Scudrunners

What are the differences between:

Castellated nuts
Metal stop nuts
Fiber stop nuts

Where should they be (or not be) used or re-used?

Why as a pilot would you give a shit?

2006 Carp Ontario:  one dead

https://en.wikipedia.org/wiki/Scott_Manning

[quote]1. "The right-wing taper bolt did not penetrate deep enough through the spars to engage the fibre locking feature of the locknut. Therefore, the taper bolt was not in safety at the time of the accident."

2. "The fibre locking feature of the left-wing locknut was worn and did not secure the left-wing taper bolt in safety."[/quote]


2011 Renv NV: 11 dead, 69 injured:

https://en.wikipedia.org/wiki/The_Gallo ... aces_crash

[quote]In the NTSB investigation report, the cause was attributed to extreme pitch-up to 14g+ caused by the loss of the port elevator trim tab due to wear in the trim tab mounts, exacerbated by lock-nuts on the mounting bolts losing their self-locking ability due to use past their normal life[/quote]

Castellated nuts will be used on bolts with drilled ends, with a cotter pin to prevent the nut from unscrewing.  Typically used where the bolt has the potential to see torque, for example when attaching a ball rod end to a bellcrank.  If the rod end were to seize, the motion of the pushrod and bellcrank would apply torque to the bolt, and potentially start to unscrew a nut.


The metal stop nut would be used in hot areas of an airplane, mainly in the engine room.  I believe it's above 200F and above where it becomes preferred.  To be used where the temperature will degrade the performance of the plastic or fibre locking feature of a conventional lock nut.  The all metal lock nut uses axial force to compress the threads onto the bolts, increasing the vibration resistance.


The Fibre (or plastic) lock nut would be used where vibration resistance is desired, where temperature is not a consideration.  The soft material applies 'grasps' the male threads resisting the tendency for the nut to loosen under vibration.


If I remember correctly you're looking for 1 to 3 threads to be clear through the nut when seated.

Castellated nuts may be re-used as often as any conventional nut.  Metal lock nuts can be re-used, but fibre lock nuts shouldn't be re-used more than once or twice, either one should be tossed if you can't feel the increased torque as it's being installed.  Personally I don't like to use lock nuts more than once.

How'd I do?
Gerry

Perfect.

BTW I believe AC 43-13 defines "in lock"
as 1.5 threads protruding.

Probably the most important thing to learn
is - [i]When Can You Re-Use Fasteners[/i]?"

People re-use fiber nuts too much, so people
over-react and say that you must always throw
them out - "one use" only.  Not true.  As long
as they retain their specified tension, they
can be re-used.

Never re-use a star lock washer, but I re-use
flat washers all the time.

It is a very interesting question as to when
you can re-use a bolt, and when it must be
replaced.  IMHO a bolt must be replaced
when the shank or threads are worn, or it
has suffered plastic deformation.

[img width=500 height=265]http://206.214.218.178/~stressindicator ... 24x543.png[/img]


You can re-use a castellated nut, but please
spring the 2 cents for a new cotter pin.

Re-using star lock washers, cotter pins or
lock wire is like re-using condoms.  Don't
do that.

As a pilot, I glance at airplanes and all the
time, I see fiber nuts being used where they
shouldn't be, bolts not in lock, improper
lock wiring, etc.

And these certified aircraft have perfect paper.

If only they could read.

[img width=500 height=281]http://images.guff.com/gallery/image/150820-deeznuts[/img]

I think Hilary is hot.  She keeps passing out
which like Bill Cosby, I find attractive.

Back on topic ... not all bolts are
subjected to tension:

[img]http://www.roymech.co.uk/images/bolt_1a.gif[/img]

Above are some bolts which are
subjected to shear loads.  You
don't actually need to tighten the
crap out of these bolts.

Case in point: The flap tracks I install on a 50-ton, nearly supersonic jet are held by two ~1.5in bolts in quadruple shear. Torque on them is only 150 in-lbs. No tension on them, just need to keep them in their happy place.

I really hate single shear in anything that moves though - always trying to pull itself apart.