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Fluting the frames

dbhill916

dbhill916

Well Known Member
Patron
Hi folks,

I've got a question before I start bending aluminum the wrong way. 10-02 step 4 states to flute the frame halves. I have no trouble with the (obvious) advice that the humps go away from the skin surface, but I'm having trouble visualizing where to put flutes to flatten the frames.

With the frames laying flat such that the flanges point up, the webs of all of my frames are bowed somewhat aft. In my mind's eye, I feel like I need to stretch the flanges to make the outside perimeter longer. Since I can't stretch the outside web, that leaves fluting the inside web, but it's very short and I'm not sure that it can be fluted with any effect.

Please let me know if I'm overthinking the problem, or just let me know what worked for you.

Thanks in advance,
-dbh
 
Not overthinking

You cannot flute the frames absolutely flat, but you don't need to. Just flute in the few places where it will pull the metal in the correct direction and gain as much improvement as you can. You'll find that there aren't that many places. The better news is that since the frames are made from thin stock and will remain quite flexible, you can move them around during the cleco-ing process to match up all the holes. Once they are riveted, the whole structure becomes one and all the desired rigidity is accomplished. It's the magic of monocoque. Build on and godspeed.
 
David, I think most builders who have gone beyond this point in the build would agree this is an area where ?less is more?.

Suggest you make sure that when applying a minimal amount of downward pressure on the web that the transition point where the web bends to become the flange will lay flat on the bench. As you pointed out, seemingly the web would need to be tweaked to accomplish that without downward pressure.

Frankly, without distorting the rounded edge on the inside of the frame (which I did not want to do) I don?t think the bulkheads can be fluted with a hand fluting tool and made to lie perfectly flat on a bench. If I remember correctly, very light fluting at a couple of points got the holes in the flanges on plane. That coupled with a little hand massaging and the frame would lie flat with very little downward pressure applied, so I moved on. Ultimately, they aligned just fine to the skins during assembly and there was no need to disassemble and tweak.

Happy Building,
 
John-G said:
Frankly, without distorting the rounded edge on the inside of the frame (which I did not want to do) I don?t think the bulkheads can be fluted with a hand fluting tool and made to lie perfectly flat on a bench.
Click to expand...

John is correct.
You are not fluting to make the part perfectly flat. You are fluting to make the flanges straight.
If you have a difficult time visualizing that using a flat surface, lay a straight edge along the line of rivet holes in the flange (you can even put a few clecos in holes to give you something to reference the straight edge to if needed).
Flute as needed to adjust the flange so that the rivet holes are all aligned (all rivet holes in skins are in a straight line).
 
dbhill916 said:
Hi folks,

I've got a question before I start bending aluminum the wrong way. 10-02 step 4 states to flute the frame halves. I have no trouble with the (obvious) advice that the humps go away from the skin surface, but I'm having trouble visualizing where to put flutes to flatten the frames.

With the frames laying flat such that the flanges point up, the webs of all of my frames are bowed somewhat aft. In my mind's eye, I feel like I need to stretch the flanges to make the outside perimeter longer. Since I can't stretch the outside web, that leaves fluting the inside web, but it's very short and I'm not sure that it can be fluted with any effect.

Please let me know if I'm overthinking the problem, or just let me know what worked for you.

Thanks in advance,
-dbh
Click to expand...

Dave,

Don't know if you have seen this, but here is an excellent demo of fluting by Alan Gilmore, a fellow builder. I found it very helpful and easy to follow. Hope this helps.

http://youtu.be/jqNoVAQLo0M
 
Last edited:
Bulkheads

I had this problem on the -8. The inside curve of the bulkhead flange makes the bulkhead curve towards the toe of the flange. In other words, the flange doesn't need fluted, it needs stretched. This is how I did it. This technique resulted in nice straight bulkheads.

IMG_2241.jpg


IMG_2242.jpg
 
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