Rear spar hole drilled with 5/16

[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]

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]

Originally Posted by Camillo

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]

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_%20Incidence.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]

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/catalo...s/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.