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Rear Spar Misalignment

Craw

Active Member
Good Afternoon All,
I have reached the phase in my RV-7A Quick Build kit where it was necessary to set the wing incidence. In doing so it has become apparent that I have a misalignment between the following components:

1. W-707G rear wing spar & W-707D rear spar doubler and the gap between the fuselage F-605C Bar doubler & F-705B centre section. I have included dimensions of the distance from the rear of the W-706 Main Wing spar to the forward portion of the F-705B Centre Section Bar in the diagram (figurer 1-1) below as well as some images of the problem.
Figurer 1-1
https://postimg.cc/Z937s5Bk
https://postimg.cc/75hj94nD
https://postimg.cc/dLLzmvBF
I loosened the bolt holding the spacer between the centre bar and the doubler on the left (starboard) side and, although I was able to force the rear spar into position, the rear spar was bent forward and the centre section bar (F-705C) was bent slightly aft. There was a great deal of pressure between the two. I was unable to force the rear spar of the right (port) into gap between the F-705B centre bar and the F605-C doubler.

2. Furthermore, the right side of the fuselage rear spar appears to be twisted by 1/16” as shown in the diagram (Figure 2-1)below.
Figure 2-1
https://postimg.cc/18LjtmBW

3. I have also noted that the rivets in the F-705D bulkheads appear to be slanted as the top of the rivet line are very close to the web of the F-705D where as near the bottom they appear to be in the middle of the bulkhead. Please refer to the diagram and image below:
https://postimg.cc/v4qGSVQ4
https://postimg.cc/qgxqxgC3

I have e-mailed Vans regarding this issue but am curious to know if other Quick Build builders have encountered this issue.

Regards,

Phil
 
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Re: Item #3 in your post. The rivets are shifted a bit toward the radius (forward) of the F-705E-L/R doublers as they nest inside the F-705D-L bulkhead side channels.

Just out of curiosity, did you already make the cut to the wing rear spars (DWG 38 Sec A-3, Sec B-3) ?
 
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Morning Brian,
No, I have not made the trim yet, however, even with the trim I would not be able to get the rear spar into position.
 
Morning Brian,
No, I have not made the trim yet, however, even with the trim I would not be able to get the rear spar into position.

You might be surprised. I remember the first time I attempted to mount the wings on my -6 and how critical it was to have the wings perpendicular to the fuse to get the rear spar tab to fit in the fuselage attach point.
 
Make the trim AND file a bit more of a radius at the top -- this will allow the rear spar to clear the AN470 rivet head that sits in between the two fuselage spar "tangs."

Also, when you insert and afix the front spars, use drift pins instead of the NAS close tolerance bolts...you'll need the wiggle room.
 
You might be surprised. I remember the first time I attempted to mount the wings on my -6 and how critical it was to have the wings perpendicular to the fuse to get the rear spar tab to fit in the fuselage attach point.

Spot on Kyle; 19/32" makes quite a bit of difference here.
 
Spot on Kyle; 19/32" makes quite a bit of difference here.

Hey guys

I was helping Phil with this on the weekend. I don't think trimming the 19/32" off the inboard end of the rear spar is going to help in this instance. We carefully measured the distance between the front spar and rear spar on the wings, and then from the center section to the rear spar attach. Both wings had the same inter-spar distance. However, the rear spar attach points (lets just say the rear spar bar F-705C) were too CLOSE to the front spar to allow the rear spar to slide in, and the port and starboard sides were 1/16" different.

The other issue is that the starboard side rear spar bar (and doubler) were at an angle WRT to the rear spar, whereas the port side was perfectly lined up vertically.

We spent several hours noodling over this, ensuring that the sweep was 0, that the incidence was 0, that we had not screwed something up. When we loosened the spacer bolt on the starboard spar doubler we were able to force the rear spar in but it took a LOT of force and left a bend. We weren't able to get the port side to fit at all.

I understand that trimming the end of the spar is important to get the right fit (I had to do the same thing on my -8 years ago). HOWEVER, the rear spar double should be coplaner with the rear spar itself and there was NO point at which we could achieve this with either wing; the rear spar double is too far forward so any trimming of length will have no effect that we can see. This, coupled with the fact the two sides are different distance from the front spar AND the starboard side spar bar and doubler are twisted WRT the wing rear spar itself, leads us to believe that there is a serious issue here.

Sorry for the long winded explanation :rolleyes:
 
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Spar

Hey guys

I was helping Phil with this on the weekend. I don't think trimming the 19/32" off the inboard end of the rear spar is going to help in this instance. We carefully measured the distance between the front spar and rear spar on the wings, and then from the center section to the rear spar attach. Both wings had the same inter-spar distance. However, the rear spar attach points (lets just say the rear spar bar F-705C) were too CLOSE to the front spar to allow the rear spar to slide in, and the port and starboard sides were 1/16" different.

The other issue is that the starboard side rear spar bar (and doubler) were at an angle WRT to the rear spar, whereas the port side was perfectly lined up vertically.

We spent several hours noodling over this, ensuring that the sweep was 0, that the incidence was 0, that we had not screwed something up. When we loosened the spacer bolt on the starboard spar doubler we were able to force the rear spar in but it took a LOT of force and left a bend. We weren't able to get the port side to fit at all.

I understand that trimming the end of the spar is important to get the right fit (I had to do the same thing on my -8 years ago). HOWEVER, the rear spar double should be coplaner with the rear spar itself and there was NO point at which we could achieve this with either wing; the rear spar double is too far forward so any trimming of length will have no effect that we can see. This, coupled with the fact the two sides are different distance from the front spar AND the starboard side spar bar and doubler are twisted WRT the wing rear spar itself, leads us to believe that there is a serious issue here.

Sorry for the long winded explanation :rolleyes:

Is it possible they installed the center section wrong? Prepunched holes won't allow 1/16" but it would mean the spars are not equal left to right.
 
Gary from Vans recommended the following:

"It is best to make a block that fits snugly in the space between the F-605C Bar doubler & F-705B center section. Then you can adjust a large adjustable wrench to fit over the F-605C Bar doubler & F-705B center section. Bend the unit slightly to adjust it to allow the rear spar to fit. This is not a large adjustment to make"
 
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Hmmm...

Ref: DWG 20, 22, and 25

If this is a QB, I find interesting that you were able to access the F-605C & F-705H spacer, or anything else along the rear spar carry through assembly. Of RV-7 QB's I've worked on, the forward and aft floor pans are in, the hinges are installed and there is NO access to this area without major disassembly (did something change -- Scott D comment?)

However, given what you are describing, including your access to the bolt that ties F-605C, F-705H together, I would continue the effort and dig further into the center section and figure out what went wrong.
 
The fix

Based on what's been posted, it certainly sounds like something is wrong with the way that the centre section has been assembled. I recently fitted the wings to my slow build -6A for the first time and the rear spars slid straight into the fuselage forks without any interference whatsoever (fortunately). The -6A centre detail is a bit different to the -7A but the principle is the same. It's the seat ribs that determine the location of the rear spar carry through, so I would be checking how they have been fitted at both ends, particularly the flanges and rivets to try and understand why there is a discrepancy. In the older kits the ribs were not all manufactured to the correct length and some flanges had to be cut off and refitted.

If Vans have recommended brute force to bend the parts to get them to fit then it would appear that the fuselage fork will need to be bent back and the end of the rear spar will need to be bent forward. I'd be a bit wary doing that especially to avoid any scratching or scoring.

Good luck I hope it works out.
 
The Vans QB kits come with the floors temporarily riveted in with only a few (maybe 6-8) pop rivets. The idea being you drill them out to raise the floor and install the step kit.

With regards to the bending I had some really good help and a little shin pad tape help prevent scoring and the bend required was minimal. The finished product turned out perfect.

Cheers,


Phil
 
...
With regards to the bending I had some really good help and a little shin pad tape help prevent scoring and the bend required was minimal. The finished product turned out perfect.
...

Great news Phil! Thanks for following up on this. I'm sure I am not the only one wondering how it was going to turn out.
 
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