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Old Dec 20, 2012, 11:21 AM
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Montag DP's Avatar
United States, GA, Atlanta
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Thomas,

The aerodynamic center is defined as the reference point which, when the pitching moment is calculated about this point, it does not vary with angle of attack. For most airfoils this is very close to the quarter-chord point, at least for small angles of attack. You can check this by running XFoil over a range of angles of attack and confirm that the moment coefficient remains roughly constant.

Dan
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Old Jan 13, 2013, 09:40 AM
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Joined Jan 2013
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hi,

right now I'm trying to do a reverse parsec using matlab to find the parsec parameters from the known airfoil coordinates. i use the "lsqcurvefit" command to find the parameter.. using that command, I can already generate the parsec parameters. However, for some airfoils, I get parameters which values are complex number.. I don't know how that could happen..
can anybody help me?
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Old Jan 24, 2014, 01:59 PM
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Joined Apr 2005
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So, if anyone is still following along, I thought I would post an update.

I've finally finished all my classes (so now all I have to do is finish research ) and have had some time to start thinking about doing a new airplane design. This got me thinking about also doing airfoil optimization again.

Since the time I originally did this in Matlab, I've gained quite a lot of programming experience, so I decided to write my own code. Instead of running XFoil externally, reading in the output files, etc., I've taken the parts of the XFoil source code that I need and have incorporated it into my own code. (The XFoil source code is NOT easy to work with, by the way, though the results are obviously quite good.) So that in itself should make it a lot faster. I plan to use the seed airfoil perturbation approach instead of the spline approach for parameterization. Also, there will be the option to initially use a global search (like particle swarm or a genetic algorithm) to find the vicinity of the global optimum and then a local search to home in on the optimum.

The code is not done yet, but I have pretty much all the guts done except for the objective function and the main program driver. The xfoil portion is done, meaning that I can pass an airfoil to xfoil along with operating conditions, and it will give me the same result as xfoil. The particle swarm optimization routine and local search routine (simplex search) are also ready to go. So I expect v1.0 of the program to be done soon, and I will post it on Sourceforge for all to use. Eventually I will probably add new shape functions for parameterization and new optimization routines, like a genetic algorithm. Also, parallelizing the particle swarm code shouldn't be too hard, so I will probably do that.

Dan
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Old Feb 03, 2014, 08:14 PM
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In case anyone is still reading this, I started a new thread to talk about the new program. It is here:

http://www.rcgroups.com/forums/showthread.php?t=2095696
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