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Improper use of Nyloc nuts


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Recently in my inspections I have been seeing improper use of Nyloc nuts and bolts. AC 43-13 is very clear in that nyloc nuts should not be used on assemblies that rotate or high temperature areas. Important assemblies that rotate are the push rod ends in the flight control system, elevator, rudder and aileron hinges and any other rotating assemblies. These areas should have a drilled bolt and a casellated nut with a cotter pin. Cheers T87

 

 

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I used to be a DeHavilland apprentice, in the '50s, and we were taught 1.5 to 2.5 threads showing, and never use a Nyloc more than once.

 

We should also remember that Nylocs are not class 1 locking - all vital fixings should be class 1. Examples of class 1 locking are peening, staking, (not often used on Microlights) wire locking and split pins or quick release pins and cotter pins, used in conjunction with castellated nuts.

 

Occasionally where a class 1 locking method cannot be used, it may be necessary to use loctite in conjunction with a nyloc nut - prop nuts/bolts are an example of this, but there are others.

 

 

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This problem with the grip length may be caused because of using imperial hardware (US) on metric designed aircraft. the GA Trinidad and Tobago (french designed) use metic hardware. be aware of this when rebuilding/repairing European Aircraft.

 

 

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Guest Maj Millard

The US standard, AC43.13 and all that, is minimum of one thread and maximum of three threads. More than three threads, you get a shorter bolt, or put a washer under the nut. Since we generally use AN hardware (Army/Navy, which is all they had back in 1930) , we should be prepared to abide by those standards, as they were developed and perfected over many years of practical testing.

 

It's annoying when some one comes along, and for no good reason wants to reinvent the wheel. The AN standard wheel isn't broken, and doesn't need to be fixed, or modified. AN hardware has always worked for me, even on the occasions where I've manage to bend a bolt or two. If you have ever had the pleasure (sic) of working on a British aircraft such as the BN Islander, you would know what an absolute waste of time it is, when somebody thinks they know better, and depart from Standard AN hardware useage. Metric hardware is a whole different ballgame, however many Euro manufacturers still use the industry standard AN hardware. 024_cool.gif.7a88a3168ebd868f5549631161e2b369.gif

 

 

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Guest pelorus32
Who exactly does the inspection and gives the CofA for factory built RAAus aircraft? the RAAus or CASA? just curious

Good Question. RAAus a/c that are not LSA do not have a CofA. They need to be of an approved type and registered with RAAus.

 

LSA a/c if factory built are entitled to a S-LSA CofA which is issued by a CASA delegate.

 

Regards

 

Mike

 

 

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You might find that the Tecnam and Jabiru follow standard industry practice.

 

DO NOT use self-locking nuts on parts subject to rotation .. They may be used with anti-friction bearings and control pulleys, provided the inner race of the bearing is secured to the supporting structure by the nut and bolt.

You should find that the nut is not used on a part subject to rotation. i.e. no movement between the nut and the part it is snug against.My copy of the AN spec (in my 40 year old copy of the Aircraft Mechanic's Pocket Manual) states "end of bolts or screws must extend at least the full round or chamfer thru the net" from which came the standard practice of at least one and not more than three threads extending thru the nut.

 

I've seen more failures and lucky people associated with castle nuts and missing split pins in control systems than with nylocs.

 

All of the certified factory-built aeroplanes that I fly have nylocs throughout the flight control system plus a few castle nuts where required.

 

 

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Major, just to update the AN prefix. The Army standard has been replaced by the Air Force standard. Still AN tho'.

 

Just some general information as to how 'standards' came about.

 

Uniform standards are by necessity an evolutionary process. In the beginning each military service came to it's own standards the Army Air Corps had AC standards the Navy had NAF, Naval Aircraft Factory, as time went on they combined into the AN standards. With the introduction of turbines and high speed these in turn became the Air Force/Navy and NAS, National Aerospace Standards, futher down the track these were consolidated into MS, Military Standards designation. so today we have 3 common standards AN MS and NAS.

 

I rely on two reference books either one i would recommend, Standard Aircraft Handbook for mechanics and technicians by Larry Reithmaier, now in it's six edition, and the Aviation Mechanic Handbook by Dale Crane, now in it's fifth edition.

 

Both of these reference manuals are referred to as 'bibles' by aircraft repairmen.

 

If you build or maintain your aircraft you should have one or both for reference.

 

Cheers

 

ozzie

 

 

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"I am suprised that our Jab 230 has just a nyloc on the 1/8, single bolt,"

 

Could that be an AN bolt? I have never seen less than AN3 which is 3/16"

 

Not being a Jab owner I cannot be sure but I doubt that a 1/8" bolt would be used for anything structural.

 

 

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what are the markings on the bolt head? the smallest AN bolt listed is AN3 (3/8 diameter.) Not to say that there are smaller sizes. i do not have a full cataloge

 

 

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