Home Engineering Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
We now have an accurate closed wing section profile that can be arbitrarily scaled. We next need to create some 3D reference geometry so that we can place two independently scaled wing sections in relative positions in 3D space. We can then loft between these two. Figure 17.30 shows the resulting placement of the two sections in relation to each other. A loft between these two will generate a wing surface whose sweep, taper, root chord, and twist can be controlled (all these steps are automated in the AirCONICS suite of course).
Figure 17.31 shows the finished result. Note also 
Figure 17.30 ‘ ‘3D” scaffold to define the relative positions in space of two independently scalable wing
Figure 17.31 Wing surface with span, twist, taper, and sweep variables.
• the naming of dimensions with meaningful text - this becomes very important when complex geometry, design tables, and external files are used. It is easy to link the wrong dimension when it is merely labeled “D15 @sketch23.”
Figure 17.32 shows how a PA-32 aircraft-type wing can be modeled using two panels. Of course, the number of variables needed to define this wing has now risen to 9 (4n + 1, where n is number of panels).
Figure 17.32 Multipanel wing.
Figure 17.33 Example of a double-curvature composite wing.
Having now created the surface geometry, an approximate structural model needs to be derived from this surface in order for a good mass estimate to be made.
As with the fuselage, a structural philosophy and manufacturing method needs to be decided before creating further geometry. Stressed skin composite structures give the aerodynamicist the most geometrical freedom including double-curvature surfaces that would result if an elliptical planform was chosen (Figure 17.33). Composite structures are, however, notoriously expensive compared to other methods of construction. In light and microlight aircraft, it is
Figure 17.34 Fabricated wing structures.
Figure 17.35 Simple wooden rib and alloy spar structure.
generally cheaper to manufacture a fabricated wing using a range of materials such as aluminum spars, wooden ribs, or polyester fabric covering, see Figure 17.34. As already seen, in most of our UAVs we adopt carbon-fiber spars supporting foam cores with fiber or Mylar coverings.
Having made decisions regarding wing structures and materials, a more realistic wing can now be constructed based on the aerodynamic surface. For example, Figure 17.35 shows a very simple wing structure popular in lightweight microlight aircraft designs.
A more sophisticated structure is shown in Figure 17.36. This assumes hollow glass-fiber leading and trailing edges with glass- fiber ribs (a material type has been assigned to the structure). A table has been created in this model that gives an accurate mass prediction for this geometry.
The geometry created in Figure 17.36 is based on the parametric wing surface given in Figure 17.31. Hence the model can still have the flexibility of the original parametric
Figure 17.36 Parametric wing structure.
model. A useful way of creating the ribs is to use a Boolean operation to create a multibody
Appendix C shows a worked example of this approach to generating a detailed parametric CAD model for a manned aircraft.
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