Quick XFoil Questions

[gi8u2racing]

1. When using 'Type 2' and putting in the Reynolds number, is that supposed to be the Reynolds number that we are optimizing for or is that supposed to be for a C-L of 1? I am trying to optimize for Re=850k and C_L=0.25

2. How do you plot multiple airfoil CL vs CD plots?

3. Is there anyway to manipulate the airfoil thickness of airfoils using XFoil after you upload them and before you plot the CL vs CD?

I am currently using this, anything I might want to do different?
http://web.mit.edu/drela/Public/web/xfoil/sessions.txt

[Lance Prior]

Have you tried XFLR5?

http://xflr5.sourceforge.net/xflr5.htm

It’s a little easier to figure out.

[Jurgen]

I got myself downloading/registering Profili2, no issues with plotting polars, they did all the difficult work for you, so you have a nice intuitive interface to start with. It also uses Xfoil as a core. Maybe other programs do other features?
Jurgen.

[tonyestep]

If you want the Re to be 850000 at CL = 0.25, you should set the Re at CL = 1 to be 425000. As the CL is decreased to 0.25, the plane's speed will double, and so will the Re.

[CloudyIFR]

http://www.rcsoaringdigest.com/pdfs/RCSD-2008/RCSD-2008-02.pdf

See page 27 for a very nice tutorial of XFLR5

Curtis
Montana

[tonyestep]

speaking of XFLR5, the latest version, when run under Vista, appears to have a fatal bug in the flap deflection function.

[nuevo]

From your questions, I'm guessing you'd rather use XFLR5.


2. How do you plot multiple airfoil CL vs CD plots?

See the documentation on the PPLO command in the OPER menu.


3. Is there anyway to manipulate the airfoil thickness of airfoils using XFoil after you upload them and before you plot the CL vs CD?

To set an airfoil to 11% thickness and 3% camber

$ xfoil airfoil.dat
gdes
tset .11 .03
exec
<return>
save airfoil_changed.dat
quit

[Bryan Quick]

XFOIL has it's own group on Yahoo groups. FYI

[AMBeck]

If you are running regular X-Foil here are some things to try.

Type 2 Re is for Cl=1.0. You will need to work backwards from your operating point (Cl=0.25, Re=850K) and find the Re for Cl=1. There are a couple spreadsheets on the web for that.

You can use PPlot to plot multiple airfoils. You'll need to save simulation files in X-Foil using the PACC command. Enter 1 when PPLOT starts up and it will ask you for filenames to plot. These files have no extension (just filename, not filename.xxx) unless you save them with one. It will plot at least 5 files at once. The other thing you can do is import the output files to Excel and plot them there. In Excel, choose "view all files" in the file opening window and it will import them as text. The plots are cleaner that way, but it takes longer (the first time).

You can manipulate thickness using the commands GDES and then TSET. This will ask for new thickness and camber. Hit return to skip the command you don't want to use. The other handy commands are HIGH, which allows you to move the thickness and camber highpoints, and LERA, which allows you to change the leading edge radius. Hit EXEC and put in 50 or so for the number of iterations. Unless you did something weird near the LE, it will usually come up with a solution in 3 or 4 passes. Hit enter when it's done and save the file! GDES will often put little hitches in the the pressure distribution, especially the LERA command.

Restart X-Foil, load the file and go to QDES. For some reason, if you don't restart X-Foil, it may not find the pressure distribution problems. Use the BLOW command to blow up sections of the pressure distribution plot and look for any wiggles. Fix them with the MARK and MODI commands.

That ought to keep you entertained for a while! Have fun and good luck with your designs.