Stanford Java Wing Analysis Program

Analysis of single tapered wings

OK SO EVERYONE AGREES you need an analysis program to design a wing. Well if you want to play around with a single tapered wing there is a very simple, quick program available over the Internet. This will give you an idea of what the experts have been preaching about the importance of wing design.

The program uses discrete vortex Weissinger computations to calculate and plot the lift and coefficient of lift distributions, and also displays efficiency and induced drag coefficients. You merely enter the wing Aspect ratio, Sweep, Taper, and Twist. You will get an instant calculation of that platform shape. The address is http://aero.stanford.edu/WingCalc.html This requires Java.

How to use the program

First you will need to decide upon a flight condition you want to optimise.

Usually cruise, and determine the Cl for that condition. Use about 0.6 as a starting point if you don't want to calculate a value. (this was a guess on my part) You do not control the input of CL on the software, it is calculated based on angle of attack. So what you do is run the program, then check the displayed value of CL. If it is too low then increase the Angle of attack and try again. If too high lower the AOA, and repeat until you get the desired CL.

Next enter your wing parameters. Aspect ratio for a single tapered wing is (2*wing span/(Root chord+tipchord) Sweep is the sweep of the 1/4 chord of the wing, Taper Ratio is Tip Chord/Root Chord, and twist is the amount of washout in degrees. Then hit the compute Button! The program will give you a plot of Cl, and Clc/Cavg.

The Cl Plot

The Cl plot is a plot of the spanwise Coefficient of lift distribution. This determines the handling characteristics, and where the wing will stall first. The wing will stall first at the highest point on this plot. This is your tip stall indicator. For an ideal wing this plot would be a horizontal straight line, indicating that the entire wing stalls at the same time. This is not possible with a single tapered platform, and you have to compromise.

Actually you want to be a little safe, and have the curve drop slowly with the highest point being at the root. This indicates that the root will stall first, thereby preventing tip stalls. If this curve is too safe then you are loosing lift from the outboard part of the wing, which reduces the maximum amount of lift that the wing can generate.

The Clc/Cavg Plot

The second curve (Clc/Cavg) is basically the spanwise lift distribution, and gives a measure of the wing efficiency. An elliptic lift distribution will give an efficiency of 1. the efficiency is displayed below the graph. Now here is the goal, and the challenge.

Here's your challenge!

You need to design a wing that as an efficiency of 0.98 or better that has good handling characteristics, all at your desired Cl. This will take a lot of trial and error runs, because each time you make a change to improve your Cl plot it will affect your Clc/Cavg plot. Keep varying your wing parameters until you maximise your design. Now that you have maximised your design, try increasing and decreasing the angle of attack, and see what happens to the efficiency and handling characteristics. They will both change for the worse, due to wing twist. This is why us F3B types don't like twist.

After experimenting you will soon become a believer in wing design tools, and you will soon discover that a single tapered wing has severe limitations. You will then be ready to graduate to software that can handle multi-tapered planforms. Good luck, if you have any questions I will be glad to answer them. Email gavinb@speakeasy.org [For support issues please use the Stanford web site - MS]