Airfoil help!

[ZRX 1200]

Boy, am I glad I found this site! I am wanting to build a C-119. I have "Airfoil Design Workshop". I found three views of a C-119 and have enlarged them to the point that I can get some fairly accurate measurments. I inputed the wing info into the airfoil program and got patterns for the ribs. The question I have relates to how to determine the lift of a specific airfoil at specific speeds. I can export the airfoil info in another program called "XFoil Flow Analysis". This gives alot of information that I am unable to decifer. I think that lift can be determined, but I am at a loss. I am looking at building a 72" wingspan. Any Ideas. Also, are there any other programs to help with the design of the rest of the plane?

Kind regards...Craig :)

[BMatthews]

The lift is more determined by the camber value and angle of attack than the actual shape. However the shape controls the airflow and determines to some extent the max lift coefficient that can be achieved before a stall occurs.

Head on over to http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html and learn to play with the settings to generate model sized wings and airspeeds and input the camber and thickness of your airfoil. Hopefully you know what those values are or can find them with a bit of measuring and calculating.

Now armed with a lift drag polar chart of your airfoil or one very similar to it play with the angle of attack and airspeeds to determine how slow you can get. Do not allow the airfoil to exceed 8 degrees in all this. I know the stall model does not cut in until closer to 10 degrees but at model sizes the airfoils are not so tolerant.

This is where that polar chart that Xfoil spit out at you will come in handy. You'll see that the curves all have a lower drag dip toward the left side of the chart. Your more or less usable range of lift coefficients is where the curves are most vertical. As they move to the upper portions then start to sweep over to the right. Just over the turn and where they flatten out and shoot over to the right is your stalled area of flight.

Armed with the Cl value for the proper Reynolds number curve you can play with Foilsim to alter the angle to set the Cl to your value. Then switch to lbs of lift and reduce the airspeed until the lift value matches your model weight. That's your minimum, almost stalled flight speed. Carrying a camera? Add in the weight and increase the speed until the lbs of lift matches the airspeed.

It's as simple as that. One kink in all this. You cannot enter the numbers directly into the boxes although it seems to take. Use the arrows and sliders or the applet doesn't see the changes. Also it requires Java be installed. Go find it at www.java.com and download the installer and run it. Then go to the Foilsim site and you'll see that the applet runs. You can also download it and run it locally if you use a modem otherwise it's a painful process.

Now go play... :D