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# AN3 hole tolerance question2

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## AN3 hole tolerance question

(OP)
hi all,

I'm working on the wing spars of a 2 seats light kit airplane.
The spars are already drilled and assembled by the factory.

Here an image of the root part:

I found out that the thread-lock-paint on some AN3 bolts was broken, so I wanted to re-torque them.
But I was surprised that the bolt had quite some play in the hole.
The bolt has a dia of: 0.1870 inch
The holes vary from 0.1900 to 0.1950 inch
Is this too much?

I though about going to a NAS6603-16 bolt because they are a bit thicker: 0.1885 to 0.1895 inch.
But these are shear bolts and have a shorter thread, so it will be difficult to use a standard washer and AN365-1032 nut and still have 1 to 3 threads protruding.
Are these joins in shear or tension?

What would be the best solution?

### RE: AN3 hole tolerance question

Do the measurements you are making match with the dimensions in the kit drawings? What do the drawings say about fit for bolts? Structural bolts are generally transition fit so there should be no "play". From the AN3 spec sheet the diametrical range is 0.186 to 0.189 so the holes are suspect to me. I would get in touch with the kit manufacturer and describe your problem.

Do not change the fastener type or size without talking to them first.

Keep em' Flying
//Fight Corrosion!

### RE: AN3 hole tolerance question

to me the hole looks ok, like a usage 2 fit.

another day in paradise, or is paradise one day closer ?

### RE: AN3 hole tolerance question

(OP)
@LiftDivergence
I've asked the kit manufacturer and the reply was that the holes are "okay"...
On the drawings, I have, no hole dimensions are written, so that I don't know.

Based on the info I have, a 3/16 or #12 drill/reamer should be used for AN3: 0.1875 - 0.1890 inch
So the pre-drilled holes 0.1895 - 0.1950 seem to have too much "play".
That's why I'm concerned.

I'm thinking about the forces on these bolts, these bolts hold the outside spar doublers (around 15 inch long) at the root of the spar.
Are these only for thickening the spar at the root and are the forces primarily in tension, in that case I can imagine that the holes are okay.
But when these bolts face shear forces I'm a bit worried.

What could happen when the forces are in shear and the bolt has to much play?

### RE: AN3 hole tolerance question

When the forces are in shear, the friction between the clamped parts takes up the load. This is how most bolted interfaces work.

You're saying in this post:

#### Quote:

Based on the info I have, a 3/16 or #12 drill/reamer should be used for AN3: 0.1875 - 0.1890 inch
So the pre-drilled holes 0.1895 - 0.1950 seem to have too much "play".

That you'd be ok with 20 thousandths of clearance; you're not ok with 25 thousandths?

For the purposes of handling shear load, clearance is unimportant. Sounds to me like this joint is designed not to have the bolts in bearing, and to use the clamp load to provide the required stiffness.

At the end of the day, by far the best course of action is to do exactly what the manufacturer tells you. By changing the bolt size, you open yourself up to the possibility of unintended consequences. Maybe those parts can't handle the extra clamping load a larger bolt can provide; maybe that joint's level of stiffness or compliance is important to the function and fatigue life of other parts. You have no way to know.

Don't change things unless the manufacturer tells you so.

### RE: AN3 hole tolerance question

PJYDE,

Maybe the drawing or a a picture showing more of the structure would help - you say we are looking at the wing root and I'm assuming the fasteners in question are shown with collars in the photo.

If that is the case it looks to me that this tapered leg doubler is installed over the web of the spar and picks up the vertical flanges of both the upper and lower chords. If I'm oriented correctly those fasteners would definitely be in shear.

But the bottom line is, if you have reported your question to the manufacturer and they confirm everything is correct, then clearly it is per design. So, you've done your due diligence.

Keep em' Flying
//Fight Corrosion!

### RE: AN3 hole tolerance question

(OP)
Here an overview photo of the spar:

### RE: AN3 hole tolerance question

Looks to me like a great deal of shear loading will be picked up by the flanges top and bottom, especially since they look like they get bolted together.

### RE: AN3 hole tolerance question

In your first photo, some of the bolts do not appear to show much protruding thread. Is there enough?
The paint you see is not "thread lock paint" it is a "witness mark". It performs no locking function. It is there to "bear witness" to two things: the presence of an inspector who verified the torque on the bolt before it left the factory, and it reveals when the bolt is loosened because turning it breaks the paint. So in your case, it did its job.

In general (not specifically to your aircraft) to make a shear-resistant bolted joint, you do not need the big AN365 nuts - those are known as "tension nuts". If you have a copy of AC 43.13-1b you can find the recommended application for these nuts. If you did want to replace the bolts, NAS6603 is a good choice but may be more expensive than necessary, and for this joint lower profile nuts suited to the NAS bolts will resist shear just fine and you may be able to put just as much torque on them. But that's not in the cards for this wing - you really shouldn't by changing the bolted joints from the one that passed the design and tests without approval from the holders of the design.

Actually, I would never use #10 bolts in any spar root unless they were installed with controlled torque such as Hi-Loks or the like. AN3's are 1950's fasteners and the world has moved on. But I'm nit-picking.

If all of the holes in question were drilled by the factory, then it's likely that the drill/ream procedure is detailed in a process specification, not on the drawing itself. The drawing may refer to the process somewhere, but since you mention it's a "2-seak kit" airplane, that's not very likely. The fastener installation data is not likely to be made available to you if it's on a proprietary spec.

I do not see a reason for these holes to be of concern, even if it can be shown that the AN3 bolt/hole size combination leaves a clearance fit in a shear joint. Firstly, as many have pointed out, the torque of each bolt ensures the shear load transfer. Second, the deflections in a wing structure in day-to-day flying don't need to take up all the clearance but the bolt torque prevents the slip. Thirdly, if discussing ultimate loads, slippage of the bolts through the hole clearance will hardly matter.

No, my only concern are the multiple moisture traps in the wing spar design. There are so many blind spaces between the shear ties and the (ahem) spar web, that I would be concerned about ever parking the aircraft outside. I can see the alodine / anodize finish but neither of these are a durable barrier to moisture if it collects long-term. The witness marks on the bolt assembly and riveting without fay sealant tells me that this spar is not coming apart again, and the best you will get is a spray-on primer of the final assembly.

STF

### RE: AN3 hole tolerance question

(OP)

#### Quote (SparWeb)

In your first photo, some of the bolts do not appear to show much protruding thread. Is there enough?
They have 1 protruding thread.
There is only a washer under the nut, not under the head; my technical counselor preferred to add a washer also under the head and use a longer bolt AN3-13 instead of AN3-12.
I did a test fit and by adding an extra thin washer I have this situation, which is approved by the kit manufacturer:

This respects these rules:
- no thread in the structure (spar)
- maximum 3 washers
- 2 threads protruding (which is between 1 and 3)
I'll torque them to 29 inch/lbs (4 friction drag + 25 max for AN3).

#### Quote (SparWeb)

I do not see a reason for these holes to be of concern...
Thanks for explaining, I will leave the holes as they are and use the standard AN3 bolts according the design.
So mainly due to the clamping force of these bolts the shear strength is given.

#### Quote (SparWeb)

No, my only concern are the multiple moisture traps in the wing spar design...
The spars are indeed anodized, the ribs are bare 6061-T6.
General practice at the factory is to use 2k-epoxy primer, but only on the mating surfaces and use Ardox AV30 for the skin overlap joins.
But no primer or sealant is used between the several wing spar layers.
I though anodized aluminium is quite corrosion resistant.
What would you advise? I still have some options at this stage of the build:
- leave the spar anodized aluminium only (fyi I protected the wing ribs with a 2k wash primer)?
- shoot some 2k epoxy primer on the mating surfaces?
- shoot the whole spar with 2k epoxy primer ?
- and/or brush Ardox AV30 in the blind spots of the spar?

### RE: AN3 hole tolerance question

Man, I've been working on commercial jets too long - I don't remember what's more common practice on light aircraft like I used to.
You're right - anodizing is an excellent corrosion protection and in combination with a primer spray on the individual parts before final assembly, you can expect a very long-lived airframe.
When assembling the components with only anodize the protection is there, but contaminants are not excluded. If the structure doesn't have moisture traps, you will still be fine, although an external application of primer will improve things.
What you have is anodize-only parts, and an assembly with several moisture traps. Those spaces between the spar web and the shear cross-tie bother me. I can see a gap between them where the root rib is installed, so I don't understand the bolt clamp-up situation there. If there will be a shim in between, then its edges are hard to mate up against the curvy edges of the spar cap, and that forms another moisture trap. There are 101 other details in moisture ingress into your wing, especially around the wing root fairing, that could make this vulnerable or protect it well - I don't know from here.
If you can remove that shear tie plate, apply primer to the root structure, and paint the shear tie separately before reassembling them (plus any other bits that surely must be in there) then you'll have put my mind at rest.

I don't think the double-washer arrangement will help you. Putting washers under bolt heads comes from distributing the clamping pressure on the surface of the part, and keeping the fillet between the bolt head and its shank from being sliced on a sharp hole edge. I can see by your photos that you have deburred all your bolt holes and by using AN3 bolts you really don't have much clamping pressure. Still, I would rather just use the thin washer under the bolt head as long as you don't run out of thread. If that means using a longer bolt, then I agree with the other advice you received.

STF

### RE: AN3 hole tolerance question

OK, I have worked on GA/Homebuilts [Thorp T-18], as well as antique military acft. This laminated construction and you comments do not feel comfortable to me.

Few points of concern.

Every BOLTED hole must have a nominal [optimum] diameter specified plus any allowable tolerances. IF NOT specified on the drawing, then there should be a master tolerance specification, IE a 'how-to-drawing or document' covering all assembly practices. This indicates the joints have been engineered... and that 'whatever' is not acceptable.

AN3-to-20 spec bolts should be reserved for mechanical installations... not structural joints... in my opinion.

It is standard for bolted structural assemblies to install close-tolerance-bolts in close-tolerance holes.

Sloppy holes relative to bolts impose greater shear-tension loads on the heads and nuts; whereas tight hole-to-bolt fit has a more uniform shear that reduces need for thru tension joint clamp-up for shear strength.

Suggest checking specs out for AN3-thru-20 VS the close tolerance version of the same bolt design AN173-thru-186. these bolts are identical in ever respect with two FUNDAMENTAL exceptions. The old AN specs can be down loaded at http://quicksearch.dla.mil/qsSearch.aspx

1. AN3-thu-20 bolts have shank tolerances ~0.0030; whereas AN173-thru-186 bolts have total shank [close/precision] tolerances less than 0.0008 [close-tolerance is denoted by the impressed triangle in the head markings for these bolts].

2. AN3-thu-20 threads are left 'as rolled' [no further action required]... however, oddly, the thread-tip-diameter could easily be LARGER in diameter than the allowed bolt shank[!!]; whereas AN173-thru-186 have a specific annotation that thread-tip-diameter MUST be at least 0.0010 smaller than the [close-tolerance] bolt shanks [but not less than thread spec minimum thread-height].

In the evolution of fasteners: (a) structural fastener shank-diameter and thread tolerances have gotten tighter; (b) mechanical strengths of the steel, CRES and titanium alloys has gotten higher/tougher and more refined; (c) stress concentration details have been refined [fillet radii, thread transition run-out, etc]; (d) head dimensions and threads dimensions are more tailored for strength/durability performance and/or weight savings; etc.

CAUTION: hole quality is defined by the hole creation process. Drill bits typically attain+/-0.0020 hole tolerance; whereas reamers attain +/-0.0003 hole tolerances. Also, to be consistent, holes must be finish-match-drilled thru to ensure the entire stack-up has dead-od hole alignment and diametrical consistency.

One final comment... regarding the application of thread marking compound to the nuts/bolt-threads.

The way the marking compound is applied in Your photos is NOT aircraft standard. Marking compound is intended to show relative movement between parts that is undesirable.

Per Your photos: the marking compound was applied across the side/top of the nuts and onto the tip-top [end] of the bolt thread protrusion. This is inadequate, since this will only reveal whether the nut turns relative to the bolt.

Thread marking compound should be applied between the tip-top of the bolt-thread protrusion, across the top and along-the-sides of the nut, along the side/shoulder of the washer(s) and onto the surface of the structure... in one long/smooth line. This procedure will positively indicate ANY relative movement between the structure-washer-nut-bolt [side-to side or rotational looseness], in-service.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

### RE: AN3 hole tolerance question

(OP)
Thanks for all replies

#### Quote (WKTaylor)

Suggest checking specs out for AN3-thru-20 VS the close tolerance version of the same bolt design AN173-thru-186.
Also with AN173 I would have sloppy holes:
AN173: 0.1885 - 0.1895 inch
Predrilled holes: 0.1900 - 0.1950 inch

AN173 is not available as oversize (-X), but NAS6603 is: 0.2016 - 0.2026 inch.
I could use a 0.2026 reamer and manual ream the holes.

What would be the disadvantage by using a 0.2026 reamer, NAS6603-16X bolt, AN965-1032 (tension) nut and use the default torque value for AN3 10-32 (20 - 25 incl/lbs)?

I appreciate your experience and help to find the best possible solution which I can present to the kit manufacturer and ask for final approval.

### RE: AN3 hole tolerance question

Just out of curosity,and I am considering a kit build,who may I ask,without prejudice either way is the manufacture of the kit ?

### RE: AN3 hole tolerance question

BTW... Your nut appears to have the wrong PN... AN965 ut spec does not exist.

I suspect Your nut is probably an AN365 or MS20365. The 'nominal' replacement for both of these nuts is the all-metal MS21042-3 or L3 light weight low height shear-tension nut.

IF You are serious about changing hardware...

NAS6603-*X requires the hole to be close reamed to 0.2031 [+/-0.0005]. Ensure the reamer has a 0.189-Dia pilot so You get a straight-ream thru the old holes.

CAUTION.
IF You ream hole to 0.2026 You might actually have trouble installing bolts... too-tight fit. Reamer size I cited [with good technique] will make holes VERY close-tolerance and close-in-size to each other for consistent/tight fastening. IF You went to protruding tension head Hi-Loks pins, I would ream the hole size to transition/net-fit 0.0201+/-0.0010

CAUTION: IF 1OS shank protrudes slightly thru the structure [as-it should, especially longer bolt grip], You WILL have to drill/ream-oversize the ID's of Your standard AN960 or NAS1148 washers.

Also... don't forget to break the sharp edges of holes... especially where head will seat... to avoid the sharp edge of the hole conflicting with the bolt head-to-shank fillet radius.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

### RE: AN3 hole tolerance question

(OP)
Thanks again

#### Quote (WKTaylor)

AN965 ut spec does not exist
Sorry typo, should be AN365

#### Quote (WKTaylor)

IF You went to protruding tension head Hi-Loks pins, I would ream the hole size to transition/net-fit 0.0201+/-0.0010
What would be better in my case: oversize NAS66XX or oversize Hi-Lok?
Which reamer do you mean for Hi-Lok?

### RE: AN3 hole tolerance question

I vote for HiLok. The installation guidance is available (very detailed) from Hi-Shear corporation (Now LISI)
http://www.lisi-aerospace.com/products/Pages/Faste...

Just an example, not a recommendation... I haven't sorted out the exact type that you actually need, so I'm attaching the link below just so you know what kind of information you can expect from a Hi-Lok/Hi-Lite datasheet:
http://www.lisi-aerospace.com/_layouts/CentralDocC...

Note 4: Hole preparation per NAS618.

I don't have a copy of NAS618, but WKTaylor's numbers above look right. You can get the specific hole size requirements from LISI/Hi-Shear.

STF

### RE: AN3 hole tolerance question

I have a hard time understanding the amount of detail that this thread has accumulated .. I believe that we have lost sight of the forest due to the trees .. The original question was about .010 slop in a HOMEBUILT aircraft spar fasteners. I suspect this wing will not see more than 20 hours a year and never see any loads approaching yield. - yet we are ready to redesign this assembly for Mach 2.
I have seen this same thought - process in the OEM repair office. Majority of the time - the damage had to be repaired 'above & beyond' the original design criteria. We had the loads .. a damaged stringer could withstand the loads 'as is' - but nope .. we had to cut it out & splice in a new segment. Fuselage scratch 'good as is' (blended & finished) nope! had to cut it out and install a repair Doubler - removing systems to gain access & drill over 100 new hole in damage tolerance structure. & this was acceptable! Sometime we should just slow down a bit and think about it .. just my 2 cents.

### RE: AN3 hole tolerance question

#### Quote (edmeister)

I have a hard time understanding the amount of detail that this thread has accumulated .. I believe that we have lost sight of the forest due to the trees .. The original question was about .010 slop in a HOMEBUILT aircraft spar fasteners. I suspect this wing will not see more than 20 hours a year and never see any loads approaching yield.

this is the classic problem are the guys who designed this idiots or genius i.e is this my failure to understand or theirs to design adequately.

How do you know its going to be only 20 hrs a year, you simply can't, it could just as easily do several hundred hrs a year overloaded (because they often are) in a region with worse than normal gust profiles (gusts in Oz are worse than the US etc etc).

From a GA perspective AN3s in a spar is just a "No". Yes plenty of homebuilts get away with AN3 but with the costs of homebuilt aircraft why not put 50.00 worth of fasteners where it matters. The wing root will likely never be inspected, & 0.010 slop is just as likely break any surface protection before considering cracking. I look at at that first pic and the question that comes to mind is how did they cut the H plate because those other older homebuilts that do have AN3s in the spar probably didn't also put them though laser or abrasive jet cut parts (that may have not had the edge manage removed). OEM repair offices don't tend to be staffed by their best and brightest. ### RE: AN3 hole tolerance question edmeister, I sympathise. Someday I may build a homebuilt of my own and I'll be faced with a similar choice. To use the specified "just OK" bolts that are not much better than the ones at the hardware store, or to pay for "good bolts" that I know I can trust. This is the spar root (yes a shear joint but there are other issues) and I wouldn't scrimp here. If it were the bolts that hold the navigation lights on, then yeah, that's what AN3's are for. STF ### RE: AN3 hole tolerance question (OP) #### Quote (edmeister) I suspect this wing will not see more than 20 hours a year and never see any loads approaching yield. - yet we are ready to redesign this assembly for Mach 2. To answer those questions about time: - 100 hours / year - 25 years in service About max loads: - 700 kg mtow - limit load factor: normal category -> 3.8 - safety margin: 1.5? - wing span 9.2 mtr - fuselage: 4 mtr wing span Very rough calculation: 700 kg * 3.8 * 1.5 = 3990 kg total / 2 => 1995 kg per wing Assume avg load half way on the wing = 2 mtr moment => 4000 kg on joint (8800 lbs) Wing spar is attached to fuselage with 8 AN6 and 2 AN5 bolts Wing spar H doublers are attached to the wing spar with 13 AN3 bolts Both the AN6 as the AN3 have around 0.004 - 0.008 inch slop. AN3 bolts have a yield tensile strength at root of 1690 lbs Multiplied with 13 bolts = 21.970 lbs But how does the slop impact this tensile strength??? Another thing I found out is that some AN3 holes are crooked. So reaming to a close tolerance bolt/hi-lok will not fix that problem, probably only make it worse; since now the bolt can settle straight due to the slop in the hole. I don't want to overthink this situation, sure no need to design this for mach 2. Although it should be airworthy and stay airworthy. And; I want to be proud of the result after spending quite some time and money on this project. ### RE: AN3 hole tolerance question #### Quote (PJYDE) But how does the slop impact this tensile strength??? It doesn't. ### RE: AN3 hole tolerance question jgKRI... it's a durability/fatigue issue. PJYDE... homebuilt construction quality is a personal issue to me. I helped my dad build his Thorp T-18 N455DT 1967-to-1971 under the oversight of John Thorp. JT was a very detail oriented engineer. I learned a lot about engineering and aircraft construction. He is the reason I changed course from wanting to be a professional pilot [like my dad] to becoming an aero-engineer. Here is why this is personal. http://www.eng-tips.com/viewthread.cfm?qid=423215 go to WKTaylor thread posted 31 May 17 19:34... and the very next thread-reply by itsmoked with a photo of T-18 N193N [which tied directly into my previous thread-post]. BTW off-90-deg angle holes can/should be straightened. Will require drilling/reaming using drill-guide block to re-establish [force] the hole to turn perpendicular... and maybe a 2OS [*Y] hole/fastener install, too. From the photos, I would not be surprised if You have adequate margin to step-up the holes to 1/4-Dia nom for close-reamed install [NAS6604, NAS6204]. Regards, Wil Taylor o Trust - But Verify! o We believe to be true what we prefer to be true. [Unknown] o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase] o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum] ### RE: AN3 hole tolerance question If this joint was designed as a friction joint, and not one relying on the shear capability of the fasteners, why do slightly oversize holes matter? As with most bolted joints, I have to imagine that any relative slip between these parts constitutes a failure of a joint; as a result, the tension applied by the bolts should be enough to prevent relative movement of the parts. Disclaimer.. not attempting to challenge the expertise of those more experienced with aerospace system design... just trying to find out if there's something to learn here (for me). From first principles of engineering, it looks to me like that joint was designed to be slip-critical and use fastener tension to maintain joint integrity, in which case the size of the holes doesn't matter much (within reason). ### RE: AN3 hole tolerance question (OP) #### Quote (WKTaylor) Here is why this is personal. http://www.eng-tips.com/viewthread.cfm?qid=423215 go to WKTaylor thread posted 31 May 17 19:34... and the very next thread-reply by itsmoked with a photo of T-18 N193N [which tied directly into my previous thread-post]. Bizar story, thanks for sharing! I'm not gonna change anything on this kit before 100% approval of the kit manufacturer. They tell me not to worry "there was never a problem with this design", but I do worry and many posts in this thread confirm my worries. It feels like dead end. ### RE: AN3 hole tolerance question I'd be pretty annoyed if I designed a kit and then someone started tinkering with it thinking it wasn't up to the job. Especially if they were not even sure if the connection was designed to work as slip critical or bearing. All this talk of changing someone else's design makes me twitchy, especially on something as safety critical as a wing root! ### RE: AN3 hole tolerance question #### Quote (RandomTaskkk) All this talk of changing someone else's design makes me twitchy, especially on something as safety critical as a wing root! Me too. ### RE: AN3 hole tolerance question that's why home-builts are owner-builder ... he who builds it takes responsibility (with very limited oversight) for it. back to the original question ... I don't think it is the end of the world; there are simple things to do to lessen the clearance. We aren't told about the entire joint ... maybe the other holes are "better" ? so it's hard (IMHO) to recommend action, other than possibly talking to the kit designer. another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question RandomTaskkk, jgKRI... "All this talk of changing someone else's design makes me twitchy, especially on something as safety critical as a wing root!" Unfortunately, PJYDE, has already stated that there is no hole size/tolerance data on the plans or with the kit [info manual... or referenced-to... etc]... a glaring deficiency in any aircraft design/plans/kit. I would be astonished [in a bad-way] if the designer left these details to 'Joe-the-assembly-guy'. I could easily accept this element IF there was specific reference to authoritative established data such as AC43.13-1 and AC43.13-2 or FAA-H-8083-30 and -31V1 and -31V2, or any number of commercial or military structural maintenance/assembly manuals. Important details such as hole-sizes for various type fasteners, installation torque-values, cotter-pinning and safety wiring, etc should never be left to 'good judgment and experience'. But lets get back to basic data, such as the photos: I have remarked on a just a few of the [bigger] issues that are evident, or suggested, in the photos, which are inconsistent with good quality assembly. There are several other lesser quality issues in the photos that also bother me. A rule of thumb I developed years ago is this. Workmanship trumps design. A poor/marginal design can be made 'better' [good-enough] by good quality workmanship and careful attention to details. However, a highly competent design can be rendered marginal/unsafe by poor quality workmanship and inattention to details. My dad had a phrase for good workmanship... 'we're doing it the way John Thorp designed it... for 'MOM'. Regards, Wil Taylor o Trust - But Verify! o We believe to be true what we prefer to be true. [Unknown] o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase] o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum] ### RE: AN3 hole tolerance question I understand that point of view, and it is sensible. What makes my eye twitch is what appears to me to be a lack of deeper thinking- the changes being discussed appear to me to make this interface much stronger and/or stiffer; on the face that's a good thing. But what unintended effects does that potential increase in stiffness in this joint impart to other parts of the airframe? What loads will now be transferred that wouldn't before? Again, I don't design aircraft.. but on the things I do design, I have spent a couple thousand hours of my career rolling back changes that other people, such as service technicians who "knew better than the pointy headed engineer", made without an eye to consequences on the rest of the system. These changes, in my experience, can often cause failures which are very predictable, and point to why things weren't done that way in the first place. The difference between what I do and what we're talking about here, is that a catastrophic failure for me usually results in some company losing a couple days of production as opposed to one or more people dying a grotesque death. ### RE: AN3 hole tolerance question (OP) #### Quote (rb1957) different question, what's happening at the four holes in the middle of the web (shown in the box) ? looks like the outer plate is not well supported ?? Here the first rib will be attached with 5 rivets, not through the whole spar but only through the outer plate. The upper and bottom hole of that rib will be attached with the same AN3 bolts through the the complete spar. Furthermore a tank-attach-bracket with be attached with 2 AN3 bolts. So in total there will be 15 AN3 bolts through the whole spar. ### RE: AN3 hole tolerance question Those holes are most likely for the root rib. The OP never did tell us what the aircraft was. B.E. You are judged not by what you know, but by what you can do. ### RE: AN3 hole tolerance question ok, a rib flange could sit on the outer surface, but there doesn't look to be enough room to install rivets/fasteners ? but NP ... we're not seeing the entire design and the questions being asked are sensible. another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question Since we are still on this same subject. Here is another aspect yet to be mentioned (perspective of the Mfr). From the image - it appears that all the hole are pre-drilled in the factory & the home builder just installs the fasteners. -Typically (in critical situations) a hole would be inline-drilled thru the assembly layers - & not each part separately drilled. So one can see the manufacture's dilemma 1/ jig/assemble the unit / drill / separate parts & finish each individual hole (& maintain the grouping of the parts during finishing & shipping) .. or 2/ Drill all the holes separately while fab'ing the part + Finish the holes & alodine/anodize the parts ..or 3/ have the home-builder drill these 'critical' holes & have no control with the end result. -In summary - I believe the Mfr optimized the Kit Quality by allowing a minor tolerance so all the parts are 'interchangeable*' and eliminating any error by the home-builder having to drill his own holes. (*interchangeable => Mfr will fab numerous kits at the same time does not have to group 'custom' drilled assemblies) If all the holes were inline-drilled with a given tolerance - then yes .. I can see some 'play'. But given the number of fasteners & the holes not inline drilled a proportion of the 'play' will be eliminated - due that some number of fasteners will always be in bearing. -One last final note - if Mfr had holes drilled individually with no tolerance; 2 issues are foreseen. 1/ Bolt would never fit through the numerous layers (due to mfr error in machining) & 2/ if the bolt get 'hammered' in - we now have preload .. & also hole damage & the finish coating in the holes gets removed (by hammering the bolt or drilling the hole) ### RE: AN3 hole tolerance question possibly mfr drilled the holes in one operation, with the spar assembled ? possibly the mfr drilled undersized holes, for the builder to expand. I'd've thought the mfr would have drilled mostly pilots (holes). another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question All... RB... RE the initial thread photo. The 4-drilled-holes in-vertical line with gap in-between was a detail I also noted and was concerned about. I am also concerned RE the fit-up gap between the 2-flanges of the upper spar-cap: if the parts are as thick as they seem, may be impossible to hand-pull-up-the-gap... shimming should be required to prevent shanking or excessive pull-up forces. NOTE. I suspect there are matched-hole templates [or an equiv CAD/CNC set-up] that established the hole locations/size for each-of-these parts... which were then brought-together and fastened ‘as is’. NOTE. The unique matched-hole-tooling methods established by John Thorp [1960s] established the practice ~as follows: locate the hole centers [center-punch] from the flat-pattern templates [FPT]; then pilot drill the actual part one-size under [for 1/8 rivet, drill 3/32 or #40]; then Cleco together [3/32] the structural details [into a major Assy]; then mate drill to #30 and swap Clecos to 1/8 as-we-went; then dis-assemble & deburr and apply primer; then re-assemble with final size Clecos; then final assemble with rivets. The matched-hole Assy practice was ingeniously tooling/jig-free but always required finish-drill [and ream for bolt-holes] of the temp-fastened ‘self-jigged’ structure to ensure mate-drilled/located hole center thru the stack-up. Even then, we occasionally had to step-up a few ‘wild-holes’ OS to get clean alignment thru the stack. BTW, the master-tooling guy who worked for JT, Vaughn Parker, often had to repair FPTs when ham-fisted builders [not me] damaged edges or holes etc. This job kept him busy, when he wasn’t assisting builders coming/going from the Burbank CA shop. NOTE. I have posted several times on homebuiltairplanes.com forums, regarding fasteners, materials and metal fabrication/Assy procedures. It seems these topics often generates emotional responses because they are hands-on/personal to those doing the building/assembly... 'gitter-done-good-enough' is an underlying philosophy since$budgets and time are limited. I get it... Dad/I learned the hard way the true meaning of the [not-so-funny] John Thorp truism: "80% done! Only 50% more to go!!" My +40-year engineering and hands-on experience/opinions have not been well received there [maybe it’s just me/my style]... so I have decided to focus my energy into Eng-Tips. NOTE. Years ago I found an informal/funny/well presented ‘Shop Awareness Briefing’ handout that helped explain the implications of assy practices/workmanship to mechanics in-relationship to the real-world element of aircraft structural durability/life. See attached. This ‘document elegantly describes the implication of workmanship discussed here... pictures are worth thousands or words. http://files.engineering.com/getfile.aspx?folder=b... Regards, Wil Taylor o Trust - But Verify! o We believe to be true what we prefer to be true. [Unknown] o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase] o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum] ### RE: AN3 hole tolerance question that doc looks like it comes from MD but that typeface looks like Boeing (as in their structures manuals) another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question (OP) #### Quote (WKTaylor) See attached. This ‘document elegantly describes the implication of workmanship discussed here... pictures are worth thousands or words. Many thanks for sharing this document. #### Quote (WKTaylor) I am also concerned RE the fit-up gap between the 2-flanges of the upper spar-cap No shim is needed because the skins are riveted through the upper layer, the second layer has larger holes so that the tail of the rivet fits in and can be pulled. You stated in one of your previous replies that you don't like AN3 in a spar and prefer AN173.... or NAS66.... or even better Hi-Loks. Would you be so kind and briefly explain why Hi-Loks would be a better choice? ### RE: AN3 hole tolerance question "why Hi-Loks would be a better choice" ... hole fill "the skins are riveted through the upper layer, the second layer has larger holes" ... if the skins attach to the outer flange, what does the inner flange attach to ? another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question No one has yet to reply to my earlier post.Perhaps my answer lies in the comments made,and speak for themselves.But tell me anyway,my kit money is burning a hole in my pocket. ### RE: AN3 hole tolerance question I appreciate that english is not your native language, but your question isn't clear. Maybe start your own thread ? (rather than hi-jacking someone else's) But if you want to build a kit plane, survey the available kitplanes, get active on kitplane sites (to get a feel for how specific kits are thought of), then take your choice and pay your money and have fun building your own plane. Maybe also talk to your local airworthiness authority to see how much involvement they have (should be very little). another day in paradise, or is paradise one day closer ? ### RE: AN3 hole tolerance question #### Quote (rb1957) I appreciate that english is not your native language, but your question isn't clear. I believe he is asking for the name of the manufacturer of the kit being discussed in this thread. Seems pretty reasonable to me. ### RE: AN3 hole tolerance question RB... RE Your comment... "that doc looks like it comes from MD but that typeface looks like Boeing (as in their structures manuals)". See attached NAVWEPS 00-25-559 Tips on Fatigue circa 1963. You may recognize some of the illustrations that were plagiarized for the Shop Awareness Briefing of the 1980s [?]. http://files.engineering.com/getfile.aspx?folder=9... BTW... that 'NAVWEPS 00-25-559' [1963 document] illustrates a teaching style that is characteristic of the era: intermix formal figures, sketches, cartoons, wisdoms/quotes and 'special emphasis' interspersed within the body of the text [text was generally limited to 1-to-1.5 columns per 2-collumn per page... before something 'interesting/visual' was inserted]. Not only is this writing style interesting and compelling and motivating to the reader, it gives the mind a useful 'break' between critical thoughts that enhances learning. Sure, these documents are a LOT more intense to write... and somewhat longer in published form... but they challenging to the author to keep it interesting. SADLY current technical writing style is extraordinarily dry: Text up-front; data tables, figures, etc all neatly packaged at the back of a document/chapter. No wonder no one wants to read technical stuff anymore@$%&(*)(&^#\$#%^&*!

BTW... that spar does NOT look lightly built... as I expect for a very light/simple aircraft. The spar looks like its intended for a high performance acft.

BTW... I'm having a hard-time deciding if there is any primer on these parts... or if I'm [just] seeing [green-yellow tint] chromic acid anodize [CAA] finish W/O primer...

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

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