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  #1  
Old 08-17-2021, 11:09 AM
bsbarnes10 bsbarnes10 is offline
 
Join Date: Sep 2019
Location: Texas
Posts: 39
Default Stub spar socket fitment

Hi,
I've got some questions about how the stub spar socket (F-1206C) is supposed to fit on to the end of the spar (W-1208B-R & L & W-1207B). Looking at step 8 on page 20iS/U-03 it states:

"File the rear stub spar rounded ends of both wings to closely fit the recessed machined curve of the F-1206C. See Figure 4. The small flat on F-1206C locates the top of the part."

What orientation should F-1206C be "clocked" to when filing the end of the spars? If I had to guess I would think it should be as shown in figure 1, with the flat on the bottom of the spar aligning with the flat on the socket. However, figure 2 & 3 show the socket rotated further and I didn't see anywhere in the plans where it is clearly described which is correct. I could also see how the orientation in figure 3 could make sense.

I did search and find an earlier post on this but the image was broken so I couldn't see what the forum members agreed was correct. Since I don't have a completed airplane handy I can't check and see the orientation of the wings vs. the fuselage socket...

Figure 1 (this is how I think it should be):



Figure 2 (rotated about midway):



Figure 3: (rotated all the way the other direction):




Any help would be greatly appreciated!
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  #2  
Old 08-17-2021, 12:57 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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The position reference should be where it fits the best before you do anything to the parts (middle photo)
Keep the material removal to the bare minimum possible.
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  #3  
Old 08-17-2021, 01:12 PM
bsbarnes10 bsbarnes10 is offline
 
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Excellent, thanks for the quick reply Scott. You're always there with guidance and it is immensely appreciated!

Bruce
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  #4  
Old 08-17-2021, 08:53 PM
RFSchaller RFSchaller is offline
 
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Scott,

My 12 is coming up on 10 years and a little over 1100 hours. I noticed a slight “click” every time I got onto the engine after a couple of years, and I shimmed the spar tongues with a .025” shim traced from the spar tab with the bottom of the shim bent under the spar tab. Problem fixed. I am wondering how critical this issue is. Isn’t the stub spar tab basically an anti- rotation device to keep the wing from twisting? If so, is a slight “slop” in fit really a big issue?

Rich
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  #5  
Old 08-18-2021, 08:44 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by RFSchaller View Post
Scott,

My 12 is coming up on 10 years and a little over 1100 hours. I noticed a slight “click” every time I got onto the engine after a couple of years, and I shimmed the spar tongues with a .025” shim traced from the spar tab with the bottom of the shim bent under the spar tab. Problem fixed. I am wondering how critical this issue is. Isn’t the stub spar tab basically an anti- rotation device to keep the wing from twisting? If so, is a slight “slop” in fit really a big issue?

Rich
The fwd. and aft stubs are there to take twisting/torsional loads but that is not the primary.
The highest loads are an inward compression load at the fwd. stub. That is why there is some pretty heavy structure on that bulkhead member.

A slight amount of fore/aft play in a wing is not a major concern but there is a limit. We have a document that has instructions on how to measure the amount of play and what is the expectable limit. It is not publicly available because we prefer to have direct communication with someone looking at a loose wing issue.

As for adding a .025 shim? I would consider that extreme, and would be way outside of what our acceptable limits are.

Of a bigger concern is that adding a shim in that manor has probably compromised the fit of the stub in the socket.
With the way the parts fit, adding a constant thickness shim will have a negative impact on the proper nesting of the two parts.

For the lack of a better illustration, I have attached a photo of a solar eclipse to mimic the two round parts. Note that as the two radiused edges become displaced, the amount of displacement varies along the edge, with the most difference being at the mid point and no difference at the top and bottom.

This should also be considered if someone decides to remove material at initial wing fitting because they can't quite get the wing inserted fully. This depiction shows that most material should be removed at the mid point and then varying the amount along the edge to where no material is removed at the top and bottom.

Another point related to a .025 thick shim is that if we evaluate the ratio of wing panel length/span to the distance of the shimmed stub from the hinge point of the movement (the main wing spar). If the .025 shim were installed at the rear stub, the dimension ratio is approx. 5:1, so that .025" shim thickness would be equivalent to a fore/aft wing movement of 1/8" out at the tip. We would consider that excessive.
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Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 08-18-2021 at 03:21 PM.
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  #6  
Old 08-18-2021, 01:30 PM
Bob Y Bob Y is offline
 
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Scott, what’s the difference between using a W-1207B-25 spar stub vs. a 0.025” shim? Don’t they both perform the same function?
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  #7  
Old 08-18-2021, 03:19 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Bob Y View Post
Don’t they both perform the same function?
No

Using the W-1207B-25 would extend the dimension of the stub in the same way as depicted in the eclipse illustration in my other post.

If a .025 shim is used, it is adding .025 to the entire radius of the end.

Look closely at the sliver of the sun that is visible. Its visible width is changing along the entire length of the radius. This is important so as to maintain contact between the spar stub and the socket within the fuselage, around the stubs entire circumference.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

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Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #8  
Old 08-18-2021, 04:47 PM
FlyingDiver FlyingDiver is offline
 
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Is this assembly specific to the RV-12 and not the RV-12iS? I couldn't find that illustration in the plans I have for the 12iS.
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  #9  
Old 08-18-2021, 05:44 PM
rv9builder rv9builder is offline
 
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Quote:
Originally Posted by FlyingDiver View Post
Is this assembly specific to the RV-12 and not the RV-12iS? I couldn't find that illustration in the plans I have for the 12iS.
It applies to both. I haven’t seen a specific drawing that shows the spars fitting into the receptacles, but read Step 8 on Page 21iS/U-03: File the rear stub spar rounded ends of both wings to closely fit the recessed machined curve of the F-1206C. See Figure 4. The small flat on F-1206C locates the top of the part.

Also see Step 6 on Page 21iS/U-13: File the curved recess of both F-1203C (the bevel locates the top of the part) to closely fit the rounded mating ends of the Stub Spar Assemblies of both wings then mark the parts to ensure they can be assembled on the side to which they were fitted.
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  #10  
Old 08-18-2021, 06:14 PM
FlyingDiver FlyingDiver is offline
 
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Quote:
Originally Posted by rv9builder View Post
It applies to both. I haven’t seen a specific drawing that shows the spars fitting into the receptacles, but read Step 8 on Page 21iS/U-03: File the rear stub spar rounded ends of both wings to closely fit the recessed machined curve of the F-1206C. See Figure 4. The small flat on F-1206C locates the top of the part.
Ah. The OP stated page 20iS/U-03, not 21iS/U-03. Hence my confusion.
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