WT_Perf / FAST Airfoils


two weeks ago Marshall Buhl informed that one should update to the current alpha-Version of WT_Perf. Today I did the update and I am having trouble with my airfolis now.
With the old version of WT_Perf I used the same Airfoil files as with FAST. If I try to do that with the current version, WT_Perf fails with

Angle of attack range of airfoil tables for segment #1 must be from -180 to 180.

However the echo-file of WT_Perf looks like this:

"AeroData\cylinder.dat" FirstHead - First line in the airfoil file. Round Root Section File: WTCRound.dat 1 NumTabs - Number of airfoil tables for segment #1. 0.0000E+00 RnAry - Reynolds number values for the airfoil tables. 1.4000E+01 ASAry - Stall AoA for this airfoil table. 0.0 No longer used, enter zero 0.0 No longer used, enter zero 0.0 No longer used, enter zero 0.0000E+00 AOLAry - zero-lift AoA 0.0000E+00 CnAAry - Cn slope for zero lift 0.0000E+00 CnSAry - Cn at stall value for positive AoA 0.0000E+00 CnSLAry - Cn at stall value for negative AoA 0.0000E+00 AODAry - AoA for minimum Cd 1.0000E+00 CDOAry - minimum Cd value -180.0000 0.0000 0.5000 0.0000 0.0000 0.0000 0.5000 0.0000 180.0000 0.0000 0.5000 0.0000
So in my opinion, WT_Perf does read the airfoil table and it contains angles of attack from -180 to 180. What is happening here?

Maybe you are missing a line in the header of the airfoil files. The current WT_Perf alpha (v3.04.00c-mlb, 13-Jan-2011) has an additional input parameter called “Control setting” in the airfoil files (not sure what it does yet). Make sure that your airfoil files have the same number of header lines as the WT_Perf alpha is expecting. Look at the example airfoil files that came with the WT_Perf alpha to see if your airfoil files match the format of those example files.

I thought I had added the control parameter only for the new-style airfoil tables; the ones with the “EOT” at the end of each table. The file listed above is not a new-style file. If you turn on the Echo flag in the .wtp file, you can look at the resulting .ech file to see where the data and their descriptions start to diverge. Try that and if you still can’t get it to work, send your input files to me so I can debug them.


The Control setting is not yet implemented, but as I was changing the input files, I wanted to make all the changes I could foresee so people wouldn’t have to keep making changes to their files. The idea is that, eventually, airfoil data will be a function of Re, Control Setting, and Angle of attack. The control setting is to accommodate tabs, flaps, and ailerons. Currently, AeroDyn can interpolate for Re and Alpha or, with minor changes, Control Setting and alpha, but not both. WT_Perf can interpolate Re and Alpha. When we overhaul AeroDyn, it will use the same subroutine as WT_Perf to read in airfoil tables.


Thanks for your reply. The second “Code”-Block of my initial contribution to this topic is the echo-File which WT_Perf writes. I think it does not diverge from the airfoil-file. Therefore I don’t understand the error message.

Best regards,


If you send me your input files, I’ll try to figure out what’s wrong.


Marshall could figure out, that there should be no blank lines at the end of the airfoil files. If these are removed WT_Perf does not complain any more.