Recent content by BP Finn

Actually, no I did not. Max speed about 7-8 m/s. Even with 2 fan on high speed.I'd suggest making the intake/outflow funnels as long as possible?

The way to solve this - first find how much gravitational potential energy the system (rod/putty) must have to swing around 180 deg. Find the center of mass of the system to do this. This gain in potential energy is how much kinetic energy must come out of the collision (K = 1/2 Iω2) - or it...

Well, I added a second high capacity fan and the air speed in the central section is now 7.2 m/s which is enough to get reasonable measurements of a drag force and measure a drag coefficient of a bottle rocket, but well below what I had hoped for.

I am using an anemometer (all that I have to measure air speed). I have wondered if that is an issue. I bought this fan with precisely the calculations you cite - expecting much better performance. I am trying the second fan to see if that helps. Thanks!

I do suspect the flow should be incompressible at these low speeds - which is why I was surprised when the equation of continuity did not work. The air speeds were always measured in the tunnel. I did also measure the air speed with the fan open and got faster speeds - more for curiosity. I...

Not yet ... that was my next step! Thanks.

tech99 - I flipped the fan so it now sucks air into the tunnel and the air speed DID improve! It is now between 6-7 m/s. Still can't explain the problem with the equation of continuity (the air speed should be higher in the narrower portion, now it is the same as in the wider portion), but its...

Actually I used a different NASA design initially. The tube is vertical and a smaller fan on the top blowing down to measure drag on a bottle rocket. But since the fan was small, the air flow was slow (only about 3 m/s) so the drag force was small. I tried turning the tube horizontal and...

Hi, this is my first post. I teach high school physics and am trying to build a simple wind tunnel. For my first attempt I used a Utilitech high capacity 20 inch fan (nominal 6800 CFM) but the resulting air speed was disappointing – only 4.8 m/s. What type of fan would be better? I was...