Wing attach blocks

[142YX]

I have found what i believe to be an error in the prints that i consider to be a big deal.

The callout is to drill the pilot for the main spar attach holes 7/16" from the edge of the wing attach blocks:


One would think you want to have the spar attach pins in line with the rest of the fasteners at the end of the spar, but this dimension will not produce this result as seen here in this picture of my spar:


This is because the 7/16" dimension is wrong:


It should be 1/2"



It seems as if many people on the Yahoo groups are complaining about the same issue that i am facing, which is their spar pins end up being too far outboard.. too close to the forward wing attach angles in the fuselage. This is the reason right here. It is already so tight that i wouldn't be able to spin a nut onto an AN6 bolt, were the bolt installed from the rear. I think i could fix my oval'ed hole problem by upsizing to a AN7 bolt.. but i dont see how it would fit without grinding off one side of the bolt head, and i will be left with far a far below standard edge distance at the end of my spar (5/16" edge for a 7/16" bolt). I had considered upsizing to a NAS6206-##X or NAS6206-##Y bolt (the "X" and "Y" being code for a 1/64" and 1/32" oversize, respectively) they use the same -6 size nut, but the bolts are impossible to find.

I have already bought myself into making new wing attach blocks, and all four wing attach angles. Because of how nearly impossible it will be to match drill the holes on the new wing attach angles to the existing dimpled holes in the spar-box sheet; i am going to re-build the entire spar box. I still have no clue what bolt size i am going to end up with, and finding out that i am pushing my edge distance because of, what i consider to be a print error is destroying my motivation.

Perhaps i am over thinking everything, and the shear web area contributes very little to the overall bolt bearing because of the size of the wing attach blocks, and therefore the bolt size is irrelevant and does not need to make contact with the shear web at all.

[N111YX]

Hang in there! Many of us had to remake attatch blocks... :x In the big picture (building and flying for years) this is a relatively small hiccup. Yeah, I hate going backwards and have done it many times already during the Pitts wing construction. If everything always went perfectly I'd be worried... ;)

As for the edge distance, perhaps there is a reason for the 7/16 dimension. I recall the wing bolt nut being close to the angle but still a good fit. You might ask Kerry before you change the location...

[142YX]

Whelp, after about two months of re-work.. i have completed fixing everything i screwed up with the wing attach. Here is what i did:

First off.. i convinced myself to rebuild the entire spar box, all four wing attach brackets, and the aft shear plates. I figured there would be no way that i would be able to drill out and match drill all of those countersunk rivets, and that i would be much happier with myself if i just re-did the whole thing. This also meant re-making those brackets that come off the aft of the spar box through which the flight control stick assembly mounts to.

I then re-made all of the bearing blocks for the main wing spars. Twice, actually, because i wasn't happy with the way the first re-makes came out. I first tried to make just the bearing blocks and match drill the existing holes into them, but with less then acceptable results.



For try #3, i just remade brand new bearing blocks and bearing block angles, which required drilling out four solid rivets in the spars. One of them got wallered pretty bad, so i up-sized it to a -6 rivet. I then jigged up the wings on some saw horses with only the blocks/angles on the forward spar and set up a drill bushing guide on the aft spar. I grabbed the location by putting a 3/8" bearing into the guide, using a 3/8'' rod inserted through the bushing and into the existing 3/8" (ever so slightly wallerd) hole in the two spars.







I then used my fancy 3/8" with 1/4" pilot bit to start a 1/4" hole in the forward side block/angle, then changed the 3/8" bearing to a 1/4" bearing and punched through all the way with a 1/4" hole.





Then i took the wings apart, installed the aft blocks/angles, re-jigged the wings back together and transferred the 1/4" hole through the aft blocks/angles using the now existing 1/4" hole in the forward ones as a guide. This process, although tedious, left me with perfectly centered 1/4" holes to the existing holes in the shear web of my wing spars.



I then re-jigged the wings to the fuselage and repeated the whole wing attachment procedure for a second time, however this time i used the fancy 3/8" with 1/4" pilot drill bit.. with the 1/4" pilot section significantly dulled out.



I was thrilled with the results, perfect holes with no slop whatsoever!!



Although extremely tedious and de-motivating at the time.. it feels pretty good to be done with it all and have an airplane sitting there in my hangar now :D

[N111YX]

Looks great. I found that despite "going backwards" sometimes for many hours of re-building, I could sleep much better when things were done to perfection...!

[sonex892]

I have found what i believe to be an error in the prints that i consider to be a big deal.
The callout is to drill the pilot for the main spar attach holes 7/16" from the edge of the wing attach blocks:.

Glad you got it sorted. Just curious though, for your second attempt did you follow the plans or are you still convinced there is an error?

Personally I dont believe there is an error in the plans with the wing attach blocks.

Mine and many hundreds of other flying sonex's are built per the plans dimensions. Yes it is tight to get that 3/8" nut on the bolt.

Steve
Sonex 892
3300 bing carb TD 118hrs

[rizzz]

I would like to know the answer to this question as well, I've just started assembling my wings.
I've cut my wing attach blocks a long time ago when I was making the parts but I had not drilled them yet since at the time I wanted to gain a bit more experience before drilling such critical holes.
I

[142YX]

..for your second attempt did you follow the plans or are you still convinced there is an error?

Personally I dont believe there is an error in the plans with the wing attach blocks.

I think it clearly works out, so i cant argue that it is "wrong", but if i was doing it over, personally i would probably use the larger dimension. It is extremely tight, there is no room to upsize if i will need to in the future, and i dont think i would be able to install the nut/bolt if i didnt do the "three flush rivet" mod (seen in the closeup photo of the bolt). I am not worried about it.. but i do think it would be just a bit better with an extra 1/16" of clearance. I was not able to change the hole location on my second attempt because i already had the holes in my shear web.

[fastj22]

My wing bolts were done to plans design. Yes, the hole on the forward side of the spar tunnel is very close to the fuse angles. I had to grind down one of the gusset rivets to get the nut to fit. But it did fit. I'm not sure the plans are wrong, but it could use some review.

[Sonex1517]

I've been following this thread closely, as I am just now clamping my spars together to updrill.

I believe the question I have is directly relevant to this thread, so I will add it here instead of starting a new one.

I currently have the blocks at 3/16" and am mating the spars to updrill to 1/4" slowly in increments. I am set up to do this tomorrow morning.


Can someone please clarify what the final, last size of these holes will be when the wings are mounted and attached to the aircraft? Is the 1/4" the final size? I was told the final bolts are AN-6 and that would mean larger holes, obviously.

I trust the source so I am just trying to think ahead and be cautious.

thanks and blue skies


Robbie
Sonex 1517

Sent from my iPad using Tapatalk HD

[MichaelFarley56]

Hey Robbie,

I'm looking at my plans, for you page # SNX-W02, and following the directions it says the main holes will be drilled to 1/4" after everything is lined up, then step drilled to 3/8" for the final size. I believe AN-6 is a 3/8" hole.

Good luck!