[Camillo]

Today I finally squared my wings and drilled the rear spar holes.
Wings are 0.0? incidence (with wood block underneat per dwgs) and equally distanced from the tail (approx. 1/32'' difference from wing tip to wing tip). Hole are exactly straight and well distanced from all edges (say 20/32'').
I drilled the holes with #30, then #12, 1/4'' and finally 5/16. Instructions says to use 5/16 drill bit.

Well, when I inserted bolts, they are a bit loose. They are not a tight fit. I am a bit upset of this, since I also had a .311 drill bit, but for some reason I did not use it (since manual said 5/16...). I read a lot of threads and found that this is not a problem, since the rear spar does not carry a lot of load.

But I am worried that with time the hole may enlarge, with wear. I would like to fix this and I was thinking on using slightly bigger bolts.
Will you think that NAS1105-6 will be OK or shall I leave them as they are?

Thanks.

 

[frazitl]

I'd get the bigger bolts.

Seems to me if the main spar needs such a tight fit on the bolts, the rear spar bolts should be a tight fit too. I used close tolerance bolts and an appropriately sized reamer.

 

[Rick6a]

I drilled the holes with #30, then #12, 1/4'' and finally 5/16. Instructions says to use 5/16 drill bit.... would like to fix this and I was thinking on using slightly bigger bolts.
Will you think that NAS1105-6 will be OK or shall I leave them as they are?....

Camillo,

It it be MY airplane and facing the identical situation, here's what my thoughts are:

Arguably, the rear spar attach holes are among THE most critical holes the builder is ever asked to produce. I really have to question your interpretation of the instructions you say call out using a drill bit. No standard twist type drill bit can produce a high quality precision hole. I don't care how good you or your equipment is. If you could examine a hole produced with a standard drill bit through a high powered microscope you would instantly understand its inherent imperfection. That is why we use reamers to produce high quality bolt holes. I do not have a copy of the instructions in front of me but Van's on-line document for drilling the rear spar bolt holes clearly indicates the use of a reamer for the final full size pass. This is routine, long accepted sheet metal practice:

http://www.vansaircraft.com/pdf/Wing_%20Incidence.pdf​

That is water under the bridge now. What's done is done. At this point you really should consult with Van's especially before considering dramatically enlarging those holes to .375 to accept AN6 bolts. I certainly would not base my decision on the merits of open forum opinion. For all I know about engineering principles, maybe Van's would consider the holes okay just as they are. That said, my experience leads me to believe what you really need are a couple of (5/16" NOMINAL) 1/64" oversize bolts. Finding them may be difficult and I don't immediately recall the part number. Perhaps someone else here can provide a part number and source. Another option may be to use a more widely available hi-loc fastener (and nut) but I am not qualified to say a hi-loc is an acceptable alternative in this application. Check with Van's for acceptability.

One final low tech option I can think of it this: Tolerances on AN bolts are by design, "generous" and you say the fit is only "a bit loose." Without knowing EXACTLY what size you actually drilled those holes up to....you need a ball gauge and micrometer to determine that....it is impossibile to determine what your interpretation of "a bit loose" actually is. What we do know is that the actual O.D. from one AN bolt to another can and will vary depending upon manufacturer and batch number. In fact, the O.D. can vary so widely on AN bolts that one AN5 bolt may not fit into a precision drilled hole that another AN5 bolt can be easily inserted into. Perhaps you can locate a couple of AN5-10 bolts on the high end of the tolerance scale so the fit in your holes is enhanced. This is one of those times using a micrometer to measure any given bolt's O.D. is worth its weight in gold.

Good luck.

 

[apkp777]

Camillo,

I would call Van's for your piece of mind. I used a 5/16 drill bit as per the instructions and yes the bold was not a "tight" fit. I don't think it is supposed to be.

I wouldn't (and am not) worry about. Do make sure that future inspections you look for evidence of "working" (black ring around the bolt head)..

IMO!

 

[TX7A]

...my experience

Camillo,

I followed the instructions just as you have done. I did use new, long drill bits. I also used a block of wood drilled on a drill press to help keep the hole square. I started with the smaller hole and stepped the sizes up to 5/16". I used LOTS of Boelube to in the process. I thought I had what looked like good holes once finished and were as good of a fit as could be expected.
It was no more than two days AFTER I had drilled the holes that I discovered Van's on-line .pdf for drilling the rear spar holes:

http://www.vansaircraft.com/pdf/Wing_ Incidence.pdf

I also discovered that the instructions differ from the ones in the manual, in that they mention the use of a reamer. I immediately started questioning my work. I 'know' the importance of the rear spar hole and the edge distance, etc, etc. I was really beating myself up for not using a reamer when I knew I should have. I called Van's about what I had done and not used a reamer for final sizing. They stated that if I had the proper edge distance and had drilled good holes, that it should be fine....ending with the proverbial "Do you know how many RV's are flying around with drilled rear spar holes...?"
Regardless, I may do the ream / oversized bolt thing if there is an acceptable method AND I can maintain good edge distance.
As Rick said, call Van's and see what they tell you.

 

[PETERD]

I suggest you contact Van. I?m sure he has run into this before and has a solution. If you do, please share his comment.

I just received my fuselage kit with the latest instructions and here is what it says:

"Initially drill an undersize hole starting with no more than a 1/4" drill. Then progressively enlarge the hole to 5/16" which should provide a close fit for an AN5 bolt. Drilling with a long stiff drill bit is a good idea because it can be held straighter for a truer hole".

Van does not mention a reamer, but I agree with Rick, you can't get a ?close fit" with a drill....even in a drill press. Maybe close enough but why take a chance when you can ream. I assisted another builder to drill this hole but can?t remember if we used a reamer or not. I remember it was not the easiest hole to drill.

 

[Camillo]

I wrote to Van's yesterday and I am awaiting for an answer.

Meanwhile, I talked to the mechanics of local Aero club and they told me to fly and inspect the holes after a few hours, adding that a stressed hole is clearly visible. They also said that a torqued nut with washer inside (as always) will make a very solid joint.

I am not very worried about the security of the part. I guess I am frustrated because I did a very nice job until the end and only after having looked again to the instructions I took the 5/16 bit and drilled with it, even if I had the .311 in my toolbox (I used it for the main gear legs holes). If I only had spent 5' more looking at the airplane instead of making the last step...

I think I will go in every case with close tolerance bolts, if Van's will tell me "no problem", as I can predict. On the opposite, if Van's answer will be "no good", I will follow their instructions.

 

[Fearless]

Don't beat yourself up over it

Camillo

Don't beat yourself up over it. We had doubled checked the wing sweep and incidence on my wings several times before I drilled the aft spar holes. Yesterday I was working on setting up the flap rods and the penetration holes in the fuselage. It was then that I discovered that the left spar was off 1/8 compared to the right one and that the flap bearing wouldn't fit inside the fuselage upon retraction. I talked to Ken at Vans this morning about it and was told not to worry. To get within 1/8 of each side was acceptable. We strive for perfection but probably will never reach it. Just don't look to close at my plane if its ever at OSH though.

 

[Bavafa]

We used reamers on my rear spar hole and the AN5 bolt was not a close fit type that I was expecting, it is certainly not loose fit but it is nothing tight like the main spare. I considered buying close tolerance bolt but was told not to worry about it and it has been OK so far. Of course I have only 185+ hours on it but so far so good.

 

[Camillo]

Well, time, as always, make things appear better.

I received an email by Van's and they told me that:
- as far as the hole is 5/16'';
- as far as there is no play on the rear spar when bolted (I imagine: when applying hand force and not >300 lbs. on it);
- as far there is proper edge distance,

all is OK, and the only reccomandation is to check the hole periodically.

I will double check the hole width on saturday (as Rick already suggested). The other "prescriptions" are OK, since I already picked up the airplane form the rear spar and edge distance is everywhere @ or more than 20/32''.

Anyway, I will buy NAS6205-11 (NAS1105-11) from Spruce:
http://www.aircraftspruce.com/catalog/hapages/nasBolts.php
HIGH STRENGTH BOLT NAS6205-11 NAS1105-11 $3.45
They are one number longer than Van's, which are -10: I will add one more washer.

For any other builder, I would reccomend using a 0.311 reamer instead of a 5/16 drill bit. Lesson learned.

 

[sf3543]

Try some other bolts

You could also try some different bolts.
As Rick said earlier, these bolts can vary in size and some have slightly larger/smaller diameters than others. You could get a tighter fit simply by trying a different bolt (s).
Good luck.

 

[Jerry Cochran]

I talked to Ken at Vans this morning about it and was told not to worry.

I worry that "not to worry" is a little too much bandied about by Van's well-intentioned tech advisors who have mostly built an RV themselves or are in the process. If inquiring about a real safety issue like rear spar bolts, I might suggest going to the actual aeronautical engineers at Van's like the man himself, Ken Krueger, etc.

I had an issue where the QB firewall would not match up with the engine mount bolt holes and was told essentially to "git er done" until I took photos, consulted directly with Ken, who told me the right way to fix things, which I did.

It could be a little too easy for one techie to consult another about a "proper"
fix thereby passing along the same advice, right or wrong.

 

[TX7A]

Camillo,

Are the NAS bolts you listed suppose to be a tighter fit in a normally drilled 5/16" hole or is there a need to ream to a slightly bigger size?

Thanks!

 

[Camillo]

Sam, I will order them and the trial fit.
If they are too big, I'll let you know.
What I am sure of, is that I will not enlarge that hole. I will not have proper edges distance (unless reaming just a little bit). This will definitely oblige me to change all parts.
In the worst case, I will have someone make dedicated bolts for me or fly for a few hours (hundreds?) and then decide to change part and redrill.
My regret is that after 4 years of building, I falled on a stupid issue. I should have waited 5' more before final drilling.
The lesson (already learned, but not enough) is that the airplane have command on your time and not viceversa.

 

[roee]

Not a fix, but a method for doing it the first time

I just did mine on Saturday. Drilled 1/8" pilot holes, then enlarged to 9/32" with a standard twist bit, then a 0.3105" reamer. Each of the 3 steps done with 1.5" aluminum block as drill guide to keep the hole perpendicular, each guide block pre-drilled on a drill press to the appropriate hole diameter for the bit.

The rear spar holes came out perfect as far as I can tell. Super clean, perpendicular, and a snug slip fit for the AN5 bolt. Takes just a little bit of finger pressure to push the bolt in or out, and there is no discernible play.

Did a lot of experimentation with different drilling methods on scrap before I committed to this approach, so I thought I'd share what I learned. This doesn't help you fix it after the fact unfortunately, but for those who haven't gotten there yet...

 

[TX7A]

Sam, I will order them and the trial fit.
If they are too big, I'll let you know.
What I am sure of, is that I will not enlarge that hole. I will not have proper edges distance (unless reaming just a little bit). This will definitely oblige me to change all parts.
In the worst case, I will have someone make dedicated bolts for me or fly for a few hours (hundreds?) and then decide to change part and redrill.
My regret is that after 4 years of building, I falled on a stupid issue. I should have waited 5' more before final drilling.
The lesson (already learned, but not enough) is that the airplane have command on your time and not viceversa.

Thanks, Camillo. I will be waiting for your reply. I agree, I will not enlarge the hole either.

 

[longranger]

Another Builder's "Fix"

The following is copied from the tail and wing construction notes section of Vince Frazier's website:

I was cleaning the S t i t s [elongated to bypass censor] epoxy primer paint out of my spar bolt holes using an appropriately sized reamer (0.373" for the 3/8" holes, and so on). It was going fine, until I inadvertantly picked up a stepped reamer that was 0.377" on the top part of the shank. Sure enough, I reamed one bolt hole out to 0.377" and the NAS bolt was a sloppy fit. I hate when that happens!

I realize that one bolt probably wouldn't make any difference but I wanted to fix it anyway. I thought about reaming up to the next size (10mm, IIRC), but wasn't wild about that option. I could always do that later, and besides, who wants one odd bolt in their spar?

Here's what worked for me: I contacted Caswell Plating (www.caswellplating.com) and bought an 8oz. bottle of their CopyChrome nickel plating solution. Following their directions, I plated the bolt up to 0.377" then baked it at 400? F for 4 hours to take care of any hydrogen embrittlement. It worked great.

I also plated some 4130 scraps and was pleased with their appearance. The plating looked like it should be pretty durable. I even soaked a 4130 piece in saltwater overnight and saw no effect. It's not quite chrome, but it looks pretty good. Vince Frazier

 

[IowaRV9Dreamer]

only 3 steps from 1/8 to 5/16 reamer?

I just did mine on Saturday. Drilled 1/8" pilot holes, then enlarged to 9/32" with a standard twist bit, then a 0.3105" reamer. Each of the 3 steps done with 1.5" aluminum block as drill guide

Great info, thanks for posting. Did you literally just use the two drill bits (1/8" and 9/32", and then up to the reamer? I was thinking I'd have to go up from 1/8" to the reamer in many more steps.

 

[roee]

Yep

Great info, thanks for posting. Did you literally just use the two drill bits (1/8" and 9/32", and then up to the reamer? I was thinking I'd have to go up from 1/8" to the reamer in many more steps.

Dave,

Yes, I did literally and exactly that. My initial thought was, same as yours, to step up gradually through many more drill sizes. But what I found through experimentation (on scrap!) was that the more steps I did the more the hole center tended to drift away from its original position, and the edge distance requirement just didn't leave me a lot of room to drift. Also, larger drill bits like the 9/32" tend to be hard to control in a hand drill (i.e. not a drill press) no matter what, even with a guide block, as they have a tendency to chatter and/or bind and/or drift around, especially when first penetrating the material. But to my surprise, I found in my experimentation that these problems actually were worse when enlarging an already large hole than when enlarging a "pilot hole" that's significantly smaller than the drill bit. I can see why that might be, but it wasn't immediately obvious.

So anyway, that technique worked well for me, and it should probably work well for you too. BUT, please don't take my (or anyone's) word for it. The most important take-away lesson from this whole thread, I think, is whatever technique you intend to use, do a test run on some scrap first, before you roll the dice on such a critical step.

Good luck!

 

[Norman CYYJ]

I have seen this problem happen when a cheap drill bit was used. The flutes of the bit were faulty causing an oversized hole. I have never had a problem using good quality bits.

 

[Camillo]

Great idea!

The following is copied from the tail and wing construction notes section of Vince Frazier's website:

I was cleaning the S t i t s [elongated to bypass censor] epoxy primer paint out of my spar bolt holes using an appropriately sized reamer (0.373" for the 3/8" holes, and so on). It was going fine, until I inadvertantly picked up a stepped reamer that was 0.377" on the top part of the shank. Sure enough, I reamed one bolt hole out to 0.377" and the NAS bolt was a sloppy fit. I hate when that happens!

I realize that one bolt probably wouldn't make any difference but I wanted to fix it anyway. I thought about reaming up to the next size (10mm, IIRC), but wasn't wild about that option. I could always do that later, and besides, who wants one odd bolt in their spar?

Here's what worked for me: I contacted Caswell Plating (www.caswellplating.com) and bought an 8oz. bottle of their CopyChrome nickel plating solution. Following their directions, I plated the bolt up to 0.377" then baked it at 400? F for 4 hours to take care of any hydrogen embrittlement. It worked great.

I also plated some 4130 scraps and was pleased with their appearance. The plating looked like it should be pretty durable. I even soaked a 4130 piece in saltwater overnight and saw no effect. It's not quite chrome, but it looks pretty good. Vince Frazier

That's a good idea, also. In the case the NAS bolt will not fill the whole hole, I can use it. Thank-you very much for your advice! Or I can give bolts to a shop to have them plated...

 

[Camillo]

Today, I checked bolt and hole with a micrometer caliper.
Hole is 0.320.
Bolts is 0.310.
Actually, play is very small. I will add negligible.
I will try to buy new AN5 bolts. I guess that the one I have are undermeasure.

 

[Bob_pipedream]

NAS oversize bolts

Hi all,

I joined the club of the following the main original Vans instructions rather than additional Vans instructions and used a drill...

I am not happy with the fit at all, however I may have found the answer in NAS bolts - not 1105, but NAS6205-9DX...

The D stands for drilled and the X is for 1/64 oversize. The beauty of these (if I can find them) is that you can use sand paper and valve grinding paste to smooth out the hole to a very tight fit.

The 9 stands for grip length - not overall length.

Here is two web addresses that may help:

http://www.eng-tips.com/viewthread.cfm?qid=262370&page=2

http://www.gen-aircraft-bolts.com/template.asp?pagename=nashhb
click on download AS hex head bolts and it has a sizing guide...

I hope to source some of these from Germany and will attempt to remember to put my findings back on here...

 

[Bob_pipedream]

Alright just got a quote of about 580 dollars each... so back to the drawing board...

 

[az_gila]

Not too far off...

Today, I checked bolt and hole with a micrometer caliper.
Hole is 0.320.
Bolts is 0.310.
Actually, play is very small. I will add negligible.
I will try to buy new AN5 bolts. I guess that the one I have are undermeasure.

The specification for an AN5 bolt is 0.309 to 0.312 inches diameter.

The NAS 1105 bolt mentioned earlier might be easier to get and is 0.3110 to 0.3112 inches diameter.

 

[Rick6a]

Thoughts & Ideas

Alright just got a quote of about 580 dollars each... so back to the drawing board...

The maximum diameter you can expect with an off-the-shelf AN5 or close tolerance NAS6205 bolt is .312. If the operator produced an oversize hole that mic'ed out at .320, by any measure that is a lot of slop and does not meet minimum engineering standards. No certified aircraft production shop would or could send an airplane out the door that way. For this repair I'd be inclined to consider opening up the hole just a wee bit more to .326 and install a (1/64" oversize) HL62-10:

http://www.hi-shear.com/standards/hl62.pdf

Genuine Aircraft Hardware lists the 1/64" oversize hi-lok fasteners in its catalog, page 165.

The only potential show stopper I envision is this: I am not certain the oversize HL62 with its 5/16-24 "modified" threads will accept an AN (5/16-24) castellated nut. I just don't know. If it does, you should be good to go. To the qualified aeronautical engineers out there...care to weigh in? This area of assembly is designed for removal so you'd have to omit using a standard breakaway hi-lok collar in this critical application because hi-lok collars are typically removed (trashed) using a chisel type tool. That means IF the AN310 nut or a lower profile variant will work, you'll have to jig up and drill a hole through the hi-lok threads to accept the cotter pin. Using the proper tools, that is not very difficult to accomplish.

Like most (but not all) hi-loks, the HL62 does appear to have a hex key hole in its shank so proper torquing to correct spec is possible. If it all works out, the total cost of the repair including the .326 reamer and 2 oversize hi-loks would be several dollars...certainly nowhere near $1160.

Final thoughts: I cannot say for 100% certain that a hi-lok would work in this application but I do know this: Anybody can insert a .312 bolt into a .320 hole. Personally, I wouldn't do my rear spar that way. Aerobatics? This is one area of assembly that standards should be highest and the builder tone deaf to the siren call of "Build on!"

 

[koda2]

Hi-loks

Rick,
I am not an AE so I am framing my comments in part as a question.

Its my understanding that Hi-Loks were designed to replace rivets in fastburners in cases where rivet strength just won't do and that they are not "bolt" strength.

They are, I think much stronger in shear than in tension. The rear spar "looks" like it would need mostly shear strength ("double shear", "tongue-in groove") but I bet there are significant tension loads in flight.

The Hi-Loks only work properly if the hole is reamed exactly for the fastener and are "tapped" or driven in place. A Hi-lok that slides in, is unsat. The Hi-loks are held in place by a special nut that is installed with a custom tool and the nut breaks off at the proper torque, which is probably less that "bolt" torque.

Hi-loks can be removed and replaced but usually only when they work loose and are replaced by going to the next size up.

It might be better to use a machined bushing to take up the slop in the hole. Any thoughts on that?

Somebody set me straight if my comments are not correct.

Dave A.
6A build

 

[Rick6a]

....It might be better to use a machined bushing to take up the slop in the hole. Any thoughts on that?....

Dave,

I too initially thought a bushing would be the ideal choice but in actual practice I see a couple of serious, complicating issues. A repair bushing would require precision technique. The bushing hole itself has to be very high quality and most likely large enough to allow a .375 O.D. bushing to be press fit into it. If the prepared hole is the slightest bit too big, the bushing will fall out or might give way when you drill a full size hole through the center of it. One the other hand, if the prepared hole is too small you run the real risk of cracking or otherwise damaging the structure when press fitting the bushing into it. But there is another major problem to deal with. To allow for wing removal, you could not use just one bushing through the stackup of parts. One solid bushing would lock the wing and the rear spar together permanently. For practical reasons, you would have to machine and press fit 3 separate bushings made in two different thicknesses in order to be able to remove the wing. To do the job right, the I.D. hole through all three bushings would have to be final reamed to .312 only AFTER after the bushings are installed and the wing properly located as if drilling for the angle of incidence. Certainly a professional shop using the correct tooling and technique and accustomed to producing precision high quality holes drilled through steel bushings can do just that...but the average homebuilder? I'm inclined to doubt it.

My thoughts about using hi-loks suppose the hi lok fastener is more than strong enough to handle anticipated loads when used in this unconventional way....replacing an AN bolt. I suspect the hi-lok is strong enough but do not know for absolute certain. That is why I invited qualified engineers on VAF to weigh in with their thoughts. Sure enough, your description of how a hi-lok is normally installed is accurate. Designed for interference fit, a hi-lok is typically inserted into the hole roughly 2/3s of its length then driven home with a hammer or rivet gun. That has the effect of "cold working" the hole which is said to increase strength. The collar is attached, run down and a portion of it breaks away. The installation is considered permanent. In this particular case however, we are seeking an economical high strength fastener that has a shank diameter close to the diameter of the holes (.320) as they currently exist. Ideally, we would use an oversize AN5 bolt but....good luck finding one. If a hi-lok would work in this application, then all the builder would have to do is slightly ream the existing hole(s) only about .006-.007 to produce a snug fit and then install the hi-lok like you would any other AN bolt. That is something I believe your average builder should be able to accomplish.

I don't pretend to have all the answers and there may well be other ways of dealing with this challenging problem in a solid, high quality and economical fashion. If there is, I'd sure like to hear those ideas expressed.

 

[GAHco]

A Hi-lok is....

Rick,
I am not an AE so I am framing my comments in part as a question.

Its my understanding that Hi-Loks were designed to replace rivets in fastburners in cases where rivet strength just won't do and that they are not "bolt" strength.

They are, I think much stronger in shear than in tension. The rear spar "looks" like it would need mostly shear strength ("double shear", "tongue-in groove") but I bet there are significant tension loads in flight.

The Hi-Loks only work properly if the hole is reamed exactly for the fastener and are "tapped" or driven in place. A Hi-lok that slides in, is unsat. The Hi-loks are held in place by a special nut that is installed with a custom tool and the nut breaks off at the proper torque, which is probably less that "bolt" torque.

Hi-loks can be removed and replaced but usually only when they work loose and are replaced by going to the next size up.

It might be better to use a machined bushing to take up the slop in the hole. Any thoughts on that?

Somebody set me straight if my comments are not correct.

Dave A.
6A build

Hi-Lok's (HL18 and HL20) are basically an NAS Bolts with a minimalist head style to save weight. The HL18 is acceptable for shear loads (smaller head) and the HL20 is for Tension or Shear (Bigger Head).

They have almost identical strengths to the NAS Bolts NAS1100, 1300, 6200,and 6600 series of NAS Hex Head Bolts.

The NAS Bolts are typically less expensive and only a slight bit heavier.

While we stock a goodly assortment of both, the Hi-Lok's we have are mainly 1/4" diameter and smaller. We also carry a large selection of Nas bolts from 3/16 to 3/4" diameter.

Here is the info on NAS Bolts http://www.gen-aircraft-hardware.com/images/pdf/nashhb.pdf

Read Carefully the codes for the parts #s that denote oversize.

For a tight fitting shear fastener where all of the structure is aluminum except the fastener being steel, there should be an interference fit of .0005 to .0015 inches. I prefer the minimum as that maximum does require a bit more effort to install and unless you can press it in with backup you could damage your structure.

This should help.

http://www.gen-aircraft-hardware.com/store.asp?subsubcat_id=457&category=Hex+Head%2C+Close+Tolerance&breadCrumb=Hex+Head%2C+Close+Tolerance%20-%3E%20NAS+Bolts%20-%3E%20Bolts&menuID=17~18~18~19~19~25~25~32~32&id=32

Please be advised the page from our reference book is NOT a stock list, we may or may not have just what part # you have decided should work best.

 

[az_gila]

Rick, I'm confused...

Dave,

I too initially thought a bushing would be the ideal repair choice but in actual practice I see a couple of serious, complicating issues. A bushing would require precision technique. The bushing hole itself has to be very high quality and most likely large enough enough to allow a .375 O.D. bushing to be press fit into it. If the prepared hole is the slightest bit too big, the bushing will fall out. If the prepared hole is too small, you run the risk of cracking or otherwise damaging the structure when press fitting the bushing into it. But there is another major problem to deal with. To allow the wing to be removed, you could not use just one bushing through the stackup of parts. One solid bushing would permanently lock all the parts together. To be practical, you would have to machine for and press fit 3 separate bushings made in two different thicknesses in order to be able to remove the wing. To do the job right, the I.D. hole through all three bushings would have to be final reamed to .312 only AFTER after the bushings are installed and the wing properly located. Certainly a professional shop using the correct tooling and technique and accustomed to producing precision high quality holes drilled through steel bushings can do just that...but the average homebuilder? I'm inclined to doubt it.
.....

...about the need for three separate bushings.

The original specification is for a "slip fit" hole for the bolt, not an interference fit, I think. The latest -6 plans still call for a 5/16 hole, and the "Incidence setting" PDF does not specify final drill/reamer size.

If a long bushing, just slightly shorter than the thickness of the three pieces to allow for a clamping effect, was used wouldn't that be similar to the original requirement? This bushing would be machined to the original fit requirement specified by Vans, and just look like a bolt to the assembly.

The hole in the bushing then can be reamed to a "tight push fit" for a 1/4 inch bolt.

No interference fits or drive fits are specified for this part are they?

 

[Walt]

..about the need for three separate bushings.

The original specification is for a "slip fit" hole for the bolt, not an interference fit.

If a long bushing, just slightly shorter than the thickness of the three pieces to allow for a clamping effect was used, wouldn't that be similar to the original requirement? This bushing would be machined to the original fit requirement specified by Vans.

The hole in the bushing then can be reamed to a "tight push fit" for a 1/4 inch bolt.

No interference fits are drive fits are specified for this part are they?

I agree with Rick on this, the bushing is there only to repair the oversize holes, not to replace the bolt. I used to get involved in quite a few bushing repairs on spars for O/S holes and we would always make seperate bushings for each piece, line ream the holes then install the original fastener.

I also like the Hi-lok suggestion, haven't done any research on it but oversize Hi-loks are readily available and in shear they are certainly up to the task.

 

[az_gila]

yes.. but in the repair case...

I agree with Rick on this, the bushing is there only to repair the oversize holes, not to replace the bolt. I used to get involved in quite a few bushing repairs on spars for O/S holes and we would always make seperate bushings for each piece, line ream the holes then install the original fastener.

I also like the Hi-lok suggestion, haven't done any research on it but oversize Hi-loks are readily available and in shear they are certainly up to the task.

...you mention the oversize holes are probably due to wear, and are not equal on all parts. In this case we have a clean hole, in the right place, it's only wrong because it's a few thousands oversize.

I also bet in the spar case you mention there is a row of bolts that need to spread the load evenly between them, hence the need for the line bore - in this case, it's a single bolt in double shear.

I think we are dealing with a different problem... so, why not replace the bolt with a suitable steel bushing, with a smaller, but higher grade bolt to provide the clamping action?

 

[Walt]

...you mention the oversize holes are probably due to wear, and are not equal on all parts. In this case we have a clean hole, in the right place, it's only wrong because it's a few thousands oversize.


I also bet in the spar case you mention there is a row of bolts that need to spread the load evenly between them, hence the need for the line bore - in this case, it's a single bolt in double shear.


I think we are dealing with a different problem... so, why not replace the bolt with a suitable steel bushing, with a smaller, but higher grade bolt to provide the clamping action?

1) No not wear, holes are regularly drilled oversize by accident...

2) No, I've seen many cases, they all get treated the same way.

3) Using the method you are suggesting the bushing would now be the "fastener", bushings are not fasteners (bolt in this case).

 

[az_gila]

Not quite...

....

3) Using the method you are suggesting the bushing would now be the "fastener", bushings are not fasteners (bolt in this case).

....the bushing would be a "bolt substitute" for shear, and the tension would be the high strength 1/4 bolt used in normal "clamp mode" for tension.

With the original -6 plans (still not changed) specifying a 5/16 hole, what is the betting that a large number of -6s are flying around with fairly loose fitting bolts in this application? A perfect 5/16 hole and a low end tolerance AN5 bolt will give a 0.003 loose fit - I bet a lot flying around are much looser than that....

 

[Walt]

....the bushing would be a "bolt substitute" for shear, and the tension would be the high strength 1/4 bolt used in normal "clamp mode" for tension.

With the original -6 plans (still not changed) specifying a 5/16 hole, what is the betting that a large number of -6s are flying around with fairly loose fitting bolts in this application? A perfect 5/16 hole and a low end tolerance AN5 bolt will give a 0.003 loose fit - I bet a lot flying around are much looser than that....

A .0320 OD bushing with a .250 ID bolt hole would leave you with a bushing wall thickness of approx. .035. I don't think this is in the same shear load catagory as a 5/16 bolt

 

[az_gila]

But if the bushing...

A .0320 OD bushing with a .250 ID bolt hole would leave you with a bushing wall thickness of approx. .035. I don't think this is in the same shear load catagory as a 5/16 bolt

...is a tight push fit on the bolt, why only consider it as a 0.035 wall tube instead of the entire 5/16 dimension?

It's not an empty tube (aka bushing), it's filled with hard steel...

I need a consultation with my friendly aerospace mechanical engineer...

 

[Walt]

...is a tight push fit on the bolt, why only consider it as a 0.035 wall tube instead of the entire 5/16 dimension?

It's not an empty tube (aka bushing), it's filled with hard steel...

I need a consultation with my friendly aerospace mechanical engineer...

Well for one thing a bushing cannot be made out of the same material as a bolt, they are usually of 7075-T6 (in aluminum structure), so now you're back to the 1/4" bolt carrying all the load.

I'm not an AE but I've been in the business a long time, I know what kind of repairs are generally acceptable and which ones are not according to most major airframe manufacturers. Sorry to say it but this one just doesn't fly.

Assuming you have good ED the oversize bolt or Hi-lok is the best idea IMO. I know I wouldn't fly any airplane with a loose fitting bolt in the rear spar, certain things you can "cheat" on, spar attachments aren't one of them

 

[GAHco]

Just do what needs to be done.

A 1st oversize 5/16 bolt should fix it unless the holes are really messed up then get a 2nd oversize.

1st oversize is 1/64th, 2nd is 1/32.

Even if the bolts are expensive Its cheaper and faster than putting new spar straps in.

Best wishes, Call me if you have further questions

 

[az_gila]

I would use steel for...

Well for one thing a bushing cannot be made out of the same material as a bolt, they are usually of 7075-T6 (in aluminum structure), so now you're back to the 1/4" bolt carrying all the load.

I'm not an AE but I've been in the business a long time, I know what kind of repairs are generally acceptable and which ones are not according to most major airframe manufacturers. Sorry to say it but this one just doesn't fly.

Assuming you have good ED the oversize bolt or Hi-lok is the best idea IMO. I know I wouldn't fly any airplane with a loose fitting bolt in the rear spar, certain things you can "cheat" on, spar attachments aren't one of them

...the bushing - I never mentioned aluminum. This part has to be custom machined to fit anyway to get the right ID and OD.

And it's not really a bushing if it's a tight fit on the bolt and a slip fit in the spar hole... it's a bolt diameter extender...

You are still thinking of a part that is stuck in the spar to fix a hole - I am suggesting a part to "fix" the bolt - a completely different scenario mechanically.

Will call my friendly Aerospace mechanical engineer tomorrow...

I agree this should be a good fit, but my point was that I bet many -6s are flying around to the original drawings with a fairly loose bolt fit anyway, and no problems have been reported.
This joint must flex a little since Van changed from the original lock nut to a cotter pin nut/bolt somewhere along the -6 production time...

 

[Bob_pipedream]

Hi Rick,

I need to check again, but I think mine will be fine and the 'slop' is very little (possibly I drilled to 0.313 - 0.315 after sanding the hole to produce smooth and no score marks). The slop I noted last week was from checking the close tolerance in the fuselage holes as I ran out the door. I had a quick look this week and realised the close tolerance bolt I had actually bunged in the hole quickly was a AN174-7 bolt so where it passed through the second bar of the fuselage spar attach (wings are not on at the moment) it only had the threaded part of the bolt. I am ordering new close tolerance bolts this week at a full 8 long (AN1745-8) and suspect that will be good.

The HL bolt does look good if it does turn out that I needed to do something later, I sent an email to them last week but no answer yet.

The thing is with this joint is that it is not a pivot joint (someone said that it was elsewhere). My understanding is that there should be no movement during service. A tight fit is a must, but the fit could be tightened (only slightly of course) by painting the holes with etch primer rather than leaving it untreated and using a standard bolt/bearing fit type of loctite. For me this would result in a firm fit with no play. I am probably being fussy with the fit of this bolt, but I am already suffering overdoitus that is being exaggerated by how flimsy the rear spar attach mount is.

Half of me wants to increase the whole rear spar plate size/thickness and put in three bolts etc. But I am managing to resist the desire to upsize everything...

 

[apkp777]

Hi Rick,

The thing is with this joint is that it is not a pivot joint (someone said that it was elsewhere). My understanding is that there should be no movement during service. A tight fit is a must, but the fit could be tightened (only slightly of course) by painting the holes with etch primer rather than leaving it untreated and using a standard bolt/bearing fit type of loctite. For me this would result in a firm fit with no play. I am probably being fussy with the fit of this bolt, but I am already suffering overdoitus that is being exaggerated by how flimsy the rear spar attach mount is.

Half of me wants to increase the whole rear spar plate size/thickness and put in three bolts etc. But I am managing to resist the desire to upsize everything...

It is a pivot joint. Though very little, there is some rotation. Don't put in 3 bolts. That would be disastrous. Prime the hole, then build on. If this hole was supposed to be machined tolerance, Van's would have made that clear. My bolt was tight. At least tight enough. Just like every RV flying I suspect.

 

[apkp777]

I wouldn't use a Hi-Lok. You need to cotter pin the nut and that'll be a problem with the Hi-Lok.

You may be able to use a taper pin, I am not a big fan of those. I really think your bolt is fine. It is not going to fail. It's also easy to inspect regularly. You'll see obvious signs of "working" if there is a problem.

 

[Rick6a]

.......I think mine will be fine and the 'slop' is very little (possibly I drilled to 0.313 - 0.315 .....

The HL bolt does look good if it does turn out that I needed to do something later, I sent an email to them last week but no answer yet...

Bob,

Fitting a .312 bolt into a .315 hole should be fine. I hate to paint with a broad brush but .003 over is generally considered within the acceptable range of tolerance in many applications. I suspect Van's will concur. Call em.

This discussion has been dealing with a hole that is .320. Now that is just too big to ignore.

 

[az_gila]

Pivot joint...

It is a pivot joint. Though very little, there is some rotation. Don't put in 3 bolts. That would be disastrous. Prime the hole, then build on. If this hole was supposed to be machined tolerance, Van's would have made that clear. My bolt was tight. At least tight enough. Just like every RV flying I suspect.

Checking old drawing revisons -

This joint must flex a little since Van changed from the original lock nut to a cotter pin nut/bolt somewhere along the -6 production time...

 

[LettersFromFlyoverCountry]

Is there a close tolerance bolt available in the 5-10 size. The smallest Aircraft Spruce seems to have is a -14.

 

[Bob Kuykendall]

If I had a .315" hole to fill, I'd just find a Class 10.9 M8 metric bolt with about the right grip length and use that. But that's just me. We use tend to use more metric hardware in the sailplanes.

 

[az_gila]

It seems that you...

If I had a .315" hole to fill, I'd just find a Class 10.9 M8 metric bolt with about the right grip length and use that. But that's just me. We use tend to use more metric hardware in the sailplanes.

...would need a 9 mm metric bolt, and that just doesn't seem to be a standard size...

 

[Bob Kuykendall]

...would need a 9 mm metric bolt, and that just doesn't seem to be a standard size...

I think an 8mm is about right. When I evaluate 8 mm/25.4 mm per in, the mms in the numerator and denominator cancel out and I get 0.315 in.

Thanks, Bob K.

 

[az_gila]

See psor #43...

I think an 8mm is about right. When I evaluate 8 mm/25.4 mm per in, the mms in the numerator and denominator cancel out and I get 0.315 in.

Thanks, Bob K.

...we are talking about a 0.320 hole... the 8 mm is just a little too small.

A perfect sized 8 mm would be only 0.0033 larger than a close tolerance 5/16 aircraft bolt. I don't have a spec. for metric bolts, but I bet the come a bit undersized too...

 

[Bob Kuykendall]

...we are talking about a 0.320 hole...

Sorry, I was thinking of the hole that Bob_pipedream drilled, which was .315 or so.

Thanks, Bob K.