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Speaking of Jam Nuts...

Eddie P

Well Known Member
Hi guys, I’m looking for opinions and techniques.

I have been quite attentive to my “nuts” on preflight thanks to the great information here and the video posted to Youtube featuring Vic Syracuse speaking on the more notorious leisure attitudes around RV preventative maintenance, care and feeding. Jam Nuts were an emphasis area among others.

So lo and behold, after many recent flights thinking, “when am I gonna find a loose nut” I saw something different. 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.

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?

I did not build my 8 as much as I wish I could have. So my question comes from a non-builder reference. On the pre buy inspection there were a few jam nuts that had started backing off in the tail so they were re torqued and striped for easy identification of possible backing off in the future. So this jam nut has about 20 hours of service before moving again. Admittedly, I have done several stalls and incipient spins to get used to the stall and departure handling of this particular airplane so the tail has been worked a few times in addition to treating the plane to about 50 landings since the nuts were torqued and striped. Interesting, none the less.
 
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Hey Eddie,

On all my jam nuts, I applied LocTite, torqued them to final spec, then applied Torque Seal, and nothing has budged in 3.5 years. It is difficult to get a wrench securely on these buggers (especially through the openings in the elevators) so I modified an offset box wrench, cutting off at least the outer third of the box...think flare wrench for brake line fittings. Works like a charm.
 
Are you speaking of actual jam nuts, as used to secure a rod end bearing ('heim joint') on a pushrod, or a nyloc nut, used on the bolts inserted through brackets and the ball of a rod end bearing?
 
Hey Eddie,

On all my jam nuts, I applied LocTite, torqued them to final spec, then applied Torque Seal, and nothing has budged in 3.5 years. It is difficult to get a wrench securely on these buggers (especially through the openings in the elevators) so I modified an offset box wrench, cutting off at least the outer third of the box...think flare wrench for brake line fittings. Works like a charm.

same for me.
 
Are you speaking of actual jam nuts, as used to secure a rod end bearing ('heim joint') on a pushrod, or a nyloc nut, used on the bolts inserted through brackets and the ball of a rod end bearing?

These particular jam nuts (of many types thought the plane) are the nuts that screw down onto the elevator spar (and attach to the rod end thread. I think these jam nuts pre load the rod end thread so it has support on both ends of the spar). The rod end threaded bolt that the nut is mounted to creates the elevator side of the elevator to stabilizer flight control hinge mount. These are also used on the rudder.
 
Thank you for that link and description. Very doable. How do you know / verify the proper spec for torque? I'm assuming in this case it's a "TAR" torque device (That's About Right)?
 
Thank you for that link and description. Very doable. How do you know / verify the proper spec for torque? I'm assuming in this case it's a "TAR" torque device (That's About Right)?

Torque value on a fastener can be measured in many different ways....

A wrench such as the one in the link, coupled with a spring scale and some simple math can give you an accurate torque reading.
 
Great idea, thanks. I'll have to see if I can google a few images of that type of torque contraption.
 
Spring scale = fish scale.

Hook fish scale to end of wrench at 90 degree angle.
Torgue = distance from center of nut to fish scale attach point x fish scale reading.

Or Torgue required / distance = what you want to the fish scale to read.

Finn
 
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.

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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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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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
 
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).

Finn
 
Torque strip (snip) is also NOT for determining if the nut or bolt is loose ....

According to the FAA (https://publicsafetyaviation.org/images/Press_Release_A/FAA_SAIB_BELL_11217.pdf) visual detection of a loosening fastener is indeed a purpose of using torque seal: "Mark installed hardware with torque seal/lacquer after it has passed torque check. The marking allows visual detection of hardware that may have loosened before it falls off."

According to Dykem (a manufacturer of torque seal) "DYKEM® Cross Check™ provides a convenient visual method for identification of vibratory loosening or tampering in nuts, bolts, fasteners, and assemblies."
 
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How do you know / verify the proper spec for torque? I'm assuming in this case it's a "TAR" torque device (That's About Right)?

The "TAR" method typically results in overtorquing of small bolts and undertorquing of large ones--most of us are surprisingly bad at feeling absolute values of force.

If instead you attach a torque adapter at ninety degrees to your torque wrench the indicated torque will be the same as the torque applied to the nut.

If the adapter is in line with the torque wrench then recalculate for the extra lever arm.
 
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