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alpinelakespilot2000

Well Known Member
Another main wing spar bolt question/concern...

Just hoping someone will give me some confirmation of a similar experience for my peace of mind....

Just fit my wings two nights ago. They went on easy, no problem. I used drift pins and then lubed hardware bolts that could be inserted quite easily--just some light taps with the mallet. Went out last night and, just for curiousity's sake, lifted up on the right wing tip. Fuselage lifted right up and it felt like a solid connection. Went over the the left wing, lifted it up at the tip and felt a little "give" (wing moved maybe a half inch max, fuselage stayed put). All of a sudden I get consumed with a fear that maybe my spar is flexing somewhere in the middle. :eek:

Alas, it's just the intersection between the wing and center section... you can see the relative movement there when the left wing is lifted up and down. My first thought was that it must just be that the hardware bolts are a little undersize allowing some play in that joint, right? Seems like a reasonable explanation, except that I reversed all the bolts on the right side for those on the left side and I still had that play in my left wing.

Why the play in one side but not the other? Could it be that the pre-drilled holes in one side are slighly larger than those on the other? (I wouldn't think so on a critical part like this.) Once I put the close tolerance bolts in will my problem on that one wing go away? (I'd put some of the close tolerance bolts in right now but they are a really tight fit. I'd rather just put them in once at the end.)

I'm now paranoid that I'll go to the airport a year from now for final assembly with the new bolts, just to find my left wing still "giving" a little! Anyone have a similar experience?
 
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Once you have the wings off again, you can test fit the close tolerance bolts in the center section and wings separately. You can tell that way if any of the holes are over-sized, but I truly doubt they are.

That is strange, though. I didn't test the play of my wings when I just had the hardware store bolts installed. I can tell you that with the close tolerance bolts in there, they are rock solid.

Dave
 
tolerances

I'd be willing to bet that once you use close tolerance bolts this will go away. If you think about it, the hole size has a tolerance and the hole position has a tolerance. These can be additive of subtractive depending on the manufacturing process. That's why one side seems tight and the other one is "loose". I help a friend put the wings on his 9A and they didn't go in with light tapping. It took some lube on the shank and a pretty good wack with hammer on a wooden block. I'd also think that during the manufacting process, these holes are gaged to veryify the size since they are so critical. I think the temporary bolts are the culprit.
 
Thanks for the comments. Last night I went ahead and put in my two smallest 7/16" close tolerance bolts because it was bugging me. Yes, they take some serious persuasion to get in (even lubed and even on that left side) and, yes, with just two of the bolts in (one on top and one on bottom) things seemed to be much more solid than they were with the store bolts. I'm sure by the time I get all 8 bolts in it will be fine. Still, it just amazes me that the only thing that holds those wings to the airplane are the 8 bolts on each side. I definitely want to make sure that they're ALL doing their job! Thanks again.
 
Steve:
I had the same concerns re. the number and size of bolts when I first attached the wings on my 9A. If I recall, a check in SAE standards showed shear strength in the area of 30,000 pounds per side. If you start pulling close to 20gs, I expect a number of things will let loose before the bolts fail.
Terry
 
Yeah, Terry, the rational side of my brain knows these things are pretty strong. I know a couple of people who are building Thatcher CX-4's. They only use two 1/2" bolts total. Granted, it's a single place plane, but also aerobatic.

BTW. I checked with Van's who indicated that all is normal. In fact, the side where there is no play with the store bolts is where they said I might have a problem since it will be more challenging to drive the bolts in on that side.

Thanks again for the comments of all.
 
How' bout three?

alpinelakespilot2000 said:
Still, it just amazes me that the only thing that holds those wings to the airplane are the 8 bolts on each side. .
Click to expand...

FWIW,
Steve,
Cessna Agwagons only have one bolt at the main spar and one at the rear spar. Another one at the strut/fuselage connection. That's why Aeronautical engineers make $10/hour and we make $5/hour :D Cessna 210's have two bolts on the main spar and one at the rear.

Regards,
 
Tapered reamer

A buddy of mine used a tapered reamer on his -6 laminated wing spar holes and fuselage before we mounted the wings. The 28 bolts (per side) slid right in with light tapping.
Steve
 
szicree said:
You do have the splice plates in too, right?
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I am virtually certain the -9 uses the new spar arrangement like the -8 - a totally different design than the -3, -4, -6. There's no splice plate and just 8 bolts per side in the new design.

Also, no reaming should be necessary. Get the holes and bolts very clean. Maybe even polish the bolts with a little Scotchbrite. The same on a split dowel for the holes. Using drift pins to align, lubed up they should go with a little bit of encouragement from a block of wood.

Get all the bolts in, and there will be no slop. You got very big problems if there's any movement.
 
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