Airfoil shape

[mark_q]

Can anyone direct me to where I can find the measurement guidelines and equations for developing popular airfoil shapes? I am developing a design table in SolidWorks to out-put certain popular shapes with as few inputs as possible.

For those who may not know, SolidWorks is a high end 3D mechanical design package.

Thanks for any information - Mark

[Sail 'n Soar]

Equations? I don't believe there area any for the commonly used airfoils other than the NACA 4 and 5 series. But if you go to the site below, you can down-load data files for the contours of a very large number of airfoils used in modeling.

http://www.nasg.com/afdb/search-airfoil-e.phtml

[Ollie]

Design is synthesis. Equations are used for analysis. Choosing an airfoil has both structural and aerodynamic implications. The airfoil choice is a compromise between conflicting objectives that is an artistic synthesis rather than a deterministic analysis. One technique for airfoil generation is conformal mapping. If you are interested in simplicity, you don't want to go there.

[mark_q]

Sail...
Thanks for the info, it's a good start.
-Mark

[mark_q]

Ollie,
Being a fabricator, designer and engineer (mechanical design) pretty much my entire life I am no stranger to synthesis and analysis. However to completely separate the two will not play in my view. Very often I have gone to the trouble of developing equations for complex curves and surfaces for the simple reason of scaling those shapes accurately.

I suppose I should have asked the original question differently, that is, I'm am all about simple and would like to find charted or spreadsheet info on a few airfoil shapes used in modeling. Measurements I'm looking for include LE radius, Chord, Thickness, Type, etc. Not so much specific equations for developing a complete shape.

Any help here would be appreciated.

Thanks,
-Mark

[Sail 'n Soar]

Very often I have gone to the trouble of developing equations for complex curves and surfaces for the simple reason of scaling those shapes accurately.

Mark,

Depending on your specific project, the NACA 4 and 5 series foils may work just fine. And they are described by polynomials for the envelope and centerlines, with the LE radius = 1.1019 times the (thickness/cord)^2. This site will calculate them for you for up to 100 points. http://www.pagendarm.de/trapp/programming/java/profiles/NACA4.html

In reality, I've found that most of the published coordinates for the more modern airfoils used in modeling give more points and significant figures than I, personally, could ever build too. So I don't worry about it.

Gerry

[Sail 'n Soar]

This site will calculate them for you for up to 100 points.

Oops, dropped a zero. The site will calculate up to 1000 points.

[markdrela]

Originally posted by mark_q
Very often I have gone to the trouble of developing equations for complex curves and surfaces for the simple reason of scaling those shapes accurately.

Measurements I'm looking for include LE radius, Chord, Thickness, Type, etc. Not so much specific

You apparently want both accuracy and simplicity, which are contradictory requirements for this task.

Any airfoil geometry representation method (spline, Bezier, etc.) will have to have no fewer than about 100 free parameters to be able to represent an arbitrary airfoil with sufficient accuracy for analysis or CNC manufacture. Just specifying LE radius, thickness, camber, etc. is woefully inadequate.

The standard way to represent an airfoil shape nowadays is via a simple x,y coordinate list, typically with 100-200 points. These points are interpolated as needed using a parametric cubic spline of the form x(s), y(s). Some people codes (Eppler's, Selig's) use a uniform spline parameter s. Xfoil uses a tangent arc length for s, which is less sensitive to irregular point spacing.

The two types of splines will of course produce two different airfoil shapes, but the differences are within acceptable tolerances in practice. One occasional exception is when insufficient point density is provided near the leading edge. When an Eppler or Selig airfoil is examined in Xfoil, the leading edge appears misshapen due to the assumed spline parameter mismatch. Xfoil's CADD function is an attempt to eliminate this nuisance.

[Ollie]

My concept of the design process is that it starts with specific objectives and priorities that are used to determine the quality of the results of the process. The objectives and priorities are are selected to suit the purpose of the model. A seed design is loaded into the process and the performance is analyzed and compared to the objectives and priorities. Then the design is modified to improve performance or rebalance trade offs in in priorites. Then it is reanalized for performance. The process is iterated until the results are pleasing.

For real simplicity there are very few requirements to be able to fly. The plane has to be stable. It has to have a lot of thrust. The control surfaces and moments have to be effective enough. In this simple approach the airfoil can be anything at all.

If the purpose of the design is to go beyond these simple requirements it has to take into account things like stalling speed, maximum speed, rate of climb, roll rate, L/D, sinking speed, stall characteristics, etc. depending on the purpose of the model. If you want to have the program capable of distinguishing between a trainer, aerobat, pylon racer, fun fly, DS sailplane, etc, etc. then the design program can't be so simple. The structural, weight, power, airfoil lift coefficient range and drag considerations come into play.

[mark_q]

Gerry,

Thanks again, the curve generator is cool, gives me some good ideas for this design table.

Mark