Your tutorials are so in depth, it's like going to an actual lecture!! Thank you so much for taking your time to go through the material so that newbies like me can follow along!! :)
Thanks, it's good to hear that these videos are value-added. I do have another XFOIL video in the works and, as always, if you're looking for anything in particular let me know and I'll throw it on the list. Have a good one!
Hi sir. First of all, thank you for the excellent, crisp, easy to understand tutorials. Will you please elaborate a bit on MSES airfoil format and explain how it is different from ISES format please? What is the significance of dual coordinates for X and Y each in MSES file format?
Very helpful video! But I have question for you sir. Is it possible to create or modify existing .dat file of airfoil to divide this airfoil on two parts with empty space between? This space should have 10% of chord lenght.
Hmm, I guess it can be done in Microsoft Excel. In my video called “XFOIL Q&A 1: How to Format an Airfoil File using MS Excel” (here’s a link to it: ruclips.net/video/vBWNOivvGrI/видео.html ) I talk about how to format an existing airfoil coordinate file to the proper format to import into XFOIL with each row being a separate coordinate point. The first column being the location on the airfoil chord (x-axis) and the second column being the distance from the chord to the surface (y-axis). Half the second column is the upper surface (mostly positive y-axis values) and half is the lower surface (mostly negative y-axis values). If you want to split between the upper and lower surface look for the (0,0) location. One surface will be from the first row to the (0,0) row and the other surface will be from the (0,0) row to the last row. If you wanted to modify the space between the surfaces you could add or subtract an offset value to one of the surfaces (or half the offset value to the entire second column, aka, both surfaces). However, with this method I would be worried about the flat spot that would result in the LE where there is supposed to be curvature or the TE gap becoming larger. Instead, I would, from the main menu, drop down into the “Airfoil Geometric Design” menu in XFOIL using the GDES command (after loading the airfoil into XFOIL, of course). In this menu, the TFAC command is used for scaling the existing airfoil’s thickness and/or camber. You will need to calculate the scale factor to use here (new value/old value). For instance, if I wanted to modify the NACA 4412 airfoil’s 12% thickness to 10% thickness the scale factor would be 10/12 = 0.83333. When I enter the TFAC command it will prompt “Enter new/old thickness scale factor r>” and I would enter the 0.833333 here. Then it will prompt “Enter new/old camber scale factor r>” and since I only want to modify the thickness without the camber I would hit enter, or return, without entering a number here. If you like the changes you would then use the EXEC command to overwrite the current airfoil with this new airfoil shape we made (that is currently in the buffer airfoil memory). Then you can go up a level to the main menu and save the airfoil to a file or then go down into the Direct Operating Points menu and run analysis on your new airfoil shape. This method will help to keep the curvature in the LE and not increase the TE gap. Try it out and let me know how it goes for you.
Hi, thanks for the tutorial. XFOIL is unable to locate my .dat file. Could you please explain where to put the file on a Mac? I am using XQuartz, and the XFOIL app is blocked. In order to run the app, I have to go in the package content -> resources -> and open the exec file. Thank you in advance for your help!
thanks for your tutorial. however i meet a problem that after enter " LOAD airfoil.dat" my xfoil flashback instantly. Can you help me to deal with this?
Yes, I'd be happy to help. Hmm, I don't quite understand the problem you are having though. What do you mean when you say that your XFOIL flashbacks instantly? Can you describe this in 3 to 4 sentences? Thanks.
@@thescienceofflight1404 I have the same problem right now, when I put "load airfoil.dat" the xfoil window close instantly, I dont know if it is because I put in my file 0 0,.....1 0,....,0 0 and its of another way or if its because I running a selig donovan airfoil :( help please
Hello! I am not sure if you will notice this comment, but I am wondering if we are to trace a certain body part of an animal and combine it with a standard airfoil, can we do that with XFOIL?
Thank you. It's good to hear that these videos are value-added. So when we load an airfoil into XFOIL we give XFOIL a list of points (a point is defined by an x-coordinate value and a y-coordinate value forming an x/y coordinate pair, think (x,y) coordinate pairs) and XFOIL has to turn this list of points into an airfoil shape. The way XFOIL determines the shape of an airfoil from a list of points is by a "connect the dots" approach. This means that XFOIL will take the first point listed and draw a straight line to the second point listed (this line will actually become a panel unless the pane command is used to redistribute the panels around the airfoil shape after loading the airfoil). XFOIL will then take the second point listed and the third point listed and draw a line between the points. XFOIL will then take the third point and the fourth point and draw a line between the points. And so on and so on until XFOIL has drawn a line between the last two points listed. This is why the points must be listed in a sequential order so that the lines are drawn between neighboring points. However, we now have a line and not a closed 2D shape since the first listed point and the last point do not have a line drawn between them. We want this gap to be at the trailing edge so that it doesn't affect the results that much (you can actually see this 'Trailing Edge Gap' on some airfoils if you load an airfoil, go to the PPAR menu, and zoom in on the trailing edge). To put that gap at the trailing edge we need the first point listed and the last point listed to be the trailing edge points. So all this means that we need to arrange our points so that the first point starts on the trailing edge and the subsequent points traverse either the upper surface or lower surface, point by point, and looping around the leading edge it traverses the other surface, point by point, until we have traced the outline of the airfoil and arrive at the other trailing edge point (each point being on its own line of course). Hopefully this helps.
Thanks for the video! and i hava a question. after i relocating all the coordinates in proper postion(TE>LE>TE), and loaded the date file i have a warinng sign which sez" poor coordinates distribution". i used a same data file from uiuc as you did in the video. can you explain why this things happen?
Yeah, no problem. For those who haven’t seen it before, the warning (found in the xfoil.f source code file) states “WARNING: Poor input coordinate distribution. Excessive panel angle xxxxx.x at i = xxxx. Repaneling with PANE and/or PPAR suggested (doing GDES, CADD before repaneling _may_ improve excessively coarse LE spacing”. This error occurs when the max panel angle is greater than 40 degs and is usually solved by using more coordinate points to define the airfoil shape, aka repaneling the airfoil. I actually have another video on my channel covering repaneling an airfoil, here a link to it: ruclips.net/video/zyJRnTMle9Q/видео.html . The idea is that the max panel angle looks at the angle created between two adjacent panels and tells us the maximum for the current airfoil paneling. The greater the angle between two adjacent panels the sharper the corner that is created which can cause problems converging along with reducing the realism of the results. If you wanted to think of it as the flow having to go around this sharp corner, the flow must change drastically between the last panel and the current panel and, depending on the set maximum number of iterations, this might mean that XFOIL can’t converge within the allotted iterations. It also might mean that you might be “missing information” about what the flow is doing between the two panels and that affects the realism of your results (i.e. instead of being accurate to four decimal places you might only be accurate to two). Step 5 in this video, "cleaning up the paneling using the PANE command", should be done on your airfoil if you see this error. Check out that video, when you get some time, to learn more about the airfoil paneling.
I am not able to load the modified ClarkY airfoil coordinates in the plain format with the headers into XFOIL. The error reads: File OPEN error. Nonexistent file: clarky.dat Please help. Before you ask, I have placed the airfoil file in the same directory as XFOIL application. Also, my system contains multiple copies of XFOIL. Will this be a problem?
Multiple copies of XFOIL will not cause any issues unless it is in a different location than the file it is looking for. The reason we put it in the same folder as the .exe application file that we used to start XFOIL is that it is the location that XFOIL is looking for the file to import. But from your comment sounds like you already checked this. You also have the correct file extension. I usually edit mine in notepad and end up with a .txt but a .dat should work as well. Something else that causes issues is whether it is a space-delineated .txt or tab-delineated .txt file. That’s why if you use MS Excel to edit the files you need an extra step to convert it from the tab-delineated file that MS Excel exports to a space-delineated file that XFOIL wants as I explain a little more in this video of mine: ruclips.net/video/vBWNOivvGrI/видео.html . It’s a video where I go step by step on formatting an airfoil to load into XFOIL. You could check on whether what ever software you are using to modify the file exports as a tab-delineated or space-delineated file. Based on the error prompt given I would guess the issue is either a location issue or a tab-delineated file issue but the header (line with the airfoil name) could cause some issues as well. If the string starts with what could be considered by Fortran to be two numbers, it will consider it as the first two coordinate points. So “00 12 NACA” wouldn’t read in right but “0012 Naca” would. Also if the name begins with “T” or “F” fortran will interpret this as a logical (true or false) variable causing issues with XFOIL detecting the name. Hope this helps solve your issue!
@@thescienceofflight1404 i had the same issue. get the clarky.txt in the same folder as the airfoil.exe and he will open is when u use the load sequence. thanks !!!
As a heads up if it is stored as a text file and the name is claky you still have to call it in XFoil by typing load clarky.txt so if you name your file clarky.txt as a text file you need to type in load clarky.txt.txt in xfoil.
Your tutorials are so in depth, it's like going to an actual lecture!! Thank you so much for taking your time to go through the material so that newbies like me can follow along!! :)
Thank you for the kind comment! It made my day.
the Science of Flight of course!! 😊
Thank you a lot for this tutorial videos! They are super helpful, I would like to see new video in your channel about XFOIL in future :)
Thanks, it's good to hear that these videos are value-added. I do have another XFOIL video in the works and, as always, if you're looking for anything in particular let me know and I'll throw it on the list. Have a good one!
Great stuff, could speak a little faster, but that's what x1.5 playback speed is for :)
Thank you for the video! But this music is driving crazy :D
Hi sir. First of all, thank you for the excellent, crisp, easy to understand tutorials. Will you please elaborate a bit on MSES airfoil format and explain how it is different from ISES format please? What is the significance of dual coordinates for X and Y each in MSES file format?
Very helpful video! But I have question for you sir. Is it possible to create or modify existing .dat file of airfoil to divide this airfoil on two parts with empty space between? This space should have 10% of chord lenght.
Hmm, I guess it can be done in Microsoft Excel. In my video called “XFOIL Q&A 1: How to Format an Airfoil File using MS Excel” (here’s a link to it: ruclips.net/video/vBWNOivvGrI/видео.html ) I talk about how to format an existing airfoil coordinate file to the proper format to import into XFOIL with each row being a separate coordinate point. The first column being the location on the airfoil chord (x-axis) and the second column being the distance from the chord to the surface (y-axis). Half the second column is the upper surface (mostly positive y-axis values) and half is the lower surface (mostly negative y-axis values). If you want to split between the upper and lower surface look for the (0,0) location. One surface will be from the first row to the (0,0) row and the other surface will be from the (0,0) row to the last row. If you wanted to modify the space between the surfaces you could add or subtract an offset value to one of the surfaces (or half the offset value to the entire second column, aka, both surfaces). However, with this method I would be worried about the flat spot that would result in the LE where there is supposed to be curvature or the TE gap becoming larger.
Instead, I would, from the main menu, drop down into the “Airfoil Geometric Design” menu in XFOIL using the GDES command (after loading the airfoil into XFOIL, of course). In this menu, the TFAC command is used for scaling the existing airfoil’s thickness and/or camber. You will need to calculate the scale factor to use here (new value/old value). For instance, if I wanted to modify the NACA 4412 airfoil’s 12% thickness to 10% thickness the scale factor would be 10/12 = 0.83333. When I enter the TFAC command it will prompt “Enter new/old thickness scale factor r>” and I would enter the 0.833333 here. Then it will prompt “Enter new/old camber scale factor r>” and since I only want to modify the thickness without the camber I would hit enter, or return, without entering a number here. If you like the changes you would then use the EXEC command to overwrite the current airfoil with this new airfoil shape we made (that is currently in the buffer airfoil memory). Then you can go up a level to the main menu and save the airfoil to a file or then go down into the Direct Operating Points menu and run analysis on your new airfoil shape. This method will help to keep the curvature in the LE and not increase the TE gap. Try it out and let me know how it goes for you.
Hi, thanks for the tutorial. XFOIL is unable to locate my .dat file. Could you please explain where to put the file on a Mac? I am using XQuartz, and the XFOIL app is blocked. In order to run the app, I have to go in the package content -> resources -> and open the exec file. Thank you in advance for your help!
thanks for your tutorial. however i meet a problem that after enter " LOAD airfoil.dat" my xfoil flashback instantly. Can you help me to deal with this?
Yes, I'd be happy to help. Hmm, I don't quite understand the problem you are having though. What do you mean when you say that your XFOIL flashbacks instantly? Can you describe this in 3 to 4 sentences? Thanks.
@@thescienceofflight1404 I have the same problem right now, when I put "load airfoil.dat" the xfoil window close instantly, I dont know if it is because I put in my file 0 0,.....1 0,....,0 0 and its of another way or if its because I running a selig donovan airfoil :( help please
@@eduardojosemedinaleon3021 having the same problem, have you found a solution?
@@peterimpossibleplays6463 Try replacing the tab spaces with normal spaces
Hello! I am not sure if you will notice this comment, but I am wondering if we are to trace a certain body part of an animal and combine it with a standard airfoil, can we do that with XFOIL?
First of all, Thanks for this nice video it was really help full.
may I ask to clarify in details how to rearrange the points for xfoil
Thank you. It's good to hear that these videos are value-added.
So when we load an airfoil into XFOIL we give XFOIL a list of points (a point is defined by an x-coordinate value and a y-coordinate value forming an x/y coordinate pair, think (x,y) coordinate pairs) and XFOIL has to turn this list of points into an airfoil shape. The way XFOIL determines the shape of an airfoil from a list of points is by a "connect the dots" approach. This means that XFOIL will take the first point listed and draw a straight line to the second point listed (this line will actually become a panel unless the pane command is used to redistribute the panels around the airfoil shape after loading the airfoil). XFOIL will then take the second point listed and the third point listed and draw a line between the points. XFOIL will then take the third point and the fourth point and draw a line between the points. And so on and so on until XFOIL has drawn a line between the last two points listed. This is why the points must be listed in a sequential order so that the lines are drawn between neighboring points. However, we now have a line and not a closed 2D shape since the first listed point and the last point do not have a line drawn between them. We want this gap to be at the trailing edge so that it doesn't affect the results that much (you can actually see this 'Trailing Edge Gap' on some airfoils if you load an airfoil, go to the PPAR menu, and zoom in on the trailing edge). To put that gap at the trailing edge we need the first point listed and the last point listed to be the trailing edge points. So all this means that we need to arrange our points so that the first point starts on the trailing edge and the subsequent points traverse either the upper surface or lower surface, point by point, and looping around the leading edge it traverses the other surface, point by point, until we have traced the outline of the airfoil and arrive at the other trailing edge point (each point being on its own line of course). Hopefully this helps.
Thanks alot
Thanks for the video! and i hava a question. after i relocating all the coordinates in proper postion(TE>LE>TE), and loaded the date file i have a warinng sign which sez" poor coordinates distribution". i used a same data file from uiuc as you did in the video. can you explain why this things happen?
Yeah, no problem. For those who haven’t seen it before, the warning (found in the xfoil.f source code file) states “WARNING: Poor input coordinate distribution. Excessive panel angle xxxxx.x at i = xxxx. Repaneling with PANE and/or PPAR suggested (doing GDES, CADD before repaneling _may_ improve excessively coarse LE spacing”. This error occurs when the max panel angle is greater than 40 degs and is usually solved by using more coordinate points to define the airfoil shape, aka repaneling the airfoil. I actually have another video on my channel covering repaneling an airfoil, here a link to it: ruclips.net/video/zyJRnTMle9Q/видео.html .
The idea is that the max panel angle looks at the angle created between two adjacent panels and tells us the maximum for the current airfoil paneling. The greater the angle between two adjacent panels the sharper the corner that is created which can cause problems converging along with reducing the realism of the results. If you wanted to think of it as the flow having to go around this sharp corner, the flow must change drastically between the last panel and the current panel and, depending on the set maximum number of iterations, this might mean that XFOIL can’t converge within the allotted iterations. It also might mean that you might be “missing information” about what the flow is doing between the two panels and that affects the realism of your results (i.e. instead of being accurate to four decimal places you might only be accurate to two). Step 5 in this video, "cleaning up the paneling using the PANE command", should be done on your airfoil if you see this error. Check out that video, when you get some time, to learn more about the airfoil paneling.
@the Science of Flight wow! thanks for the such a detailed reply!!
I am not able to load the modified ClarkY airfoil coordinates in the plain format with the headers into XFOIL. The error reads:
File OPEN error. Nonexistent file: clarky.dat
Please help.
Before you ask,
I have placed the airfoil file in the same directory as XFOIL application. Also, my system contains multiple copies of XFOIL. Will this be a problem?
Multiple copies of XFOIL will not cause any issues unless it is in a different location than the file it is looking for. The reason we put it in the same folder as the .exe application file that we used to start XFOIL is that it is the location that XFOIL is looking for the file to import. But from your comment sounds like you already checked this. You also have the correct file extension. I usually edit mine in notepad and end up with a .txt but a .dat should work as well.
Something else that causes issues is whether it is a space-delineated .txt or tab-delineated .txt file. That’s why if you use MS Excel to edit the files you need an extra step to convert it from the tab-delineated file that MS Excel exports to a space-delineated file that XFOIL wants as I explain a little more in this video of mine: ruclips.net/video/vBWNOivvGrI/видео.html . It’s a video where I go step by step on formatting an airfoil to load into XFOIL. You could check on whether what ever software you are using to modify the file exports as a tab-delineated or space-delineated file.
Based on the error prompt given I would guess the issue is either a location issue or a tab-delineated file issue but the header (line with the airfoil name) could cause some issues as well. If the string starts with what could be considered by Fortran to be two numbers, it will consider it as the first two coordinate points. So “00 12 NACA” wouldn’t read in right but “0012 Naca” would. Also if the name begins with “T” or “F” fortran will interpret this as a logical (true or false) variable causing issues with XFOIL detecting the name.
Hope this helps solve your issue!
@@thescienceofflight1404 i had the same issue. get the clarky.txt in the same folder as the airfoil.exe and he will open is when u use the load sequence. thanks !!!
@@florwalgraeve5877 how do that help me pliiiiz
As a heads up if it is stored as a text file and the name is claky you still have to call it in XFoil by typing load clarky.txt so if you name your file clarky.txt as a text file you need to type in load clarky.txt.txt in xfoil.
@@ralf-hansen thanks man!
hi, good video... where can i download that software... the link from the first video doesn't work anymore