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Is fluting still necessary?

K

Keebs64

Member
My RV-14a wing kit will be arriving on Thursday, and I’m mentally preparing for the prep work on all 56 ribs…

When I was working on my -6a back in the late ‘90s, fluting was important in order to get the centerline of the non-punched ribs to line up with the pre-punched skins. Fast forward to my -14a in 2021 and all of the ribs are match-drilled to the skins. This leads to my question- Is fluting still absolutely necessary/required if the alignment of the parts is no longer a factor?

I understand that you wouldn’t want parts to be pre-stressed during assembly, but the amount of force required to flatten a non-fluted rib is extremely minimal. It doesn’t seem like there would be a negative to let the clecos/rivets straighten the ribs during assembly.

Thoughts?
 
Due to the distortion created when the parts are stamped into a rib shape, yes, flutes need to be created to straighten the ribs. At least that’s the way it is on my -8 prepunched ribs. Less fluting is necessary on the straighter sections, but the more curve in the rib (like the curve around the nose of the rib to create the airfoil shape) the more fluting the part needs. When you get your -14 ribs and you sight down the holes, you’ll see this.
 
Keebs64 said:
My RV-14a wing kit will be arriving on Thursday, and I’m mentally preparing for the prep work on all 56 ribs…

When I was working on my -6a back in the late ‘90s, fluting was important in order to get the centerline of the non-punched ribs to line up with the pre-punched skins. Fast forward to my -14a in 2021 and all of the ribs are match-drilled to the skins. This leads to my question- Is fluting still absolutely necessary/required if the alignment of the parts is no longer a factor?

I understand that you wouldn’t want parts to be pre-stressed during assembly, but the amount of force required to flatten a non-fluted rib is extremely minimal. It doesn’t seem like there would be a negative to let the clecos/rivets straighten the ribs during assembly.

Thoughts?
Click to expand...

Forcing the parts into alignment isn't enough to account for the bow in most all parts. Also, clecos don't have the aligning power to assure holes are exactly centered when the part is fighting to not be. Attempting to rivet with holes mis-aligned can make riveting more difficult (tipped rivets, of center shop heads, etc.)

So yes, the RV-14 kit does require fluting on parts with curved flanges.
 
Fluting

I struggled with fluting until I finally got it through my thick skull that I am straightening the holes, not the ribs (thanks Scott!). Watched videos, etc. Nothing worked better than laying it on a flat table open side down, holding one end and fluting where the rib started leaving the table. After that I put two clecos a few inches apart to align my straight edge with the holes and sighted down the rib to fine tune. Got easy after a while.
 
Fluting

As Scott said, flute so the holes line up
On the 7, there were parts that had to be fluted into a compound curve so holes would line up. Outboard seat ribs for example. It's flat out of box. Bottom and top holes are in different line. Its curved like the side skin after fluting.
 
Fluting is probably one of the easiest things you can do. Maybe you think that it isn’t necessary. Loads ad up. You want those ribs to lie totally flat so the the holes in skins line up, without any side load. These are ‘stressed skin’ airplanes. The skin shares the load with the skeletal structure. The less preload you put on these structural load paths, the better. I’m not saying that a wing will fall off, but cracks may appear around certain rivet heads in areas that were a little over stressed because of a slight rib misalignment, because the builder didn’t take the five minutes to flute the ribs properly. It’s pretty easy to do, and yes it’s important.
 
Also....

Section 5.13 discusses fluting and it is also important to ensure the flange is perpendicular to the web prior to fluting. I failed to check this in the beginning and had a couple parts that required flange adjustment to lay flat against the skin and re-fluting to align the holes. Most flanges have been stamped sufficiently, but throw a square on there to check.
 
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