Wednesday, September 19, 2018

Putting the Drag & Lift devise to the test

I have cut and prepared airfoil blades with six different degrees of twist from root to tip, ranging from 40 degrees to 23 degrees as shown above. And one airfoil blade with no twist (not shown).

The test. Each blade will be placed in the Drag & Lift devise in the wind tunnel at a wind speed of 4.5 m/s. Each blade with the exception of the one with no twist will be set to a pitch at it's tip of 0, 10, 20 and 30 degrees. A shown in the picture.

Four gauges as shown here, set to the individual pitches of 0, 10, 20 and 30 degrees will be used.

Each blade will be tested at the four different pitches and tested. The net drag and lift forces will be measured and calculated using the Vernier force sensors in the drag & lift devise and recorded. My hope was that the "best" blade would produce data that would be a predictor of how that specific blade design would preform when multiples were made and assembled into a rotor hub and generator.

To see if I could find a correlation I tested two previously made sets of airfoil blades. One set with no twist and one set of 6 with a 37 degree twist from root to tip. I would set these blades to 0, 10, 20 and 30 degrees at the tip as shown in the picture. Then record the energy produced in 30 seconds with 30 ohms of load running a KW generator on a 32:1 gear ratio.

Best energy output in 4.5 m/s wind speed -
6 blade airfoil with no twist for 30 seconds with 30 ohm load and 10 degree pitch at tip
322 rpm at rotor
10,310 rpm at KW generator
9.2 volt average
300 mA average
82.70 Joules produced

Conclusion: Although the airfoil blades with a 37 degree twist did well the airfoil blades with no twist out performed them with the following results in the wind tunnel. I can see no clear indicator in the drag and lift data that would have caused me to select the airfoil blade with no twist to choose as the "best" design and build a 6 blade rotor.

Next -
Using the hot wire and pattern process I will now make 6 airfoil blades with no twist but will thin them out toward the tip attempting to reduce drag at the tip and increase output performance above 82.70 Joules.

Results to follow in next post.

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