KS20 airfoil simulation


Cl – Cd(low reynolds numbers also included, plus also flapped version (+10deg and +20 deg)

L/D vs. alpha:

Cm vs. Alpha:

Cl – alpha:

Printable profile picture of KS20 (black on white background):


Calculated polar for: KS20

1 1 Reynolds number fixed Mach number fixed

xtrf = 1.000 (top) 1.000 (bottom)
Mach = 0.270 Re = 5.000 e 6 Ncrit = 9.000

alpha CL CD CDp CM Top Xtr Bot Xtr Cpmin Chinge XCp
------- -------- --------- --------- -------- ------- ------- -------- --------- ---------
-2.500 0.0172 0.00639 0.00156 -0.0630 0.5734 0.1263 -0.9628 0.0000 3.9974
-2.000 0.0779 0.00594 0.00135 -0.0638 0.5687 0.2065 -0.7727 0.0000 1.0832
-1.500 0.1376 0.00529 0.00111 -0.0647 0.5613 0.3515 -0.6885 0.0000 0.7246
-1.000 0.1985 0.00466 0.00091 -0.0657 0.5560 0.4943 -0.7241 0.0000 0.5818
-0.500 0.2604 0.00434 0.00082 -0.0667 0.5474 0.5909 -0.7638 0.0000 0.5048
0.000 0.3235 0.00430 0.00084 -0.0677 0.5380 0.6224 -0.8063 0.0000 0.4565
0.500 0.3863 0.00438 0.00088 -0.0686 0.5260 0.6346 -0.8489 0.0000 0.4238
1.000 0.4491 0.00445 0.00094 -0.0696 0.5127 0.6478 -0.8954 0.0000 0.4002
1.500 0.5115 0.00461 0.00102 -0.0704 0.4945 0.6510 -0.9563 0.0000 0.3823
2.000 0.5732 0.00475 0.00111 -0.0712 0.4723 0.6587 -1.0304 0.0000 0.3682
2.500 0.6344 0.00497 0.00124 -0.0719 0.4472 0.6628 -1.1188 0.0000 0.3567
3.000 0.6941 0.00529 0.00142 -0.0723 0.4114 0.6656 -1.2143 0.0000 0.3470
3.500 0.7516 0.00577 0.00168 -0.0724 0.3616 0.6675 -1.3096 0.0000 0.3385
4.000 0.8098 0.00619 0.00194 -0.0726 0.3230 0.6691 -1.4113 0.0000 0.3313
4.500 0.8664 0.00670 0.00226 -0.0725 0.2804 0.6702 -1.5275 0.0000 0.3247
5.000 0.9229 0.00719 0.00260 -0.0724 0.2437 0.6718 -1.6463 0.0000 0.3189

KS20.dat Airfoil file for QFLR5, XFLR5 or Xfoil

    • Exo Cruiser
    • February 20th, 2009

    Remember the script I linked to, which was to calculate the wing Area from washington.edu. Sorry to say that it has a bug as usual.


    After checking why it gives so larges wing areas, I found that there is a bug. The bug is such that there is mph used directly when it should first convert it to ft/s.

    You can go around that bug, if you feed the desired landing speed as ft/s NOT mph as the page says.

    I will try to put a corrected script somewhere if I have time.


    • Exo Cruiser
    • February 21st, 2009

    Here is now the new and fixed version of the wing area calculator. The script is basicly the same, but now you should really enter the speed in mph as the page asks.


    I have checked the script with Piper Cherokee, see:


    If you enter weight=2150 lbs, altitude=0 and speed=54 mph and choose “hinged flaps” as in Cherokee, you should get wing area 160 ft^2. And that is exactly what Piper Cherokee’s wing area is.

    I also checked the estimated CLmax and that is very much ok if one compares that to the NACA 65(2)-415, partially plain flapped would have.

    So that can be used to do raw estimates of some wing areas.

    • Karoliina Salminen
    • February 21st, 2009

    I am using my own calculation software for calculating the wing area, it does it correctly. It does not calculate everything correctly (there are known bugs on it that I haven’t had yet time to fix), but the wing area calculation is correct.

    You can get the latest source from the katix.org gforge subversion repository or you can download either Linux or Mac binary from here: http://www.katix.org/karoliina/packages/

    • Exo Cruiser
    • February 22nd, 2009

    I was iterested to get it to run as a javascript and on some web page. I might as well transfer the most easy parts of my code on line, where it would be easy to use.

    It is always a good idea to double check the most critical calculations and assumptions.

    It is really funny how much design bugs there are. Take as an example the swiss flying wing jet. Since it is a high wing with some sweep, it should have some negative dihedral to avoid the “dutch roll”. That is also reported by the pilot and designer. Maybe he does not know that factor? or fixes it later.


    • Karoliina Salminen
    • February 23rd, 2009

    If you have calculation code, feel free to contribute it to my calculation program. It is very simple: the calculation part is in one file and each equation forms a function. So the functions are very simple and anyone can read and write these despite it is C. The more complicated part is separated (the UI and the data model). This enables making UI-less program and the program with UI very easily. I started it without graphical user interface from a command line interface.

    • Exo Cruiser
    • February 24th, 2009

    OK. Most of my "main" code is in C++ (Visual C++). Now since I found this "javascript" hassle, I might transform some of it to java, mostly due to interest of the language java.

    There are some benefits having it in javascript. It is platform independent (windows, linux, whatever) and the code is easy to distribute: just open the page and run it. Especially for the smaller parts. I have them at ExoAviation ->


    BTW: If you are doing airfoil design, you have to chek Martin Hepperle's JavaFoil. It is very impressive and I think it is even better than the XFLR5, more functions and better quality.


    • Karoliina Salminen
    • February 24th, 2009

    >BTW: If you are doing airfoil >design, you have to chek Martin >Hepperle's JavaFoil. It is very >impressive and I think it is even >better than the XFLR5, more >functions and better quality.

    I have used Javafoil in the past. The problem is that in contrary, I am seriously doubting it being better than XFLR5. It does not seem to model laminar bucket at all correctly, the Xfoil engine on XFLR5 does better job on that. Also it does not have any wing design features that are standard in the XFLR5. In my opinion, the Javafoil has a lot less functions than the XFLR5 and the XFLR5 code is easily tailorable. I can write my own stuff on the QFLR5 (like now I am planning to do a CAM-exporter), but I can not and don't want to touch Javafoil or anything that is made with Java.

    I was using Java in the 2000s at the Java-hype time, but that time is long gone now, it was almost 10 years ago. I don't buy the hype anymore and I am kind of glad that I got over it. Java is not very good for about anything. Program with compiled code runs more efficiently on resource restricted devices and Qt is a solution of the future to cross platform compatibility.

    • lincoln
    • March 25th, 2009

    Have been messing with airfoil stuff lately. Not realistic yet but have trouble not thinking about USA part 103 compliant motorglider.

    Anyway, messing with airfoils,I checked out your KS20 vs NACA 63(3)618, which Xfoil, as seen through Profili, really seems to like. Seems like the NACA section has somewhat more usable lift and very similar polar, although perhaps I’m not using the right parameters. This at Re=1000000/sqrt Cl, ncrit 13. Not sure what all the extra lines on your polars are.

    Found out about it through the Strojnik books, Laminar Aircraft Design, L.A. Technoligy, L.A. Structures. If you don’t have them you’d probably really like them.

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