I still don't understand how & when you assemble the components in your first picture.
There's not much assembly. The threaded rod takes an M5 nut/wing nut either side of the frame. Remove the nuts to reposition the bolt up or down in the frame arms for deeper / shallower fuselage. To allow for a narrower / wider fuselage alter the position of the nut/wing nut along the length of the threaded rod.
Most of the time the height setting is likely to remain the same so in the field it'll usually just be a case of adjusting width by backing off the nuts and moving the threaded rod in/out as necessary.
I'll go away and scribble something and / or take a few more pictures to see if I can explain things more clearly but may not make it back with a reply this evening
Thanks you for a patient & tolerant resopnse.
I've finally worked out what I didn't understand about the existing set-up, that the "lash-up" alu. tube goes through the M5 bolt section. I had read your explanation, which is fairly early in the thread, more than once & managed to misconstrue it.
Meanwhile the creative half of what little brain I have left has been fermenting (fomenting
) reduced design constraints.
First thought is that the 1.5mm hole doesn't need to be very deep. I was thinking about a depth of 2 or 3 diameters to provide support against bending. I think the strucural engineering term is pin-ended column. The rest of the hole (opposite end from aeroplane) could be bigger, up to the maximum that could safely be drilled with the M5 thread. With a root diameter just over 4mm, that might be as high as 3mm, given that the greatest bending loads are at the support plate, which is where the drilling would start & so be least eccentric. The larger drill, being stiffer, should be able to penetrate much deeper for the same eccentricity.
Second thought is one I've already suggested, viz increasing diameter. M6 looks attractive, possibly using tapped holes in the support plates.
Third thought is pushing the boundaries a long, long way. I was reflecting that in a cycling forum, the obvious source of single strand steel wire for the retaining wire is spokes. I have built with 2.0/1.5/2.0 mm double butted spokes, & the centre 1.5mm section would be more than long enough. The more common double-butted size is 2.0/1.8/2.0 mm. Would that fit through the motor peg? 1.8mm drills are not common, though I have one. The final idea is a plain gauge 2.0mm spoke. I doubt it would fit through the motor peg. I had already ruled out any modifications to the aeroplane, so I'm asking whether that is an absolute design constraint.
That's all a bit of a brain dump, not properly reviewed, & doubtless not clearly expressed, but I need sleep after last night
.