Brian Potter, How to Build 300,000 Airplanes in Five Years, Construction Physics, May 23, 2024. This is a long and fascinating article. I'm not going to attempt to summarize it or excerpt the whole thing. But I'll give you two excerpts. The first is about production volume:
Prior to the war, aircraft were produced using small scale, job-shop type manufacturing methods: Individual aircraft were assembled in place piece by piece, largely by hand, not unlike the way cars had been built prior to Ford’s Model T. It was a slow, expensive, and labor-intensive process: On a per-pound basis, it cost about 30 to 40 times as much to build an aircraft than it did a car. And while the auto industry produced 1,500 times the number of cars as the aircraft industry did planes, it did so with just eight times as many workers. In other words, it took almost 200 times as many workers to build an aircraft as it did a car.
In part this was due to the comparatively small volumes of aircraft being built, which precluded the use of capital-intensive manufacturing methods with high upfront costs but low unit costs. But it was also due to the unique challenges of aircraft themselves, which made adopting efficient mass production methods difficult. For one, aircraft were far more complex than other mass-produced goods. While a car had around 5,000 parts, a B-25 bomber had around 165,000, not including the tens of thousands of parts in the engines, instruments, and other equipment, or the 150,000 rivets needed to stitch the plane together. And the performance requirements for aircraft were much higher: An aircraft piston engine, for instance, was much more powerful, much lighter per horsepower, and was pushed much harder than a car engine. A 1930s-era Ford V8 could generate about 85 horsepower, while aircraft engines generated 1,000 to 2,000 horsepower, and a car engine weighed about 6.9 pounds for every horsepower it generated, compared to 1 to 2 pounds for an aircraft engine. And while a car engine rarely exceeded 22% of its maximum power, an aircraft engine regularly ran at maximum power, or even above maximum power.
This meant that aircraft manufacturing had much tighter production tolerances than car manufacturing, and much more machining was required to make parts as light as possible. It also meant using lightweight materials like aluminum sheets and magnesium castings that other manufacturers had limited experience using. Meeting these strict tolerances required greater control over the production environment: Aircraft engine factories were air conditioned to minimize heat fluctuations and kept at constant 50% humidity to minimize surface rust.
Ensuring aircraft would meet their demanding performance standards also required much more inspection than other types of manufacturing. An aircraft engine and its constituent parts might undergo 70,000 inspections during the manufacturing process. When Ford engineers visited a Pratt & Whitney factory to learn about aircraft engine manufacturing, they initially thought the job “looked easy” and that the quality and precision requirements were excessive, but as they studied the engines, their performance requirements, and the need for reliability, they changed their minds. At a Ford aircraft engine plant that eventually employed around 15,500 workers, 3,000 of them were inspectors.
Here's three paragraphs on design drawings:
Even the seemingly simple task of assembling a complete set of drawings and parts list for an aircraft to be built proved monumentally difficult. When Ford first began work to produce the B-24, it found that drawings only existed for about 80% of the aircraft, and the ones that did exist had numerous inconsistencies. Ford ultimately redid the entire set of drawings, turning the original 7,500 drawings into more than 20,000 that could be more easily understood by workers inexperienced in aircraft manufacturing. Similar efforts were required by nearly every airframe manufacturer as they scaled up operations and transferred their designs to other companies.
One of the reasons for this poor state of production control, and another difference between aircraft manufacturing and other types of manufacturing, was that aircraft designs were constantly changing. With conventional manufacturing, design of the factory took place once designs were “frozen” and no more major changes to the design would take place. Mass-production factories achieved their high efficiencies by having carefully arranged and timed flows of material, which would be disrupted by major design changes that might require new tools, different parts, and changed material routing.
But while attempts were made to “freeze” aircraft designs to make manufacturing easier, ultimately this proved infeasible. Designs had to be constantly improved to address deficiencies, improve performance, and deliver aircraft that were capable of overcoming the enemy. Engines were upgraded to be more powerful, parts that were found to fail frequently were redesigned, and new guns and other equipment was installed.
There's much more at the link.
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