Optimization including stability derivatives

[Daniel-E-B]

I am trying to optimize a flying wing for fabrication on a CNC hotwire. I can therefore only vary:
two chords,
span,
twist,
dihedral,
sweep.
Area is fixed.

I would like to ensure the static stability of the model but found this not to work. I am curious what I am doing wrong.
I can constrain aero["Cm"] = -0.02 and nothing else. If I add any constraints (even things like <10 or ==0) for Cl or Cn or change my Cm constraint I get an Infeasible_Problem_Detected error.

Objective function is currently max L/D. My code is based on the 3D VLM example with all surfaces except the main wing removed.

Any ideas?

[Daniel-E-B]

I think I confused Cm with Cma, etc. Ignore this question

[sumitkumarsahoo2017]

Can you tell here how to calculate Cma and use it as a constraint?

[peterdsharpe]

Here's a tutorial!

https://github.com/peterdsharpe/AeroSandbox/blob/master/tutorial/10%20-%20Miscellaneous/02%20-%20Constraining%20Gradients.ipynb

Could also finite-difference Cma and constrain that.

[peterdsharpe]

Hi Daniel!

Glad to hear you found a fix.

As a side note: if you are optimizing for max L/D, I might suggest using the asb.AeroBuildup aerodynamics engine, rather than asb.VortexLatticeMethod - AeroBuildup will include profile drag, which is important here. API is identical between the two, so you can probably just do a drop-in change.

EDIT: section below is irrelevant following AeroSandbox v4.1.0+

If you're using AeroBuildup, you can further improve accuracy by downloading XFoil and auto-generating airfoil polars (see Line 12 and 13 here; Airfoil.generate_polars(...) does an in-place modification of the airfoil). This will replace the default 2D sectional aerodynamic data with more accurate ones specific to your airfoil.

It probably goes without saying, but: if you're optimizing while applying stability (e.g. Cma) constraints, be sure you set a sensible xyz_ref in the AeroBuildup constructor (this should be the CG location).

Happy optimizing!

-Peter

[chiefenne]

Hi,
I am doing a similar activitiy. Can you please explain the Cma in more detail. Does it exist as a variable?
Andy