Vincenti, 1990

• Walter G. Vincenti, 1990, What engineers know and how they know it: analytical studies from aeronautical history, Johns Hopkins.

• This is a classic in the history of technology. It covers five illustrative cases of aero technology change over time, partly in our early aero period. Each gets a big chapter. Vincenti was a long time professor of fluid dynamics and aeronautical engineering at Stanford. These chapters were published in T&C as articles.
• case 1: (in casual language) the Davis wing, which performed unexpectedly well and it was hard to understand why; the theories at the time were in conflict but it appears to be that partly by happenstance Davis's design kept smooth airflow along the wing until relatively far back; normally smooth ("laminar") airflow breaks into turbulence earlier, and this reduces lift.
• case 2: the lengthy development of science and tech to address "flying qualities" -- stability and control as experienced by an airplane pilot -- and turn those qualitative experiences into quantifiable design objectives for the aircraft designers. The book focused on work at Langley Field for 25 years from about 1918-1943, with occasional references to NPL.
• case 3: "control-volume analysis", 1912- Focus on engineering versus physics framing of boundary-value models, to model changing-pressure
• case 4: Durand and Lesley's decade of experiments on aerial propellers, 1916-. useful for us.
  • Their work didn't find sharply better propeller shapes, but measured across variations of them (parameter variation is Vincenti's invented term which turns out to help classify research activity), and helped match aircraft designs to the best propellers for them.
  • There's a key empirical relationship of "efficiency curves" in propeller measurement, and it will be helpful to fill it out clearly. A key chart is on p153 and we can photo it or get it from Durand's work.
    • propeller efficiency is measured; it's some version of energy in, called torque, and forward thrust/power/energy an aerial propeller produces. Efficiency is denoted η (eta). It's constructed from measured thrust T and torque Q by η=TV/2πnQ. Observed efficiencies is between 0 and about .8. V/nD is measured too, and put on the horiz axis with efficiency on the vertical axis, and we see hump-shaped curves which are zero at each end, and as propeller "pitch" increases the peak efficiency moves away from zero, toward higher V/nD. V is external airflow velocity before it hits the propeller. n is revolutions per unit time. D is diameter of the propeller.
    • nD is a metric of how much the propeller is DOING; how much pressure or speed it's putting on the air going behind it. V goes the other way; I'd think that if V is faster, the propeller has to move faster just to avoid creating more drag. So V/nD isn't that far from torque or thrust, itself.
    • I'm surprised at the efficiency-defining equation, and which things are on the top and which on the bottom.
    • Torque Q is a force times a distance, e.g. kg*m²/sec². Energy, in joules, is equivalent dimensionally but has a different "kind" of meaning.
    • variable pitch propellers weren't found to be practical until the 1930s. That limits the designer's choices. The designer has choices of n and D; V will be chosen to suit the airplane's expected tasks, I guess.
• case 5: the adoption of flush riveting in american aeroplane manufacturing in the 1930s. Flush riveting on airplanes is difficult because the sheets of metal are thin. there are many variables and variations. it improves top speed by ~2.5% versus the previous practice. (Rivets are smooth, without screw threads, and have one wide head and a soft tip which gets hammered to make it have a wide head on the other side too.)
• Vincenti emphasizes aspects of engineering science vs physical science. One is that engineering mistakes are literally more dangerous than scientific ones. The author seems not to frame the issue as learning the universe vs making, or the mokyrian split of sci and tech (what is vs how to do). He categories sources of engineering info/discovery generically, philosophically.
• long concluding chapters after the 5 cases.

Notes to fold in

• usefully characterized work of Stefan Drzewiecki -- called the blade element theory or something like that

Original title	What engineers know and how they know it: analytical studies from aeronautical history
Simple title	What engineers know and how they know it: analytical studies from aeronautical history
Authors	Walter G. Vincenti
Date	1990
Countries	US
Languages	en
Keywords	engineer, aerodynamics, flight qualities
Journal	T&C
Related to aircraft?	1
Page count	326
Word count
Wikidata id	Q7991092