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It seems like every engineer learns about the Tacoma Narrows Bridge in college. It’s an interesting piece of history and perfect for the classroom: a spectacular failure without human casualty. The unfortunate bit is that it’s pretty much the only piece of engineering history that’s taught. At least it was for me. I learned about Tacoma Narrows in an engineering ethics class. In that context, failure becomes an ethical choice; spend enough money and don’t cut corners and everything you make will succeed. Problem sets seem to reinforce that idea by suggesting that a perfect solution can always be found. Failure is reduced to an anomaly and engineering is reduced to a perfect science. What we lose is the humanity of engineering: its beauty, its flaws, its traditions, and its biases.
Of course, I’m not claiming to have reached some sort of all-encompassing engineering enlightenment, but I have been enjoying digging deeper into my interests and learning about how things got to be where they are. Hope you find some of it as interesting as I do.
The most clicked link from last week's issue (~23% of opens) was theprepared.org's feature on Apple's supply chain and the pencil marks inside the iPhone 5c's plastic case.
Engineering & Design.
- If you’ve been paying (extremely close) attention to the NHL playoffs, you may have noticed a weird-looking stick with a hole in the blade. The hole apparently allows for two different properties: stiffness above it and flexibility below. According to Bauer, this produces a slingshot effect -- almost like a smaller version of the stick’s shaft (which, as explained in this video, bends almost unbelievably to whip the puck forward). These days, ‘twigs’ are made of carbon fiber, though as the hockey lingo suggests, wood used to be the material of choice. The evolution of the hockey stick from wood to carbon fiber gives us insight into a material property called resilience. Resilience is basically the opposite of damping. High resilience materials bounce back with most of the energy that you put into them. As Stevel Vogel illustrates in Cats’ Paws and Catapults, spider silk is a great example of low resilience material. “A web of high resilience would, like a trampoline, tend to fling the prey back out.” Vogel goes on to note that “resilience management highlights the dichotomy between nature and human technologies.” Natural materials, like wood, tend to have lower resilience whereas man-made materials, like carbon fiber, tend to have higher resilience.
You can see why carbon fiber, with its higher resilience, has overtaken wood as material du jour; more of the energy you put into the stick comes out on the puck for a faster shot. But a stick can be too resilient/springy -- when receiving a pass, you don’t want the puck to bounce off the stick away from you. Players call it “feel”. Some damping is beneficial, as shown in this slo-mo video of a stick that combats springiness with a urethane insert. These hole-y sticks try to solve the problem a different way, adding a softer spring into the mix with the aim of providing “feel” without taking away energy from the shot. So, is it worth buying the latest in hockey tech - a stick with a hole in it for $450? If you’re a beer leaguer like me, clapping your usual head-hunting bombs twenty feet wide of the net, probably not.
- Composites of natural fibers, like flax or hemp, present an interesting middle ground between the characteristics of wood and carbon fiber discussed in the last bullet. McLaren points to the improved damping characteristics as one reason for pursuing a seat made of flax fibers in their Formula 1 car. If there was one post to sum up all of my interests, this would be it.
- I prefer imperial units to metric, because they’ve evolved over time from identifiable, real world references and, as a result, are easier to eyeball and visualize. Take the units of force: lb-force vs Newton. The Newton is admittedly much, much easier to calculate with, but even a person who was brought up in a metric household would have no feel for a Newton. I think visualization is massively undervalued in STEM, despite examples like James C. Maxwell, who brilliantly unified electricity, magnetism, and light. Though he worked on complex, theoretical problems, Maxwell created models, like this one and this one, to help him visualize concepts.
Making & Manufacturing.
- It’s been a year and a half since the unfortunate fire at the Notre Dame Cathedral. Soon after the fire, there was debate about whether the spire should be restored exactly as it was or to take the opportunity to modernize it. Facing that difficult question, some pointed to the last time the spire was rebuilt in the mid-1800s. At that time, the architect in charge took the original vision to its extreme rather than sticking to a faithful reproduction. The debate for the current rebuild has yet to be resolved, but one group made a compelling demonstration using medieval manufacturing methods. What stood out to me was one of the researchers questioning whether modern constructions would still be standing in 200 years, and contrasting that with medieval techniques which have stood for 1000 years. This brought to mind the Lindy Effect, explained here by author N.N. Taleb, which in essence is the idea that the longer something has been around the longer it will continue to exist. If you buy into Lindy, it’ll be no surprise that traditional manufacturing methods can be shown to have demonstrable advantages, like riven (split) wood that, unlike sawed wood, does not expose end-grain and is much less affected by moisture.
- Though nobody is going to argue whether the reconstructed Notre Dame is still Notre Dame, the idea of what constitutes the “soul” of an object is a fascinating one. As someone who’s modifying a classic car myself, I often think - how far can I go before it’s not the same car? I really appreciated Leo Goolden’s (video) take on this subject, which applies the Ship of Theseus thought experiment to Tally Ho, the boat rebuild project that has already gotten a lot of chatter in this newsletter and in the paid subscriber Slack.
- The People’s Mosquito has set out to rebuild the legendary de Havilland Mosquito, a WWII combat aircraft. Because of material shortages, the extremely successful “Wooden Wonder” utilized plywood and balsa in a wooden monocoque design. The People’s Mosquito is just getting underway but I’m looking forward to continued updates, particularly on their YouTube page.
Maintenance, Repair & Operations.
- Dive watches need to stay waterproof even when under immense pressure. Historically, this was accomplished with stiffness and complexity. The Vostok Amphibia took a different approach, turning flexibility to its advantage: Its domed crystal expanded circumferentially under pressure to improve its seal to the case. Cheaper and more robust. But even cooler than all that, the Amphibia was the watch of choice for Steve Zissou in The Life Aquatic.
Distribution & Logistics.
- Having worked in Mojave and lived in the Antelope Valley, the legend of Skunk Works looms large. They’re working on a massive new airship, envisioned as a way to efficiently deliver cargo and personnel anywhere on Earth. It joins a few other airship designs in advancing a field of technology that has ebbed and flowed in popularity since its beginnings as ballooning in the late 1700s. It’s hard to imagine just how foreign it must have been to see man take flight for the very first time, but this account of Jean Pierre Blanchard’s first aerial voyage in the US in 1797 paints a wonderful picture. The fascinating tale includes a “passport” of sorts from George Washington and a bribe of wine to enlist the help of a frightened farmer. I’m very much looking forward to a renaissance in lighter than air travel, though my personal pick for deliveries to areas with poor infrastructure would probably be a Dakar Rally truck.
Inspection, Testing & Analysis.
- How can you tell if there’s an issue with your part or assembly without cutting it apart and taking a look? That’s a question that a whole field called nondestructive testing strives to answer and, as it turns out, one that we’ve been attempting to solve for some time now. Check out this passage from Weston Martyr’s The Southseaman, published in 1929:
“Before any plank was put into place, MacAlpine and Tom and anyone else who happened to be about held a consultation over it. First they examined it very carefully, and then they bent it, tapped it, listened to it, and, as I live by bread, I swear that once, at least, I saw MacAlpine tasting it. At any rate he applied his tongue to the wood, and then went through all the motions of an expert tea-taster - even to that final feat of expectorating through the clenched teeth with precision and gusto.”
How cool is that? In fact, the tapping method has continued to be a recognized method for assessing the quality of wood. As this otherwise rather dull article about wood airplanes mentions, a hollow sound is apparently a sign of moisture or rot. Tap testing has proved so useful that it’s transcended materials, and is now used as an inexpensive way to inspect carbon fiber parts; a hollow sound can be heard when tapping over a void (air bubble). This video does a great job of illustrating the change in tone on a bike frame. As you can imagine though, there’s a fair amount of skill required with a tap hammer. To add in a dash of automation, that same idea of sound waves building a picture of an unseeable interior of a part can be turned into something “higher tech”. If you guessed something along the lines of sonar, you’d be right. Nowadays, ultrasonic testing has taken over in the inspection of composites. It’s fun to see the progression from the 1920s. Maybe MacAlpine was on to something; someone should try taste testing carbon fiber (don’t actually do that).
- I would consider it a success if my life is 10% as interesting as Ken Wallis’. Everything you need to know about him is in this video, where he - at 95 years old - is shown flying and fooling around on an autogyro that he himself developed.
- Wearing masks might be slightly annoying, but at least we don’t have to wear masks to fend off tigers.
Thanks as always to The Prepared’s paid subscribers for supporting The Prepared. Thanks also to Kristóf for the great link about the Vostok watch, Xavier for the insight about riven wood, and you for making it, somehow, all the way to the end.
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