Jury strut AN bolts, nuts and washers

Gordon Misch said:

The jury struts only stabilize the lift struts. They aren't really directly subject to flight loads. So in my opinion that AN3 bolt is simply the smallest readily available "bolt", and its stress capability really isn't important. It would be interesting to compute for comparison the edge pullout strength of the thin jury strut material. I'd be surprised if it's even close the bolt strength. But I've been wrong before - - -

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I agree Gordon, but when you have an A&P license and you have to place your name and number in a log book you have to be able to back up doing such.

IF an A&P gets in the habit of making minor substitutions such as this, what else does he do without justification? What happens when Mr. FAA happens to notice the substitution while he is wondering about the airport and decides to look into who did it? What if that Mr.FAA is an a$$ h--- (There are some you know) and decides to put you, the A&P on his s--- list? You are using your A&P license to earn a living. Do you really need this hassle just because you used an AN-3C bolt on a jury strut in plain sight?

In this example it would be relatively easy to set up a test rig to find out which would fail first, the jury strut, the attachment to the lift strut or the AN-3C.

I can tell you from personal experience how much pleasure is derived when one of these above mentioned Mr.FAA types is put in his place. In the end Mr.FAA will come to you asking for your assistance, never harassing you again.

skywagon8a said:

I agree Gordon, but when you have an A&P license and you have to place your name and number in a log book you have to be able to back up doing such.

IF an A&P gets in the habit of making minor substitutions such as this, what else does he do without justification? What happens when Mr. FAA happens to notice the substitution while he is wondering about the airport and decides to look into who did it? What if that Mr.FAA is an a$$ h--- (There are some you know) and decides to put you, the A&P on his s--- list? You are using your A&P license to earn a living. Do you really need this hassle just because you used an AN-3C bolt on a jury strut in plain sight?

In this example it would be relatively easy to set up a test rig to find out which would fail first, the jury strut, the attachment to the lift strut or the AN-3C.

I can tell you from personal experience how much pleasure is derived when one of these above mentioned Mr.FAA types is put in his place. In the end Mr.FAA will come to you asking for your assistance, never harassing you again.

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Well said Pete. I read lots of posts from people who have nothing to risk like their A&P license and Inspectors Authorization. It makes you think differently especially when you sit across the table from the FAA and their lawyers because none of it has to do with what really happened and what caused it. It's about hanging out to dry.

The AN3 thru AN20 drawing does not differentiate between steel and stainless steel as far as strength. Both the AN3 and AN3C have to meet the same strength requirements. An AN3DD has lower strength requirements, so it would not be acceptable as a replacement part. That’s what you call a Minor Alteration, and is within the preview of an A&P to do using “acceptable” data (the AN drawing). Of course you should also consider the galvanic action between the steel tubing and the stainless bolt, washer, and nut. By changing to a stainless bolt, you are changing from the bolt (cad plating) being the sacrificial material to the jury strut becoming the sacrificial material. The AN3 thru AN20 drawing was canceled in December 1999, and was replaced by NASM3 thru NASM20.


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dgapilot said:

The AN3 thru AN20 drawing does not differentiate between steel and stainless steel as far as strength. Both the AN3 and AN3C have to meet the same strength requirements. An AN3DD has lower strength requirements, so it would not be acceptable as a replacement part. That’s what you call a Minor Alteration, and is within the preview of an A&P to do using “acceptable” data (the AN drawing). Of course you should also consider the galvanic action between the steel tubing and the stainless bolt, washer, and nut. By changing to a stainless bolt, you are changing from the bolt (cad plating) being the sacrificial material to the jury strut becoming the sacrificial material. The AN3 thru AN20 drawing was canceled in December 1999, and was replaced by NASM3 thru NASM20.


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Was going to go dig thru all my books and see if I remember or even knew how to find all that stuff. Where do you get all the info like that.

DLA quick assist has most of the AN drawings on line, along with the cancelation notices. The new NASM drawings are only available if you pay for them.


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Thanks. Found my way to the bolts. Not sure I'll ever need it but nice to know where it is.
I used to have a little black book I got from Spartan with some of that stuff on it.

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This has been interesting to follow and it's made me do some reading. AC43.13 doesn't differentiate between AN bolts in general use. I've read through the bolt section several times and can't find any reason not to use corrosion resistant bolts where they're beneficial.

From AC43.13-1B-

7-41. STANDARD AIRCRAFT HEXHEAD BOLTS (AN3 THROUGH AN20).These are all-purpose structural bolts used forgeneral applications that require tension orshear loads. Steel bolts smaller thanNo. 10-32, and aluminum alloy bolts smallerthan 1/4 inch diameter, should not be used inprimary structures. Do not use aluminum boltsor nuts in applications requiring frequent removalfor inspection or maintenance.

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Since corrosion was mentioned, and we're talking about mild steel parts being pinned by stainless steel bolts, is galvanic corrosion a threat? We're bolting painted parts together so the corrosion cell potential would be unimportant, wouldn't it? At least in this application?

How are you guys seeing the ASSIST bolt specifications? I can't get into that site using search criteria that I've tried.

When looking at the galvanic chart, cadmium is more anodic compared to steel, so the cad plating on normal AN bots becomes the sacrificial material. When comparing steel with all the nickel alloys, steel is anodic as compared to stainless, and is farther apart than cad/steel, so the corrosion the steel becomes the sacrificial material, and it corrodes faster than the cadmium would. I hope that makes sense.

Best option would be not to scratch the cad plate on regular AN bolts, and coat with a protective coating to keep moisture out. If you use stainless hardware, without adequate protective coating, you will likely be replacing your jury struts and clamps before the bolts and nuts.


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When you get to quick assist site, in the document ID field put AN3, first item in the list is AN3thruAN20, click that, then on the next page click revision 12 to get the drawing.


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I'd stay away from stainless hardware in that application. When you put two dissimilar metals in contact, the "lesser" metal is going to corrode. In the case of stainless hardware attaching a jury strut, the jury strut becomes the "sacrificial" part..... I'd rather have the bolts corrode, because a) they're cheaper than jury struts and b) with the specified steel bolts, there's no question about legalities.

I ran a Beaver and a Super Cub, and owned a J-3, all on floats, and operated regularly in salt water in Kodiak. All external hardware was coated with Paralketone and/or the heavy LPS. These airplanes (except the J-3) were subject to 100 hour inspections, and the mechanics hated cleaning them up at each inspection, but our Chief of Maintenance told me to keep gooping them up....no corrosion.

When that Super Cub went in for recover, I fully expected it to require major repairs. It was a 1969 model, and was recovered in 1984 (original factory cotton). When the fabric came off, everything looked new under.

I'd stick with steel hardware, and apply some sort of anti corrosion coating, like paralketone.

MTV

dgapilot said:

When looking at the galvanic chart, cadmium is more anodic compared to steel, so the cad plating on normal AN bots becomes the sacrificial material. When comparing steel with all the nickel alloys, steel is anodic as compared to stainless, and is farther apart than cad/steel, so the corrosion the steel becomes the sacrificial material, and it corrodes faster than the cadmium would. I hope that makes sense.

Best option would be not to scratch the cad plate on regular AN bolts, and coat with a protective coating to keep moisture out. If you use stainless hardware, without adequate protective coating, you will likely be replacing your jury struts and clamps before the bolts and nuts.


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AN "stainless" isn't typical of other stainless alloys, is it? How does the AN alloy differ from standard stainless bolts with respect to galvanic corrosion?

Typical mild steel jury strut parts are prone to corrosion based upon material and design regardless of bolts used to assemble. Treating the strut parts seems like a good practice.

Just taking care of your existing hardware with coatings and maybe once per year disassembly to re-coat will likely do just as well as stainless. And, cheaper.

MTV

stewartb said:

AN "stainless" isn't typical of other stainless alloys, is it? How does the AN alloy differ from standard stainless bolts with respect to galvanic corrosion?

Typical mild steel jury strut parts are prone to corrosion based upon material and design regardless of bolts used to assemble. Treating the strut parts seems like a good practice.

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Someone up thread said Stainless AN bolts are typically 431 which is a martinsitic stainless. It has iron in it, so it would be somewhat magnetic. In a passivated state, it would only have about 0.45v galvanic rating to mild steel. Unpassivated, it is about .25v.


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Ruh roh.... new words to look up!

I appreciate the comments. I used stainless bolts. Most of the Cubs I know have the same. No discoloration on the bolts. No signs of galvanic damage. A little Corrosion X HD in the tubes will take care of internal rust for several years. It seems like the simple solution to me. I like solutions.

DGA is correct about carbon steel being sacrificial to stainless steel, however for that to really matter the junction has to be in an electrolyte. Similar to zinc adjacent to steel - if the junction is dry the zinc won't get used up. So it's essentially an non-issue at the jury struts.

edit:
https://galvanizeit.org/hot-dip-gal...e-seminar/hdg-bridge-design/dissimilar-metals
See chart and paragraph 4.

stewartb said:

Ruh roh.... new words to look up!

I appreciate the comments. I used stainless bolts. Most of the Cubs I know have the same. No discoloration on the bolts. No signs of galvanic damage. A little Corrosion X HD in the tubes will take care of internal rust for several years. It seems like the simple solution to me. I like solutions.

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Wouldn't regular AN hardwear and corrosion X HD last that long also?

Glenn

An exposed jury strut bolt in rain and snow? No. That's why corrosion resistant bolts are available. Use them or don't. I don't care. I just shared what I do.

While understanding that stainless is more noble than mild steel, and having heard all my life to watch out for stainless in aluminum (or mild steel)... I've just never seen stainless hardware (structural or otherwise) be detrimental in terms of causing adjacent corrosion. Maybe it's because the stainless is more inert? I don't know, but it's not a factor in my experience. That said, I do like to use aluminum washers under most hardware, and let that be the sacrificial anode.. besides, they are lighter.. Again, if it's going to stay together a while, wet paint (your choice of what kind) is, in my opinion, the best assembly compound. But something like EDO float hatches? Stainless non-structural screws, aluminum thin washers, and a whole bunch of Fluid Film....