Takt time – Even more about origins in German aircraft manufacturing

Earlier this week, I ran into John Paxton’s 2008 paper called Myth vs. Reality: The Question of Mass Production in WW-II, in which he makes a convincing case that production methods were far more advanced in the US aircraft industry than in Germany or Japan. It is really not in doubt. The point in trying to understand the Junkers Taktsystem is simply as one of the sources of TPS. World War II German and Japanese engineers could design advanced planes, like the first jetfighter, the Messerschmitt 262 that you can see in the Smithsonian today, or the Mitsubishi Zero. But, in production, they could not come anywhere near the one-bomber-an-hour performance of Ford’s Willow Run plant.

Yesterday, I was able to go to the main library at Stanford University, where they have about one foot on one shelf in the basement with books on the German aircraft industry in World War II. including in particular Lutz Budrass’s work on the subject and Holger Lorenz‘s Kennzeichen Junkers. Budrass’s book is a forbidding 1,000 pages of small print with a few grainy pictures, long on armament policies and politics, but short on technology:

Lorenz’s book is much more accessible and contains many high-quality photographs, which contradict Paxton when he says:

“Photographs from the era show this  difference. Classic photos from Vickers and DeHavilland (British) and Junkers and Heinkel (German) production facilities show  isolated aircraft in ‘final assembly’, in  stationary jigs, being assembled by ‘work  gangs’, embodying the ‘craft production’  process. In contrast, photographs from  Grumman, North American, Republic, and others show rolling final assembly processes, with aircraft moving from station  to station, much like Model T assembly  twenty years earlier.”

What Paxton writes is not consistent with what little I have seen about  the Junkers Taktsystem, and it is not consistent with the photographic evidence either, which shows that, at Junkers, the final assembly methods in the 1930s were eerily similar to those today for airliners, as you can see in the following side-by-side comparison:

Junkers clearly had a rolling assembly line, albeit one that, unlike the Boeing 737 line, was not continuously moving, Otherwise, the similarities extend even to the kits of parts that are rolled over to each plane. Of course, this is Junkers, not the whole of the German aircraft industry at the time, but Junkers is the one we are interested in, because of their Taktsystem and their transfer of this method to Mitsubishi aircraft in Nagoya, through which it reached Toyota. Other companies used a variety of methods. As we can see on the following picture Heinkel 111 bombers appear to have been assembled on fixed stations in 1939, but Messerschmitt fighters on assembly lines in 1943:

These and more pictures of German aircraft manufacturing before and during World War II are available from the Bundesarchiv Picture Database.

Upstream in fuselage assembly, the comparison looks as follows:

In 1934, for Ju-52 fuselages, Junkers used a nose-to-tail assembly line; in 1940, for the Ju-88, a side-by-side line. Today, Boeing 737 fuselage assembly, Spirit Aero in Wichita, KS, appears to be using parallel fixed stations. Fuselage assembly in this context, however, is limited to fastening together sections that have been assembled separately, with automated riveting.

Paxton’s article contains other assertions that are also difficult to accept. He claims, for example, that the abundance of cars in the US spread mechanical skills throughout the population and that these skills made it easier for large numbers of workers to learn how to build airplanes. He quotes the following statistics for the number of people per vehicle in different countries in 1926:

  • Australia:  30
  • China: 31,871
  • Japan: 1,789
  • Britain:  49
  • France:  54
  • Germany: 194
  • Italy: 353
  • United States: 6

The US was the only country in which almost every family had one car, and American cars of that era were designed to be maintained by their owners. They came with a kit containing the necessary tools and instructions. The US aircraft industry during World War II, however, is known to have employed women in large numbers, as in the following photo of  women installing fixtures and assemblies to a tail fuselage section of a B-17F Bomber (Library of Congress).

If do-it-yourself car maintenance pre-trained World War II aircraft workers in mechanics, then car maintenance must have been done by women. Single women in isolated farms certainly had no choice but to maintain  their cars and tractors, but, in the culture of the 1920’s and 30’s, it is difficult to imagine that women who had a man at hand didn’t delegate changing spark plugs to him rather than learn it themselves. Paxton’s article also asserts that German aircraft production required skilled craftsmen, but most of it during the war was done by forced laborers from occupied countries who were not trained mechanics or machinists.

On the other hand, the article fails to mention two obvious reasons for the superior performance of aircraft manufacturing in the US:

  1. Among all the belligerents, the US was the only one with aircraft factories that were out of the enemy’s range. Germany’s ABC program, on the other hand, had defense against air attacks as a central design consideration. Whatever you do to spread out the facilities and protect the supply chain from bombs does not help you in productivity or quality. The Junkers factory in Dessau was bombed in 1944.
  2. The US aircraft industry in World War II had a highly motivated work force. Not only were these manufacturing jobs the best these women had ever had, but they knew they were producing equipment for the men in their lives who were fighting for a cause they believed in. By contrast, in Germany, Rosie the Riveter’s counterparts were Polish or French workers building bombers against their will for the worst thugs in history, and they would have been happy to see these planes crash on take-off. In addition, most of them didn’t speak German.

The picture that emerges from the documents I have seen so far is that, in the late 1930s, Junkers had organized production in what is now called pulse lines. Final assembly was divided into operations of balanced durations, so that the planes didn’t move during operations but moved forward in unison at fixed time intervals, with upstream processes and the supply chain organized to support this mode of operation. And this is the Taktsystem that was taught to Mitsubishi Aircraft by Junkers engineers in 1942.

4 comments on “Takt time – Even more about origins in German aircraft manufacturing

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