Problem Difference in C.G in Mass Props

[Simon Boudoux]

Good afternoon,

I have a question regarding a problem in Mass Props, I have an model with a body and wings and when I use the Mass Props analysis to find the C.G of the model I have a result and when I check the details in the MssProps.txt file i see the C.G for each parts of the model and I see that the result is different for my body when I compute it alone and within the model. Is it like a normal issue ? 

Sincerely yours,

Simon 

[Rob McDonald]

Your wing and fuselage likely overlap.

Where they overlap, what value for the density do you want OpenVSP to use?

There is a priority score -- OpenVSP chooses the density of the overlapping component with the highest priority.  If all the priorities are equal, it picks one.

Figure out what you want -- then set the priorities accordingly and you should be good.

Rob

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[Simon Boudoux]

Thanks for the information. I just checked and it didn't change and i think the issue is that my body as a mass area and not a density, does it affect the priority ? 

Simon 

[Rob McDonald]

The area based mass only computes the mass contributions of the OML -- the triangles on the outside of the configuration that survive the trim operations.

So, if your fuse and wing overlap, all the overlap bits get trimmed and do not contribute to the mass.

The priority does not influence the area based mass.

Rob

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[Simon Boudoux]

So is there any way to make both works together or do i have to convert my mass area to a density if I want an accurate priority and overlap mass props ? 

Simon 

[Rob McDonald]

You can absolutely use both.

Use the volumetric density and priorities to handle the volume.

Use area density to handle the skins.

The Mass properties calculation will combine them both.

Rob