Marian

Hi to everybody,

I want to import an airfoil from Autocad to the program Profili.
Profily has a possibility to imprort from a ".dat file" containing coordinates of several points of the airfoil.

The difficult step for me is to obtain a list of coordinates.

Do you have any macro / Auto Lisp for Autocad which would export coordinates of points into a ".dat file"?
Or maybe to excell ... then I will find a way to convert it into .dat format.

Regards,

Marian

Tall Paul

AutoCad will export a .dxf file, which is pure text.
You can manipulate that file to get rid of the drawing commands and end up with the coordinates in the form the aero program needs.
It can be a lot of work.

Jim_Purcha

My Feedback: (8)

Profili will also import an dxf file. You export this from autocad.

BMatthews

Just a silly thought but you also need to pay for the unlock code to convert from the limited free version to the full version. It's cheap though.

CoosBayLumber

My Feedback: (1)

Marian....

If you ever used Compufoil, they have a DWG to coordinates converter. Have to set up the length as Unit One, the beginning at 0,0. You have to e:mail Bruce at Compufoil, for the "Convert" software is not always included with each version. It works at a DOS level also.

This will then take your linework, and calculate intersections and write to a file. Which in turn you can edit and rename to xx.DAT then. I don't know what these others are offering to you, but have gone through such in taking some obscure airfoil off a plan and then trying to locate one near to it.


Wm.

dreadnaut

My Feedback: (5)

There is a way to do it that is a little but of work, but not that bad really. The explination is a little involved, but some of the basic techniques I discuss in her are just plain helpful to have for all work in AutoCAD.

If the airfoil in the AutoCAD file is not a pline, or a spline, you have to make it into one by using the 'pedit' command, with the 'join' option. If they do not join, it is because the person who drew it was 'scribbling' and did not use osnaps. You have two choices. Select everyting on the airfoil and use 'gripedit' to go over every joint to make sure that the are connecrted exactly end to end, or set the 'running osnap' to 'enpoint' and trace over it with a pline starting at the trailing edge and going all the way back to the trailing edge. The order you pick the points is very important. Start at the trailing edge and go all the way around back to the trailing edge. If you start in the middle, skip around, and join every thing after, it WILL NOT work right. If you miss a point, and get a little 'spike' keep going. You can use 'gripedit' after you finish to clean it all up.

Once you have a good continious pline that runs from trailing edge all the way around back to the trailing edge you are ready. Type the command 'pdmode' and when prompted to enter point style, enter 34. Now get rid of everything except the pline you just made. The best way to do it is to create a layer to put the pline on a freeze everything else. This way you do not have to delete anything you may need later.

Now enter the command 'divide'. Select the pline and when prompted to enter the number of points, try a number like 96. Zoom into the leading edge to check the 'resolution' of the curve. If it is not smooth enough, undo and repeat with a larger number until you get a fairly smooth curve around the l.e.

When you are satisfied with that, select all of the points. Do this by making sure that the command: is empty and drawing a box with the mouse from top left to lower right that encloses over half of the points, but does not completely enclose the pline. THEN WITH OUT TOUCHING ANYTHIN ELSE draw another 'selction' box -upper left to lower right- arount the poins on the right that were missed on the forst pass, but not completely enclosing the pline.

The above is a basic ACAD skill that, unfortunatly is not taught very often, but is a very important technique to know. It allows you to select all of the points very quickly, wiltout selecting the pline.

Once all the points, and nothing else, are selected type list. you will have to hit enter several times until allt of the points are listed. Now hit the F2 key to call up a text box. Select all of the points listed in the text box, and paste this into a word processor.

To clean this up quickly, I use MS word. The text you pasted into Word will have a lot of 'junk' words like 'handle' and point', etc. In edit use the 'Find and Replace' to delete all instances of these words.when you get it all cleaned up to where you have two columns that look like this;

X0.1234 Y1.2345
X0.1256 Y1.3546
. . .

use 'find and replace' and replace all 'X' with a space, and the same for 'Y'. Now all you have to do is 'save as' to a .txt file, and use the 'my documents' to change the file extension to .dat.

This works, and is a lot less trouble that the rather long explination suggests.

Marian

Very nice solution Drednaut.
I have tryed it:
Step 1: I have traced spline CLOCKWISE over airfoil starting on the trailing edge. Strange but the order of the points at the output of the whole process depend on direction of the spline
Step 2: Change format of point (pdmode) ... it is only a change of appereance and has no effect on the final result
Step 3: Divide to x segment OK
Step 4: Selection of points: if I do it according to your instructions, the point from the first selection block are listed first and then are listed point from the second point.
What is the reason that you use two selection boxes?
I have selected the whole airfoil in one box (from left to right or oposite, it does not matter) and it worked just right.
Step 5: Edit in Ms editor to clean the text OK

Thanks,

Marian

dreadnaut

My Feedback: (5)

1. Not strange at all if you consider that what CAD does is NOT drawing pictures, but creating a graphical database. When you draw a line, the start point and end point are stored in the vector data file (.dwg) in the order in whict they are input. If you create a query, as in dividing a line, pline, or spline, the CAD program retreives the data and processes it in the same order. This is why if you create a pline by joining lines created in random order. the points created by the divide command will not be generated in the order desired for a .dat file that compufoil can use. This is the one benefit of a spline that I can think of since converting a pline to a spline generates one start point, one end point, and cubic polynomial expresion that fits the curve.

2. Yes. The default pd(point display)mode is 0. There are a number of pdmodes that will place different style markers on the points so you can see them. They are numbered 1-36, but for some unkown reason, not ALL numbers from 1-36 are used. 34 is my personal favorite.

4. I was out of town last week, so did not have access to ACAD to give an illustration of this. Here it is. I wanted to select all of the points, but not the line. By draging my selection box from left to right, I select only the objects that are completely inside the box. By doing this twice, as shown below, I can select all of the points quickly without selecting the line.

If I drag the selection box from right to left, I will select all of the objects that are completly and partially inside the box.

Understanding how the ''selection set'' function in ACAD works, makes ACAD very easy to use. Unfortunatly this is not taught very often. In the next week I will probably post something in ''tips and tricks'' on it.

Marian

Hello,

I have a Lisp for Autocad that exports coordinates of an airfoil into a dat file.
You select the object to be exported, enter the number of points and the name of the airfoil and the rest is done automatically.

If anybody is interested in the lisp, I can send it to him by e-mail.

Regards,

Marian

dreadnaut

My Feedback: (5)

Check your pm. Which version do you use. I have 2000 at home and work on 2007. I beta'd 2009and didn't like it. I had issues getting my old lisp's to run. That "ribbon" thing was anoying, and did nothng to improve functionality.

fritzke

My Feedback: (1)

See post #20 for how I do it, very much like dreadnaught:
http://www.rcuniverse.com/forum/m_29...tm.htm#3858437
Dave

"I pulled a scan from the plan into
Autocad, traced the airfoil, scaled the chord to "1" unit, moved the L.E.
to the origin, snapped points to the airfoil lines, then erased everything
except the points out of the drawing, exported as .dxf, and snagged
the x,y coordrinates from the dxf file to make the "COR" text file to use
in Compufoil. There is no doubt an easier way to do it, but I have
done it this way so may times it's a no-brainer now. (I have done this for the
ZAGI and the old Marks Models "Bushwacker" airfoils too.)"