Transitional Airfoil Plots
 

I'm trying to develop the rib airfoils for a 1/12th scale model of the P2V-7. I use MacFoil to plot the ribs. Navy data give the root airfoil as NACA 2419; the tip is given as NACA 4110.5; offsets for these profiles are available from UofI data base. The model's 1/2 span is 70 inches; root chord is 12.5 inches; tip chord is 7.2 inches. Is there any approximate method for determining the proper profiles for the intermediate ribs (chords can be determined from the layout I've made) if they are spaced 3 inches apart? Any suggestions would be appreciated.

Dave P.

RE: Transitional Airfoil Plots
 

Although it isn't all that difficult to plot all the intermediate points using a BASIC program, Profili V.2 available at:
http://www.profili2.com/eng/default.htm
will do this for you and insert the spars and things.
Highly recommended!

RE: Transitional Airfoil Plots
 

Hi T.P.!

Thanks for the feedback. Unfortunately, Profili won't work on a Mac, so I'm stuct with MacFoil. However, just as a matter of curiosity, did you mean that you can enter the root and tip airfoil profiles (in Profili) along with the spar length (and perhaps washout) and rib spacing, and get the intermediate rib plots?

Regards,

Dave P.

RE: Transitional Airfoil Plots
 

Yes, Profili will take your root and tip airfoils, your number of stations, your spars, sheeting, lightening holes, LE, TE, washout, building jig tabs, etc... and plot each rib individually, or all of them on a single sheet... as space dictates. It will also calculate polars for your airfoils, using XFoil.

It's a fantastic program, but PC only. I'm glad I use a PC. ;)

-David

RE: Transitional Airfoil Plots
 

Since you're stuck in the orchard... (Just think,you have to put up with NO Internet Explorer related viruses.)..
To do the intermediate ribs, take the root rib coordinates and the tip rib coordinates...
Determine the difference at each x-ordinate for each y-ordinate between the two.
Determine how many ribs you want.
Divide the differences you've found by the number of ribs for each intermediate location.
For each intermediate rib then, add/subtract the ratio'd difference for each y-ordinate at the corresponding x-ordinate.
Plot the result.
I wrote a program many years ago to do this, and ouput the results in Autocad script file format, and Generic CADD batch file format.
It's very easy to do with BASIC, but the program I've written that does this runs only on a DOS machine. Sob! :)
If the spirit moved me I'd move the program to a Windoze thing, but Profili does it so much better..

RE: Transitional Airfoil Plots
 

You could do as Paul suggests, but use a spreadsheet, then get it to draw charts of each rib.


Read in the coordinates as tab or comma separated values and go from there.

RE: Transitional Airfoil Plots
 

What Phil says... I tried to romance Visual Basic 5 into accepting the Quick Basic program and it didn't like ANY of it...
A spreadsheet which can add the headers and things a CAD program wants for an input program would work just as well.
Here's an example of what Profili can do.. a few seconds selecting the root and tip, and does all the stuff! :)

RE: Transitional Airfoil Plots
 

Hi TP and others providing feedback to my original post!

As I wrote earlier, Profili will not work with a Mac. I can do the interpolation with an Excel spread sheet (then go back to MacFoil), but was hoping there were some Mac users out there that might have some 'back-of-the-envelope' solutions.

Thanks to all for trying to help.

Dave P.

RE: Transitional Airfoil Plots
 

Just make a root rib template and a tip rib template. Stack the correct number of layers of 1/16 balsa for all the ribs. aligned by the SPAR and the zero AOA line. Drill and screw the stack together. Carve a straight transition from the large rip to the small one. You will have a stack of the correct ribs. (assumes the wing has a constant taper angle)

No ned to go through the meathematicl gymnastics... and plotting all the points. Just cut the ribs.

*********

BTW... QuickBasic is a "superset" of Q-Basic. Q-Basic (which shipped with MS Dos 5.0 to Win98 (yes, its there you just have to search for it. qbasic.exe) will run almost any QuickBasic code. The primary difference is QuickBasic has a compiler.

You can also search the net... Q-Basic interpreter is available for DL on a ton of sites. And yes... it will run in WinXP. (so will the compiler.)

RE: Transitional Airfoil Plots
 

Pay attenction because this method doesn't work well if the wing is tapered AND root and tip airfoils have different thicknesses.
Doing so the wing thickness in the middle part will be thinner then desired.

If you have a Windows emulator on your Mac you can use Profili.

ciao
Stefano