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Old Aug 17, 2012, 05:16 PM
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Airfoil .dat File Conversion

Hi:

I got this file of off the UIUC site and it's in the wrong numerical data arrangement. Can anyone direct me to a conversion program?

- Jim
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Old Aug 17, 2012, 05:25 PM
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Attached. Just change the file extension back to .dat from the .txt I changed it to to upload here.

You aren't going to use that on a model are you? The performance and stall characteristics will be very poor below Re = 1^6.

Kevin
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Old Aug 18, 2012, 03:46 PM
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Kevin:

I had been intending to use it on a model after I managed to look at its polars. Where did you find them? How did you convert the data in the text file, which was a .dat originally?

- Jim
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Old Aug 18, 2012, 04:51 PM
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Kevin:

I looked at the lift-drag polars for the LS(1)-0413 at rcadvisor.com and that don't strik me as bad. What do you think?

- Jim
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Old Aug 18, 2012, 06:26 PM
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I can't find any polars at RCAdvisor.

Since I don't know anything about the model you are planning, I just did a quick Profili (XFoil) run at Re=200k against a Clark Y. The Clark Y has considerably better performance everywhere, and much better stall characteristics (attached). There may be better airfoils for your application than the Clark Y, but it would certainly be better than the LS(1) at model Re.

The NASA General Aviation (GA) airfoils were designed for long laminar flow runs for low cruise drag at considerably higher Re than on models. At lower Re they have poorly controlled laminar separation bubbles as evidenced by the high drag in the "bucket" at moderate Cl. They also have a strange stall at lower Re as the bubble moves and collapses, as seen at the sudden decrease and then increase in drag around Cl = 0.9. Airfoils with nice smooth curves at the appropriate Re will be much easier to fly, and the Clark Y also has considerably better performance as well.

If I need to rearrange airfoil ordinates into a dat or other format, I use Excel to do the data sorts because I have used it for 30 years. I happened to have a dat file of the LS(1) on hand, so I didn't have to do anything this time.

Kevin
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Old Aug 19, 2012, 04:48 PM
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Kevin:

To get to the airfoil plots at RC Advisor open the calculator which is in the left sidebar. (You may have to register, which is free, to use this.) Go to the "Admin" tab and select "Load Airfoils." (I had to email Carlos to find this out.) Then chose the "Airfoils" tab. Select from the dropdown list of airfoils, which is incredibly long. Use the Filter to fix this. (You may want to open the "Calculator Tutorial" in another tab of your browser and read up on filters.)
The plots are in the graph section at the bottom of the window. The lower left drop down list is for selecting what plot you want. The right is for selecting a comparison item.

I believe Carlos Reyes uses X-Foil for generating his data as well.

- Jim
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Old Aug 19, 2012, 06:07 PM
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Jim,

I really don't want to go through all that to see data that I'm not sure of.

Why do you want to use that airfoil in particular? There are literally hundreds of airfoils designed for model use since the 1980's that would be a better choice, as well as the real Clark Y, some of the NACA 4 series, etc. The NASA GA airfoils are great for the size, application, and speed range they were designed for - full size General Aviation - but they are not a good choice for models operating well below Re =1M.

This must be for a power airplane, in which case airfoil choice is not likely to be very critical. Anything with nice smooth curves at the appropriate Re will work fine. If you need a certain wing thickness for structural reasons, or want maximize performance for one particular area like aerobatics, short take-off, max endurance, max flying weight weight, max speed or some other parameter, then airfoil choice will become more important.

I've attached a Profili plot of the Clark Y and the LS(1) airfoil max LD. The Clark Y is better over the entire positive Cl region by a large margin except maybe at the one peak in the LS(1) curve. The Clark Y has a nice smooth curve so will be easy to fly and get pretty good performance..

Of course you can use any airfoil you want, and with power to overcome the deficiencies you can get away with a lot. I'm pretty sure you would be far happier with another airfoil though.

Kevin
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Old Aug 22, 2012, 05:35 PM
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Kevin:

Thanks for your input. I am going with the Eppler 205 for this model.

- Jim
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