Experimental Design

Table of Contents

Experimental Design

The objective of this experiment was to quantitatively measure how the dependent variables, wind speed, torque and revolutions per minute (RPM), changed under varying experimental conditions. These changing conditions were the independent variables as shown in Table 1 below. The independent variables were manipulated in 42 different ways.

The resulting torque, RPM and wind speed were measured ten times per manipulation to ensure accuracy and reproducibility. In total, 420 measurements each of torque, RPM and wind speed were made.

Weight in Newtons (N) was measured by using a spring scale that was connected perpendicular to the rotating axis with fishing line.

The torque (Newton-Meters) calculation for a rotating axis perpendicular to the weigh scale is as follows:
Torque = Force (N) X Radius (meters)

RPM were measured using a digital photo tachometer.

Wind speed was measured using a digital anemometer.

Dependent Variables:
1. Torque
2. RPM
3. Wind Speed
Independent Variables:
1. Fan speed
2. Number of rotors
3. Horizontal distance between rotors
4. Position of rotor on horizontal axis (i.e. rotor blades offset or in line)
5. Size of second rotor

Controls:
1. The same test unit, retort stand supporting the spring scale and electric fan were used for all tests.
2. All of the testing was done in the same location at ambient temperature.
3. The equipment was positioned exactly the same for every test. The test station and retort stand were clamped onto the workbench and the required fan position was marked on the floor.
4. The rotor placement on the axis was checked with a T-square to ensure that the rotors were perpendicular to the axis.
5. A ruler was used to mark the required distance between rotors.
6. The same measuring instruments were used for all tests.
7. The anemometer was held in approximately the same position for every measurement.
8. The tachometer was placed so that the beam was centered on the reflective tape.
9. The weight of the duplicate rotors was checked to ensure they weighed the same and both were 38 grams.
10. The same length of fishing line (60 cm) was used for all tests.
11. All testing was repeated a total of ten times to ensure accuracy and reproducibility.

Experimental Design Chart:

Table 1

Note: IL = blades in line; OS = blades off set
eg. 2 rotors 28 cm-IL-7cm is the rotor variable using two, 28 cm rotors, placed 7 cm apart with the blades in line.

Material & Equipment