Are the static margin calculations robust?

[jkwn...@gmail.com]

Does OpenVSP calculate the neutral point for static margin as I have noticed unusual behavior with the aero reference module?  is there a method to insure the SM given is for the aircraft rather than for a component.

I am balancing an asymmetric design laterally however I have noticed the SM does not change.

[jkwn...@gmail.com]

The use of the a blank geometry to attach a matrix of parts seems to cause errors in CG (position) calculations.

[Rob McDonald]

The aerodynamic center calculations are based on pretty simple relations.

The menu callbacks for this stuff start at about line 1160 of
screenMgr.cpp. The actual calculations for a wing are done in
ms_wing.cpp about line 3282.

There you'll find that the AC calculation is just a simple formula for
a multi-section wing component. This calculation does not do any
actual aerodynamic calculations on the entire aircraft.

If you create an asymmetric wing out of a single component, it might
work. If you created it out of two wing components, the calculation
will only be based on one.

I'm not sure about the problem you're reporting for the CG
calculation. Are you talking about the CG which results from the
slicing operations by selecting 'Mass Prop...' from the menu? Or are
you talking about something else?

Rob

On Mon, Mar 4, 2013 at 1:31 PM, <jkwn...@gmail.com> wrote:
> The use of the a blank geometry to attach a matrix of parts seems to cause
> errors in CG (position) calculations.
>

[Rob McDonald]

Ok, thanks for the clarification on your problem.

I dug into it a bit tonight and I think I've tracked it down. Do you
have the ability to compile VSP and try out a fix? Otherwise, it will
have to wait until I can test it some more and roll a new release.

The fix is in a new branch on GitHub:

https://github.com/ramcdona/OpenVSP/tree/CG_fix

Point mass components were only considered using their local
coordinates -- which neglects any positioning from any components they
are connected to.

Rob


On Mon, Mar 4, 2013 at 3:58 PM, <jkwn...@gmail.com> wrote:
> Thanks for the explanation of the AC calculation.
>
> I have used point masses on the torso of passengers which are part of a
> nested group. I've had to remove them from the group as the CG calculation
> confused their position throwing off the calculation.

>
> On Tuesday, March 5, 2013 10:19:22 AM UTC+13, jkwn...@gmail.com wrote:
>>

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[jkwn...@gmail.com]

Hi Rob,

Apologies I wasn't expecting a response.  Thanks for all the good work.  VSP is a great piece of software

On Tuesday, March 5, 2013 10:19:22 AM UTC+13, jkwn...@gmail.com wrote: