I'll model most of it as shells, but I can pull surfaces off the solids so that's not a problem. I suppose, for analytical purposes, I could make rib one and the tip rib, and then make a straight-line surface between the two, but I know the airfoil varies on the outboard ribs. I don't think structurally, it matters much as it won't affect the loads, but I know when you actually build, the cross-section at each rib has to be respected. I saw that the surfaces didn't line up exactly, but that's OK -- it won't have any significant effect on the loads.


One thing though. I recommend when you could build something, if you could put it in standard aircraft coordinates that would be very helpful. +z is up, +x is aft, and +y is RHS (right hand rule). To start, I'll probably just do the inboard and outboard ribs. I do have some digital software, but it's pretty primitive (for reading off graphs). If you could scan just the inboard and outboard ribs, and scale them in your cad package, that would speed me up by a couple of weeks. Again, this will be just a loads and stress model, so it doesn't have to be so super accurate. I am appreciative of whatever you can do.


Last night I did some wood research. I'm going to model the ribs in a way that I normally don't do at work. Usually we use she;;s and make the composite lay-up, or else the materials are isotropic. I did some research and got the properties in all 3 directions and will use solid orthotropic material properties. I could do it more simply, but I won't learn as much!
Cheers, Kenny

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Subject: Re: [Carbondragonbuildersandpilots] step 2
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Date: Friday, April 6, 2012, 7:04 PM




Kenny,

Like the cloth or OML not in solids but in real surfaces? Does the spar and rib also need to be surfaces? Not up on FEA input and trying to understand what is needed to do the analysis. Reverse engineering takes a time and good software. We ain't talking Delta Cad 2D or AutoCad.

I have been working off of the 1/4 scale .pdf raster files and it is not easy accounting for all the scaling errors of the copies. Measuring raster prints is like throwing darts. Solids are needed to compare weights and I was trying to establish a baseline model and try and understand how the Carbon Dragon is put together. Redesigned components could be modeled for weight or FEA input more accurate than napkin sketches.

I take the raster (bitmap) .pdf file and import it into Solid Works as a sketch. I then scale it to sheet size. I then try and find any scaling info or dimensions to verify some defined feature size. I then create sketches to extrude into solids. I can sketch on the solid to make gusset sketches then extrude them and merge the solid bodies into one if everything lines up. This makes a part like the rib that I exported as a step file. To make a wing assembly I start with a part like the spar as a base. I then bring in other parts like the ribs and align them to the drawing coordinates and spar features. Any errors on the part show up like the alignment of the notch in the leading edge for example. So now the little square leading edge stringer does not line up with the rib notches when aligned with the root and tip ribs. You can see this in the pdf picture in the files folder of the spar with ribs on it.

If all you need is a surface representation for Nastran elements like shells and plates you assign material properties to I can try and figure out if I can use the geometry I have created to make surfaces.

Regards,

Charlie