proppastie
Well-Known Member
There are various ways to define the Outer Mold Line (OML) of an aircraft surface. This is the outer surface of the aircraft, be it the wing or fuselage etc. Often the bulkheads/ribs/transitions are drawn first and the surface developed from those shapes. Here is how I do it using the tools I am most familiar with. Perhaps others will show us how they do it.
This is using AutoCad V14 which I have a license for. That this cad program is so old I would guess the techniques are applicable to many cad programs. I use Ruled Surfaces to define my OML. convert to solids and slice them to get my intermediate bulkhead/rib contours.
Plate 1 shows the whole process.
Plate 2 is a digitized root rib and tip rib from the paper plans of the Carbon Dragon. These must be Closed Polylines or defined curves.
Plate 3 shows a line drawing at the upper half, we are only defining the upper half because my old cad program will not solidify more than that. The tip rib has been moved to the tip in the 3D drawing. Refer to plate1 # 2
Plate 4 shows the trimmed upper half.
Plate 5 shows the ruled surface generated.
Plate 6 shows the rest of the 3D operations. I use m2s.lsp to solidify the ruled surface at #5. That is now a solid to 1" below the lowest point. I have made a slice at rib 2 and broke out the rib contour. #6,7,8 The vertical line is to define the plane I want to slice with.
The #8 can now be trimmed and a contour of the upper surface of wing at rib # 2 is defined. This can be turned into a 2D drawing for fabrication (in fact it is a 2D line) of the rib, or assembly fixtures or molds.
A pretty 3D model I often see here is useless except as a cartoon/pretty picture unless one can get usable data from it to make parts.
This is using AutoCad V14 which I have a license for. That this cad program is so old I would guess the techniques are applicable to many cad programs. I use Ruled Surfaces to define my OML. convert to solids and slice them to get my intermediate bulkhead/rib contours.
Plate 1 shows the whole process.
Plate 2 is a digitized root rib and tip rib from the paper plans of the Carbon Dragon. These must be Closed Polylines or defined curves.
Plate 3 shows a line drawing at the upper half, we are only defining the upper half because my old cad program will not solidify more than that. The tip rib has been moved to the tip in the 3D drawing. Refer to plate1 # 2
Plate 4 shows the trimmed upper half.
Plate 5 shows the ruled surface generated.
Plate 6 shows the rest of the 3D operations. I use m2s.lsp to solidify the ruled surface at #5. That is now a solid to 1" below the lowest point. I have made a slice at rib 2 and broke out the rib contour. #6,7,8 The vertical line is to define the plane I want to slice with.
The #8 can now be trimmed and a contour of the upper surface of wing at rib # 2 is defined. This can be turned into a 2D drawing for fabrication (in fact it is a 2D line) of the rib, or assembly fixtures or molds.
A pretty 3D model I often see here is useless except as a cartoon/pretty picture unless one can get usable data from it to make parts.
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