Jet Stream 500 10
Adjusting the wind speed:
Once the tunnel's fan is activated, you may turn the wind speed control dial on the
control panel to the desired wind speed. As the dial is adjusted, the desired wind speed is
displayed on the LCD to show the final test speed. Several seconds after the dial is
released the displayed wind speed will switch to the actual measured wind speed in the
tunnel. Wind restrictions created by the test model will be compensated by the
microprocessor to maintain the desired wind speed even if the model is adjusted to
modify the frontal area of the model, altering the tunnel's internal wind resistance.
Turning the control panel wind speed dial will set the desired speed and accurately
maintain the speed throughout the test. As the speed is controlled by the microprocessor,
it may take several seconds before the tunnel reaches the desired wind speed.
Viewing the results:
The LCD panel will display the current wind speed in miles per hour (or kilometers per
hour) along with the lift (both positive and negative), and drag forces exerted on the test
model due to the wind. The lift over drag (L/D) of the test model is also calculated and
displayed which is a common measurement in airplane wing designs.
IMPORTANT:
If the test model should become loose or disconnect from the test bed during a test,
quickly press the stop button on the control panel to shutdown the tunnel. Once the wind
speed has reached 0 MPH, you may remove and repair the test model. If the wind tunnel
has been damaged, have the tunnel repaired before continuing any further testing by
contacting Interactive Instruments.
Analyzing the test results:
The wind speed is displayed on the LCD panel as a measured wind speed. The static
pitot tube in the test area takes a sample of the active and passive air pressures and passes
them to a sensor that calculates the wind speed. This speed is used for two reasons. One
is to display the wind speed for your reference, and the second reason is for the
microcontroller to control the speed of the fan. Without the wind speed control, the
microprocessor would not be able to compensate for test variations and fluctuations in
line voltage.
The Lift and Drag force calculations are measured with sensitive electronic sensors that
are capable of measuring up to 1 lb. The measurements are averaged over a 100
millisecond period to remove possible errors due to mechanical vibrations or electrical
noise. As noted earlier, since the model exerts its own weight on the sensors, this force
must be subtracted from the measured force when the wind speed is 0. The wind speed
and drag force is also automatically zeroed at this time to automatically calibrate the
electronics before every test. This is to insure accurate and consistent results on every
test.
The L/D ratio is derived by dividing the lift force by the drag force. This measurement is
an important parameter in the study of airplane wing design. As you can see, if the lift
force is high and the drag force is low the model wing would be very good for gliders.
Inversely, if the lift is low and has a large drag, it would be very poor in a glider design.
The larger the L/D ratio the longer a glider can stay up. Varying the angle of attack or
placing the wing into a stall condition will vary the L/D for a wing. The L/D ratio can be
positive or negative depending on the direction of lift. If the lift force is in the positive
direction (upward) the L/D ratio is positive, but if the lift is negative (downward) the L/D
ratio will also be negative.
