Does anyone know the "airfoil" number for the Four Star 40? I'm trying to make a model in my Phoenix sim fly a little more like my 4star 40 with no dihederal and a shortened wing. The airfoil number I'm refering to has the letters NACA infront of it. Sorry for my ignorance, just trying to get my thumbs warmed up for my 4*!

Thanks

I'm not sure what the NACA number is, but I have aCAD drawing for the 4*60 ribs that Iscale down for smaller wings. Drop me a PM with your Email and I'll send it to you if you like. The drawing is in Rhino 3D, but Ican export it to just about any CAD format.

Don

Thanks for the offer Don, but the program I have just has a selection for the NACA number. The CAD drawing sounds cool, what did you use it for?

Rhino 3D. I fumbled around with four or five other CAD programs and it was the only one that was somewhat intitutive for me. I've been using it for about five years now and I'm almost up to the rookie class. You can do just 2D work with it, which I do mostly. For laying out a turtle deck, you can't beat it. Draw the front former, Draw the last, the one straight line can be used to skin the two pieced. Slice the solid where you want more formers and you end up with a set of formers that will cut exactly to size. You can get a demo version that will only allow something like 5 saves, but you can play with it for as long as you like. It may not print either if I remember right. They sell a full function educational version also which is fine for our work. Iended up upgrading from ver 3 to ver 4 and that gave me the comerical version. Rhino3D.com

Ialso have a couple Epson ink jets, a photo 1280 and a photo 870. The 1280 will print on roll paper up to 24 feet long and 13" wide. You can lay out a set of ribs on 3" or 4" x 36 rectrangles, print them with the minimum line width and the cut the rectangle and some 3M77 spray and stick it to a sheet of balsa. Cut and sand to the fine line and then peal the paper off. You have a set of ribs that are as accurate as any laser cut ones. Of course a nice CNC router would work also.

Don

It is my understanding that the airfoil on the Four Star does not conform to a standard NACA airfoil. I read, perhaps on Bruce Tharps website, that the airfoil on the 4* is a modified semi-symetrical shape where the bottom section of the foil from the main spar to the trailing edge was designed to be perfectly flat. This was done to facilitate the building of the wings on a flat surface without the need of tabs or other methods to hold the wing straight. This is one of the reasons that the 4* makes a good entry kit into kit building. Plus, the're a lot of fun to fly. One of the bigest problem with the 4* is the secondary effects of the rudder on pitch. Bruce Tharp, who originally designed the 4* has come out with a plane he markets directlly called the Venture, where he has made improvements to the design to help eliminate the problem. There may be a NACA that is close, but I have no idea what the number would be.

Scott

It is a mod but if you go with something like the NACA 2412 you should be close.

I emailed B. Tharpe about the wing design, and asked him if it was purposely designed with turbulators. He said it wasn't intentional, but he has been asked that before. He said the reason for lack of sheeting is to keep down the parts count, economy, etc. I didn't even think to ask what airfoil he used.

BLW sent me a quick email with a link to this thread (thanks!). In a nutshell, saramos got it right, I didn't use a published airfoil. The guys at Sig used to call this an "FCR" airfoil - french curve and ruler. The main priorities were the flat section on the aft bottom portion (for ease of building) and efficient use of balsa. Gray Beard gave good advice, but I think it's a little thicker, like 14-15%. Maybe a NACA 2415 would be a slightly closer approximation.

Great to hear the answer from the Designer of the Four Star directly! Thanks Mr. Tharpe!!

Scott

P.S. Sorry for the misspell[sm=red_smile.gif]