Week 7- How Much is a Pound Again?
Week 7, without fail, is one of the hardest parts of the quarter, because any cheerful energy you had at the outset is gone, and you’re still basically only halfway done what with all the homework assignments, midterms, and finals left to come. Life goes on, though.
On Monday I spent my day analyzing the data we got from the force balance lab, some of it better than the rest. The first thing I decided to do was convert the lift and drag data we calculated from pounds to Newtons. A simple calculation, just multiply by 2.204 pounds in a kilo, and multiply by 9.81 for gravity. This is the plot I got from that conversion:
Nothing broke thankfully, but I realized pretty quickly that I don’t actually have a sense for how much a Newton is, let alone a pound. My sense for the performance of wings comes from CL and CD numbers. That was the next step of conversions. It turns out that my original math was wrong somewhere, because I got a peak CL of around 6. I’m an optimist, but I’m at least realistic in my expectations. It turns out instead of multiplying by 2.2 to turn pounds into kilos, I should have divided. Oops. These are the correct plots (with some extra data, which I will explain)
The circular points represent the experimental data, while the solid lines represent theoretical data obtained by Neiman from XFLR5. Neiman also modified my code to produce these plots.
The lift data is fairly close to what we expect from a 4412. The drag, and thus literally ever other plot, however, is not. I don’t really have a theory for why this is. It seems like a systemic error, because every other group that I’ve talked to has the same information. It can’t be the sting, though, because we’re subtracting wing-off data from the rest of the data we have. Maybe we’re not doing this correctly, but if that were the case the lift data would be off too, wouldn’t it?
In any case, the trends appear correct, and there are still a few useful bits of data that can be gleaned from these sets. For example, the high AR wing has a steeper lift curve and stalls earlier than the low AR wing, which matches the expected data. The drag trends are flipped, as the high AR wing experiences more drag, not less, than the low AR wing. The drag polar matches the expected trend (barely), and the L/D plot doesn’t actually have enough resolution to see what we want to see. Errors are still fuel for the report though!
The second lab session was when we had been assigned our mini projects and broke into teams to research the projects. It turns out that Dr. Doig was right (who would have thought?), removing the rear view side mirrors- RVSM, as they’re called in the biz- is a relatively untouched topic (although I did find an article from 2014 reporting on Tesla’s attempt to change automobile mirror laws). For some reason, people seem more interested in changing the design of RVSMs using active flow control, among other things, rather than doing away with them altogether.
Perhaps it’s the strength and intimidation factor of dealing with challenging a federal entity, or perhaps it’s the fear that the public will not be receptive to cameras instead of mirrors. Personally, I’m still a bit skeptical of the camera solution. For one, I do believe there is some merit to the hardware malfunction concerns (if only because the backup camera on my first car had some serious issues just through normal use).
More importantly though, I think that the ergonomics of replacing mirrors with cameras pose some issues. The Honda Civic has an augmented RVSM with a camera, but only on the passenger side. Why? Isn’t the blind spot on the left side just as important? The explanation that I accept is that it doesn’t make much sense intuitively to turn your head right to the center dash, to then move your car to the left. If both mirrors get replaced with cameras, the driver will have no choice but to move their head right to move the car to the left, assuming the technology we have doesn’t update too much. There are transparent OLEDs that could maybe somehow be integrated into the window or windshield, but what happens when the windows are down? Now the driver has to turn their head all the way back to look at their blind spot to change lanes, which doesn’t alleviate my concerns about keeping one’s eyes at least a little bit on the road. If these cameras are activated by the turn signal, what happens when BMW drivers want to change lanes?
In spite of those concerns, I do feel that replacing RVSMs with cameras is more likely to happen sooner rather than later. The economy of scale argument is hard to ignore: there are 190MM drivers licenses issued in the US. At an average of 12k miles (20k km) per year, that comes out to 2.3e12 miles (3.8e12 km) driven on American roads alone (while America is big (>4MM miles (>6.7MM km)), it has far from all the roads in the world (>20MM km)). At those scales, even a 1% change in any value for a vehicle gets multiplied over a million-fold. The first step is generating interest in the movement!