2022-01-24 7 min read


Notes, 2022-01-24.

In Managing the Flow of Technology, his 1977 book on knowledge transfer and communication within science and engineering organizations, Thomas J. Allen offers an almost exuberant assessment of corporate cultural capital. “The human brain has a capacity for flexibly restructuring information in a manner that has never been approached by even the most sophisticated computer programs,” he writes. The best way of transferring knowledge, then, is to physically move people from one company to another - the organizational equivalent of the station wagon full of tapes speeding down the highway.

Allen’s research is very much centered in post-war American industrial giants. He describes companies which are dead set on IP secrecy - ones that “exclude the technologist from informal communication channels outside his organization.” The life Allen describes in these companies is rather bleak:

While the academic scientist finds his principal reference group and feels a high proportion of his influence from outside the organization, for the engineer, the exogenous forces simply do not exist. The organization in which he is employed controls his pay, his promotions, and, to a very great extent, his prestige in the community.

A physics professor’s colleagues are other physicists - in their own department, sure, but also at other institutions. Allen calls such informal social bonds “invisible colleges,” and says that they not only provide individual scientists with professional validation, but also serve to align the edges of frontier research.

Anyway, I suppose my project right now is to build invisible colleges for folks like you, dear reader - or, at the very least, to line up a couple of loose ends every now and then.

Be in touch, eh?

-Spencer Wright

The most clicked link from last week's issue (~7% of opens) was a blog post praising the environmental benefits and overall resilience of cheap boxy buildings.

Last week in The Prepared's Members' Slack (our own invisible college par excellence) we discussed new research on fatigue life prediction in laser powder bed fusion parts, and the fact that someone (not me!) added a custom Wera emoji to the instance. This week in the Reading Group, we're discussing Construction Physics' series on How to design a house to last 1000 years with the author, fellow Member Brian Potter.

Planning & Strategy.

  • I’ve been running Ste 332, The Prepared’s co-shop in Bed Stuy, for a little over three years, and over the past few months I’ve been reflecting on the experience and planning for the next ~three years. It's definitely an invisible college, and while it may sound like splitting hairs, I think it's important that its culture draws more from bike co-ops and shared cabinetry shops than from the world of makerspaces. I'm sure our experience is not unique, and I’d like learn about how other shops organize and operate. If you run or work out of a similar space, I’d love to hear from you; won’t you reach out here?
  • A compelling argument for implementing a part numbering system that relies only on numbers and hyphens, with no semantic significance anywhere. “The easiest and simplest solution is a purely sequential numbering system where the number has no significance other than [as] a tracking ID.”
  • Sidewalk Labs’ founder, Dan Doctoroff, has ALS and is stepping down as CEO; Sidewalk Labs’ subsidiary companies will be rolling up to new homes within Alphabet.

Making & Manufacturing.

  • A rad three minute long video of ski lift towers being installed. The prefabricated tower sections are lifted in by a Kaman K-MAX single-seater helicopter, whose intermeshing rotors (which spin in opposite directions and whose axes of rotation tilt out from the helicopter’s centerline; you can see a slow motion video of them here) are capable of lifting over 2700 kg. Intermeshing rotors means that the K-MAX doesn’t need a tail rotor, so all available engine power goes right to providing lift, and the K-MAX’s narrow body allows pilots to lean out of the window and use vertical reference flight - good for cases when a load must be placed precisely, as when installing the upper segments of a ski lift tower. Anyway, the whole operation is pretty remarkable, especially the process of aligning the bolt holes in mating towers 👌

    As a side note: Kind of incredibly, the K-MAX’s rotors are made of a wood-fiberglass composite. The blades’ main structural component is a Sitka spruce layup, and their afterbodies (their trailing edges) are fiberglass. Articles around the internet make reference to wood’s damage tolerance and fatigue resistance, which the Kaman representative I spoke with confirmed: apparently Charles Kaman, before he died, said something to the effect that “trees stay out there for hundreds of years, and they twist and turn in the wind just fine.”

    Why did Kaman care about twisting? Helicopters are steered by varying the rotor blades’ angle of attack as they spin around the rotorhead. Most helicopter rotors are mounted to the rotorhead using a big bearing, and a hydraulic actuator system pitches the rotor blades back and forth with every revolution they make. But Kaman’s helicopters are steered using a unique servo-flap design, which Charles Kaman patented in 1949. Kaman’s rotors are fixed to the rotorhead, but they have little servo-flaps (like the elevators on an airplane wing, but smaller) that are operated electronically. As the servo-flaps change pitch, the end of the rotor actually twists around the longitudinal axis - which it does a couple hundred times per second in order to stabilize and steer the helicopter.

    Because it lacks a tail rotor and a hydraulic pitch actuation system, Kaman claims that the K-MAX is less complex than helicopters with articulated rotors. But Kaman’s rotors need to be capable of twisting, repeatedly, every time the rotor revolves around the rotorhead, for years’ worth of flight time. And apparently Kaman decided that the material to use was sitka spruce.

    A few additional side-side notes:
  • Kaman’s representative confidently dismissed any concerns about moisture content affecting the Sitka spar, but apparently old Bell 47 helicopter blades (which were also made of spruce) tended to come unbalanced as different parts of the spar absorbed water differently. Pilots would carry masking tape to correct imbalances throughout the day.
  • Nevertheless, wood - and Sitka spruce in particular - has a long history in aerospace, as this in-depth article describes.
  • Aircraft-grade Sitka is increasingly rare, as the trees that produce it are on the order of a hundred feet tall. Spar-grade 1” x 6” stock currently sells for around $16.75 per foot, making it $33.50 per board foot - compared to around a $1.20 per board foot for commodity lumber (which includes a few varieties of spruce). Also, note that ~$1.20 for framing lumber is still way out of whack with historical prices, which at least one lumber dealer attributes directly to climate change.
  • If you’re curious about what a wooden helicopter blade looks like, this blog post has some nice pictures of cross-sections of various designs.
  • Finally, here’s a masters thesis predicting the lifespan of a wooden wind turbine blade, which includes the note that “the behavior of wood in response to cyclic loading can be very complicated” and concludes that twenty years is a reasonable lifespan for the blade in question.

    Finally finally, a Twitter thread from me on Sitka spruce, which includes a few fun photos and some other rabbit holes to nuzzle into 🤗
  • A short video of a really clever manual spring winding tool, which looks like it wouldn’t take long to print from this Thingiverse part.
  • My five year old recommends this stop motion video of a wooden milk crate being made with kitchen utensils. I recommend it too.

Maintenance, Repair & Operations.

Distribution & Logistics.

Inspection, Testing & Analysis.


A snow plow ballet, set to Shakespeare's Romeo and Juliet.

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