Airfoils

Posted 21 Feb 2013.

People have been studying airfoils – the basic shape of stuff like wings, fan blades, propellors, and helicopter rotors – for a really long time. The Wright Brothers, Lilienthal, and others learned about and studied airfoils while conducting their first flights. They even came up with an equation for it so that the lift of an airfoil could be quantified.

There are two kinds of airflow around an airfoil: Laminar and turbulent. In general, Laminar flow is smooth, more efficient, and desired to be maximized in airfoil design. Other characteristics such as stall and spin behavior have to be taken in to consideration, particularly in airfoils for smaller GA aircraft.

Links

The following links are a good way to get started learning about and thinking about 2D airfoils:

• The Airfoil page on Wikipedia is a great place to start.
• Very early on the National Advisory Committee for Aeronautics developed a numbering system for airfoils so that different airfoil designs could be created and discussed easily. These NACA Airfoils are still commonly used and discussed today.
• The Incomplete Guide to Airfoil Usage is a fantastic list of lots of different airplanes and the airfoils they use. Find your favorite airplane and learn about the airfoil it uses.
• The UIUC Airfoil Coordinates Database contains a ton of airfoils in a text-based X/Y plot format. You can even render these airfoils with LaTeX.
• Wolfram|Alpha knows about airfoils. For example, search for NACA0012 and it will show some basic information and draw the airfoil in action with a selectable angle of attack.

Software

It doesn’t seem like a lot of effort has been put in to airfoil design software in recent years.

• XFOIL seems to be the 2D airfoil design and analysis software that I see mentioned most often.
• PDAS or Public Domain Aeronautical Software is a bad of older software in the public domain.
• FoilSim by NASA’s Glenn Research Center is an educational java applet you can view in your browser or download to your computer.
• Hanley Innovations has some commercial software for designing and analyzing airfoils. I ran across a few videos of his on YouTube that looked interesting. Probably one of the more modern feeling software packages.
• It is possible to design a complete airplane and simulate it in X-Plane.

Publications

• Airfoils: Stable or Unstable High Lift or High Speed by George Collinge, EAA 67 from 1958.
• Eagle 1: The Ultimate Airfoil for Sport Aircraft by Michael Myal, EAA 7978 which includes some sample FORTRAN code from 1983.

Books

• Theory of Wing Sections by Abbott is an inexpensive Dover book that looks like a worthwhile read. It’s on my wishlist.
• GA Airfoils by Harry Riblett is a spiral-bound book available at the EAA store. I remember seeing it on the shelf at AirVenture last year and should have picked it up. This is geared toward homebuilders and is all about designing an airfoil to build and fly.

Things to learn about

• Computational Fluid Dynamics seems to be the three dimensional simulation-based view of the world and something to learn more about once I have the basics down. There’s also a lot of software in this field that might be more up to date than the 2D stuff I’ve seen so far. OpenFOAM is an open source CFD package that looks powerful but a little cumbersome to deal with.