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  #61  
Old 01-04-2013, 03:37 PM
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Quote:
Originally Posted by jc11378 View Post
I have made a decision on final assembly all moving parts in the flight control system will have castle nuts and cotter pins. It is moves or changes direction or can cause a major failure then it will have a mechanical locking device on the nut no matter what.
Not a bad idea but there are some places where that will be very difficult/darn near impossible on the RV.
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  #62  
Old 01-04-2013, 03:49 PM
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Geico266 Geico266 is offline
 
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Quote:
Originally Posted by Walt View Post
Not a bad idea but there are some places where that will be very difficult/darn near impossible on the RV.
I find it hard to believe they can come loose. The new nyloc nut is tourqued. The bearing is doing the turning not the bolt. What am I not understanding?
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  #63  
Old 01-04-2013, 03:55 PM
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dhammer dhammer is offline
 
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Default Never enough

FWIW Personally I like cotter keys on flight controls. As a point of reference Dassault goes all the way. On Falcon Jets all flight control bolts have lock nuts that also require a cotter pin. On top of that the bolts are a pip pin device that requires pushing the release on the bolt head to rectract the little ball keeping you from extracting the bolt. The cotter pin keeps the nut in place and also locks the pip pin. Even with the nut off you can't take them out until the pip pin is depressed. Try buying one of them bolts. $$$

It's wonderfull to say that if the nut is tight it won't loosen, but I've seen rod ends that froze up and promply loosened the nut. Never seen one break a cotter key though.

Cheers
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  #64  
Old 01-04-2013, 04:43 PM
apirkle apirkle is offline
 
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Quote:
Originally Posted by dhammer View Post
I've seen rod ends that froze up and promply loosened the nut.
This is what worries me about using a lock nut on the inner race of a bearing/ball joint.

Thought this was an interesting read: http://aerospaceproducts.com/disconnect.html

Quote:
Originally Posted by Military Specification Mil-F-18372, Flight Control Systems: Design, Installation and Test of Aircraft
(a) Each removable bolt, screw, nut, pin or other removable fastener must incorporate two separate locking devices if--
(1) Its loss could preclude continued flight and landing within the design limitations of the airplane using normal pilot skill and strength; or
(2) Its loss could result in reduction in pitch, yaw or roll capability or response below that required by Subpart B of this chapter.
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  #65  
Old 01-04-2013, 05:39 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by jc11378 View Post
I have made a decision on final assembly all moving parts in the flight control system will have castle nuts and cotter pins. It is moves or changes direction or can cause a major failure then it will have a mechanical locking device on the nut no matter what.
I am not saying that is a bad idea, just pointing out that you shouldn't assume it is automatically better.

There are instances of accidents caused by cotter pin safetied fasteners that came apart. Depending on the technique and skill level applied by the installer, a cotter pin can be left vulnerable an many different ways. It is not unheard of for pins to become bent open because of catching on tall grass, rags while washing the airplane, etc.

The fact is, that pretty much every aircraft that flys, has many (sometimes hundreds) of critical system connections held together with self locking nuts.
If they are appropriately chosen for the location used (I.E., not using nylocks in high temp locations, etc.), and are installed properly, in most instances they are as reliable as a cotter pin safetied fastener would be. There are specific instances where a cotter pinned fastener is the only appropriate choice and then should be used.

I think this thread has taken a wrong turn and people are loosing site of the fact that you can just as easily forget to install a cotter pin, as you can forget to install a self locking nut (or install it properly).

I do not know if that is even for a fact the cause of this accident, but it is always a possibility that we as airplane builders need to be doing all we can to mitigate.

Since there is often more than one of us doing final assembly work in our shop, keeping track of what has and has not been final torqued can be even tougher than for someone working alone. For that reason we have a policy that parallels what has been mentioned by others already.
When we are at a point that final assembly has begun, we torque seal each fastener immediately after we torque it.

When the airplane is finished and ready for flight (other than all inspection panels open), we physically follow the complete control circuit of all critical systems and inspect every fastener along the way....
Stick grip attachment to control stick
Control stick attachment to rod end on push rod
Rod end attachment to pushrod end.
pushrod end attachment to push rod tube

and on and on.

If this thought process is used in the context of "the airplane is finished... I am no longer an airplane builder... I am now an airplane inspector, and you inspect without distraction (no one hanging around asking questions, etc), you will probably find everything that needs to be found. Then give a flashlight and mirror to someone else and ask them to do it all over again (again, without any distraction).

BTW, inspecting means just that, if you find something not right, make a note for resolving it later (when you switch back to airplane builder mode) and continue. If you jump back and forth between finding and fixing, you will always skip over things (this is the standard procedure used by aircraft mechanics... Inspect, then resolve any problems that were found).

My 3 cents...
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  #66  
Old 01-04-2013, 05:39 PM
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Walt Walt is online now
 
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Quote:
Originally Posted by jc11378 View Post
I have made a decision on final assembly all moving parts in the flight control system will have castle nuts and cotter pins. It is moves or changes direction or can cause a major failure then it will have a mechanical locking device on the nut no matter what.
Quote:
Originally Posted by Walt View Post
Not a bad idea but there are some places where that will be very difficult/darn near impossible on the RV.
Quote:
Originally Posted by Geico266 View Post
I find it hard to believe they can come loose. The new nyloc nut is tourqued. The bearing is doing the turning not the bolt. What am I not understanding?
I was not trying to imply that that this method (castle nuts & cotter keys) needs to be standard practice, only that it can't hurt if it makes you feel better. Personally I am perfectly comfortable with lock nuts used with rod ends with bearings. However I do use locktite on critical fasteners for a bit of added insurance.
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Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
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Authorized Garmin G3X Dealer/Installer
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  #67  
Old 01-04-2013, 07:07 PM
N427EF N427EF is offline
 
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Default 7960 flying RVs

The method of securing a nut and bolt to connect a push rod to the control column has been successfully employed in 7960 RV's.
Since everyone is speculating on the cause of this failure I put my money on either, no nut was ever installed or nut was finger tight only.
It boggles my mind how so many people freak out about this and think we need re-engineering of the control system.
Just like the doors on the 10, if you forget to close them, even the "third mandatory service bulletin latch" won't do any good.
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Last edited by N427EF : 01-04-2013 at 07:18 PM.
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  #68  
Old 01-04-2013, 07:11 PM
Rick S. Rick S. is offline
 
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To apply a simple principle to all of this discussion. A fastener is only as good as its installation. Avoid blaming a nut for failure if the nut never had the chance.
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  #69  
Old 01-04-2013, 09:03 PM
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Quote:
Originally Posted by Rick S. View Post
To apply a simple principle to all of this discussion. A fastener is only as good as its installation. Avoid blaming a nut for failure if the nut never had the chance.
Excellent!

On a homebuilt experimental aircraft, a builder does not have to follow the plans.

IMHO, the plans show a technique that works and was designed in by someone that has more experience than most builders. IF a builder does not follow the plans and makes changes, be prepared to SHOW the FAA / DAR what supporting document is used for the change.

Our EXPERIMENTAL aircraft are not required to meet MIL specs or part 23 requirements that were not designed in by the designer.

Is the "improvement" that the builder does really an improvement or is it just a more expensive way that takes more time to do?
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  #70  
Old 01-05-2013, 03:03 AM
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rleffler rleffler is offline
 
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Quote:
Originally Posted by Rick S. View Post
To apply a simple principle to all of this discussion. A fastener is only as good as its installation. Avoid blaming a nut for failure if the nut never had the chance.
Rick,

That's a quote worthy of putting on everyone's wall during the build process!

Bob
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