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Glenn
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You can download your own copy of this applet by pushing the following button:
The program is downloaded in .zip format. You must save the file to disk and then "Extract" the files. Click on "Tunl.html" or "Foil.html" to run the program off-line. "Tunl.html" includes this tutorial, "Foil.html" runs the program alone.
This simulation works exactly the same way that the Wright Brother's 1901 wind tunnel worked. The layout of the simulator shows an overhead view into the tunnel test section at the upper left. You can choose to test the wing model on either the lift balance or the drag balance by clicking on the appropriate label in the view window at the upper left. Clicking on the words "Wind Tunnel", "Lift Balance", or "Drag Balance" will also display pictures of the actual machines. In the upper middle part of the simulator is the output dial. This dial is the only output from the program. For the lift balance, the dial gives the angle between the brackets holding the model and the reference drag plates. The sine of this angle is the major portion of the lift coefficient used in the lift equation as understood by the Wright Brothers. For the drag balance, the dial gives the angle which the model is deflected by the flow through the tunnel. The tangent of this angle plus the angle of attack gives the drag coefficient used in the drag equation divided by the lift coefficient. To the right of the output dial are the sequence buttons which take you through the operation of the tunnel. The white button is the current operation, and you must push the red/white buttons before doing the procedure.
Most of the procedures to operate the lift balance and the drag balance are the same. But the differences are noted in these instructions:
"Step 1. Select Model" Choose between the lift balance and the drag balance by clicking on the word on the schematic. The yellow label is the balance selected. Select the model to be tested by clicking on a blue and white drawing at the lower left or lower right of the program. There are 30 different models which you can choose from and we have put them into three groups. You select the group by using the blue buttons below the output dial. The current selection has a white background. When the selection is made, a photo of the actual model used by the Wrights is shown at the lower center of the program and the number of the model is displayed on the schematic.
"Step 2. Set Angle of Attack" Set the angle of attack of the model. You can set the angle by typing into the input box and hitting "Return" to send the information to the program. Or, you can move the trailing edge of the airfoil by using your mouse on the "hand" in the schematic.
"Step 3. Start the Tunnel" Clicking this button causes air to move through the tunnel., You will see the balance and the output dial slowly deflect. Wait until the dial quits moving before taking data.
"Step 4. Adjust for Drag" For the lift balance, the upper cross beam must be moved to eliminate the drag of the model from the measurement. Clicking on this button will cause Wilbur's arm to enter the tunnel and make the adjustment. The resulting angle on the lift dial relates the lift of the airfoil to the drag of the reference flat plates. You don't have to make any adjustment for the drag balance.
"Step 5. Record Data" Record your data on the appropriate data form. You can get a copy of the lift form by pushing the "Lift Data Form" button and using your browser's "Print" command to get a hard copy. Use the "Back" button to return here. The data form has boxes for you to record the lift of two different models so that you can compare their lift. The drag data form can likewise be obtained by pushing the "Drag Data Form" button.
"Step 6. Reduce Data" You will have to do some additional math on the raw data to obtain the lift and drag coefficients. Engineers call this reducing the data. For the lift balance, you calculate the lift coefficient by using the formula on the data form. You will need the area of the model which is given on the model drawing. Since you also need the sine of the output dial angle, we have included a table of sin(angle) which you can display by pushing the "Table of sin(a)" button and using your browser's "Print" command to get a hard copy. Use the "Back" button to return here. For the drag balance, you calculate the drag coefficient by using the formula given on the data form. You will need to record the angle of attack and to compute the tangent of the output angle. You can obtain a table of tan(angle) by pushing the "Table of tan(a)" button. You can compare cases by graphing the results of your tests using graph paper. Push the "Graph Paper" button and use your browser's "Print" command to get a sheet of graph paper.
The brothers selected the shape of the models to study the various design variables which affect wing performance. They would run a series of tests which would isolate the effect of a given design variable. We suggest that you visit the models page and duplicate the conditions yourself. The wing design of the 1902 glider was never actually tested, but was based on models 9, 12 and 35.
NOTICE: In this simple program we are using a very simplified analysis to compute the lift. We have applied some correction factors to account for the wing stall which occurs at high angles of attack. If you compare the results of this program with actual data from the Wright experiments of 1901, you will notice some numerical differences, but we have tried to properly model the trends of the data. Similarly, we have made rather simple curve fits of the brothers' drag data. You will notice numerical differences, but the trends are correct.
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Last Updated Thu, Oct 14 08:55:30 AM EDT 2004
by Tom
Benson