A few days ago, I was watching tv and folding laundry, when I saw a trailer for a movie about windshield wipers. A lesser (or more normal) man might ponder the question "How could there be a feature film about windshield wipers?". But not I. I know what fertile creative ground the topic of rain removal is; I was reminded of a conversation I had in high school.
It pouring buckets, naturally. My best friend and I were discussing cars. This was not a new discussion, it had continued uninterrupted since our freshman year. Our english teacher, Ms Strohm, was grading some papers as Tad and I were hashing out the minutiae of various forms of valvetrain engineering. During a lull in the conversation, I looked out the window and lamented the fact that I needed to replace the wipers on my Mustang. Tad inquired whether I would be using blade refills or replacing the actual wiper assembly. I told him that I probably needed to replace the assembly, but would opt for the refills, as they were cheaper. Tad pondered aloud the possibility that there might be a better way to remove rain from the windshield. The problem arises from the shape of the windshield versus the type of motion available to wipe it clean. The glass is more or less rectangular, but the only way to move the wipers themselves is with a motor, which produces only rotary motion, hence the round arcs we are all so familiar with that leave a fairly large portion of the windscreen unwiped. I told him about the system installed on some aircraft, wherein hot, dry, compressed air from the engines is ducted to the front of the windshield, creating a "boundary layer " of air that diverts rain up and over the fuselage. We figured out a way to adapt this to existing automobiles, then dismissed the idea due to exceedingly high cost/benefit ratio. He brought up the exceedingly complicated system then installed on some Mercedes cars, a system that uses a single wiper that extends on the horizontal part of the sweep, then shortens as it nears vertical.Its advantages and drawbacks were discussed at length.
Unbeknownst to us, we had attracted the attention of both our teacher and several classmates. Ms Strohm asked us if we were discussing windshield wipers. I answered in the affirmative, but let her know we were ready to get back to work when she was. Ms Strohm, to her eternal credit, was never one to shy away from some useless knowledge, and asked us to rehash what we had discussed so far, for the class' benefit. She was actually interested, and it wasn't a new thing to be asked to make an impromptu presentation on something in her class if she though the topic was interesting. But never on windshield wipers. We obliged, a bit sheepishly at first, but were surprised to find ourselves deluged (ha!) with questions from the class.
David wanted to know why larger vehicles had their windshield wipers mounted near the roofline, upside down. He pointed to a fire truck idling outside as an example. I had never though about it before, but the answer came smoothly, as though I had rehearsed it for years. "Larger vehicles often have vertical, or nearly vertical windshields. Wipers mounted to the bottom would actually push more water up the glass than wipe it off." Someone else, pointing to the same fire truck, mentioned that the wipers went in opposite directions, rather than the overlapping arcs on most cars. Tad fielded this one, even though I was sure he had as little time to think about it as I had. "The same larger vehicles usually use two separate plates of glass for a windshield, divided by a metal frame. There is no advantage to having the wipers in the same direction, as they cannot overlap each other. Instead, they wipe towards the outside of the vehicle to reduce the amount of rain that runs back on to the glass." I added that this was also seen in pre-1949 automobiles, which were produced before the curved glass we are familiar with was readily available.
I felt like Isaac Newton. Everything about windshield wipers suddenly made sense to me. It was like someone pulled back just a little of the curtain obscuring the engineering that takes place behind everything mankind produces, and the part I peeked at was the chapter on windshield wipers.
Melissa asked about her boyfriend's Mustang, a car I had worked on and raced against. "He took the wipers off to save weight, but when I changed the wipers in my car, they weighed next to nothing." She was right. They weighed nothing. But her boyfriend hadn't just pulled off the wipers. He pulled the wiper motor, which is a hulking, power-hogging heavy beast of a thing. (His Mustang, of course, was faster than mine. But I had windshield wipers, air conditioning, and a back seat.) I told her that removing the big electric wiper motor was common among drag racers, and most of them just made sure to Rain-X their glass every week, and didn't drive in rain very much.
The Q and A lasted a bit longer, and amazingly, stayed on topic. Tad and I covered other points, like vacuum-powered wiper motors, the three-wiper system on some British cars, and intermittent circuitry, with a grace and ease that we couldn't seem to find when discussing Ethan Frome. Afterwards, Ms Strohm thanked us, mentioning that she had never considered the intricacies involved in cleaning rain off a car window before. We nodded as solemnly as two high-school seniors could, hopefully leaving her with the completely bogus impression that we were serious men, who considered serious issues like this on a regular basis, and not just two lucky friends who bullshitted their way out of thirty minutes of class time talking about car parts.