How to create a Conformal Engine Nacelle

Rhino
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Conformal Engine Cowling.3dm (331.6 KB)

Completed Aircraft
Completed Aircraft914×480 82.6 KB

We are struggling to determine how to create an engine nacelle. In the attached cad file, we have the main upper and lower surfaces along with an engine housing with engine mount. I also included a photo of a finished system. We need to smoothly blend the engine housing to the main upper and lower surfaces.

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screenshot of your file:

image
image1344×932 112 KB

what is the purpose of the data you re trying to model ?

currently your object is
571.01, 470.30, 125.53
a scaled modell ?
only visual / rendering

→ do it with subD, especially if you re not so familiar with more advanced modelling-techniques.

if you really need it for engineering purpose - you still can start with form-finding in subD and later switch to nurbs / polysurfaces.

maybe sketch on the screenshot what your after exactly…

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Hi Ronald - something like this?

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image863×508 16.2 KB

-Pascal

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Hi Pascal … That is exactly what we need. We can run the surface through CFD code, and then make slight adjustments for minimize pitch instabilities. What steps did you use to create the Nacelle and then trim the main top and bottom surfaces?

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Hi Pascal,

Did you capture the steps used to make that nacelle? Several of our students are eager to try!

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Hi Ronald - I’ll lay out the steps tomorrow.

@ronald1 - I can imagine there are a few ways to do this - I did it relatively cheaply by using FilletSrf to get the basic transition surfaces made. I used radius-50 as that seemed about right, and I would uncheck Trim in the filletSrf dialog - do the trimming afterwards. The top is pretty straightforward -

  1. Extend the basic outer cylinder of the red thing into the body of the plane and beyond the back - ExtractSrf, UntrimBorder, ExtendSrf, Type=Smooth, Merge=Yes.

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  1. FilletSrf - you’ll see that the single-surface-with-a kink does not like this command -

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So DivideAlongCreases the airplane surfaces, then fillet. I’d unset Trim contrary to my image…

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image928×620 103 KB

  1. At the front, the fillets from each side will cross each other so trim them back with a line along the X axis to make a miter:

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  1. At the rear, ExtendSrf the fillets and trim them back with the trailing edge curves of the wing. Note the top and bottom trailing edges are slightly different so this operation on the bottom fillets will not match 100%… that needs a little work.

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image416×502 40.6 KB

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The bottom is exactly the same only at the front, the crease between the two wing surfaces has a different effect - they don’t cross at the centerline in the same way as on the top:

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I might be tempted to modify the wing surfaces to be tangent in this area, it would save a bit of trauma for these transitions but for now, you’ll need to clean up by hand.

One way is to split the fillets with an isocurve, snapping the the Quad of the edge:
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Then make tangent blend curves across:

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image678×558 51.3 KB

Trim the wing surfaces with the front most blend asnd construct surfaces from the mid points:

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You will need to do some surface matching to get all the edges tangent where they need to be tangent and meeting cleanly on the center line - see Help on MatchSrf and all the possible settings…

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Then trim…

-Pascal

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