Some confusion over fluting - Pics included

ChrisL · #1 10-04-2007, 06:47 AM

All-
I have been working on the HS rib preparation am having some minor issues. I think I get the general idea of fluting - flute the mid rib flange area to bring the center of the web backdown to the table. But, I am having a lot of ribs curve up on the ends and can't seem to bring them down. Putting extra flutes on the edges don't help and seaming the center section isn't the clear answer either. Any thoughts?

Rib curved on the ends - suggestions on where to flute / seam to get this one flat?

As a sanity check - hows does this one look? Is it good enough for a general standard?

Thanks!
Chris

Camillo · #2 10-04-2007, 07:02 AM

As I can see from photo (and as I can suggest without having rib in my hands...because this tecnique is a sort of trial and error...) I will un-flute (i.e.: remove or lower the flute already done) the second flutes from the left (both sides) and then the first ones. The left part of the rib will then stay flush with the table. You may then want to gently flute the external part of the rib (from the hole to the left) if such part will bow on the opposite side.

The second rib seems OK.

The general purpose of fluting is, apart from making holes on the rib match with holes on skins (or longerons, etc...), which is actually an effect, making structure work perpendicular.

Hope this will help.
Camillo

cytoxin · #3 10-04-2007, 08:22 AM

they lay flat flange down not web down. the idea is to get all the holes lined up. ymmv

keen9a · #4 10-04-2007, 10:13 AM

First pic looks like you need to "un-flute" a bit towards the left side where its not sitting flat. Just sqeeze the flange a bit with a seamer.

Second one looks good to me.

DaX · #5 10-04-2007, 12:48 PM

Yes, you need to un-flute some. As cytoxin said, the whole idea with fluting is to get the holes straight - the instructions aren't very clear on this. If you can hold a straight edge to the bottom of the line of holes and it matches up, you're good.

alpinelakespilot2000 · #6 10-04-2007, 12:57 PM

Chris-
Yes, the first one looks like you fluted slightly too much, but at risk of sounding like a heretic here, get them close and move on. As long as you are able to cleco everything together without having to use any significant force or preload, you'll be fine. By the time you get to some of the wing ribs and fuselage bulkheads, you'll realize that no amount of fluting will lead to perfectly flat parts. Good luck, and enjoy the building experience!

az_gila · #7 10-04-2007, 04:45 PM

Quote:

Originally Posted by DaX

Yes, you need to un-flute some. As cytoxin said, the whole idea with fluting is to get the holes straight - the instructions aren't very clear on this. If you can hold a straight edge to the bottom of the line of holes and it matches up, you're good.

Well there is a second idea as well....

You must make sure the flanges are bent at the correct angle (usually 90 degrees, but not on fuselage bulkheads) before you flute to get the line of holes straight...

Bending the flanges usually affects the curvature of the rib, so do that first...

gil A

ditch · #8 10-04-2007, 05:05 PM

I noticed that on my HS, I only fluted every third space and they came out straight. I don't think you have flute every space unless they are really bad.. Try it lightly and every other one. I would do one space then turn to the other side and do the same one, then back and forth. It is true though, if the holes line up and flanges are straight, you're golden.

rzbill · #9 10-05-2007, 04:14 AM

With more fluting practice ( your first rib is over-fluted on the ends and second rib is fine as others have said) you will see that the location and depth of the flute is directly related to the amount of local curvature desired in the wing shape. Straight ribs (like the rudder stiffeners and flat wing parts behind the spar) require none or very little while some nose ribs require a lot.

As Gil says, I would go to the trouble of making the flanges 90* to the web too. They are usually 5 or 10 degrees off as recieved from Vans due to the mfg process and the intent to push this work into the builders 51%. Getting them perpendicular will make your fluting results more consistent and make the assemblies go together better since the part will be closer to its designed shape. Sometimes I needed to go back and tweak the 90* after fluting. No biggie. The tail doesn't have much for rib curvature so the effects of our advice may not be all that noticable yet. The wing ribs are where the learning starts. Mostly because you get lots of practice because there are so many and they look like potato chips when removed from the shipping box.

ChrisL · #10 10-05-2007, 05:49 AM

Thanks for all the great replies. Though it didn't come out 100% perfect, I was able to get that rib and several other straight. I would imagine if the holes are in the a straight line and after the first cleco or two, every hole lines up fine, then I am good to go.

Thanks again!