Fuselage modelling techniques

[MichaelkSA]

I want to build a CAD model of a fuselage and have been playing around with some success, but I have 'gone in blind' and am not sure whether the technique I am using is
the best or commonly used.

Is there a preferred method to model the shape of a fuselage?

Some additional info: The fuselage is to have a double bubble design with the fuselage ending in a sharp trailing edge.

I will also appreciate it if someone can refer me to any literature with instructions in this regard.

PS: I know my question is broad, but that is really the idea. I am looking for advice on fuselage (and aero) modelling in general, not just for the specific example I mentioned.

Thank you in advance
michael

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Here's looking at you, looking at me, looking at you

 

[KENAT]

Lofting & surfacing are terms worthy of investigation.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Andries]

MichaelKSA,

Purposes for FE modelling of airframes:

1. To obtain internal loads for design purposes.

2. To obtain detailed stress / strain distributions in airframe components for fatigue and damage tolerance analysis

3. For vibration and aeroelastic analysis.

Each requires specific elements suitable for the task as well as the fineness of the mesh.

I presume that you are looking at case 1 above. Usually the mesh is coarser and coincides with the structural members (ribs, frames, skin panels).

In a pressurised fuselage the skin panels would be modelled using membrane elements, the frames using bars, the stringers using rods or bars. For substantial frames or bulkheads the flanges are often modelled using bars or rods for the flanges and shear panels for the webs.

Regards,

Andries

 

[MichaelkSA]

Thank you KENAT and Andries.

Andries. My question was more in terms of general CAD modelling (solid modelling) than in terms of FE modelling, sorry if my question was not clear on that.

BUT, I do plan on going into the structural analyses of the fuselage so your reply will certainly help me in the future! Than you very much for that

Kindest regards
michael

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Here's looking at you, looking at me, looking at you

 

[tbuelna]

When it comes to modelling something like an aircraft OML or class A auto body panels that require precise definition and smooth curvature, it is best to use surfacing rather than solids. You can use a surface model of an aircraft to perform CFD analysis.

However, it is not easy to produce high quality surface models. It requires a high level of skill and experience. There are very few guys that are good at this work, and they get paid quite well. This is one of those skills that is not easy to teach, and can only be developed thru experience.

 

[dwallace1971]

To add to what tbuelna said, when it comes to surfacing all 3D CAD tools are not created equal. The mid-level tools (Solid Edge, Solid Works, and Autodesk Inventor) are much less capable and I would be hesitant to model aircraft loft surfaces with those. The high end tools, CATIA, CREO, and NX have good surfacing tools, but I think those tools might be an add on for CATIA and NX.

"On the human scale, the laws of Newtonian Physics are non-negotiable"

 

[tbuelna]

Some additional info: The fuselage is to have a double bubble design with the fuselage ending in a sharp trailing edge.

When creating a CAD surface model that will be meshed for some FE application, you should try to avoid thin sections or tiny features that are smaller than the minimum element size used in the FE mesh. They will cause all sorts of problems with the FEA that will need to be fixed manually. Normally, these tiny elements are too small to have an effect on the FEA results. So they should be removed wherever possible.