result from the aircraft analysis

[Rebecca Ong]

Good day all,

I have run an analysis of the aircraft using the VLM and panel method. However, I have some doubts about the results that I have obtained. 

1) The values of CL, CD, CM are so large and when running on VLM, CD value becomes negative. Which is not supposed to happen, as CD is a steady flow and can not be a negative value.

2) Why is the aircraft directional and lateral unstable?

3) In the VSAERO, under the moment reference tab, if I set the Xref to 1.6 for example, does it mean that I am setting the CG to be at 1.6?

Attached are the aircraft file, the Cd alpha plot and the matlab script to extract the information from the result.

Rebec

[Edward ZENG]

I’ve been in similar situations before. I think you might need to change your mesh or vspaero settings a bit to fix the issue.

On 16 Aug 2022, at 12:42 am, Rebecca Ong <rebec...@gmail.com> wrote:

Good day all,

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[Rebecca Ong]

Hi Edward zen, 

Are you saying to increase the mesh for model? What setting in the vspaero are you referring to? 

Rebec

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[Edward ZENG]

You might need to change your reference area section. Because the graph looks right to me, they got a offset by something which is likely the reference area settings.

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[Edward ZENG]

And for question 3, yes it does mean that the cg is at that location.

[Rebecca Ong]

My setting for the reference area is at the main wing. So you suggesting that I select other part? How does it matter? I'm just curious.

Thanks for the help Edward.

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[Edward ZENG]

Oh, that is just a possibility, because sometimes Vsp sets the reference area to some odd value, which makes the cd an cl really weird. If it is set correctly, than maybe check something else.

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[Edward ZENG]

I haven’t looked at the file yet, was on a plane actually, I’ll have a look at it later an hopefully I can find something out. 

[Edward ZENG]

Hi,I had a look at the file. It seems fine when I run VLM but I have some issues with panel method. Panel methods really didn't work for me previously as well. Sorry that I can't really help much, (I am a student as well)

[Rebecca Ong]

Thanks for running the file.

So you getting huge value as well right? 

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[Edward ZENG]

No, if I run VLM method, it works alright. 

On 16 Aug 2022, at 5:50 pm, Rebecca Ong <rebec...@gmail.com> wrote:



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[Rebecca Ong]

I see. Appreciate your help. 

Thanks! :)

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[Edward ZENG]

No worries, Panel never really worked out for me no matter what, I have no idea about that either 

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