1. Hide the rest of the model.

2. In the Layer panel, temporarily unlock the "Front Drawing" layer.

3. Create a Point object, snapping to the Center of the reference circle for the inboard propeller.

4. Re-lock the "Front Drawing" layer.

5. Move the point aft 349 units.

6. Start the CPlane command, set the All option to Yes, and snap to the Point in any view to place the origin of a new set of construction planes.

7. Delete the point.


8. Draw a profile Curve of Degree 3 in the Right view.

9. Revolve the curve around the origin of our custom CPlane.

10. Delete the curve we revolved.


11. Draw three Line objects in the Right view.

12. Use those lines to Split the surface into 4 pieces.

13. Delete the lines.

14. Select the surfaces and run ShrinkTrimmedSrf on them. The points were turned on for the larger surface here to show how the surface is 'shrunk' to remove the trimmed-away area.

Quad snap
Quad snap

15. Use Split again, this time with the Isocurve option, and with the Shrink option set to Yes, to cut the largest piece of the revolve in half vertically using the Quad Osnap.

(Sample videos are hosted on YouTube. Videos in the actual tutorial are, of course, larger and sharper. For full-quality video you can download a more extensive "demo CD" here.)

16. Since a straight revolved surface can't be point-edited smoothly, select the outer half of the larger surface and use ChangeDegree to raise it's Degree to 5 in both directions, with the Deformable option set to Yes.

Point snap

17. We want to add two rows of control points to this surface in a predictable location. Well, where they are is not so important as that your model match this precisely, so to help run ExtractIsocurve on the surface, snapping to a Point on the control point cage.

End snap

18. Run InsertKnot on the surface, adding one knot, snapping to the End of the curve we extracted.

Point snap

19. Repeat the ExtractIsocurve procedure, snapping to the control Point.

20. Run InsertKnot on the surface again, adding one knot snapping to the End of the Extracted curve.

21. Delete the extracted curves.

22. The reason we kept the right half of this surface around was this step. ChangeDegree will not try to maintain edge continuity, so MatchSrf each edge of the modified surface back to the unmodified. Specify Tangency Continuity, and none of the other settings should have any effect but enable Match edges by closest points just in case.

23. Delete the right surface.

We'll now do some fairly extensive point-editing on this surface to form the main part of the engine shroud.


24. Select 20 points on the first 5 columns and move them down by 8.5 units.


25. Select 15 points and move them down an additional 5.5 units.


26. Now move a couple of the points we just moved back up by 2 units.


27. Move this point up 1 unit.


28. Move this point up by 0.5.


29. Move two points up by 1.8.


30. And move these up by 2.8.

Center of rotation
End snap

31. Select the last column of points and Rotate them 90 degrees. Use the upper End point for the Center of rotation.


32. Use SetPt to align these four points with a Y value of 207.96.

Zero in on the points we just aligned and tweak them:


33. Move the outermost point in by 2 units.


34. Move the third point out by 2.95 units.


35. Move the second point out by 6.51 units.


36. Select these two points and move them in by 4 units.

37. Move the forward point of these two in an additional 0.5 units.


38. Move to the next point and nudge it in by 2 units.


39. Select the next whole column of points and move it back 20 units.

Reference point
Origin point
(124.714,24) Point snap
Shear angle

40. Shear the points we just moved.


41. Adjust two of the points we just sheared. Move them in by 2 units, then move the more forward point in an additional 0.5.

End snap

42. Draw a Degree 5 Curve for the profile of the intake, snapping to the End of the main shroud surface.


43. Draw a Degree 3 Curve in the Front view.

Rail curve
Section curve

44. Use the last curve as the rail and the profile curve as the section for a Sweep1 surface. Set the Style to Freeform, set Do not simplify in the Cross-section curve options, and the other settings are not applicable.

45. Delete the input curves for the sweep.

46. MatchSrf the intake to the shroud. Specify Curvature Continuity, enable Refine match and Match edges by closest points, and set the Isocurve direction adjustment to Automatic.

47. Draw two Degree 5 Curves in the Right view. snap to the to the End of one to place the end of the other.

(23.39,-16) End Snap

48. Use the curves to Trim out the unmodified piece of the shroud.

49. Delete the curves.


50. Draw a new Curve in the Front view.

51. ExtrudeCrv it a distance of 23 units.

52. Delete the input curve.

53. Move the extruded surface back by 17 units.


54. Select the back row of points on the surface and move them down by 1 unit.

55. Trim that surface to trim off the intake surface.

56. Delete the trimming surface.

0.9 Blend bulge
0.9 Blend bulge

57. BlendSrf between the intake and the shroud piece. The blend should turn out okay without specifying any guide sections, and set the Blend bulge to 0.9 on both edges.


58. Draw a Rectangle in the Right view.

59. Use it to Trim off the intake and blend surfaces, the main shroud surface, and the upper part of the smaller shroud surface.

60. Delete the rectangle. [End of sample section, return to Hydraulic Design.]