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Old 10-19-2017, 03:40 PM
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Default Sanity Check -- AN6 Torque

For clarification, AN6's get torqued 160-190 inch pounds, right? 180 inch pounds just didn't feel that tight .. for an engine mount .. if someone could verify, just a sanity check
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Old 10-19-2017, 03:47 PM
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https://www.vansaircraft.com/pdf/rev...V-12_05-10.pdf
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Old 10-19-2017, 03:50 PM
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Yep, that's where I got my numbers .. I just expected to have to really muscle these bolts .. guess I'm underestimating how strong these parts are.

Thanks!
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Old 10-19-2017, 04:04 PM
BobTurner BobTurner is offline
 
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What you and many people are doing is over-estimating the amount of pre-load a bolt needs, in order to have that maximum strength available when really needed.
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Old 10-19-2017, 04:07 PM
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my seat of the pants observation is that people tend to over torque small bolts and under torque large bolts when relying on feel rather than a torque wrench

erich
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Old 10-19-2017, 08:47 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by bkervaski View Post
For clarification, AN6's get torqued 160-190 inch pounds, right? 180 inch pounds just didn't feel that tight .. for an engine mount .. if someone could verify, just a sanity check
Depending on the actual friction coefficient present, that torque will result in about 3,000 pounds of clamping force on that size/pitch bolt, which is about 25% of their tensile strength. Lots of margin in bolts holding aircraft together is a good thing! Don't squander the margin by honking down bolts by "feel".

A separate but related fun-fact: Critical bolts subjected to cyclic loads (think about the studs holding the cylinders on) are often specified to be torqued to a value which maximizes their fatigue life. Torqued below or above the spec and their fatigue life will likely be lower.
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Old 10-20-2017, 07:39 AM
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It's the leftover military mentality for me .. give me a hammer and a direction and by God it will get done .. so if the bolt still turns then keep on turnin'

Of course, I'm following the torque specs to the letter (just so it's clear to readers). I just expected to have to enlist the large torque wrench and some muscle and it's simply not the case.

Good information, thanks all!
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Old 03-23-2018, 02:06 AM
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Default AN6, AN7

Another sanity check, so for mounting the engine to the engine mount the manual states:

"BOLTS ARE TIGHTENED TO BOTTOM-OUT RUBBER MOUNTS ON SPACERS, THEN TORQUED TO STANDARD AN7 VALUES."

And in section 5 I find the value for AN7 to be 450-500 inch pounds, that is a lot I have to ask before using that force., Correct?
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Old 03-23-2018, 05:42 AM
Tom023 Tom023 is offline
 
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Be careful of units. 400-500 in/lbs is about 40 ft/lbs. The average lug nut on a car is tightened to 80 ft/lbs and SUVs/pick up trucks somewhere in the 140 ft/lbs range. So, that 400-500 inch/lbs can be over torqued if you're not careful.
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Old 03-23-2018, 06:28 AM
BillL BillL is offline
 
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Default What is torque . . . really ??

Quote:
Originally Posted by bkervaski View Post
It's the leftover military mentality for me .. give me a hammer and a direction and by God it will get done .. so if the bolt still turns then keep on turnin'

Of course, I'm following the torque specs to the letter (just so it's clear to readers). I just expected to have to enlist the large torque wrench and some muscle and it's simply not the case.

Good information, thanks all!
Like Alex said. There is a sleeve in the mounts that can be crushed, so too tight is not good. Did you get an instruction with the mounts?

And - 99% of the aircraft applications for fasteners are loaded for shear, not tension, that is why careful attention is paid to the hole sizes and why threads are not allowed in the joints. Other terrestrial things we are familiar with are primarily tension applications. That is where the bolt tension holds something and takes additional load, or the bolt tension clamps parts together and the tension/force prevents the parts from sliding. Engine parts are one example, all heavy duty machinery, off highway machines all are built to those standards. This allows hole sizes to be larger for assembly. Sliding causes fretting and won't last very long. Another difference is dry vs oiled threads for torquing. Dry threads result in a wide variation in actual tension of the bolt. Like plus/minus 20%. All (nearly?) the aviation fasteners are dry torqued. So NEVER build an engine without oiling the threads before torque.

[ok so the engine mount frame is tension loaded to the firewall and appears to be an exception, but it isn't.]
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Last edited by BillL : 03-23-2018 at 02:24 PM.
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