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  #11  
Old 06-26-2019, 09:35 AM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by Eddie P View Post
Hi guys, I’m looking for opinions and techniques.

One of my torque paint stripes on a Jam Nut was partially missing. Sure enough, the jam but on the outer left elevator backed off a few degrees after the last flight. I tightened it up before flight. And admittedly, it was an awkward fit for the wrench I was using.
The torque strip is primarily a QA marking to indicate that it was torqued to final torque during initial installation, but it does nothing to keep it backing off. It is also NOT for determining if the nut or bolt is loose (although it might do that function). The torque paint can wear off or chip off at some point. It is not that durable. As mentioned Lok-tite is the way to go. It comes in different flavors. One is temporary (where nut or bolt comes out for maintenance) and one is permanent (self explanatory and you can still take the fastener out but just more difficult). You only need a drop on threads of Lok-Tite.

Quote:
I would love to hear and see how you guys “keep your nuts in check” without buggering up the nuts or airframe with wrenches. Also, what torque and how do you measure it?
Nuts and bolts most likely to come loose are under the cowl... where there is vibration.

At condition inspection (every year, everytime your cowl comes off) you should check the securiity of all nuts, especially in engine bay and flight controls. Some times you can do it by inspection, depending on they type of nut (safety wired or Castellated). Jam nut locking is hit or miss. If suspect untorque and retorque. I much prefer the nut be drilled for safety wired if it's critical. If a fastener is suspect take the fastener out, inspect the structure, reinstall. If hardware is damaged replace it.Fasteners don't cost much. Some nuts with nylon inserts can be reused but some will replace them everytime. Spruce Aircraft, Wicks, Van's Aircraft can be sources for hardware. If the finish is scratched replace it. That is for corrosion prevention. Steel bolts and aluminum don't go together. That is why steel bolts have a finish, platin, typically clad or passivated.

To keep hardware from being buggered up use PROPER TOOLS... Box end wrenches, crow foot, high quality wrenches that fit the bolts with out slop.... Many consumer grade tools are for use on low quality hardware not high tolerance aircraft hardware....

Research the different nuts and locking devices (google). EAA Sport Pilot, Kit Plane magazines and Google are good places to look. Each type has it's advantage and best application. You will see MS or AN specs for hardware which stands for Mil Spec and the older Army-Navy Spec..... Spruce and Wicks catalogs are great for learning hardware.

TYPES OF NUTS:
Nuts with inserts (nylon).
Nuts with all metal clamping for high temperature applications
Castellated nuts used with drilled bolt and cotter pin.
Nut drilled for safety wires.
Jam Nuts (typically two back to back plain nuts)
Plain nuts used with LOCK washers (split, star, serrated)

What nut or washer to use? Good starting point is VAN's building manual and drawings. If you did not get the planes order an electronic one. They will specify the proper nut and washer as applicable.

#1 thing is to have PROPER TORQUE to start with. Torque and stretching the bolt creates clamping and friction resists the fastener getting loose (as it is stretched). This is typical on engine bolts. HOWEVER don't over torque fasteners. There are standard torques for different sizes, know them. Get yourself a good torque wrench. I recommend more than one torque wrench. A smaller lower torque range dial gauge, and a higher range torque wrench for larger bolts and nuts. The larger ones come in CLICK type or beam type. You can develope a "good and tight" feel, but use a torque wrench when possible. I maintain a BMW motorcycle and EVERY screw, nut bolt has a torque. It is WAY too easy to over torque.
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Last edited by gmcjetpilot : 07-14-2019 at 03:43 AM.
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  #12  
Old 06-30-2019, 02:52 AM
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Eddie P Eddie P is offline
 
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Thank you GMCJet and every one else here. All great information. It takes effort to share and I appreciate it. I'm taking it all in!

(PS, the torque paint strip in my case was not understood to be any sort of mechanical advantage to a jam nut not backing off. Rather, I understand this a visual indicator to me that on a pre-flight, where a torque paint strip is broken or mis-alinged, said jam nut should be investigated for proper fastening as it is now suspect).
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Last edited by Eddie P : 07-01-2019 at 07:33 PM.
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  #13  
Old 07-13-2019, 08:12 AM
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Eddie P Eddie P is offline
 
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So... as we know there are many jam nuts in the RV series of aircraft. When I was in the search process for my RV-8, I came to realize a vast majority of the aircraft I looked at (and I did look at a few over the course of a year or so) - many did not have the flap actuator safety wiring SB accomplished. (Safety wire modification).

In researching how to accomplish this on a flying aircraft I came across all the existing threads that describe a variety of ways to meet the SB's intent. And apparently there is a drawing error in the SB making the subject ripe for interpretation errors and other mods to the intended modification plentiful. I ran across this article that may be of interest to some. It shows a newer style of jam nut backup assembly used in industry and some history as to why it came about.

http://aerospaceproducts.com/disconnect.html
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  #14  
Old 07-13-2019, 08:44 AM
FinnFlyer FinnFlyer is offline
 
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Default Flap motor jackscrew

I think what's unique with the flap motor jackscrew (actuator rod) is that the motor may have a tendency to try to turn the rod. All other rod ends in the RVs, that I know of, do not have rods with a turning force. Thus properly torqued jam nuts should be sufficient.

Alternatively, even with maximum travel, there is no way either end can be completely unscrewed and with no or just one jam nut the integrity of the connection is assured. I made my flap actuator tubes so long that they can only be rotated a turn or two with no jam nuts (minimizing hole size in the fuselage).

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