Thumbs up for the videos and the channel. I’ve only just found the first video and I’m looking forward to seeing the rest. This is a really laudable effort and much credit to you sir for undertaking this series. 👍
Hi buddy I want to create my own airfoil from scratch. I think you said you can import coordinates to Xfoil but that means you need to design a shape first ¿How is that made? ¿ Do I have to draw a random shape using a Spline? I want the airfoil for a car rear wing ¿What would be your suggestions to create the airfoil? ¿Is there any bibliography about airfoil design?
Hi friend, how to de-rotate airfoil please ? green line is not aligned with TR et LD edge for me. I have tried the command dero, but it doesn't work, do you have an idea how to use it, please?
Both Xfoil and Designfoil are software for the design and analysis of airfoil shapes. As such, there is both similarities and differences. For instance, Xfoil is free and open source while Designfoil costs money and is proprietary (paid isn’t always better). Xfoil is a menu-driven command prompt and Designfoil is GUI. Designfoil has a 2D virtual wind tunnel and lots of airfoil shape exporting functionality but it appears that XFOIL has more features for modifying airfoil geometry and modifying the surface speed distributions. But let’s get to the root of the matter: the algorithm. Since Designfoil is propriety I don’t have access to their algorithm, but the basic algorithm is described on the website ( www.dreesecode.com/designfoil/science.html ). Reading this page I see more similarities than differences. Both are panel methods (I have a video talking a little bit about the basic panel methods here: ruclips.net/video/-chWU93PLjE/видео.html ). The basic panel method of both is to break the airfoil shape down into panels, add a source to each panel, calculate the velocities of the sources, use the surface speed velocities to calculate a pressure distribution around the airfoil, use the pressure distribution to calculate the lift and moment coefficients, and then maybe use a boundary layer model to determine drag coefficients. This is the method used by both XFOIL and Designfoil. Panel methods do have the tendency to overpredict lift and according to the site it looks like this might be part of the proprietary nature of Designfoil would be to use empirical data to correct this. Is it worth the price? Not sure myself as I’ve not tested it extensively and I don’t know if I want to pay to buy and test it. Maybe in the future.
I have the weirdest problem ever with Xfoil that I can't solve. I am using Xfoil for airfoil optimization for small wind turbines and I am coupling it to a MATLAB code such that the MATLAB opens Xfoil to calculate the lift and drag for each airfoil, and depending on these values, the optimization algorithms try to find the best solution. The problem is that after several iterations in the optimization algorithm, the Xfoil starts to get unrealistic results although the airfoil coordinates wouldn't have changed much and the same xfoil settings are used for all the airfoils. And if I try to solve one of those airfoils having unrealistic results on xfoil separately and change a little bit of information such as one of the coordinate points or even changing the reynolds number by 1, the xfoil solves it correctly. Did anyone face such a problem when dealing with xfoil?
The solution that you mentioned, i.e. changing the Reynold’s number by one or slightly changing one of the airfoil points, is a common suggestion to fix solutions that do not converge. The method used by XFOIL to obtain a solution is an iterative method that is designed to converge on the solution by using the previous solution as the initial guess for the next iteration. Every once in a while, you’ll encounter a situation where the solutions will bounce between two numbers. Using random numbers for illustration, the first solution will be -2. With -2 as the initial guess, the solution of the next iteration is -3. With -3 as the initial guess, the solution to the next iteration is -2. As you can imagine, the method has become stuck in a loop. Using a Reynolds number that is slightly different by, let’s say, 1 will have a different result. With the first solution of -2 leading to -2 as the initial guess, the solution of the next iteration is -2.99998. With -2.99998 as the initial guess, the solution on the next iteration is -2.23456. As you can see, the slight change lead to slightly different solutions that prevented the method from getting stuck in the loop. Some other things to try on solutions that do not converge would be to increase the number of iterations that XFOIL tries before it gives up (using the ITER command in the XFOIL -> OPER menu) or changing what is considered to be an acceptable solution (I don’t think this is possible currently using the commands in XFOIL. I would have to take some time looking in the source code to figure out this solution). Hopefully this is enlightening and helpful!
Thanks very much for your reply. In fact, xfoil does converge to a solution which is unrealistic that is the problem, it doesn't go in an infinite loop or display a 'Not Converged' message it just gives a result which is very unreliable. For example, the optimization algorithm would be generating airfoils which give lift to drag ratios in the order of 50s and suddenly we start finding airfoils having 100+ lift to drag ratio although we don't find these values anymore when I make slight changes as I mentioned.
Hmm, interesting. I do wish XFOIL had some built-in checks on how reasonable the answers it gives are (like telling if the angle of attack is past stall or if a separation bubble might be present so that we know we're a region that XFOIL isn't very accurate). Maybe when I'm not so swamped at work I'll try and write some code to this effect. Let me know if you find the reason it was giving weird results.
Yeah, this was one of my first videos when I had a LOT less experience editing videos. I have since learned my lesson and, as you will see by my more recent videos, I have taken off the background music. I wish there was a way to do that with this video and still leave it up. Anyways, hope you suffer through the first few videos and get to the better ones in the series!
Thumbs up for the videos and the channel. I’ve only just found the first video and I’m looking forward to seeing the rest. This is a really laudable effort and much credit to you sir for undertaking this series. 👍
Thank You! Lots of good things planned for the near future so stay tuned.
I absolutely will stay tuned. I'm looking forward to the series and what follows on. :-)
Highly useful for Aerodynamics study!
Thanks!
A beginner. Aerodynamics assignment brought me here.
That's awesome! Anything the assignment wanted you to do that my series hasn't covered yet? Might be good topic for a future XFOIL video.
Excelent videos!
Thank You!
excellent video! music is not necessary though
Hi buddy
I want to create my own airfoil from scratch.
I think you said you can import coordinates to Xfoil but that means you need to design a shape first ¿How is that made? ¿ Do I have to draw a random shape using a Spline?
I want the airfoil for a car rear wing
¿What would be your suggestions to create the airfoil?
¿Is there any bibliography about airfoil design?
Hi friend, how to de-rotate airfoil please ? green line is not aligned with TR et LD edge for me. I have tried the command dero, but it doesn't work, do you have an idea how to use it, please?
Is Xfoil similar to Designfoil?
Both Xfoil and Designfoil are software for the design and analysis of airfoil shapes. As such, there is both similarities and differences. For instance, Xfoil is free and open source while Designfoil costs money and is proprietary (paid isn’t always better). Xfoil is a menu-driven command prompt and Designfoil is GUI. Designfoil has a 2D virtual wind tunnel and lots of airfoil shape exporting functionality but it appears that XFOIL has more features for modifying airfoil geometry and modifying the surface speed distributions. But let’s get to the root of the matter: the algorithm. Since Designfoil is propriety I don’t have access to their algorithm, but the basic algorithm is described on the website ( www.dreesecode.com/designfoil/science.html ). Reading this page I see more similarities than differences. Both are panel methods (I have a video talking a little bit about the basic panel methods here: ruclips.net/video/-chWU93PLjE/видео.html ). The basic panel method of both is to break the airfoil shape down into panels, add a source to each panel, calculate the velocities of the sources, use the surface speed velocities to calculate a pressure distribution around the airfoil, use the pressure distribution to calculate the lift and moment coefficients, and then maybe use a boundary layer model to determine drag coefficients. This is the method used by both XFOIL and Designfoil. Panel methods do have the tendency to overpredict lift and according to the site it looks like this might be part of the proprietary nature of Designfoil would be to use empirical data to correct this. Is it worth the price? Not sure myself as I’ve not tested it extensively and I don’t know if I want to pay to buy and test it. Maybe in the future.
I have the weirdest problem ever with Xfoil that I can't solve. I am using Xfoil for airfoil optimization for small wind turbines and I am coupling it to a MATLAB code such that the MATLAB opens Xfoil to calculate the lift and drag for each airfoil, and depending on these values, the optimization algorithms try to find the best solution. The problem is that after several iterations in the optimization algorithm, the Xfoil starts to get unrealistic results although the airfoil coordinates wouldn't have changed much and the same xfoil settings are used for all the airfoils. And if I try to solve one of those airfoils having unrealistic results on xfoil separately and change a little bit of information such as one of the coordinate points or even changing the reynolds number by 1, the xfoil solves it correctly. Did anyone face such a problem when dealing with xfoil?
The solution that you mentioned, i.e. changing the Reynold’s number by one or slightly changing one of the airfoil points, is a common suggestion to fix solutions that do not converge. The method used by XFOIL to obtain a solution is an iterative method that is designed to converge on the solution by using the previous solution as the initial guess for the next iteration. Every once in a while, you’ll encounter a situation where the solutions will bounce between two numbers. Using random numbers for illustration, the first solution will be -2. With -2 as the initial guess, the solution of the next iteration is -3. With -3 as the initial guess, the solution to the next iteration is -2. As you can imagine, the method has become stuck in a loop. Using a Reynolds number that is slightly different by, let’s say, 1 will have a different result. With the first solution of -2 leading to -2 as the initial guess, the solution of the next iteration is -2.99998. With -2.99998 as the initial guess, the solution on the next iteration is -2.23456. As you can see, the slight change lead to slightly different solutions that prevented the method from getting stuck in the loop.
Some other things to try on solutions that do not converge would be to increase the number of iterations that XFOIL tries before it gives up (using the ITER command in the XFOIL -> OPER menu) or changing what is considered to be an acceptable solution (I don’t think this is possible currently using the commands in XFOIL. I would have to take some time looking in the source code to figure out this solution).
Hopefully this is enlightening and helpful!
Thanks very much for your reply. In fact, xfoil does converge to a solution which is unrealistic that is the problem, it doesn't go in an infinite loop or display a 'Not Converged' message it just gives a result which is very unreliable. For example, the optimization algorithm would be generating airfoils which give lift to drag ratios in the order of 50s and suddenly we start finding airfoils having 100+ lift to drag ratio although we don't find these values anymore when I make slight changes as I mentioned.
Hmm, interesting. I do wish XFOIL had some built-in checks on how reasonable the answers it gives are (like telling if the angle of attack is past stall or if a separation bubble might be present so that we know we're a region that XFOIL isn't very accurate). Maybe when I'm not so swamped at work I'll try and write some code to this effect. Let me know if you find the reason it was giving weird results.
ı don't like the music that you put to the video. It distracts me.
Yeah, this was one of my first videos when I had a LOT less experience editing videos. I have since learned my lesson and, as you will see by my more recent videos, I have taken off the background music. I wish there was a way to do that with this video and still leave it up. Anyways, hope you suffer through the first few videos and get to the better ones in the series!