Hi,

Yeah sorry for the confusion, I believe that is one of the extra points for the circles. There are four exrta points to make the circles. Then you have to add two more points that are tangent to the circles manually. I was working on the picture attachments when you responded. Make sure to check the attachments again, as I updated them. It's hard to show, but hopefully between the pictures and the screencast it will start to make sense.

Here is the actual NACA document with the points they specify. They have 0, 0 in there as well. But this isn't a point you would use for the spline. It is a point you would use for the leading edge arc/circle. If you compare the table of points in the Fortran code versus the NACA document, any differences are for the circles/arcs.

Edit; this document is now included airfoil_model.zip file in a later post or on my website.

Thank you Anthony.

I'll need to study on the extra points, and arcs, and more on the "aerodynamics" and terminology.
The simple factory creates curves through existing surface points, (if they exist via the NACA,) so extra coding would be needed to deal with the arcs, and the extra points.

I'll add in the 1000 meter to millimeter scaling.

My missing 27th point, is actually a missing 1st element. The problem was due to the zero indexing in Javascript,
and the crash was due to trying to acces the 28th element in an array with 27 entries(I think).
So indexing M3 from 0 to <27, ++, should fix this. (I think).

:-)

Attached is a script to produce the Air Foil portion of Prop_Design_Geo. The Rail portion is commented out, as it needs additional
LeadingFactory/Factories, TrailingFactory/Factories, and QtrChordFactory/Factories work, which should be fairly easy. :-)

The 26 original NACA points were restored to the AFXTAB and AFYTAB arrays, with (per original GEO,) AFYTAB element .019 rounded down to 0.0.
The two each center point coordinates were added to the END of the AFXTAB and AFYTAB arrays. Adding them to the end makes it easier to keep
them separate, (otherwise they could be extracted from their old locations, if it is necessary to keep them in the old locations.)


The two radius arcs have not been done. Can do mirror easy in MoI.

As an amusement, I set up the NACA formula (for the symmetric non-cambered profiles) in Excel. It meant I could experiment with the X point spacing. Putting more of them at the front gives a more accurate profile. 26 points is not enough really. I found that 100 points gives a better profile when imported in to MOI, with the points biased to the front where the curvature is greatest.

Hi bemfarmer,

I downloaded and setup your script. It is running too far to the right of my screen. My screen resolution is 1366 x 768. I attached a picture of the problem. I set it up so that Ctrl+P launches the script. When it launches it runs automatically and a message pops up. Is there a way to have it open but not run right away.

Thanks

Anthony

Hi SteveH,

Does the equation you are experimenting with work for the NACA 65A009 airfoil? If so, could you share the equation with me. I would be interesting in trying it out. It could be a better way of doing things depending upon how it deals with the leading and trailing edge. I have modeled a bunch of blades using the data file I have, and haven't had any issues. MoI is easily able to curve fit the data from the NACA file. Creating a very smooth airfoil. But I'm always interested in a better way to do things. Perhaps your method will be better.

Thanks,

Anthony

Here is the formula:



Y is half the thickness above the datum
t is the thickness of the aerofoil as a decimal of the chord

I have attached the spreadsheet I used. It shows the formula at the top as a picture. I have broken down the steps of the calculation to correspond with the formula. I am only showing 29 rows here but you can easily change this to whatever you want. The X figure is in mm direct.

I understand this formula works for all NACA symmetric aerofoils, the variance being in the thickness (t in in the equation). There is some maths rounding error here as in the sheet I have attached, at 500mm (the chord maximum), Y should be zero but calculates to -.225mm. This may be a limitation of Excel, as several of the factors of the equation are very small.

Just doing a quick google search that appears to be the equation for the NACA 4 series airfoils. Which are not good for transonic use (i.e. aircraft propellers).

I did another search and found a document that uses equations to obtain the ordinates for the 6A series. However, looking over it, I don't think its worth the effort to go that route. I already have the points I need. This wouldn't justify the effort to code.

Yes, just realised that the equation I used was for the 4 series airfoil. Back to the drawing board.

Here is the correct formula for a 65A. Too late and too tired to put this in Excel.

http://www.pdas.com/naca456thick6.html

Oh thanks, I was just on that site, but didn't see that page. Way easier than the document I found.

Edit; Oh looking over it more, it appears to be the same. Rather involved. I don't think this will help me any, as I'm getting good results the way I'm doing it. However, its nice to know how the data points I was using were determined.

Thanks

Looking at some of the maths for these airfoils, it seems that the profile is determined by experiment, then the formula is back fitted using polynomials.

////I downloaded and setup your script. It is running too far to the right of my screen. My screen resolution is 1366 x 768. I attached a picture of the problem. I set it up so that Ctrl+P launches the script. When it launches it runs automatically and a message pops up. Is there a way to have it open but not run right away.

Hi Anthony. The (very wide) menu screen displays correctly in MoI3Beta, and is scrolled in MoI2. I do not know off-hand how to widen the MoI2
side pane body short of maybe some side pane.htm or CSS changes.

To delay execution, there should be a way to add a "begin" button, somehow.....

oh thanks, I did not see the scroll button. now I can check it out.

P.S. Maybe there is a way to have it float, rather than docked in the side. That way you wouldn't have to worry about width.

Looks good bemfarmer,

I imported the points and they lay right over the curve your program generates. Like you said you still have to work out the radius but I like how you have the curve and then the points to make the radius. The only thing would be on your curve fit it looks like the "through points" option whereas for this curve you want the "control points option". I think you'll see that once you start trying to get the radius in there. The first and last point of the curve will change once you get the radius in there too, since they will become a point tangent to the circle.

But looking good man. thanks

Hi Anthony

I made up a "skinny" menu for MoI version 2. (Not as nice having abbreviated names). (Mostly, I use MoI Beta 3 now, where the wide menu works fine.)
(At this time, believe one must own MoI2 to download Beta3)

Don't know how to "float" a menu. There are lots of posts on "custom UI"...

Working on Rail section now...

Tried it out, works good with my version.

Getting close, after many corrections to rails script.

Looking good. Just a reminder. The rail spines should be made with the through points option. Where as the airfoil should be made with the control points option.