VSPAero Aerodynamic Center

[gm2gabriel]

Hello everyone,

Does the VSPAero calculate and display the aerodynamic center or the center of pressure?

Thanks in advance,

Gabriel

[Rob McDonald]

Not directly, but with a little work it is pretty easy.

Run VSPAERO once at a given angle of attack. Open up the *.history
file, and make note of the CL and CM results.

Then, run VSPAERO again, but at a different angle of attack. Again,
note the CL and CM results.

The CM was taken about the specified point in the input file -- and
the moments and forces have been nondimensionalized by the specified
reference quantities in the input file.

Using the two CM,CL results and the data from the input file, one can
easily solve for the X location about which the moment is constant --
the aerodynamic center.

Rob

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[gm2gabriel]

Thanks for the reply Rob,

I did as you said and found results close enough for my application. VSPAero is a woderful new tool, thanks for the support.

Gabriel

[daniel fouquet]

What equations would I be using exactly if I wanted to find this. I multiplied both CM and CL values by qSwc to get it out of coefficient form. But I'm unsure of what to do from here. Sorry if I should have started a new topic.

Daniel

[Rob McDonald]

Do you have access to any text covering static stability? If you
understand that, you should be able to write the equations by just
thinking through the problem.

It really is just summing forces and moments about the reference
point. By taking two data points, you'll be able to solve two
(linear) equations and two unknowns. The unknowns will be the
zero-lift moment and the length of the moment arm (the location of the
aerodynamic center relative to the reference point).

Rob

[gm2gabriel]

You can check it at Aerodynamics for Engineering Students - Houghton, for example.

After you run VSPAero for two AoA, if VSPAero calculates CMy around y = 0, you can get the CA from

x/cref = (CMy_2 - CMy_1)/(CL_1 - CL_2)