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Torque by hand....

bret

bret

Well Known Member
I just received my 1/4 drive tq wrench today for tq ing all the hardware on the project. I was surprised at the incredibly low values while playing with it. I under stand a lot of the bolts are for shere and not tension. This is very hard for me, as a mechanic for 30+ years and knowing what a grade 3, 5, 8, or higher bolt should have, (excluding component assembly requiring tq values, engine assembly ect) am I alone on this? Disclaimer.... All my fasteners on my build will be tensioned as per specifications.
 
Trust your mechanical feel when tightening. I knew an IA that never owned a torque wrench. The only time I use one is on internal engine parts.
 
If you do torque-to-specs on the small hardware, don't fail to remember to measure and add the torque drag of the nylocs. On such small torques it makes a real difference.

I predict that you'll get tired of measuring every bolt tq, and will revert to "feel". I tend to over-torque if I'm not careful.

Pete

PS: "Fail to Remember" = "Forget" :p
 
I too often torque by feel, but really, really encourage the use of an inch-lb torque wrench on control system fasteners. The reason is simple. New builders tend to over-tighten AN3's. I worry about about a stretched AN3, the one with a crack at the root thread which can't be seen without dis-assembly. Think about the AN3 in your elevator horns next time you fly.
 
rocketbob said:
Trust your mechanical feel when tightening. I knew an IA that never owned a torque wrench. The only time I use one is on internal engine parts.
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I agree with this for the most part, but a good way to keep your "feel" calibrated is to use that TW for the accessible hardware and then check it with your favorite 1/4" ratchet and/or 3/8 wrench.

I try to use a TW on all engine hardware as well, aluminum threads and heli-coils don't like incorrect torques (and I hate replacing them even more :eek:).
 
Well, as a first time builder I always use a torque wrench. The torque wrench has also allowed me to develop some`feel' for the different sized fasteners, but what's the point of having the right tool if you don't use it?
 
As an old time mechanic, I too was surprised by how little torque is specified on some of the parts, much less than I would have put on them by the wild guess method.
 
I agree, it's a big change from working on the Harley... "Tighten until the head snaps off, then back off 1/8 turn." Since this is the first airplane I've built, I'm using the torque wrench.
 
Most of our RV's bolts are in shear, but most of the nuts, An365 as an example, can be used in shear or tension and are actually called out in the torque tables for tension applications. So your range of acceptable torque values might be wider, and higher, than you think.
Correct me if I am misunderstanding or oversimplifying this.
 
I was also surprised at the relative low tension of smaller fasteners when I went through initial technical training in the Air Force. Since that "calibration" many years ago, I now reserve the torque wrench only for critical fasteners.

In fact, we used to challenge each other to see how close we could get with the "calibrated elbow" and most of us could get within a few percent.
 
A fastener only has so much strength. If you think about it, it's really only got so much strain energy that it can withstand before it fails. If you load too much on to it by overtorquing, then the amount of load it can carry is reduced.

Torque does two significant things to a bolt. It clamps the parts together, helping to carry shear, and it applies a tension load that the bolt can carry before it gaps. That helps the fatigue life of the bolt.

Bottom line -- torque using a torque wrench, to the specification.

Dave
 
Torque

Just for fun, put a AN3 in your vice and tighten to failure or to the point it begins to yield. It takes a lot. I like the little snap-on 1/4 drive stubby rachets for these little bolts. Using the correct wrench, it seems unlikely that the bolts would be over torqued to any significant degree.

In the steel business we calibrate our bolt installation procedure on a daily basis. Torque is an indirect method of measuring tension. It doesn't take long to figure out that torque is variable based upon thread cut, lubrication, manufacturing tolerance and many other factors. I have always suspected that the torque/tension relationship for small fasteners varies more than we often realize.

Here is a device which measures tension in large fasteners. While the info on the site is not directly applicable to our fasteners, it may be interesting to some. I have always been surprised that someone doesn't offer tension control bolts or washers for other industries.

http://www.skidmore-wilhelm.com

I do agree that all critical fasteners should be installed with a TW as this is the best tool we have in most cases.
 
Torque Wrenches

Now that we all agree that we should use a torque wrench probably more than we do - any good suggestions for good torque wrenches? Some of the new digital units look amazing, but probably a bit of overkill for our application.
 
Torque wrenches

I've had my two torque wrenches, 1/4 and 1/2 inch click type for about 40 years. I have always stored them at their lowest torque settings but they have not been calibrated since I've had them. Should they be ok or should they be calibrated periodically. I know in the Air Force our torque wrenches were calibrated quite often.
 
I wonder if any one has lost a control surface in flight, due to improper Tq, that would be my biggest concern with these tiny fasteners.
 
rv8ch said:
Now that we all agree that we should use a torque wrench probably more than we do - any good suggestions for good torque wrenches? Some of the new digital units look amazing, but probably a bit of overkill for our application.
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I use the click type of inch pound torque wrench. I wish I would have bought a dial type instead. It gives you some indication of how close you are to you torque goal.
 
I bought a Parktool TW-1 inch-pound wrench. 1/4" drive with a 3/8" adapter. It's apparently used mostly for bicycle work, but I think the in/lbs are the same on an airplane. :) Anyway, it was FAR FAR less expensive than most of the alternatives, dial or click. I paid under $40 shipped for it, brand new. There's a bigger TW-2 as well.
 
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Torque vs fastener size

Years ago I read a paper on bolted connections. It indicated that when torquing by "feel", small fasteners tend to be over torqued and large fasteners tend to be under torqued. The rationale given is that humans tend to scale things up linearly (i.e. a 1/2 inch bolt should be torqued twice as much as a 1/4 inch bolt), but the bolts themselves follow an exponential curve.

I always use a torque wrench.

FYI, an over torqued bolt will have less shear capability than a correctly torqued bolt.
 
I've been working with 3/16", 1/4", and 5/16" bolts for about 25 years now, and the torque values on these seem ridiculously low. A couple of times I've been able to get them almost to "book value" by fingers alone without a wrench. That just ain't right. I've personally done a couple "torque to failure" tests on AN hardware myself - I recommend it, it's educational.

3/8" bolts and larger, the torque values approach something I consider reasonable. I will admit I tend to run close to book values on "critical" fasteners.
 
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Put me down as someone who used a torque wrench on every bolt.

I also used torque seal after each bolt was torqued. How else are you going to know that each bolt is tight?
 
My first Torquing (sp????) experience was on the 4 bolts on the rear HS spar- I borrowed the local A&P's torque wrench and tightened it to spec- drag torque and all! I then asked the guy to check my work- and he said it was too loose and cranked it down another turn or so!!!!!!!!:eek:

The guy was pretty experienced in RVs and said if I needed to replace those bolts down the road it would make for an unsightly repair. All being said I will be torquing all my nuts to spec by myself from here on out!
 
Slightly off topic, but...

I found a copy of Carroll Smith's "Nuts, Bolts, Fasteners and Plumbing Handbook" a very useful addition to my technical bookshelf. Though the author is a race car builder, he covers the topic comprehensively, and he is certainly aircraft friendly. It helped my non engineer mind get a better grasp of what is really going on at a bolted connection. Lots of info on rivets and aircraft type plumbing
 
daveyator said:
I found a copy of Carroll Smith's "Nuts, Bolts, Fasteners and Plumbing Handbook" a very useful addition to my technical bookshelf. Though the author is a race car builder, he covers the topic comprehensively, and he is certainly aircraft friendly. It helped my non engineer mind get a better grasp of what is really going on at a bolted connection. Lots of info on rivets and aircraft type plumbing
Click to expand...

RIP Carroll Smith.

I once knew Carroll's son through a mutual friend (granddaughter of Earl Fouts, founder of Earl's Peformance Plumbing). I have all of his books. Great reading material, even for an engineer.

Skylor
 
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bret said:
I wonder if any one has lost a control surface in flight, due to improper Tq, that would be my biggest concern with these tiny fasteners.
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Bret - I have not heard of any specific instances. It is extremely unlikely that an under torqued nylok would back itself all the way off of the bolt. I guess one could over torque it and stretch the bolt weakening it and it could lead to a fatigue failure but again, never heard of that happening in the RV fleet.
A rule of thumb i use for the control surface AN3's is the nut should be tight enough that the bolt does not turn. If this introduces friction you need to find the cause not just loosen the nut. I know I have it torqued where I want it when the bolt does not turn with movement of the surface but I can still turn it with a wrench.
I guess this falls in the category of torque by hand.
 
Torque or not what does it matter

On some things it really matters - Here is a little story:

I once bought a sport biplane from an elderly builder. It was well built and passed a detailed pre-buy without question, however it was never flown. The wings were removed and the airplane was trucked to me, the wings were reassembled and rigged. A thorough condition inspection was performed, paper work put in order and we began flying off the time. After 6 hours flight time I took off one afternoon and after climb out I went to level out and nothing happened. The stick would not operate the elevator. The only vertical control I had was power as there was no trim system in this design. The end result was a destroyed airplane and a damaged pilot. In examining the wreckage it was apparent that the An3 bolt connecting the elevator horn to the heim joint broke at the last thread and fell out. It was obviously over torqued and fractured. Perhaps the builder thought "this needs to be tight so it doesn't come loose" I will never know. What I do know is I do not reuse hardware in critical locations, I torque fasteners on control surfaces and other important connections whenever possible, and I don't fly airplanes without trim systems. So "Torque or not what does it matter" well it could matter greatly. Your choice - calibrated hand or calibrated wrench?
 
JonJay said:
A rule of thumb i use for the control surface AN3's is the nut should be tight enough that the bolt does not turn. If this introduces friction you need to find the cause not just loosen the nut. I know I have it torqued where I want it when the bolt does not turn with movement of the surface but I can still turn it with a wrench.
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To add a bit to this, the bolts that capture rod end beariings must be tight in order to lock the inner bearing race to the mount.

The way you suggest above means the bearing may still be rotating around the bolt shaft.

You should not be able to rotate the bolt (easily) if it is tightened down properly. If you can rotate the bolt easily then it is not applying the proper clamping force to the bearing.
 
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airguy said:
I will admit I tend to run close to book values on "critical" fasteners.
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I wonder which fasteners are "non critical". I suppose the critical fasteners are those that if they come loose or break then you are in trouble. So far in by build, I haven't come to any nuts where I said to myself, "this doesn't seem critical; I don't care if it comes loose or breaks during flight".

On a similar subject, I wonder about screws into platenuts. I imagine there is an optimal tightness, but I'm not aware of there being a specification to tell me what it is.
 
A "critical" fastener is one that if it were to fail would jeopardize the safe operation of the aircraft, ie: flight controls, engine mounts/controls, fuel systems.
 
Walt said:
To add a bit to this, the bolts that capture rod end beariings must be tight in order to lock the inner bearing race to the mount.

The way you suggest above means the bearing may still be rotating around the bolt shaft.

You should not be able to rotate the bolt (easily) if it is tightened down properly. If you can rotate the bolt easily then it is not applying the proper clamping force to the bearing.
Click to expand...

Understood Walt.
 
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