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chriscencula

Active Member
The RV-6/RV-6A plans show the F-604 bulkhead 'tipped' relative to the firewall by 7/16" top-to-bottom. They also show F-605 being vertical, therefore F-604 & F-605 are not parallel. The main and rear spars of the wing DO appear to be parallel. What this means is that something in the rear-spar - fuselage attach will need to twist. If I 'do the math' on this, I get approximately .028in difference from the top edge of the rear spar attach to the bottom edge of the rear spar attach (I guess this could be 'interpolated' to be .014in difference at the top and bottom if the 'center' distance is matched between the wing and fuselage... Hope this makes sense?

I'm wondering if anyone else remembers this?

Did anyone take any special measures not to 'build-in' a twisting moment when the bolt is torqued to hold the rear spar to the fuselage attach 'fork'???

Thanks,
Chris
 
Chris, my RV-6 QB main spar to rear spar distance did not match alot more than "angular" differences you are talking about. Build on!

Mike
 
It all sorts itself out...

When you build a non-QB wing the spar is levelled (in a side view on the jig) but the aft spar is just set by the stamped ribs. There may be the slight angle you mention incorporated as part of the ribs.

No special procedures needed, just let the ribs set the verticality of the rear spar.
 
The seat ribs are the key here. Both of the front and rear flanges of the seat ribs are formed parallel. The front of the seat ribs attach to the F-604 bulkhead (main spar carry through) and the aft end of the seat ribs attach to the F-605(A,B, and C).

This will naturally align the wing's front and rear spars to the spar carry through.
 
RV-6 spar/fuselage interface

Hi guys,

Thanks for the responses... Looks like I didn't describe the situation adequately.
The main and rear spar of the wing are parallel, as built (as Gil noted, this is determined by the wing ribs). The seat rib front and rear flanges can't be parallel, since the front of the seat ribs fasten to F-604, which isn't parallel to F-605, where the rear of the seat ribs fasten...

Because of this, something will need to twist, most likely the rear spar & rear spar carry-through attach...

If there are 2000+ RV-6's flying, I'm probably not the only person that noticed this?

I wonder if anyone 'pre-twisted' the F-605 carry-through 'fork' to match the spar?

Maybe most didn't notice the discrepancy & those that did simply let the attach bolt do the twisting by clamping the two together?

Thanks,
Chris
 
chriscencula said:
Hi guys,

Thanks for the responses... Looks like I didn't describe the situation adequately.
The main and rear spar of the wing are parallel, as built (as Gil noted, this is determined by the wing ribs). The seat rib front and rear flanges can't be parallel, since the front of the seat ribs fasten to F-604, which isn't parallel to F-605, where the rear of the seat ribs fasten...

Because of this, something will need to twist, most likely the rear spar & rear spar carry-through attach...

If there are 2000+ RV-6's flying, I'm probably not the only person that noticed this?

I wonder if anyone 'pre-twisted' the F-605 carry-through 'fork' to match the spar?

Maybe most didn't notice the discrepancy & those that did simply let the attach bolt do the twisting by clamping the two together?

Thanks,
Chris
Click to expand...

I think the item that will "twist" will be the bottom section of the F-605.
When the fus. frame is all riveted together, the bottom of the bulkhead will get tweaked by the seat ribs as noelf says and it all works out ready for the wing installation...:)

I think that is the same as you are saying, but I'm not sure...:eek:
 
chriscencula said:
Did anyone take any special measures not to 'build-in' a twisting moment when the bolt is torqued to hold the rear spar to the fuselage attach 'fork'???

Thanks,
Chris
Click to expand...

Nope. I built it per plans and the rear spar dropped right in place. I've followed the RV-list and this forum diligently for 15+ years and this is the first time anyone has raised this issue.
 
I'm going to have to pull out the plans on this..............as nothing was forced to twist. The spar angle is for positive wing incidence. Yet the rear spar "exactly" slid into the fork, as designed in the plans. My 6A was a "slow build", and I constantly made sure that the measurments at the attach points, were exactly the same as the wing dimensions. In other words, there is no screw up on the plans, that require a forced or twist fit.

L.Adamson --- RV6A
 
Hi Gil, Kyle & Larry-

Thanks for the replies -

Gil, My *guess* is that the spar attach 'fork' would be the part that would twist the most when the bolt attaching the rear spar is tightened since the rear spar attach at the root end of the wing is made of double 1/8 plate & is fastened to the top & bottom skins very close to where the attach bolt is...

Since F-604 is tilted 7/16 over it's height and F-605 is not tilted it seems there must be a 'built-in' mismatch in the angles between the wing rear spar and fuselage rear spar attach... (Because the wing main and rear spars are parallel - & F-604/F-605 aren't)

I haven't yet checked my seat ribs to see if the forward and rear flanges are parallel, however they really *can't* be because the forward end attaches to F-604 and the rear end attaches to F-605... The fit is decent (minus the problem that the seat ribs are too long by ~0.060") so the flanges can't be parallel since they attach fairly well to non-parallel bulkheads!

Larry,
If you've got the time/inclination, pleas pull out your plans and see if you can figure out what I might be overlooking... I know it is a small angle mismatch (approximately 1degree, which translates into approximately .028" over the 1.5inch width (height) of the rear spar attach fork. By 'ratios': 7/16 divided by ~ 23in height of F-604 'is to' X divided by 1.5inches --> 0.028"

Chris
 
chriscencula said:
Hi Gil, Kyle & Larry-

Thanks for the replies -
....
I haven't yet checked my seat ribs to see if the forward and rear flanges are parallel, however they really *can't* be because the forward end attaches to F-604 and the rear end attaches to F-605... The fit is decent (minus the problem that the seat ribs are too long by ~0.060") so the flanges can't be parallel since they attach fairly well to non-parallel bulkheads!
......
Chris
Click to expand...

I think the bottom of the F-605 bulkhead could twist forward a fraction and compensate for the lack of tilt. The bulkhead flanges are not even continous around the bend at the bottom of the F-605, and these flanges are all that keeps the bulkhead "straight". You wouldn't even notice a slight twist.

It would be forced into this position by the seat ribs.

The plans do show the forms for making your own seat ribs, and the form dimensions show that the ends are parallel.
 
Drawing extended lines on my "wrinkled" wing rib plan..........it appears that the spars are "not" parallel. I do remember that holes were drilled through both spars, with a line and plum bob........to align everything exactly. It's been 14 years since I completed my wings; yet I know that the rear spar fork becomes very ridged when all is riveted, and there is no twist required. In fact, you simply couldn't twist it, without damage.

L.Adamson --- RV6A
 
L.Adamson said:
Drawing extended lines on my "wrinkled" wing rib plan..........it appears that the spars are "not" parallel. I do remember that holes were drilled through both spars, with a line and plum bob........to align everything exactly. It's been 14 years since I completed my wings; yet I know that the rear spar fork becomes very ridged when all is riveted, and there is no twist required. In fact, you simply couldn't twist it, without damage.

L.Adamson --- RV6A
Click to expand...

...but the rib form block dimensions in the plans say that they are parallel...:)
 
az_gila said:
...but the rib form block dimensions in the plans say that they are parallel...:)
Click to expand...

But...................my plan was wrinkled! :D It was like an eighth inch in two feet.

What I don't want to hear, is anymore reference of "twist" to make it fit! :)
It doesn't twist. But after pulling all of these plans out, I seem to .....no longer have the patience to check for all the why's and wherefors. It was tough back then.........you know.. :)

L.Adamson
 
L.Adamson said:
But...................my plan was wrinkled! :D It was like an eighth inch in two feet.

What I don't want to hear, is anymore reference of "twist" to make it fit! :)
It doesn't twist. But after pulling all of these plans out, I seem to .....no longer have the patience to check for all the why's and wherefors. It was tough back then.........you know.. :)

L.Adamson
Click to expand...

The reference to "twist" was that the fus. frame aligns itself when you rivet it.

Any twist that might exst in the F-605 is built-in and not applied later....:D
 
Hi Gil,

The F-605 'side channels' (can't remember the # at the moment) extend below the lower crossmember with their flanges pointing aft... This being said, there will be a fair amount of twisting moment necessary to twist the carry-through fork-end into alignment with the spar end (as a guess, I would think it would be between 5&15ft-lbs) The assembly will be totally riveted by the time the wing is mated, so the holes will have been drilled with the F-605 carrythough in it's 'natural' vertical plane...
A couple of options come to mind to address the issue:
1) Pre-twist the rear spar fork pieces outboard of the outermost seat rib to match the rear spar (match the tilt of F-604) - this might not work too well since they only extend a few inches past the seat rib
2) purchase 1.5x0.187 bar stock and machine the angle into the end with a smooth 'transition zone' to the 0.125 length, so as to not create any 'stress risers' This would need to be done for both 'forward' and 'aft' portions of the fork parts.
3) Build it with the design-inherent mismatch in angle (approximately 1degree) then the bolts twist the components when the wing is mated to the fuselage and the rear spar bolt is torqued down.

Other ideas?

I'm also just looking at the F-6101 gussets and finding that those supplied in my kit have the same problem Colin Peterson had; the pre-cut parts don't match the plans and won't fit the fuselage if built per plans... If they are going to supply pre-cut parts, they need to be at least 'close' - this one isn't. Here's a link to Colin's kitlog site showing the issue:http://www.mykitlog.com/users/display_log.php?user=ccpeterson@y&project=754&category=5724&log=105249&row=205
Looks like Colin re-made this part; I may do the same...

Thanks,
Chris
 
chriscencula said:
Hi Gil,

The F-605 'side channels' (can't remember the # at the moment) extend below the lower crossmember with their flanges pointing aft... This being said, there will be a fair amount of twisting moment necessary to twist the carry-through fork-end into alignment with the spar end (as a guess, I would think it would be between 5&15ft-lbs) The assembly will be totally riveted by the time the wing is mated, so the holes will have been drilled with the F-605 carrythough in it's 'natural' vertical plane...
A couple of options come to mind to address the issue:
1) Pre-twist the rear spar fork pieces outboard of the outermost seat rib to match the rear spar (match the tilt of F-604) - this might not work too well since they only extend a few inches past the seat rib
2) purchase 1.5x0.187 bar stock and machine the angle into the end with a smooth 'transition zone' to the 0.125 length, so as to not create any 'stress risers' This would need to be done for both 'forward' and 'aft' portions of the fork parts.
3) Build it with the design-inherent mismatch in angle (approximately 1degree) then the bolts twist the components when the wing is mated to the fuselage and the rear spar bolt is torqued down.

Other ideas?
Click to expand...

Something is wrong here. Nothing had to be twisted or pulled into place to fit. My RV6A kit was from 1996. No pre-twist, no 5-15 lbs. of force, and cutting of angles into bar stock. And there certainly was no design-inherent mis match.....that had to be pulled into place. I had a wood stick, with exact measurements of the distance between the front & rear spars. I continually used this stick, to check that the fuselage mating points remained the exact distance, until all was final drilled and riveted.

As I said previously.............the rear spar slid right into the fork, as the final few inches of the front spar was pushed in. No bending, no forcing, and no re-alignment as the rear spar bolt is tightened. I do believe, that you're on the "wrong" track here......as there is no issue. I have notes on my plans for specific changes that were used for improvements over the years. There is no reference to angle angle change for the rear spar. Have you looked at the Frank Justice --- supplemental plans? I used then often.

BTW--- I'm not trying to be argumentive. It's just that in the last 17 years or so, that I've been around RVs.........I do not remember this "issue". During my build, I went through the Matronics builders forums every day. I used the Frank Justice supplemental guide book, and had the Orndorff RV6 videos. There was so much information out there, that I never had to call Van's. As my RV is on the heavier end, it still is fast, and trims easily. Controls have a better feel than some RVs. I must have built it "straight"... :D

edit: try this. It's back in 1996. There are several replies to the question.

http://www.matronics.com/searching/...ITNUMBER=58?SERIAL=1248002908?SHOWBUTTONS=YES

L.Adamson --- RV6A
 
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L.Adamson said:
Something is wrong here. Nothing had to be twisted or pulled into place to fit. My RV6A kit was from 1996. No pre-twist, no 5-15 lbs. of force, and cutting of angles into bar stock. And there certainly was no design-inherent mis match.....that had to be pulled into place. I had a wood stick, with exact measurements of the distance between the front & rear spars. I continually used this stick, to check that the fuselage mating points remained the exact distance, until all was final drilled and riveted.

As I said previously.............the rear spar slid right into the fork, as the final few inches of the front spar was pushed in. No bending, no forcing, and no re-alignment as the rear spar bolt is tightened. I do believe, that you're on the "wrong" track here......as there is no issue. I have notes on my plans for specific changes that were used for improvements over the years. There is no reference to angle angle change for the rear spar. Have you looked at the Frank Justice --- supplemental plans? I used then often.

BTW--- I'm not trying to be argumentive. It's just that in the last 17 years or so, that I've been around RVs.........I do not remember this "issue". During my build, I went through the Matronics builders forums every day. I used the Frank Justice supplemental guide book, and had the Orndorff RV6 videos. There was so much information out there, that I never had to call Van's. As my RV is on the heavier end, it still is fast, and trims easily. Controls have a better feel than some RVs. I must have built it "straight"... :D

edit: try this. It's back in 1996. There are several replies to the question.

http://www.matronics.com/searching/...ITNUMBER=58?SERIAL=1248002908?SHOWBUTTONS=YES

L.Adamson --- RV6A
Click to expand...

I agree, nothing should be pulled, pushed or twisted....:)
The seat ribs will align everything when they are riveted in.
 
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