Attached are a couple of pics of a trial weighin of my cabin mod.Murry, does your engine mount have a diagonal to eliminate lateral movement? Maybe I can't see it in the photo....
Your right Sam, there is no lateral diagonal in the engine mount. I tried and tried but couldn't get a tube between the mag and the starter. No way. Vertical diags but no lateral. My bum legs don't want me stumbeling around out front so I probably will keep the starter.Murray, I wonder about the impact of eliminating the tubes that tie the XL station 1 to the top longeron. This leaves the nose of the fuse with the full weight of the engine cantilevered with no direct connection with the cluster at the top of the forward cabane. Of course some aircraft do this, but this removes a major source of rigidity of the very light Eagle fuse. The reason the Eagles can be built out of light material is because of the strict use of triangulation in the design. Eliminate some of the geometry and tube sizes need to be increased to maintain rigidity. Now weight creep sets in.... all this takes me into an area far beyond my shadetree engineering abilities. ;)
The diagonal into station 2 on the left side is mid span, no cluster as you politely point out Sam. On the right side the comparable diagonal clusters with a square tube conventionally. As you say the station 2 verticals are working pretty hard. But I did a finite element analysis a year ago with many revisions to the cabane and verticals. As I see it the four longeron design with the cabanes and diagonals used, works because the X bracing in the center section helps the cabanes carry the asymetiric wing drag loads. The X up there is important, it didn't work with one diagonal leg of the X. It needed the whole X. None of this is of interest to straight plans builders. Stick to the drawings. While doing my computer thing, I did a finite element analysis of the XL and everything rang out just fine up front there.