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Old 05-09-2007, 09:50 AM
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Default Bent Longerons

I know some of you come from a woodworking background so I'm sure you would have thought of this but I'm not sure if the Cozy uses the same technique or not.
The lower longerons on the Long-EZ are triangular and are bent to match the profile line of the bottom of the fuse. Plans call for making several vertical cuts to provide the flexibility to make the curve.

I'm thinking that I could cut the wood perpendicular (with a band saw) to the fuse sides down the length of the longeron so that it is more of a sandwich of strips (about 4 feet long), jig & bend it to shape and reglue the strips together in the new profile. (Same technique they use for curved molding to match up with the top of curved windows.)
It just seems that this would offer more strength than the plans method.
........or maybe this area isn't that critical?

Thoughts?
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Old 05-09-2007, 10:17 AM
Wayne Hicks Wayne Hicks is offline
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My guess is you're worried about the wood being a load carrying member? You're worried about the vertical cuts in the wood decreasing its strength?

No need to worry.

In all of our upper and lower longerons, the wood is the core for the surrounding composite sandwich structure. The fiberglass is what takes most of the structural loads.

The wood is used to:

(1) hold the shape of the fuselage sides until you can get glass on both sides.

(2) provide the bearing and compression areas for fasteners installed in follow-on chapters. (Like seatbelt bolts, step, canopy hinges, canopy fasteners, and for the Long-EZ folks their engine mount extrusions.)

Oh, and you don't really want to slit that triangle piece full length, do you? While not being difficult to do, it would decrease the width of the triangle piece by a blade's width each time you slit it. The overall width would be a lot less than what you started with. And, it's probably a jigging nightmare to hold it to some shape for cure. You'd have to build a multi-dimensional jig to hold it for cure. The upper longerons are easy. They're curved in and out, but flat top and bottom. The lower longerons are not flat. They're curved in and out, and curved top to bottom along the length to match the bottom curve of the fuselage sides.

For this op, I highly suggest taking the EZ approach and simply follow the plans. Make the vertical cuts, apply the flox, and cure it in place on the fuselage side.
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Old 05-09-2007, 10:28 AM
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Yep - do it per plans - it end up being a guide when sanding the corner for the curve
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Old 05-09-2007, 07:00 PM
chasingmars chasingmars is offline
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For what it's worth...

I didn't cut slots in my upper longeron reinforcement to aid bending. I laminated it all up in one step using doubled up jigs, I found it bent just fine without any cuts. My upper 60" long doubler is poplar rather than spruce (about a 20 gram penalty) btw, as I first messed around trying to heat bend my spruce piece, bent it the on the wrong axis, then broke it trying to straighten it...

I'm planning for the moment on making the cuts for the lowers though, as the curvature is compound and there's less to clamp it to.
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Old 05-09-2007, 07:59 PM
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Quote:
Originally Posted by Wayne Hicks View Post
The lower longerons are not flat. They're curved in and out, and curved top to bottom along the length to match the bottom curve of the fuselage sides.
If you cut the wood into strips such that you get pieces whose cross-section is a lot bigger in one axis than the other, the piece will be easier to bend one way, and relatively difficult (wanting to twist and buckle) in the 90-degree direction. This may make it difficult to do compound bends described above.
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