied with a cotter pin, is used. Finger-tighten the nut, then install the cotter pin. The cable end fitting must pivot freely when the installation is complete". Not relevant here exactly but adds to my confusion.
 
Why is it castellated then? The only reason I can think of for a castellated nut is if the torque is not adequate to retain the nut. Also - why bother with anti-seize here if the nut is locking the structure into place. Not disagreeing with you, but confused as to the "whys"...

Van's section 5 says (regarding castle nuts for bolts used as pivot points): "In specific cases, bolts are intended to be used as axis of rotation. The most common example is the attachment of control system cables. Here, it is intended that the cable end fitting pivot on the bolt. In these instances, the nut must not be torqued to the standard torque value. Instead a castellated nut, safetied with a cotter pin, is used. Finger-tighten the nut, then install the cotter pin. The cable end fitting must pivot freely when the installation is complete". Not relevant here exactly but adds to my confusion.

You correct.... it is not relevant because in this case (vert stab fwd spar attach) it is not intended to be used as an axis of rotation,
but the castellated nut and cotter pin is instead used because even though it is not intended (as part of a system function, there is still the possibility of slight rotation under high load.

That is the same reason that castellated nuts are used at the rear wing spar attach points.

Since these fasteners are not intended for rotation they should be torqued to standard values like any other other structural fastener.
 
General rule for castle nuts is finger tight. But since the v-stab bolt is not rotating but rather moves sightly in lateral direction, probably OK to slightly tighten past finger tight for hole alignment. I've noticed that castle nuts tend to be a little looser than the original state after they've been in use for a while anyway.

Definitely do not fully torque as that would defeat the purpose of using a castle nut in the first place.

However as in all things important may be worthwhile to check with the mothership....

Not correct.

A castellated nut should only be less than standard torque when it is specifically used as a rotation point. Details in Section 5 of the manual.
 
Not correct.

A castellated nut should only be less than standard torque when it is specifically used as a rotation point. Details in Section 5 of the manual.

And to add to that, if there is no bearing involved and the axes of rotation is round the bolt itself .
A couple of examples are the engine control cables that has a rod end bearings.
 
And to add to that, if there is no bearing involved and the axes of rotation is round the bolt itself .
A couple of examples are the engine control cables that has a rod end bearings.

Correct, because in those cases the bolt isn’t being used as a rotation point.
 
I am glad I asked. I will recheck all castle nuts. To confirm, the tailwheel axle is not a rotational and should be treated with standard torque, yes?

Scott - Thanks for jumping in!
 
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Not correct.

A castellated nut should only be less than standard torque when it is specifically used as a rotation point. Details in Section 5 of the manual.

I am glad I asked. I will recheck all castle nuts. To confirm, the tailwheel axle is not a rotational and should be treated with standard torque, yes?

Scott - Thanks for jumping in!

As in most things in life, there is no such thing as an absolute (maybe saying that is also a contradiction to that idea :p) My above statement was just to make sure no one got the idea that they should be finger tightening all castellated nuts.

In RV kits there are at least two exceptions (that I can think of at the moment... possibly there are others) to my above statement.

1- The tail wheel axle bolt -
The bearings in the kit supplied tail wheel are not tapered roller bearings so they are not designed for a high axial (lateral) load, so the nut should only be tightened just enough to take out all of the play and then safetied with a cotter pin.

2- The bronze bushings used at the base of the control sticks and in aileron bell cranks on some models. The bronze is soft enough that with standard full torque on the bolt it can deform enough to induce friction in the pivot point. Particularly if the end profile isn't adjusted for an exact net fit between the points where it is mounted. That is the reason that castellated nuts are used. That allows for torquing just enough to remove all play and prevent the bushing from rotating, but avoid distorting the shape of the bushing.
 
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