Do All Bolts Get Torqued?

I was wondering if ALL bolts should be torque even when not called out in the manual? Specifically I am finishing the rudder and putting the two bolts in the skin to hold the rudder counter-weight. I believe these are AN539-832A bolts (or something like that). The manual doesnt say to torque these and even if it did, the 5V section on torque doesnt mention AN539 (unless you just refer to AN5 as the same. Any pointers?

Yes, all bolts should be installed with a torque wrench. The problem for most new builders is that the bolts are installed over torqued if a torque wrench isn't used. After a while, you'll get a pretty good idea on what the right amount of torque should be and know what it feels like.

Also, another good practice is to use torque seal inspection lacquer once you have torqued the bolts to ensure that they haven't moved after installation. The lacquer is also a good memory jogger if you termporarily install bolts. i.e. no lacquer means you have to re-torque the bolts for finally installation.

bob

Any idea how to find the proper torque for this bolt then? Is the AN539 the same as the AN5 they refer to in the build book? It says 100-120Lb/Inch.

Not too sure of plans sets for anything but a 10, but my torque spec table was in the first few sections of the plans, the ones that come in 8 1/2" x 11" binder.

Section 5 as I recall.

Not sure about the 10 hardware but I'm positive the balance weight is not held on with a AN5 (5/16") bolt

The 7/8 aircraft use a #10 CS screw if I recall correctly.

If you provide the exact hardware call out then I can help.

Thanks. The exact bolt is listed as AN509-8R14.

That's a #8 screw, I always recommend attaching the weight with an adhesive like proseal then tighten the screw "Gudintite" with a screwdriver. Screws don't have a torque spec. per se, just tighten them with a screwdriver.

Official torque specs start with the AN3 (#10) bolt and go up from there.

rleffler said:

Yes, all bolts should be installed with a torque wrench...

Click to expand...

I agree in theory, but not in practice.

Bob K.

Good maintenance practices require all bolts being torqued. If construction or maintenence documents don't call out a specific torque, standard torque values should be used. FAA Circular, AC43.13-1B provides standard torque values, methods and practices with accompanying hardware identification resources to aid in identifying the correct torque tables to use (ie: course thread vs. fine thread fasteners).

Now sayng all that, I realize human nature is difficult to fight. I have worked in aircraft maintenence, maintenance management and development for 34 years and have come to a set of personal rules I use on my airplane.

1. Over-torqued is just as dangerous as under-torqued.

2. If the failure of a fastener can potentially, or precipitate related failures that have the potential to, hurt/kill me, endanger others on the ground, or damage/destroy my airplane, it gets torqued. Fasteners not meeting this definition receive German Torque (gutentite). This process makes you think about each and every fastener in a unique way. It is sort of like doing a quick, mini FMECA on everything (Failure mode, effects, and Criticality Analysis).

3. All safety-of-flight hardware recieve torque stripes: flight controls, landing gear, control and flying surface mounts, engine mounts etc.

4. Never use a dog bone or crows foot in anything but the 90 degree position. If unable, suck it up and do the math (not a frequent need).

5. Use torque wrenches slowly and properly. Not doing so WILL change the applied torque.

Jekyll

A few should not be torqued such as rudder pedal pivot points, rear spar attach, or anything going into the nylon blocks (the block will deform before you get to the intended torque)--ask me how I know. There are probably some similar othe ones not immediately coming to mind.

Steve Johnson
RV-9A --flying
Abilene, Tx

Yes, but not always with a torque wrench. Torque a few bolts and compare with your hand. You'll see that its pretty easy to replicate the appropriate torque. IMO where a torque wrench is really important is when you have multiple bolts sharing a load. Such as the empennage attachments. Still, with so few bolts on an RV, you should torque most of them with a quality wrench. Of course, since most people don't have access to a calibrated low torque value wrench, it's possible that some do more harm than good using a torque wrench. There has been lots of threads dealing with this. You'll find lots of great insight by viewing them.

Screws get torqued, too

Here is a nice online reference (thanks, EAA Chapter 818). Note that it is for 'bolts, studs, or screws'. Aircraft Spruce's catalog is often handy for figuring out tensile strength of fasteners but I also like GAHco's online rereneces. For instance, their pdf link on the MS24694 page gives tensile information, size specs, and a chart that correlates the old AN509 numbers to the new MS numbers. So you could see that an AN509-832R14 (often the 32 in 832 is left off; what else would it be?) with a AN365 nut should be torqued 12-15 in. lb.

'German torque' is often too tight, especially for the smaller AN bolts, until you've 'calibrated' your hand by using a torque wrench for awhile. I did the AN3 bolts for the rib/spar connections in one of my -6A wings before acquiring a torque wrench. Fortunately I went back and checked; they were all severely overtorqued (up to 100 in/lb!) and had to be replaced.

It is true that pivot bolts don't get torqued (or, sometimes, torqued to shank) but they have castellated nuts and cotter pins to secure them. However, don't take that to mean that torquing castellated nuts is not important. On your engine mount, for example, the nuts should be torqued and shim washers used to ensure that a cotter pin will secure the nut while it is torqued within the acceptable range.

Some other torque issues: The torque values I found for 300 series stainless don't mention tension or shear torques and are listed as higher than that listed for structural aircraft hardware (despite, from what I can tell, having less tensile strength), so I try to stick to the same torque values. I haven't used stainless screws other than where called out by Vans, but I know others have used them extensively in non-structural locations.

I generally regard nutplates as tension nuts for torquing purposes. And for soft materials, I try to get as close as I can without actually deforming the part; I find I can torque AN3 in nylon but not AN4. And, lastly, I don't consider myself an authority by any means but these guidelines have worked for me.

Just curious... how many folks here actually own a calibrated torque driver that goes from 0 to 25 in/lbs and torque EVERY fastener on their plane?

MY 0.02

Like most of you, I torque every reachable bolt..for the others I depend on common sense and experience, and if in doubt, use the "gudentite" method. Is every bolt perfect and every rivet show-quality?...Hardly. I'm almost done, and have come to the conclusion that if any one rivet will cause it to fall from the sky, I am toast. It's a little more likely that a bolt torque failure could cause an accident, but considerably less likely than human factor failures, and other unknown issues (i.e. a poorly manufactured bolt or rod end bearing).

We should remember that gravity is always present. Anytime we try to defy it, there is an inherent risk. All we can do as builders is be aware of our limitations, buy quality products, and do our best to install them according to the best information available, using good judgment. This is what aviation and building is all about...and I'll leave the rest to the Almighty.

Merry Christmas to all builders and aviators!

Yes and yes. There is no point in being sloppy unless you absolutely have to for access.

Walt said:

Just curious... how many folks here actually own a calibrated torque driver that goes from 0 to 25 in/lbs and torque EVERY fastener on their plane?

Click to expand...

Walt said:

Just curious... how many folks here actually own a calibrated torque driver that goes from 0 to 25 in/lbs and torque EVERY fastener on their plane?

Click to expand...

Uh....sure....uh.......well.....maybe.....okay, never!

Nope, but when I assembled my engine i bought a nice digital Snap On wrench that is supposedly consitantly accurate across the entire range of torque. I did compare my torque wrenches to each other. I have a Craftsman click type, Craftsman bent beam and the Snap On. They all were pretty close to each other. At some point I will chase down a Snap On truck and send off my wrench for cal. Anyone know what they charge for that?

An item that I haven't seen mentioned yet on this subject is "drag" torque. If an exact torque is desired you must also factor in the amount of drag the self-locking nut or nutplate has. This includes any drag on the bolt, such as a prop bolt, and the amount of torque that is required to turn it.

Drag compensation

I added 4 in/lbs to all of my an3's that used a nylon locknut to compensate for that. I find it impossible to torque a an3 bolt that uses a nut plate because the torque is already reached just by screwing it into the constricted hole.

I do the same thing. I actually torque my AN-3's to 30 inches to account for drag.

Originally Posted by Walt
Just curious... how many folks here actually own a calibrated torque driver that goes from 0 to 25 in/lbs and torque EVERY fastener on their plane?

Phil said:

Yes and yes. There is no point in being sloppy unless you absolutely have to for access.

Click to expand...

I gotta admit Phil, you're a better man than I am!

I can't say in my 30 years in the aviation maintenance business I've ever seen anybody torque every single fastener, including myself!

In the real world (or my world) you torque critical fasteners, the rest you install using common sense, with a dab of experience to guide you.

(I gotta believe that if any mechanic got caught actually torquing each of the various hundreds (probably more like thousands) of fasteners that get installed on a typical jet during an overhaul they would first be laughed off the dock by their peers and then fired).

If I observed someone actually torquing all the access panel and interior screws on their RV I'd probably have to walk away to stop my uncontollable laughing.

I torque every bolt I can get to and the rest I go by feel. Because I don't do this for a living I don't find it to be that tedious. My small torque wrench goes from 10 to 100 in/lbs.

CharlieWaffles said:

Thanks. The exact bolt is listed as AN509-8R14.

Click to expand...

Just to keep the subject of this conversation "in context", we were originally talking about #8 screws and I asked the question "how many folks actually torque Every fastener" which includes #8 screws (as well as #6 and #4 if you have any). The reply by some was "I torque every fastener".

So, do you torque all your screws?

No only bolts.

Any screw that has a nut, yes. I also torqued specific screws, such as the ones for the antenna mounts. Others, such as fairing screws, I did not. However, if I can ever lay hands on a torque-stop driver (or chuck for an electric driver), then I will use it everywhere.

Jekyll said:

SNIP

1. Over-torqued is just as dangerous as under-torqued.

SNIP

Jekyll

Click to expand...

This is generally only true for those bolts which undergo significant cyclic loading (great example of this are connecting rod cap bolts). In other words, where high fatigue stress is present. Most bolts in our planes are not of this nature, although some absolutely need to be treated as such (engine assembly bolts, flight control bolts, etc.).

In the case of non-cyclically loaded bolts, it is well developed in mechanical engineering (see the classic Shigley Mechanical Engineering Design book) that, for higher strength bolts, if they don't fail during tightening, they will not likely fail later. This is true even if the bolt has been plastically deformed during tightening.

The empirical evidence also supports this. As others have written, many, many bolts are tightened on aircraft without torque wrenches, and it is almost unheard of for a bolt to fail. And, people typically apply more torque than the specifications when not using a torque wrench. I'm of course not saying this is a good practice (to over torque bolts).

Real life practice might be to use a torque wrench on all cyclically loaded bolts as described above, and have a "calibrated" hand when tightening bolts simply used to attach things, or in locations where a torque wrench is impractical.

The biggest risk around this topic probably arises when more than the recommended 3 threads are showing above the standard AN stop nut. When this happens, the tightening torque may simply be going into trying to cut new threads, instead of being converted into clamping force. I see this very often when inspecting planes. Bolts that have been torqued can be spun by hand. Big eye opener for the offender!

I don't torque bolts/screws that go through umhv. Examples include rv7 aileron trim mechanism, rudder peddles, flaps etc.

I took my tanks off and put them back on so many times that it became second nature to torgue them by feel.