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To Flute or Not to Flute

E

ecurington

Well Known Member
I am not clear on what, when and where to flute the wing ribs. I see different examples on builder?s web sites. Is it done on an as needed basis when you are installing the skins or prior to priming? I do not see specifics in the plans to explain this. Can someone help with the need to flute the wing ribs on the RV-10?

E. Curington
RV-10 Empennage Serial # 40596
 
Section 5

E.,

Check section 5 of your builders manual. At least for me (RV-7A) it's section 5. This section only comes with the preview plans. There is a brief section on Fluting.

As I understand it, it is as needed, but it looks like most ribs need at least some fluting. You're just trying to straighten the ribs which flex and develop a curve during the fabrication.

I have found that clamping a straight edge to my work bench and placing the rib next to it is a good gauge of straightness. Sorry I'm not near the shop or I would post some pictures of my process. YMMV.

Good luck!
 
confusing at first... natural with some experience

fluting is one of those things that is natural once you know what your doing but to get to that point takes some head scratching and experience... all that you are really trying to do is relieve stress from the rib so that it fits without twisting... to do that you need to make sure that the line of rivets is straight since the forming process will put a bit of a roll to the rib... so flute (pinch the metal to pull the roll out) as needed... generally, more light flutes works better than fewer heavy flutes but there is no need to go flute crazy... start with a few light flutes, infill with light and heavy additional flutes until you are happy. sneak up on it as it is much easier to add flutes versus taking them out.
 
the point of fluting

is so you can get the ribs to lay flat, thereby allowing the skins to sit on strait. if your ribs lay flat then you do not need to flute, if they do not lay flat you need to flute the edges to pull it flat. It is easy once you get the hang of it and is easy to fix if you mess up.

http://www.youtube.com/watch?v=jqNoVAQLo0M

here is a good video explaining it with a good technique.


ecurington said:
I am not clear on what, when and where to flute the wing ribs. I see different examples on builder?s web sites. Is it done on an as needed basis when you are installing the skins or prior to priming? I do not see specifics in the plans to explain this. Can someone help with the need to flute the wing ribs on the RV-10?

E. Curington
RV-10 Empennage Serial # 40596
Click to expand...
 
take note of 'flat' side

be cautious of the 'sits flat' direction, the bent rib flange length can vary and is not a reliable measure of flat... the flat reference is only good on one side, the prepunched holes will parallel the flat side with a uniform edge distance. edge distance on the outboard will vary.
 
You have gotten good advice. Fluting is easy, but can be overdone. I can almost guarantee that you will get really good at it on the last rib! Mistakes I have seen--fluting at (or too close to) a hole. Allow at least 3/8 to 1/2 inch between the hole and the flute. AND have the flutes bend to the inside. Don't ask how I know that can be done wrong...

Another thing that is overlooked, although usually not a problem is the angle of the web to the flange. It should be 90 degrees. It is usually very close, but you should check to see. It makes a better looking finished product if it is right on. Good luck!

Bob Kelly
 
Thanks for Replies

Thanks to all who replied. I now have a basic understanding of the fluting process. The video was helpful. I fluted the left wing ribs last night and it is pretty easy once you understand what you are trying to accomplish and the techniques to use to get there. The RV-10 plans did not include the preview sections. This is my first build so I'll have more questions.

Thanks
E. Curington
 
As a point of interest, one of the local AME's here had the horizontal stab from a Luscombe all apart a while ago, and I couldn't help but notice that *none* of the ribs were fluted, and none of them laid flat on a bench either, they all had a curve to them. It only took a little bit of pressure to straighten them and cleco the structure together, and when the whole horizontal stab was riveted back together it all lined up straight and true. I always wondered how critical fluting really was after seeing that.
 
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