> Week 6 (Part II) - Something Different
- May 9th (Wednesday)
Our group for the 4412 project had our day of testing today.
But rather than bore my reader(s?) with an overview of the experiment, what we did, are what our plans are (everything that you will be hearing in the next couple weeks anyway), I have something more interesting to talk about.
After our 307 lab period, I went on a tour of the new residence halls that are being built at Cal Poly, yakʔitʸutʸu (which means “our community” in the Northern Chumash language). Since I am a housing ambassador at Cal Poly I had an opportunity to have one of the first looks at a nearly completed residence hall. While I was on the tour, I kept thinking to myself how nice these buildings were: with the floor-to-ceiling windows, fancy all gender bathrooms, and a large amount of study and communal living spaces.
We entered one of these communal living spaces and I looked up towards the large ceiling fan above us.
I suddenly realized something peculiar about this ceiling fan.
WINGLETS
Not only were these ceiling fans in an airfoil shape (I wonder how the specific airfoil geometry), they also had winglets on each of the blades!
While looking up, I immediately and unintentionally said, “Hey, those are winglets!” and everyone around me just looked at me confused. Then it dawned to me that I was the only aero student there and I was probably the only one who gave a damn.
While walking back out of the construction site, I was telling one of my friends about how winglets improve efficiency by reducing drag caused by tip vortices. I then began to ponder about what the purpose for putting winglets on the blades was (besides the obvious answer of “efficiency”). I hypothesized that perhaps the vortices shed at the end of the blades could produce a downforce on the top surface without the winglets. This down force could then perhaps thus cause the fixed blade to bend unfavorably.
In terms of their airfoil shape, I think it has a structural implication as well. This ceiling fan sports rather long blades and thus might be more subject to “droop” than a smaller fan. Assuming these blades are at a non-zero lift angle of attack, they will produce a lift force that might help counteract the bending it theoretically experiences.
But why are these blades so long if they could have the adverse effect of structural damage to the system. According to a NASA study:
“Similarly, for a given wing area, a high aspect ratio wing will produce less induced drag than a wing of low aspect ratio because there is less air disturbance at the tip of a longer, thinner wing. Induced drag can therefore be said to be inversely proportional to aspect ratio.”
These blades certainly have a relatively high aspect ratio and therefore will produce less induced drag, furthering the efficiency of the installed winglets. Nifty!
It was cool to be able to identify a concept that I have been taught about in the aero curriculum and apply it to a non-aerospace-vehicle object. It was also nice to be able to explain an aerodynamic concept to others outside of a traditional exam or lab report scenario.
