Huge Rib to Sparflange gap

Hello Group

Look what I found out, after I start to build up my wings:

- There is a gap between the rib and the spar-top-flange, 2.0mm ( 0.08") at the rib to spar, 2.6mm ( 0.1")at the rib to skin. This is the worst case in 2/3 centered over the wing, so 10 to 12 ribs are effected.

- At each end it is better, the gap there is within 0.5mm ( 0.02") to 1mm ( 0.04").

- The angle at the top-web-flange is 90?, on the plan it looks that it should bee less then 90?, I would say 87? or so.

- The distance from the top to the bottom flange is 195.0 ( 7.67") at both ends and 197.0 (7.75") in the middel (2/3) area.

- All the rib- flanges are 90?, the ribs are straight.

- The bottom side is ok

On the second wing, it looks not so bad, but also not good, the gap there is between 0.5mm ( 0.02") to 1mm ( 0.04").

To all that, I attached 4 pictures which shows the problem exactly.









I askd Vans, they did not had something like this. They tell me to bend the flange down, but I think, the anodizing will crack. And or center the gap ro both sides of the spar.

What do you think about this? Could you support me with a few mesurements at your spar's?

Thanks alot

Dominik

I have experienced the same problem. I talked to Van's and found that the angle of the top spar flange is supposed to be 88.5 +-0.5 degrees. My spars are closer to 90 degrees. If they were bent down 2 degrees, the gap would be reduced by about 1 mm (0.040 in). The gap can also be reduced by adjusting the rib flanges with a hand seamer.

I am going to bend the spar flange a little, and bend the rib flanges a little. I plan on touching up the spar with an alodine pen if bending it damages the alodine surface. I don't expect the small amount of deformation will cause any damage.

Hello Dave

Interesting things I found out last night, I mount one rib upsidedown, so that the top flange is the bottom one ... and the ribs fit much better! (Yes, I know, I can not build up the wing like this)

It looks that my spar flange are bend the wrong way around.

Vans told me, the spars meet the specifications, as I ask for this spec. for the angle of the flange and the distance between them with tolerances, they did not answer

The bad thing is, only one of my spars are in this condition, so it would be very diffiult to build two equal wings.

Next week I go to a other builder and mesure his spars.

Dominik

Measuring spar flange

Hi Dominik, I really don't have any way to measure my spars now that the wings are closed.
I don't have any tool that will get in there, but you are welcome to come and measure if you've
got some special calipers!

Hello Mickey (another swiss eagle )

Special tools are not required, only a ruler, and thru the inscpecting cover it is still possible to mesure. Angle are impossible after wing completition.

I look in when I'm near your home next, but at the moment, business is quite low.

Thanks Dominik

PS: I saw your trimtab "upgrade" on your page, I forgot to order one by you

Dominik,

Toady I tried bending the top flange of the spar with a hand seamer to about 88 degrees, or about 1 mm past 90 degrees at the end of the flange. It gave a significant improvement to the fit of the wing rib.

The additional bend very slight and there was no visible damage to the anodized finish on the spar.

Your observation that your spars might be bent upside down is interesting, but I do not think that is possible. The bottom flange can always identified by the extra holes for the access cover platenuts. If the unbent spar is laying flat on a table with the root to the left and the bottom flange toward you, then you can make a right spar by bending both flanges down, or a left spar by bending both flanges up. There is no way to make an upside down spar.

I think the problem is that the spars are slightly under bent. Your observation that the fit up with the ribs is good on the ends worse toward the middle middle is consistent with a common bending problem. When a part is bent to 90 degrees on the ends, the high loads on the dies toward the center of the part can cause some deflection in the press brake that results in the center of the part being under bent. This is because the deflected dies never completely close at the center of the part.

I am confident this is not a serious problem. Just bend the flanges a little bit to get a better fit and press on.

Dave

Hello Dave

Thanks for all your information about the bending process.

I try to explain what I meant in my last post:

I have a right and left Spar, they look as the plans show them. To me, it just give me the picture that the upper flange ist bent as an bottom one and vise versa, the upper flange has an angle of 90?+ and the bottom one 90?-.

Look at the pictures, the first one show the rib in the correct position, left is bottom, right is top



Here the rib is 180? turned, left is bottom (of spar), right is top. The rib fit much better but is the wrong way around.



I will try to bend the flange, but I allready have the platenuts riveted on, so its more difficult to grab the flange for bending.

To close the angle of the flange, I think the anodize will not crack, but where I have to open it, you can clearly see (and hear) the cracs in the surface. The anodize is as hard/elastic as glas!

Will report my bending results.

Dominik

Flange bending

Hello all

I mesured a 2nd set of spars by another RV-7 Builder in Switzerland and someone from USA gave me his mesurements, it seams it is a general problem. Also the Part-Productions-Number of the bend part are to far away from the left to the right side, so they produces by different batches. Now I can report my results:

I build up the spar as in the picture, clamping on both sides and a gap to put the bending wood between.



By pulling on the wood, I can bend the flange to the angle I needet. Pullforces up to 60lbs are necessary.


The design mesurements are:
- bottomflange inside 89?
- topflange inside 88.5?
- gap between them 7.63" (by Vans), but the average of the ribs have 7.67", so I go for 7.67"

I set the bottom Flange correct, and then set the upper flange until I reached the gap mesurements. I'l go over each area by 5-8 times, always moving the spar along the spanwith



In the outboard section, I could also work with an handseamer, because there are no nutplates.

The anodize will crack, there now a lot of smal lines across the bending area. maybe, I cover it with an alodine pen.

Hope this helps others.

Dominik

Same problem encountered

For more info, see these pages:

http://www.our7a.com/20070426.html

http://www.our7a.com/20070428.html

http://www.our7a.com/20070430.html

http://www.our7a.com/20070501.html

There was something about this in a recent RV-ator (one of the online ones, if I recall correctly). I believe the corrective action was to gently bend the flanges to fit. A good flange bending tool can be made by cutting a slot in the end of a 2x4.

Edit - A quick check of Van's site: third RV-ator issue, page 10 describes the problem and fix.

There were several 9 wing spars that got sent out with misbent flanges, I got one of those sets, but this is the first I've heard about the 7's.