See the previous post. What you're pointing out is the limitation of all of these types of equation based simulators. In order to have a closed form equation one has to assume a degree of mathematical linearity in the behavior of whatever is being modeled. Flow separation is a non-linear behavior. If you know enough about the subject of the model you can use the equation based model to identify where the result has reached a point where the non-linear behavior is likely to occur. But then you need to use a different and far more complex modeling technique to predict the subject's behavior through the non linear region. These techniques often rely on experimental data as a basis for the modeling of these non linear behaviors. They are also inherently less accurate as they must rely on more assumptions and approximations. The new mathematics of chaos theory (fractals, etc) is opening doors for new simulation solutions for these types of behaviors; however, that whole science is still very new and is a long way from filtering down to the freebie or cheapie offerings on the web.OK here's a couple of screen shots of XFLR5 working on the NACA 23012. I wonder if there is some combination of settings that would show the same abrupt stall as you see in the NACA high density wind tunnel tests.
Here's the pressure coefficient plot from Profili. Notice the little peak in the green line at 70% that peak represents an abrupt change in the boundary layer and also shows up in the coefficient of friction graph and it moves forward with increasing AoAsuch as being able to follow the flow separation point as it moves from trailing edge forward
You are correct they don't. However, I suppose it could be argued that there are currently a number of good airfoils to use and there are independent researchers. You can see some of them in the list here: The Incomplete Guide to Airfoil UsageI get the impression that NASA doesn't do GA aerodynamics much anymore.
I think that statement has more to do with avoiding liability than any technical limitation. The developer is an aeromodeller, and has written his program with that use in mind. It seems he is (understandably) nervous about the use of his program for man-carrying aircraft. That said, I don't see anything in his methods (so far, anyway) that are different than what we would use for full-scale. He seems to have done his homework.The Re num are differents and in program Guideline stays:
The code has been intended and written exclusively for the design of model sailplanes, for which it gives reasonable and consistent results. The code's use for all other purpose, especially for the design of real size aircraft is strongly disapproved.
Although I think there is some CTA involved the disclaimer is also acknowledging the real limitations of panel codes. You can expect this kind of program to give reasonably accurate predictions of lift, drag , and pitching moment within the linear range but what happens at the stall is not so well represented.I think that statement has more to do with avoiding liability than any technical limitation.
Although he dose design and build models Dr Mark Drela is the dean aeronautics and astronautics at MIT so I guess he has "done his homework".The developer is an aeromodeller, and has written his program with that use in mind. It seems he is (understandably) nervous about the use of his program for man-carrying aircraft. That said, I don't see anything in his methods (so far, anyway) that are different than what we would use for full-scale. He seems to have done his homework.
Can't argue with that! Just wish I could afford wind tunnel time. Oh well as long as nobody's life is on the line I can live with some uncertaintyPersonally, I would not rely on a single software program without some way of validating the results, no matter where the program came from. To paraphrase a famous 1980's quotation, "Trust, but verify."
I get the impression that the real gripe against Ribblet was that he was releasing computer designed airfoils to the general public before the code had been proven to be reliable. For some obscure reason that was deemed irresponsible. He uses the Eppler code which, as I understand it, isn't any better than Xfoil.David Lednicer (who worked for John Roncz) had some skepticism about Riblett back in 1988: Riblett airfoils (Walter Lounsbery, David Lednicer, "highflyer")
However, Riblett has also been discussed here on this forum.
What I've generally heard is that these types of airfoils pretty much do the job.
That is certainly true! Not to mention his work on Deadalus, which holds the records for distance and duration for human powered aircraft. However, I was actually referring to Andre Deperrois, the developer of XFLR5, the product Typhoon was asking about.Although he dose design and build models Dr Mark Drela is the dean aeronautics and astronautics at MIT so I guess he has "done his homework".
In Xfoil (and XFLR5), you get to specify whatever Reynolds number you want (along with a bunch of other criteria) prior to each analysis run. Xfoil is not limited to any particular RE range.So, if this software is for model airplanes then there is no adjustment due to increase in Reynolds Number?